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About lovekraft

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    Rabid Apathist
  • Birthday 11/25/1956

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    South Central ... Alabama
  1. Just out of curiosity, what simulation software are you guys using? I love my Circuitmaker Student 6.2, but it doesn't always tell the whole truth, and it occasionally gets so confused it simply gives up. Any better options (preferably for less than $1000)?
  2. Curtis: That's a nice little AGC circuit - it does, however, share the inherent problems of any JFET gain control circuit, ie, that both threshold and dynamic range will vary with the Idss and Vgsoff of the individual FET. Since the driver signal isn't part of the audio output (at least it isn't if we do things properly ), it probably won't matter much in this application. The feedback resistors around the FET will help linearize the response nicely, so you can probably adjust for device variance by trimming the FWR's gain - you'll simply have to try a few dozen FETs to be sure . Of course, using an optocoupler will give you more dynamic range, but since a little clipping apparently doesn't interfere with the driver signal's efficiency, it probably doesn't matter either. "Close enough" may be more than sufficient. In that spirit, you may find that a pair of 100K resistors will make a sufficiently "stiff" supply divider, and a JFET source follower could buffer the input, so you could use a dual opamp, further reducing current consumption - just a thought. Col: I'm not sure we have to worry about the lower threshold, since the drive signal should never enter the audio output path, and noise shouldn't drive the strings at all, but it may be a concern. I'd love to play with this myself, but I'm in the final stages of "product development" for a stompbox that's supposed to be available first of the year, and prototyping isn't going swimmingly, so my time is spoken for, at least until I can get something I'm happy with working consistently. Besides, it would take me months to get a coil wound, and I expect you lot to have a working system by that time. If you'd like a couple of these VTL5C2s to play with/blow up/whatever, by all means, don't be shy (ask Pete - I fried 2 JRC386 chips back in the early stages of this thread ). As for simulating them, when I was designing my (unfinished) compressor, I just modelled the sidechain to generate enough current in a red LED to turn the LDR on without frying the LED (according to the vactrol specs - I targeted a max current of about 35mA, as I remember). The breadboarded "first draft" worked, but didn't sound as good as Johan's LA Light circuit, and I never got around to tweaking everything out, having other commitments at the time. Let me know. Pete: Glad to hear things are improving, even if it's incrementally. Hang in there. And finally, Bancika I cannot thank you enough for the layout software! It's really spectacular - keep up the good work!
  3. They surely can't be any more varied than JFETs! Even the best made/most expensive JFET devices (Toshiba, Linear Technologies, et al) are all over the map, spec-wise, so they're gonna have to either be sorted for suitability (buy 1000, test 'em all, sell whatever won't work on Ebay) or trimmed in circuit somehow. A trimmer in parallel with an optocoupler's LDR should be sufficient for our purposes, and probably won't even be necessary if we use a production optocoupler like the Vactrol® or Siliconix Audiohm® devices. The only major problem with LED/LDR devices is the LDR has it's own attack/release characteristics, so you'll have to pick a model that's fast enough for your design. The good news is that LDRs are virtually distortion-free, have incredible headroom, and can be treated just like a standard resistor. Just my two cents - I think most FET compressors are prized for their non-linearities rather than their transparency, but that's just me. More info here: Silonex Audiohm site PerkinElmer VTL5C series Analog Optoisolators I've got a few VTL5C2s that I can spare, if anybody wants to try one - might be a wee bit slow, but "close enough" for proof-of-concept work. PM me if interested. I'd give it a go myself, but there are already too many irons in the fire around here, at least for the next few months. A limited bandwidth (~60Hz-3KHz?) opamp "ideal rectifier" (with some gain) driving the opto looks to me like the simplest practical sidechain, but what do I know? Y'all have at it - I'm looking forward to developments!
  4. Adjust the trimpot until you measure 4.5 - 5.0 volts from the drain of the FET to ground - this is to compensate for the huge variations in devices, an unfortunate by-product of the manufacturing process. The Fetzer Valve page has an in-depth explanation of this.
  5. This thread needs a full-time historian/anthologizer! Seriously, I've been "away" for a while, and just recently got my computer back up to full working status, so I've missed and/or skimmed through a lot of the recent developments. Anybody up for a semi-current "State of the Project" report, so we can avoid tripping down the same blind alleys we were exploring back in 2004? Apparently most of the recent work has been in driver design - can somebody do a basic comparison of the current ideas, contrasting the pros and cons of each design? I'd be ever so grateful!! If we can catalog what has ( and more importantly, what hasn't) worked in the past, we might narrow things down a bit, and not waste time pursuing approaches that have been proven repeatedly unsuccessful. Just my two cents - now I've got some in-depth reading to do.
  6. +1 - you can use 12 AWG solid Romex if you'd like, and it'll never affect the sound of the guitar (other than the result of all that body mass you'd have to remove to fit that much 12 AWG into the cavity!). All this "special" wire/pot/cap mojo obsession is simply designed to separate you from your hard-earned cash - remember, all those exceptionally sweet-sounding vintage guitars were built with the cheapest available wire, caps, pots and often wood back in the Fifties!
  7. Ah yes, the Holy Grail of audiophile caps - if Orange Drops are a wee bit silly, Hovlands are at least an order of magnitude sillier! For fifteen bucks, you can get either one Musicap™ or 100 or so 100v Xicon polyesters - that had better be a really good cap! Oh, and if you're into "designer" colors, check out the Wima FKM/MKM or FKP/MKP series for a really striking red hue (might go well with a cherry sunburst?). Short leads might be a hassle, but they're high quality, and very pretty!
  8. I hate to bust anybody's bubble, but Orange Drops first came to prominence in the mid 70s as replacement caps for real vintage amps - AFAIK, their use in guitars began with all the crossover mojo and misinformation that was marketed in the 80s. If you want vintage vibe, you're going to have to do better than that, like some real bumblebees or black cats, or those cool old oil and foil waxed caps - good luck finding the real thing for less than a small fortune. Use whatever you like, but keep in mind that using a 630V cap in a guitar tends to reflect on the judgement of the builder and/or the buyer, at least for some of us! To each his own, I suppose!
  9. There's nothing wrong with using Orange Drops, but there's no compelling evidence that they sound better (or make any audible difference, for that matter), at least in passive guitar electronics. Orange Drops got their street cred in tube amps back when they were pretty much the only readily-available film caps that modders could replace their coupling caps with, so using them in guitars is just transferring the Mojo. Frankly, I'd be surprised if anybody could reliably distinguish them from any other film cap when used as a tone cap, but then, I really didn't have any issues with the sound of the ceramic tone caps that were used universally for many years. The only caps I would absolutely avoid using here are tantalums and electrolytics - anything else is fair game! If you can afford Hovlands, it probably won't ever make an audible difference, but it'll sure impress some of those guys over at the Gear Page!! As always, YMMV!
  10. The two major disadvantages of using relays are switching noise and current consumption - since this project already has issues in both areas, CMOS switching would seem to be a better solution (although it has its own problems). Keep in mind that switching a relay coil on and off will not only generate another magnetic field to be dealt with, but the inductive nature of the relay coil will probably induce switching noise in the power supply as well. I know of at least one homebrew Ebow project that used a relay coil as its driver. Just my two cents - YMMV. And I wouldn't use a 4066 - a CD4053 gives you 3 SPDT switches on a single chip (see RG's ...Switching with the CD4053... article over at Geofex for more info).
  11. There's sure a lot to love about this bunch, from that gorgeous SG to the quirky hollowbody, but in the end, my inner child worships Neal Moser, and he outvoted me! How can you not love a bass in which the control cavity lights up for no apparent reason!!??!
  12. Did I say that? Actually, what I thought was that a square wave would be good enough, especially with a hex driver and bandpassed signals for each string. Now that we're down to a single channel, and having near universal problems driving the higher strings, I've developed a sneaking suspicion that optimizing the driver signal to drive the most difficult strings has become much more important. But that's just me -YMMV!
  13. The problem with clipping as compression is that as much as 20% or more of the energy generated is harmonic content that will not reinforce the fundamental, and may even interfere with it, so while the overall level is limited, the level of the fundamental (and hence the drive) may actually be reduced. Gain control should be noticably more efficient at driving the string, and limiting the preamp's frequency response with a steep low pass filter should eliminate almost all of the higher overtones, resulting in a reasonably clean driver signal, especially for the smaller strings, which are apparently more difficult to drive - somebody with a spectrum analyzer (and too much time on his hands) could probably figure out the necessary filtering in short order. Just my too sense...
  14. Not to hijack the thread or anything, but this might be important. Pete and I have discussed gain control in theoretical terms several times, and rejected it as too complex and fiddly, but this idea (from Brett Robinson, another proud Aussie ) might just make it a lot easier. Brett's come up with an ultra-simple compressor based on the 386: Brett's Aussie Compressor Since it works using a super simple feedback sidechain and a single MOSFET, it should be fairly trivial to integrate into Pete's basic power amp. For more info, see this thread over at Aron's DIY Stompbox forum. Unfortunately, I don't have the time to pursue this right now, but it's too good an idea not to share with the group - it could (theoretically) help even out the response curve over the entire frequency range, and make for much smoother sustain. Now, you maniacs take it and run with it - both BS170 and 2N7000 MOSFETs should be easy to find and fairly cheap, and the rest is stock components. If anybody gets truly superb results, please let us know!
  15. No, the LM386 has been around for over 20 years now - it's almost certainly the power amp pictured in the original Heet patent. It is definitely the chip in Bruce Zinky's original Smokey amp from the early 80s, so it was available even back in the dark ages.
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