Keeley TR-2 Tremolo

[TimF]

Does anybody know if Keeley changes the VCA (voltage controlled amplifier) in his TR-2 mod? I'm looking for a lower noise version of that chip. It's a Mitsubishi M5216AL.

[Andre]

Tim,

Looking at the schem, I think the VCA is IC1 which is a M5207L01.
I don't know if there's a lower noise version of M5207L01

Funny thing is, IC2A is a M5216AL, while IC2B is a M5281AL.
As the rest of the opamps used are all M5281AL I assume that IC2A is also M5281AL.

[TimF]

Sorry, my mistake. I was looking at the opamp part I had removed....

Ya so I've replaced all the parts in the audio path with metal film resistors, polyprop caps, the FETs with J201s the OP bjt with an MPSA18 and the opamps with an OPA2134. I beefed up some of the cap values and changed the resistor that contols the peak volume of the trem to remove that slight volume loss everybody talks about.

I was kinda hoping that all that would get rid of the noise but it didn't get to much quiter (it did a little) so the only thing left is the VCA.

[TimF]

one last bump

[Mark Hammer]

Um, are we sure about those various part numbers?  The M5207L seems legit enough (no replacement that I'm aware of), but Boss has a penchant for using M5218AL dual op-amps in a number of their pedals (and a damn fine op-amp it is).  I'm not saying there isn't an M5281AL chip, but the only reference I could find for it on the net was this TR-2 schematic:  http://www.freeinfosociety.com/electronics/schematics/audio/bosstr2.pdf

You will note that while the main body of the drawing shows the identical connections for each op-amp section on the "5281" as you'd expect to see on a 5218 and any other normal dual op-amp, the power connections shown indicate V+ going to pin 3, which conflicts with what is shown in the drawing (where pin 3 is the '+' input of one op-amp).  I appreciate the effort the person has gone to to draw the schematic (it is not a factory schem) but the possible part- and pin-numbering inconsistencies may be sending us on a wild-goose chase here.

So, just to allay my suspicions, is this REALLY a 5281?  Or might it be a 5218 with print so small that you relied on the posted schem to clear up what was otherwise hard to read?  I'm not questioning your judgment or honesty, just trying to find out if there is a typographical error at the heart of this.

And BTW, don't expect that all the"Keeley-fication" will always make a difference.  Bob's not an idiot or charlatan.  There ARE things you can do to improve noise specs in something that introduces lots of gain, and there ARE things you can do to eliminate audible ticking or other modulation-related noise sources in devices that don't have much gain.  But something like the TR-2 introduces very little gain, so whatever noise might be introduced in the audio path inside the pedal is not being amplified a few hundred times like it might be in a DS-1 or any other distortion pedal that established Bob's reputation.  If there isn't any ticking to get rid of, then you've pretty much hit the zenith of audio performance with what comes out of the box, unless there are bandwidth issues.  There may well be other tricks you can make it do, but improving the quality of the sound likely isn't one of them.

After all the laudable effort you've put in, I hate to say it, but even though there is plenty of stuff out there that can turn into something wild and wonderful with just a couple of pokes, prods, and substitutes, sometimes things are about as good as they can be.

I hate when that happens, too.

[A.S.P.]

btw: those new B********-pedals for compression and for tremolo
have certain "2159" SIL chips in there...

don`t I remember those from old times,
when "dbx" didn`t sell them,
and "THAT" didn`t exist yet,

but they were being produced/sold as: "That`s" by some dbx spin-off company??

[TimF]

Mark, for sure there is some mistakes on the schematic. I see that IC2A is a 5216 while IC2B is a 5281 and then there even an IC2C thats 5281 (there is even 2 C1's on that schematic), IC2C doesn't exist on the PCB because the IC2 on the PCB is a 5218 dual SIP opamp. I have the part i removed on the desk in front of me as I type this. Pin 3 had 4.5V on it because the 5218 is a dual supply opamp but since there is only a 9v battery the way around this is to simply bias the opamp at +V/2 (4.5v). I do this all the time at work.

Anywho, not sure what I'm trying to say here. I guess I still just want to find a replacement for the VCA cause since I replaced everything else with low noise audiophile grade parts it has to be the onlything left causing all that noise in the TR2

[Mark Hammer]

Well, my point is that replacing everything with "audiophile components" doesn't necessarily produce any improvement in this context the way it would in other contexts.  That's just a reality.

As for VCAs/OTAs, there are a variety of VCAs out there, but short of the LM13600/LM13700 and the different CA3080 equivalents, it is rare (if ever) that anything is a pin-for-pin upgrade the way that transistors or op-amps are.  There ARE better and worse OTAs (and the  5207 is considered to be among the better), but they will invariably need a re-engineering of the board to adapt a different one.  So unless you are willing to star cutting traces and stuff, there is nothing to change to.  That doesn't mean that you are stuck with the "weak link", because quite frankly I don't know if the 5207 IS a weak link.  But you certainly won't have an opportunity to find out unless you are willing to do some serious hacking, and it just ain't worth it.  My sense is that you will not do better than what you started out with here.