EPFM Super Tone Control problem

[taeagan]

Anybody ever built this?  The problem I'm having is that the bass/low control doesn't work.  Everything else seems to be fine.  I've tried it with guitar and bass.  It just doesn't do anything - basically it's a two band control, only the treble and bandpass controls work.  I've checked my wiring a million times.  The only thing I did differently from the schematic was to use a 100k dual pot (instead of 10k dual) for the frequency control.  I tried different values for R18 and R19, but no impact on the effect.

[RickL]

I've built it (using a board from PAiA), and it works fine. In fact it was one of my first projects several years ago. I added the envelope follower project from EPFM and it makes a wonderful envelope controlled filter.

[Jakeb]

The circuit is quite picky about the capacitors you use. I had to swap a couple of capacitors to get my circuit work, but bandpass control is quite weak in my STC.

Try using precision caps and resistors for tone network, check your wiring and OP-amp.

- jakeb -

[toneman]

use polystyrene caps for stability.
these caps have a 5% or 10% tolerance.
this can make a big difference in the "actual" freq response.
measure them with a cap tester.
see the tread on capacitance testers..
staytuned
tone

[Mark Hammer]

Like Rick, I've made them several times over, in several decades.  Never had a problem.  I wish they were ALL so easy.

There is a nice mod in one of the issues of DEVICE posted at my site (http://hammer.ampage.org   probably around page 9 or 10), that shows how to increase the range of the frequency pot, so that it covers a broader range of corner frequencies.

[Mark F]

I built this circuit many moons ago. I included the mod from DEVICE & I mounted it in an old CryBaby shell. It worked right off first time. I was quite pleased with the sound & operation actually. I think I still have it somewhere.

[Joe Viau]

FYI, the mod appears in Device #8, page 13.  It's very simple and probably worth doing.

By the way, thanks to everyone here for such an excellent forum where knowledge is shared so freely.  There's always so much good stuff!  

[taeagan]

Joe, thanks for that link!  That may be pointing me in the right direction.  The edition of EPFM that I have includes this mod - sort of.  There's a note saying that if you don't use the dual 10k in the spec, you have to increase those two 33 ohm resistors.  I did that, but in that issue of Device it still has the resistors at 33 ohm with the dual 100k (which I used).  It also says that increasing those resistors increases the lower limit frequency.  Sounds like that could be my problem with the bass control having no effect.  I'll try it this weekend with the 33 ohm resistors in that mod.  Thanks!

[Joe Kramer]

Hi!

FWIW, the 2nd or revised edition of EPFM, which is probably more commonly refered to nowadays, already has the 33ohm resistor mod built into the circuit. Only the first and very early edition of EPFM doesn't incorporate the mod in the STC.  The article in Device is refering to the earlier version of the STC.  

Regards,
Joe

[Joe Viau]

In a related story....

GGG has a layout of the STC using the 5532 IC rather than the 4739.  Is anyone familiar with these ICs, and is one better? I know that the 4739 is fairly difficult to get a hold of, and that PAiA has an adapter that matches the 5532 to a 4739 footprint.  Is the 5532 lower noise?

TIA,
Joe

[Joe Kramer]

In a related story....

GGG has a layout of the STC using the 5532 IC rather than the 4739.  Is anyone familiar with these ICs, and is one better? I know that the 4739 is fairly difficult to get a hold of, and that PAiA has an adapter that matches the 5532 to a 4739 footprint.  Is the 5532 lower noise?

TIA,
Joe

Hi Joe,

The STC takes a quad op amp and the GGG layout still uses the 4136 quad.  The 5532 is only a dual.  The STC circuit itself is pretty easy to perf: it's the off-board parts that you have to pay attention to.  As far as op amps for it, I've had good luck with everything from the 4136 (if you have them) to TL074, to NJM4741.   If you wanted more options, you could build it for two dual op amps and use 5532's or your favorite flavor.

Regards,
Joe K.

[Joe Viau]

Whoops, sorry! I was looking at another project, not the STC.