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The NEScaf Story

Contributed by Dave Siegrist, NT1U

The NEScaf is a switched capacitive audio filter. It is designed to be simple to build and use.

It is more flexible than previous filters for QRP rigs. It has two panel-mounted controls — a single center-detent potentiometer that sets the center frequency of the filter’s bandpass (default value settable between ~415Hz and ~1kHz), and a dual-ganged potentiometer that provides a continuously variable bandwidth control (from ~60Hz to ~1500Hz). This ability to smoothly vary the bandwidth is very useful.

The NEScaf is designed to be driven with a phones or speaker level signal. No hacking into your rig — just connect it to the headphone or speaker output of the radio. This makes it usable with several radios. The board is small enough, at about 2 inches square, to build inside many radios however, if you so choose.

This kit is suitable for all experience levels. It uses all thru-hole components, and the construction and adjustment is very straight-forward. It is reasonably priced and will be a nice addition to the QRPer’s arsenal of tools.

The NEScaf is only $38 postpaid in the U.S., including the connector kit, which used to be optional.

Theory

The integrated circuit at the heart of the NESCaf is made up of two CMOS active filters. These filters are extremely configurable (low pass, band pass, notch etc). We have chosen to set up both filters as Butterworth band pass filters and to cascade the filters. Butterworth filters have the characteristic of constant amplitude in the band pass region, while the cutoff knee is not be as sharp as if the filter were configured as a Chebychev. We considered this an acceptable tradeoff, wanting constant volume out regardless of the bandwidth or center frequency setting of the filter. There are two on-board trimmer pots. One is used to “calibrate” the center frequency pot. This allows you to adjust the frequency at which the center detent occurs. If you are using a rig with a transmit offset and sidetone of say, 700 Hz, you can use this trimmer to make that the center-detent frequency. The other on-board trimmer adjusts the audio level into the filters output amp. Using this pot, you can set the overall gain of the filter. This can be used to set the filter for unity gain, if desired. This way, the filter could be switched in and out, and still maintain a comparable volume level in the headphones. The NEScaf has no panel mounted volume control of its own. It is designed so that you use the volume or RF gain control (if present) on the rig it is being used with.

Comments from the past:

  1. I saw two new NEScafs at our local Saturday morning ham breakfast today. They were built by Gene (AB1FN) and his son Vince (KB1JHG) of Charlestown, NH. Both got the kits at Boxboro last weekend. Gene won his kit at the QRP forum.

    Both looked great. Gene built his into a nice black enclosure with beautiful panel labeling he did. He added a “VU” signal level meter to the front panel. It looked really slick.

    Vince had built a 40M RockMite into an Altoids tin and wanted to add the filter. He had previously removed all the paint from the RockMite’s tin. He did the same to a second tin, and built the NEScaf into that. he then soldered the two tins together to make a nice compact package.

    Both gents said that they really liked the performance of the filter. I hope to have pictures to post of these sometime soon. Those who have built a NEScaf and would like to share a photo can post it to the NEScaf Gallery page.

  2. OK one more up and running on the Left Coast this time. Set it up for my NorCal 40A and centered the pass band on the side tone. Besides the noise reduction, it really does indicate “zero beat” with the filter set with a very narrow pass band.

    Neat project, thanks for doing this guys!!

    73

    Doug W7RDP

  3. 2/2/07 OK I installed the LMF100 and the CMOS 555, not sure what the CMOS 555 did but the LMF100 is much more quiet than the LM10, very big decrease in noise level. I will have to see if MAXIM will send me some samples of their version to compare with the LMF100.

    Still a very cool project, you guys just need to stock up on some XL t-shirts 😉

    73, Doug W7RDP

  4. Steve KA4NRF, Came back from Boxboro with the kit and before I could build it received the 2 LCD freq display kits so I was swamped. So between the Kids and work finally got around to building all 3 kits and the NEScaf is awesome,share it with my FT817 and SW40+. Worth its weight in gold.
  5. hi guys,

    I really liked the New England QRP club’s switched capacitor audio filter kit,

    but i thought it could be better, a little quieter. at first i thought the lm386 was adding some hiss. instead of using the lm386 i used a tda2003. used the circuit from page 27 of the sprat passed out at lobstercon, titled “High Performance Headphone Amplifier”. i think most of the noise thats added is coming from the scaf itself and not just the 386. if the band is noisey its not objectionable but if the band is very quiet and especially if the signal is not very strong then there is room for improvement. regardless I still find it very useful for figuring out where zero beat is, and i have been amazed at how well i can sometimes isolate a signal from nearby interference.

    if you used a 20 pin socket (radio shack 276-1991) then replacing the scaf chip is very easy. National made the MF10 supplied with the kit. if you go to their site they recomend an LMF100 as an upgrade. this is a ‘pin compatible’ drop in replacement. couldn’t find it at mouser but they did have them at digikey for $6.09 for one (in addition to tax and shipping, digikey adds a $5 charge if your order total is less than $25). the other alternative drop in replacement is a MF10 made by maxim.
    http://www.maxim-ic.com/parts.cfm?p=MF10
    couldn’t find them for sale anywhere but if you sign up with maxim you can request a sample, the MF10CN and MF10BN are 20 pin dips, not sure about the others or what the cn & bn mean.

    i have tried both the LMF100 and the maxim chips and they are quieter than the National MF10. not sure which is the best as both the replacements seem about the same to me but enough different from the stock National MF10 that i think you will notice it and be pleased with the improvement.

    72
    jerry terres aa1of
    franconia nh

  6. I have built the NEScaf into 3 rigs, and find it terrific. I am ordering one more to set up separately. VERY useful kit!

    John-W2AGN

  7. The minute I put power to my newly built SCAF, it came to life and worked! I guess you could say it was CLEAN!

    Dennis–K1LGQ
    Brookline, NH

  8. Hi Jerry,

    as I checked with Maxim (even directly with their manager) they are not able to produce the MF10 -> they are not sending the samples MF10BN/CN as You mentioned.
    Can You specify where You got them please?

    73, Petr OK1RP

  9. They may or may not be willing to send you a sample, its up to them. the “+” designation at the end of the part number, for Maxim, means lead free. the BN version is a DIP (dual inline pin vs surface mount type).to request a sample try using this link: http://www.maxim-ic.com/parts.cfm?p=MF10
    next to “MF10BN+”, click on “sample”
    on the resulting page click on “sample now”
    up near the top of the same page click on “Sample Cart”
    put what you want under “customer part or reference number#”
    under “sample quantity” change to “1” if you want (2 is ok)
    under “annual usage” i estimated ”
    under “annual usage” i estimated ” click “continue”
    click “Register if you are a new user”
    register for membership by filling out the contact information and click “submit” then check your email.
    To my ears the Maxim brand MF10 sounded as good as the MF100. If the kind folks at Maxim decide to send you a sample then you can decide for yourself.
    72
    jerry terres aa1of
    franconia nh
  10. Jerry,
    thank You for reply. I know how to order Maxim samples and I did exactly as You mentioned but…instead of the shipping I got message from manager of Maxim that they are not able to produce that product and that is not possible to ship any samples. Even for my second request I got reply that there is no way.

    73, Petr OK1RP

  11. I recently received my NEScaf kit, and the .33uF capacitor is missing. I was unable to locate a like-value replacement at Radio Shack. Is there a substitution value that is suitable for this component; or can I get a replacement from NEQRP?

    Thanks,
    Roger Lange, KC3DI

  12. Hi Roger.

    Sorry for the delay in replying. I have forwarded your message on to Dave, NT1U. He should be able to get you a replacement cap shortly.
    73,
    Bruce N1RX

  13. Nice Kit! I have it hooked to my Rock Mite 40m. The only snag I have run into is setting it up, I find the instructions here Very confusing.

    Page 49(!) says to hook the right tab, front view, to the “correct” circuit board location. The schematic shows the wiper hooked to one of the other tabs, which one, who knows! So it is anyones guess which way to hook it up.

    Page 59 says to adjust the Bandwidth (R7?) to it’s widest position, not sure which way, I adjusted it for loudest sidetone.

    Then it says to narrow the bandwidth and adjust the center freq. to keep it audible. It then says to set the BW to its narrowest setting and peak the audio with the Center Freq control. What is the point? Why not set the BW to minimum and peak with the CF. What are we doing here?

    What about R9, the pot on the PCB going to the 555? No mention of it’s setting that I can find…..

    Thanks for the help

    Rich

  14. Hi Rich.

    I don’t see any other replies yet, so here goes.

    First off, the manual needs some updating/correction. When reading the manual, “page49” should be read as “4 of 9”. Editing oversight. On to your specific questions…

    R7 is the front-panel mounted, dual section potentiometer. It will control the bandwidth of the filter. Each section (front and rear) are wired to a separate set of holes on the PC board. For each section, the “wiper” or middle lead, goes to either R7a_W or R7b_W. doesn’t matter which, as long as you wire the corresponding “end” connection for each section to it’s corresponding pad.

    So, if you call the front section “a”, then the wiper of the front-most pot section will go to point R7a_W. One of the end connections will go to R7a. Which “end” of each pot section you use depends upon your personal preference for how you want this control to behave. The filter is at it’s narrowest (minimum bandwidth) when the pot is turned towards it’s minimum resistance end.

    If you want the filter to get narrower as you turn the pot clockwise, then use the pot connection that the wiper moves toward when you turn the pot clockwise. If you want the filter to get wider as you turn the knob clockwise, then use the other end. The important thing is to wire both pot sections the same. You can always swap the leads over to the other side of the pot if your preference changes.

    Re page 59 (5/9)bandwidth pot initial setting: The intent here is to initially set the bandwidth pot (R7) to it’s widest setting. Which way to turn it will be determined by how you wired the pot in the step above.

    Thoughout the procedure that follows, the front panel frequency pot (R10) should be left in it’s center-detent position. The frequency pot pot being adjusted in this process should be R9, the board mounted trimmer for the 555 clock generator. The goal through this procedure is to end up with the center detent spot on the front panel pot to be set at your sidetone (transmit offset) of choice.

    I hope this helps to clarify things.

    73,
    Bruce N1RX

  15. Thank you Bruce, that helps a lot. I think the key missing bit was any mention of R9.

    I will try it again. Other than the setup instructions the filter kit is very nicely done and a real value.

    73

    Rich

  16. Jerry,
    thank You for help -> but again…there is copy paste of the reply from Maxim:

    Petr,

    We would like to sample you this product, but we are no longer manufacturing this part. We do have many filters, perhaps you could browse our webpage. Maxim-ic.com and find an alternative. From what I know, the MF10 series has been killed for more than 6 months.

    Thank you,

    Kyoung Kim
    Maxim Integrated Products
    Inside Sales Associate

  17. Just finished building the NESCAF and wow, it works great. Received it in 2004 I think and finally got around to it. It works really well. I hooked it to my MicroR2 receiver that was just completed a couple of days ago. Makes a great combination.

    Just ordered the M100 chip. Thanks for a great kit!!

    John Arnold WA6YSY
    QTH: Ocean Shores, WA abt 75 miles West of Olympia

  18. I just completed my NESCAF and I’ve tested it out. I built it to use with my backup rig, an Alinco DX-77T. I have to say that I am completely impressed. Not only has it worked well for me on CW, but I cranked open the bandwidth, moved up the center frequency, and listened to some SSB using it.

    I put my unit in a Bud cast aluminum enclosure painted gray to match a passive SSB LP filter I built previously. With both of these in line the band noise is cut down considerably.

    Excellent job to all who put this one together.

    Andy N1KSN
    NEQRP #176

  19. Can I just bypass the Vreg and power it from a PP3 battery?

    73 cheers
    Nick m0NjP
    SW England (old)

  20. Hi Nick. I assume a “PP3” battery is a 9 volt type? If so, then the answer is yes. The Nescaf can be run from a 9 volt source if the regulator is removed, and replaced from input to output pin by a jumper.

    Download the manufacturer’s data sheets for the MF100, LM555, and LM386 for the operating voltage ranges of these IC’s, if you are interested.

    73,
    Bruce N1RX

  21. Just got my NESCAF up and running. Seems to work great!

    However, there is one “undocumented feature” that has me a bit confused.

    I plugged the NESCAF into my Rockmite 40 and I was amazed at the fabulous performance of the NESCAF. Worked so well, I started calling CQ in hopes of a FB QSO. Sure enough, I contacted some fellow way off about 1500 miles to the east.

    HOWEVER – about half way thru the QSO, audio went flat – a little bit of internally generated noise, but no signals and no static.

    Fiddling with the two knobs did nothing, so I cycled power with the on-off switch and all was well again.

    This has happend numerous times. Usually as I am in the middle of a QSO, – you know – pounding away with the paddles, and then BTU but no dice cuz the audio has gone away again. I then quickly cycle the power and try to guess what the other fellow’s first word was. Once or twice the audio just diminished rapidly as I was “reading the mail”.

    What gives?

    Anyone else ever experience this?

    Carl
    WA7CS
    Pasco, WA

  22. That’s a new one on me, Carl. The situation you describe sounds as though something is failing after it’s been running a while. Perhaps a poor solder connection somewhere.

    If you have access to some test equipment like a voltmeter, etc you could do some tests to narrow the possibilities. For instance, when the audio seems to disappear, check the output of the 9 volt regulator. Is it still OK? Similarly, you could check to make sure power is getting to the appropriate IC pins when this happens.

    Of course, an oscilloscope or frequency counter would allow you to see whether the clock generator (LM555) is still producing it’s output pulses, and are they getting to the SCAF chip. An oscilloscope would allow you to follow the rig’s audio signal through the filter’s signal path.

    I’d start be double checking ALL the connections, looking for cold solder joints, etc. Also check all the IC pins. If you used IC sockets, make sure a pin is not bent over, and just touching the socket not actually entering it.

    GL,
    Bruce N1RX

  23. Thanks for the input – however I was hoping against hope that this was an oft-encountered scenario that could be cured with some simple and obvious magic.

    Darn – I just hate it when the first suggestion is to check for cold solder joints. I guess that is probably because that is usually the problem.

    Since this phenomenon is unheard of to date, I guess I’ll just do what I knew what I’d end up doing in the first place – checking those solder joints.

    Maybe I’ll get lucky and find a bent IC pin. I’m glad I put those sockets in there!

    Of course, I have already managed to shoe-horn the board into a teensy little tin. A perfect fit that will probably never be replicated.

    For some reason, if I just clobber a project together it works like a charm the first time and forever more.

    If discipline wins out over speed and a burning desire to get ‘er done, I ALWAYS end up taking apart a beautiful bit of craftsmanship.

    Taking it apart will give me a good excuse to add a nite-time bypass switch for the BCI resistor at the RCVR input. Right now I just poke the resistor into the ckt board holes when needed.

    I wasn’t kidding about the performance of the NEScaf – it really does work better than I expected.

    Good stuff!

    Carl
    WA7CS
    Pasco, WA

  24. I have my SCAF going and it is very nice, I got an extra MF100 to make a notch filter but have stalled out. Has anyone built a notch filter (band reject) with this? I find some information on the web but I guess I need a paint by number sort of detailed plan.

    Thanks for any help.

    73 Jerry

  25. Hi Jerry.

    The datasheet for the LMF100 chip provides guidance on using the IC as a notch filter. I have not done it myself, so I cannot provide you with ‘paint by number’ directions at this time.

    I will say that if you decide to set up a separate stage as a notch filter, in tandem with the standard bandpass filter, you should feed it with a different clock generator. Otherwise, the notch would be at the same frequency as your peak (!). It should have a separate clock so it’s center frequency can be controlled independantly.

    GL,
    Bruce N1RX

  26. I measured the resistance of the dual gang pot, and am reading 50.8K on the front section, but, only 46.2K on the rear section, as measured with a Fluke 110 DVM.
    Will this cause any problems in the operation of the Scaf Filter? I don’t think so, but want to be sure, before I mount it.
    73, Bill, k6mgo
  27. This won’t be any problem with the performance of the Scaf, Bill.
    -Bruce N1RX
  28. I would like to use the NEScaf filter between the audio output of my Elecraft K1 and the input to my Soundworks PC audio amp/speaker system. From some preliminary experimenting, the Soundworks amp needs little drive and I think I might be better off if I eliminated the LM386 from the design. I’m not a designer, so I am wondering at what point in the schematic would it be best to “tap-into” the circuit and eliminate the LM386. I am thinking right after capacitor C9, but I’m just guessing.

    I would greatly appreciate comments from the more advanced builders out there on my plan and especially the tap-in point.

    Thanks and 73,

    Hank/KEoCU

  29. Hi Hank.

    Yes, on the output of C9 would be the place to tap your output. You would still want the on-board volume control in-line, so you can set the proper level.

    GL,
    Bruce N1RX

  30. Thanks, Bruce. Can I just not attach the components at all to the right of C9 (all the audio amp circuitry) and expect everything to work ok?

    Hank/KEoCU

  31. Yes, Hank. For your ‘line level’ ouput application, you can just leave off all the LM386 circuitry. Or…. you could put all those components in. Just put an 8-pin socket in place of the amp IC. That way, if you decide to use the amp later, you can just plug the chip into it’s socket.

    73 es GL,
    Bruce N1RX

  32. In putting my NEScaf kit together, I couldn’t find any polarized caps labeled “105” per the wiring manual (March 2008). I did find 3 unused caps labeled with 1 microfared and the number “35”. I assume these are OK, and I am going to use them, but I also wanted to check with the Pros. Comments? Thanks and 73!
  33. Looking at the March 2008 version of the wiring manual, there are, what look like to me, some contradictions which has put my completion of the NEScaf filter on hold. They are all on the page which contain “Stage 3: Clock Generator” and “Stage 4 The Scaf Filter”.

    About R10, the last line of the first paragraph says “The right tab and center wiper tab on the pot are connected together with a short piece of wire.” This is not shown on the schematic included in the manual. So which is it?

    About R7, the 4th paragraph is very confusing as to which is the wiper terminal and where it is connected. We have “Take care that the wiper connection (middle pin on pot.) goes to the designated W connections on circuit board.” But 2 sentences later “Looking at the front of the potentiometers, connect the right tab of each gang to the correct circuit board location labeled W.” Huh??

    I’m pretty sure I know what to do here, but this part of the manual doesn’t make sense and I would like to have this cleared up. Any takers?

  34. The three caps you have are correct. The “35” indicates the maximum working voltage for the cap. Just take care with polarity when you install them. There should be a small “+” symbol near the positive lead.
    GL,
    Bruce N1RX
  35. Regarding the instructions for the pots- R10: It doesn’t really matter if you short the wiper to the “unused” end or not. The pot in this case is being used as a two terminal variable resistor (or “rheostat”). In general practice, the unused end of a three terminal potentiometer is shorted to the wiper. This prevents the device from presenting an open circuit if the wiper should fail. In the NEScaf, it doesn’t matter if you do this or not.

    R7: This is the dual section “bandwidth” pot. You are right, this section of the instructions is, at best- confusing. At worst- incorrect.

    The first two sentances are correct- The wipers, or middle tabs or each section go to the R7a_w and R7b_w connection points. (W is for wiper) The Third sentence is incorrect. The right tab of each pot section should go to the R7a and R7b connections, respectively. I have rewritten that paragraph below. Hopefully this is clearer.

    “Panel mounted, dual gang 50k Ω potentiometer–Take care that the wiper connection (middle pin on pot) goes to the designated W connections on circuit board. The circuit board is labeled R7a and R7a_w for the first ‘gang’ or section, and R7b and R7b_w for the second. The W stands for wiper (middle tab on each potentiometer section).
    Looking at the front of the potentiometers, connect the center tab of each gang to the correct circuit board location labeled W. The center tab (wiper) and the left tab are connected together with a short piece of wire. Next, connect the right tab of each gang to the correct circuit board location for each gang( R7a and R7b). So, if you connect the center tab (wiper) of the pot section closest to the shaft to R7a_w, then connect the right tab of that same pot section to R7a. Twist the two leads to each pot separately as it makes it easier to keep track on the PCB. Some components already mounted on the circuit board might ‘hide’ the W so be familiar with the PC board layout. ”

    Hopefully this will help sort this out, Hank.

    73,
    Bruce N1RX

  36. Bruce, thank you very much for your post. I did end up wiring the components correctly, and the NEScaf is working, although I have yet to install it in an enclosure. Still looking for the right one.

    73,

    Hank/KEoCU

  37. You know right at the end of assembly Stage 1, where it sez power it up, and then warns the builder to be extra careful regarding reversing polarity. Well, you guessed it!. I let the magic smoke out of the 78L09.
    I am organising a replacement 78L09, but I am wondering if I have damaged any other components in the Stage 1 build. All the resistors appear unharmed, but I have no way of checking the capacitors. Anyone any thoughts ?

    A very embarrased Wallace MM0AMV

  38. I don’t believe that anything could have been affected by reversing the polarity at this point. Until the ic’s are inserted, pretty much everything there is immune. You may want to take a look at an article Joe Everhart wrote which is posted on the njqrp site

    http://www.njqrp.org/quickies/quickie2.html

    about various reverse polarity scenarios. In this particular application, a reverse diode in series with the power may be all you need…but I still recommend reading Joe’s article.

    cheers
    /dave

  39. Hi Dave,
    and thanks very much for the info. Its put my mind at ease, and hopefuly when the replacement 78L09 turns up tomorrow I can press on with the build.
    I am color blind and I suppose I really shouldn’t build stuff, but I enjoy it and I am normally very very careful. I will put it down to a moments madness!
    Thanks also for pointing me at Joe Everhart’s page. I cannot track down IN6277 over here, but I have located the alternative 1.5KE18A. I will be incorporating that neat little bit of circuitry into future builds, and also doing a bit of retrofitting.

    73 Wallace MM0AMV

  40. I am going to start soldering my kit but also need to get a box for it. I want something sturdy, doesn’t have to be bulletproof like the Hendricks BLT cases but I would like something tough.

    Any info on the right size box, name or model number, etc. would be appreciated.

    Thanks and 73

    Rem
    K 6 B B Q
    The BBQ Ham Shack
    10 miles North of the Golden Gate Bridge

  41. Hi Dave,

    Well, the replacement voltage regulator finally turned up and the rest off the build went like a dream.
    The filter works really well in fact much better than I had anticipated. This accessory is a keeper.
    Thanks once again for your help.
    I have put a couple of pics (without the burnt out 78L09) in the NEScaf Gallery.

    73 de Wallace MM0AMV

  42. John,
    I have a k2 -10 watt use it for Qrp. How does the filter preform on SSB.? Have you heard of anyone using it for SSB
    with the K2?

    tnx
    carl W3IY

  43. Hi Carl.

    The NEScaf has been used by some for SSB, though it was designed primarily for CW use. You would set the center frequency somewhat higher than you would for CW, and use the filter near the upper end of it’s bandwidth range. One could also recalculate resistor values in the filter stage to provide a wider response.

    That said, the K2 has excellent IF-stage filtering already. The K2 XFIL values can be adjusted to your preferences, and tailored to your specific likings using a program like Spectrogram. The four available settings would be in discrete steps, however.

    I have tried my NEScaf on my K2, with the K2 XFIL set for it’s widest settings, and it works pretty well.

    72,
    Bruce N1RX

  44. A very nice filter!

    I was particularly impressed with the quality of the pots and power connector. Where did you obtain them from ? It is hard to tell what you are getting when ordering things online.

    Thanks

    Phil Sanders
    AB8EO

  45. Hi Phil. Thanks for the nice comments.

    We did a bit of research on the potentiometers during the prototype phase. The ones used in the NEScaf kit are purchased from Mouser. The manufacturer is Alpha.

    The power connectors are from Jameco.

    73,
    Bruce N1RX

  46. ‘rx’d the kit a few days ago and fired it up today..no smoke & it even works…my faith in kit building is restored! all that remainn is to complete the custom enclosure.
    thanks, Randy

    Argo 515 & IC706MKII
    truck&rv mobile too

  47. I would also be interested in using the NEScaf on SSB and even AM if possible. While I do a lot of QRP, I would like to have a filter to get rid of all the hum and noise in vintage tube recievers, especially when listening on modern headphones which seem to be almost too sensitive for these old sets. I have a LogiKit SCAF-1 dedicated to one rig now, and would like a smaller unit to use with phones on other rigs. Can you provide any guidance on recalculating the componet values to get 2500-3000 Hz bandwidths?

    Thanks,
    Parker

  48. My NESCAF is cutting out after a few minutes, works fine again upon recycling power; then audio gradually dissappears. I’ve reflowed all the solder joints, checked the voltages. Nothing obvious.

    When I take IC1 out of the socket, the audio is fine and doesn’t cut out.

    Since I didn’t observe strict anti-static practices; I’ve ordered a new MF100.

    BTW, tThe filter works great – just what was needed for my Rock-Mites. I just hope I can get it to work longer at a stretch :>)

    73,

    Jim, K4AXF
    Strasburg, VA

  49. I reported gradual distortion coupled with loss of audio through the filter. Although the filter seemed to be working fine, it would go dead after a few minutes. I replaced C17, the input cap with an exact replacement from Radio Shack and the problem ceased. My NEScaf now works perfectly. Thanks to Bruce, N1RX for some helpful hints.

    73,

    Jim, K4AXF
    Strasburg, VA

  50. I am trying to finish building a NeSCAF filter, and it is not working properly. I think it was working properly, but I didn’t have long enough leads on the various offboard components, so I removed and resoldered all of them. Now, the audio is fine until I switch the filter on, then it makes a loud buzzing noise. I thought that I may have torn up the traces when I removed the old wires, but I checked all of the leads with an ohmmeter, and they all appear to be correctly soldered. The tone of the buzzing noise changes when I adjust R14, but adjusting any of the other variable resistors has no effect. Any ideas would be greatly appreciated!

    Mike, KL7MJ

  51. Dear folks,

    did somebody tried to improve the noise floor of the LM386 by adding the 10k resistor and 10n capacitor in series between pin 8 and the output pin as it was published in the Oklahoma QRP News Letter and then after by KA4UOS in Sprat nr.79 please?
    I am interested in the results…

    Thank You for responses in advance.

    73 – Petr, OK1RP

  52. Well, we shovled out the bathrooms….then it was time to attack the Argo 509 with soldering iron and duct tape!!

    Got the stock 4-pol filter replaced with the INRAD #751. It is a wire-in mod NOT a drop in replacment as the older T-T filter was. The results (viewed on Spectragram) are very interesting. The RX bandwidth is definately narrower, still not narrow enough for serious CW but definately much better than the stock fiter.

    Got the SCAF filter out of the bag, put it on the ops table with some clipleads and tied it all together on the AF output of the 509. MAN!!! What a filter!!! I LOVE the continuously variable BW. It really makes a difference. I only wish I had it up and running in a box to demo at the local club meeting last night. It would have really raised some eyebrows!!

    At any rate, it will be going in a box (sans clipleads) and I will use it until I order another one (with the newer chip) to include in the “Argo-Mate”. As I understand it, from reading the comments, the newer chip seems to be quiteter than the older version I have. Also, there was some discussion about fiddling with the LM-386 to reduce noise. Will have to look into that.

    All in all, gang, you guys done good!!! I am writing Dave Ingram’s “How it Works” column while Dave is in hospital recovering from a wicked heart attack. Just got the word from Rich Mossesson, W2VU at CQ, who asked me to pinch hit for Dave for the forseeable future until he gets back on his feet. Realize this: I will be sure to plug the SCAF filoter in that column. NO reason for anyone to go to AF DSP with the additional costs when this $30 wonder works so damned well!!

    Vy 73

    Rich Arland, K7SZ

  53. It turned out that I had one (or more) cold solder joints. A few minutes reworking them last night and all is well

    This is a great filter!

    73,
    Mike, KL7MJ

  54. I just ordered two of the new NESCaf kits. Is there any change in the schematics/layout or can the old Manual Rev. 2008 still be used?

    73 de Hermann W4/DL8MCP

  55. Hello Hermann.
    There are only a few minor changes to the parts included in the kit. The layout on the board has not changed. One capacitor, C3 has changed to 100 uF from 10 uF. We are using a new SCAF chip, the LTC1060. Also, the trimmer potentiometers may come in one or two style of pin layout, due to parts availability. Either will work fine with the board. I am completing a revision to the manual that will include these changes. I hope to have it on the web page by 30 April.
    -Bruce N1RX
  56. Hi folks,

    did You compare the results of the NESCAF filter using the old MF100 and new LTC1060 replacement please? I am interesting the differences and results…

    Thank You for Your time,

    73 – Petr, OK1RP

  57. Hi Petr.
    I have compared the published spec sheets for each. There are some minor differences, but neither stands out as a clear winner. I have done some “A/B” audio testing as well. I have not noted any significant difference between the LMF100 and the LTC1060. In our application, they appear to be operationally equivalent.
    73,
    Bruce N1RX
  58. I am surprised that no one has mentioned this. C17 should be reversed, with the + end going to the filter IC, and the – going to the audio input. The input pin on the IC is sitting at ~ +4.5 volts, and the audio input should be at 0 volts DC level. With the capacitor reversed bias as shown in the diagram, it will draw significant amounts of leakage current. I found that the leakage from having the capacitor reversed would pull the bias at the IC down and cause distortion, when I switched the input from one rig or another. With C17 put in the right way, and a 150 ohm resistor (or even smaller) at the input to assure that the external source is at zero bias, this is no longer happening. – Al N7HO
  59. Hi Al.

    Thanks for your post on this. What you say makes sense. It -is- interesting that you seem to be the first to have a cap leaky enough to cause a loading issue. I agree that it would be a good idea to install C17 with the positive lead toward R2, and the negative lead to the audio input jack.

    I will look into changing the documentation and possibly the board silk screen on any later runs.

    72, Bruce N1RX

  60. Can the NESCAF be used on digital modes like PSK31, RTTY, Olivia, etc?

    Thanks!

    Pete WB9FLW

  61. Yes, Pete.

    The NEScaf can be used on these digital modes. -Bruce, N1RX

  62. Spend some time listening to true binaural CW and you will discover a new listening experience. If you have a few moments… read on.

    A bit of background:

    I believe it was a lat 70s article in Ham Radio Magazine (no longer published) that first introduced me to “binaural” CW reception. Over the years I have build several variations of “binaural” CW audio filters. The intention was to purposely split the incoming audio into two bandwidths – at and lower than the desired CW beat and at and above that beat.  As I suspected, when accomplished correctly the resultant “panoramic” sound image adds a new dimension to CW listening. The first thing you notice is that received background noise is divided into a lower and a higher audible frequecy spectrum with each ear hearing only one. This splitting action significantly reduces the apparent overall “heard” noise levels. But more importantly, incoming CW signals are heard literally through your head… from one ear through to the other. Tune through a single signal and listen as it is first heard in one ear and then slowly moves through your mind’s sound stage to the center. Keep tuning at it moves from that center off to the other side. Have trouble zero beating a signal? Binaural reception makes it almost automatic.

    It is amazing how much filtering our brain can accomplish automatically if we apply differing audio signals to each ear. You don’t need complicated stereo simulators either. Simply use two filters to split the audio for the left and right ears. A low pass design with its high cutoff right at the desired CW beat, and a highpass filter with its lower frequency cuttoff at that same beat. Now rather than add increasingly sharp filters (with distortion and ringing) to get a single CW signal, you open up the receiver bandwidth (say 900 hz of so) and listen to the clean audio images as they image through your head. The signal you want is heard in the center…. signals lower in frequency are heard progressively toward one ear, while signls higher in frequency are heard progressively toward the other ear. Add to that natural separation, the broadbanded background noise is also split into two frequency halves and that additional separation creates an amazing overall reduction of apparent “heard” noise.

    Enter the NEScaf filter:

    Up till now, my binaural filters all had one issue or another that left me unsatisfied, to say the least. About two years ago I first saw info on the NEScaf filter and had a though…. “what if I used two of them?” It took some time for this project to move to the top of the pile, however it did and I am very satisfied.

    Naturally the simplest approach was to install to NESaf boards into a single project box… parallel a mono input to both filters and then take the output of filter A and apply it to one half of a stereo headset and the output of filter B to the other half. Simple enough it seemed, but I did encounter two issues with my approach.

    1. Hum. This turned out to be easy to fix and really had nothing to do with putting two filters in the same box. My mistake was to use a standard 12 vdc wall wart. The hum completely disappeared once I connected my NEScaf filters to the regulated power supply that I use for the Argonaut V. I could find no mention of this in the manual.

    2. Mutual self-oscillation. This one had me going at first. Individually the filters worked great but once they were in the same box in close proximity to one another they output more oscillation spurs than signals by far…. and toucing or adjusting either filter’s frequency control only created differing oscillations. Filter one’s control effected both filters and visa versa. I quickly deduced that the approximate 70 kHz waveforms from the 555 timers were coupling back and forth to each other. The fix? I stripped off a few inches of RG-8X braid and ran the two signal wires from each board to its center frequency contol. Grounded the braid on the body of the control itself…. Put a little shrinkwrap at each end to protect from shorting other circuits (it is a small project box)…. and viola! No feedback.

    The NEScaf binaural listening experience:

    Paralleling two NESaf filters together really does create a fantastic binaural CW filter. You can adjust both filter’s to center the image on theCW offset of choice. And you can talor the upper and lower spectrum halves independently.

    Food for thought:

    Already have one NEScaf filter? Add a second one. They don’t have to share the same box. Just parallel the inputs and apply the outputs to a pair of stereo headphones. Keep note though. If you build your filters into non-shielded enclosures you may experience the self-oscillations problem. If you do just add a piece of braded shield around the two wires to each filter’s frequency control.

    73,

    Jerry, KG6TT

  63. This kit was a VERY easy build and it performs quite well on the air. I particularly like how it enhances my SW40+ and other less capable Manhattan style receivers and transceivers. I have been meaning to put it in a case for a little while now. The XYL and I were out at a local “dollar” store and I found a bunch of kids puzzles packaged in flashy tins. The filter is mounted in a Winnie the Pooh tin. You can see it in action on my YouTube page:

    http://www.youtube.com/user/N2BHA?feature=mhum#p/u/5/YCRyk6samz8

    and

    http://www.youtube.com/watch?v=HZF5IN2oqhQ&feature=channel_video_title

    Many Thanks es 72,

    Vaughn  N2BHA

  64. Wallace,

    I just did the same thing.  What were the responses to your query regarding that problem.  I heard a pop, but saw no smoke.  Plan on replacing the voltage regulator but wonder what other things I blew…

    72,

    Dave K8WPE

  65. Hi, Dave.

    Sorry to hear about your mishap. I would suggest looking closely at C15 (0.33uF tantalum). It is directly across the input DC line. It may have failed, and that may have been the “pop” you heard. Also the voltage regulator. Did you use IC sockets? If so, remove the ICs from their sockets after you replace the regulator. Check the DC voltages on the appropriate IC socket pins when you reapply power. In some cases, IC2 (LM386) may be damaged by reverse polarity, as well as C11 (100uF electrolytic).

    I suggest adding a series diode with the positive power lead to prevent recurrance. Let me know If I can be of any further help.

    GL, Bruce, N1RX

  66. Hi

    I see that the LTC1060 data sheet offers a lower noise/offset configuration on page 18 of the datasheet,

    Set Sa/b low, connect S1 to LP out.  We may be talking about miniscule differences here – but I was just curious.  I guess the real question is – with the input disconnected & the volume control on max – is there any audible noise ??

    Villy  ve6sq

  67. Hi folks,

    Found an easy way to get the SCAF properly calibrated using the FT-817:

    Set SCAF center to detent and bandwidth to full narrow.

    Set 817 to any frequency and mode to CW.

    PAH (Press And Hold) the HOME button and screwdriver the pot in the 555 circuit to max volume in the speaker.

    Then the filter is set for 770 Hz (or whatever you have the sidetone set to).

    Slick, quick and effective. Done deal almost instantly. Only had to flip up the top cover and stick a small screwdriver in and diddle :-).

    PAH on the HOME button just emits the sidetone when in CW mode.

    Great to zero beat too.

    Love the 817 :)!

    72 de Vikki (WV9K).

  68. HI,
    Received my kit here in Japan fine. After building it, it appears trying to work but as I slowly turn the R10 frequency pot from max to min and back there appears to be many spurious oscillations that can even be heard in the receiver without the audio connected. After many inspections of soldering and proper component insertion, Im at a loss. Has anyone had anything similar happen? Any suggestions would be greatly appreciated.

    tnx
    Rick in Tokyo

  69. I thought I better follow up my previous post with the solution to my problem. Due to my location on the 5th floor of a Tokyo apartment building my receive antenna is a simple active loop located in the same room as the receiver. The original enclosure for the filter was a box that had plastic ABS front and rear panels. Anyway the 555 timer harmonics were being picked up by the antenna!. The solution was to rebuild the filter in a tightly sealed aluminum box, shield all internal audio cables and also to use ferrite clip-ons on the external power and audio cables..
    Now the filter REALLY works. Being able to smoothly vary the filter frequency and bandwidth makes using this filter a real joy.
    My thanks to all at NEQRP who have made my new toy possible.
  70. Hello,
    I built my NEScaf few years ago and find that it is excellent! Ive been thinking of building another one, but modifying it into a notch filter. Has anyone done anything like this? Ideas? Advice?

    Thanks and 73!

    Paul
    N6MYA

  71. I built my NEscaf into a nice black metal box and it works fine but at various times I get BCB interference at certain frequency positions and it is worse when I touch the box.  I assume I can bypass certain parts of the filter with caps but don’t know where to start.  Any suggestions?  Thank you.  K8WPE

    PS the filter works great to reduce or get rid of local electronic noise in my house and the neighbors plasma TV set.  Please respond to DjWilcox01@aol.com