DIY "Keeley"-TS9 mod questions

[red]

Thanks! I think I found the input transistor - it should be the one in the upper-left side of the pictures in my post.

Does anyone know why the old 0.02 cap has been changed? Does it have a different capacitance value, or was it just changed to metal film for better quality? Aren't the see-through yellow plastic ones also metal film?

Thanks for the transistor suggestion, I'll see if it's available around and try that one too.

[Suhnton]

I think the yellow ones are mylar caps. As for the 0.02uF cap, if you're talking about the one at the base of the input transistor, then it's about right. The value I have is 0.027uF (close enough).

[red]

I think the yellow ones are mylar caps. As for the 0.02uF cap, if you're talking about the one at the base of the input transistor, then it's about right. The value I have is 0.027uF (close enough).

The 0.02 cap I'm talking about is the yellow one right above the numbers 12 and 13 (12 is where the red wire connects) in the picture labeled "TS-9 Modifications". Yes, in the schematic it looks like it's connected directly to the input transistor.

Anyway, yes, I know the value is 0.02uF, both from the schematic and from reading what it says on the capacitor in my TS9 reissue pedal, my question was: do you know if the Keeley mod uses the same value for that capacitor (if you look at the second picture I've posted in my initial post, you can see that the yellow cap has been replaced with a red metal film cap), or if the mod uses a different value for the replaced capacitor?

[duhvoodooman***]

I doubt the transistor change would have an audible effect. You'd be better off changing all the higher rated resistors (anything 100K or higher) to metal flim. Carbon films at high ratings tend to be a little hissy.

Keep in mind that you've doubled the pedal's gain with that change of the 4.7K resistor to 2.4K, and that doubles the noise, too, when the gain is dialed up. So you're fighting physics, to some extent.

I wouldn't worry about that 0.02 cap. It's at the start of the input buffer and I've never seen any mention of it being tonally important.

Can't comment on that 8.2K resistor; that's not a rating I've encountered in a TS.

BTW, your bass didn't increase with that switch to a 0.1uf cap--it just compensated for the 2.4K resistor. The two form a frequency filter, and when you cut the one in half, you have to double the other to keep the bass response the same. If you really want more low end, increase it to 0.22uf.

[red]

I doubt the transistor change would have an audible effect. You'd be better off changing all the higher rated resistors (anything 100K or higher) to metal flim. Carbon films at high ratings tend to be a little hissy.

I don't expect to completely cure the noise, just cut it down as much as possible. I found this article that stated:

"Note that in going to higher gains, you will inevitably increase the noise in the output. This may be curable to a degree by changing the input transistor to a quieter part (MPSA18 or 2N5089 is good) as well as swapping to a more modern and quieter opamp like the LM833 or both."

The Keeley Baked Mod page also specifies:

"I also change the input transistor to a MPSA18 for lower noise operation."

Now, I like the RC4558P very much, so I won't be changing that, but I though I'd give the transistor swap a try. It might not cure all of the background noise when going to higher gain, but it if cures some of it I'll be happy.

I wouldn't worry about that 0.02 cap. It's at the start of the input buffer and I've never seen any mention of it being tonally important.

Well, this is where I've seen a mention that it might be tonally important. I've also tried it out - I put a 0.1uF cap there and I got more bass than I had bargained for. But I really like the 0.02uF cap, and I don't think mr. Keeley changes that value, so I'll just swap it for a 0.022uF metal film for better quality and leave it at that.

BTW, your bass didn't increase with that switch to a 0.1uf cap--it just compensated for the 2.4K resistor. The two form a frequency filter, and when you cut the one in half, you have to double the other to keep the bass response the same. If you really want more low end, increase it to 0.22uf.

Indeed you are right, sir. I did try a 0.22uF, I thought the pedal got too muddy though and went back to the 0.1uF.

Thank you for your reply!

[duhvoodooman***]

Whenever I've seen discussions of punching up the bass on a TS circuit, it's been via that 0.047uf cap in the opamp feedback loop that you already changed. I'd agree that the 0.02uf on the input buffer is best left as is. BTW, if you still want a bit more bass, you might want to try a 0.15uf cap where that 0.047 was.

Can't hurt to change the buffer trannies, though the pinout on the MPSA18 (which is what I've used in all my TS clones) is different, as you mentioned. Just leave the legs a bit long and bend them around carefully to avoid contact between them, and you shouldn't have any problem. I recently did the same thing to change from higher gain trannies to mid-range ones in another distortion pedal, and it worked fine. I'll be interested to hear if you discern any improvement from the switch.

FWIW, my favorite opamp in that circuit (and I've tried a LOT of them) is the TI TLC2272ACP. Seems to strike just the right balance of fidelity and low noise without sounding too antiseptic. Some people swear by the Burr Brown OPA2134A, but I found it a little too hi-fi in that circuit; sounded a little lifeless to me compared to others. But I have one in my MOSFET-conversion TS clone, and it sounds great in there. So go figure....

[red]

Can't hurt to change the buffer trannies, though the pinout on the MPSA18 (which is what I've used in all my TS clones) is different, as you mentioned. Just leave the legs a bit long and bend them around carefully to avoid contact between them, and you shouldn't have any problem. I recently did the same thing to change from higher gain trannies to mid-range ones in another distortion pedal, and it worked fine. I'll be interested to hear if you discern any improvement from the switch.

Thanks, I'll let you know as soon as I make the change - I had to order the MPSA18 online and now it's still on its way, should be here sometime next week I think.

FWIW, my favorite opamp in that circuit (and I've tried a LOT of them) is the TI TLC2272ACP. Seems to strike just the right balance of fidelity and low noise without sounding too antiseptic. Some people swear by the Burr Brown OPA2134A, but I found it a little too hi-fi in that circuit; sounded a little lifeless to me compared to others.

Thanks for the suggestions, I'll hunt around for those and try them out, should be easy enough with the IC socket I've installed...

[red]

Can't hurt to change the buffer trannies, though the pinout on the MPSA18 (which is what I've used in all my TS clones) is different, as you mentioned. Just leave the legs a bit long and bend them around carefully to avoid contact between them, and you shouldn't have any problem. I recently did the same thing to change from higher gain trannies to mid-range ones in another distortion pedal, and it worked fine. I'll be interested to hear if you discern any improvement from the switch.

I've done it. There is almost no difference until the DRIVE knob is turned up about 2/3, but after that the difference is audible. It's not a huge difference, the background noise is still there, but IMHO it's definitely an improvement. Which is great for me, because I'm using only single-coil guitars (mostly a Telecaster) and I can use all the breaks I can get from the hum. I'll probably shield the pickup and controls cavities as well in the near future.

The change is probably not worth it at all for people using humbuckers or noiseless single coils, but it did make a difference, albeit small, for me. YMMV.

[thegnu]

Hey all, I'm new. I did the Monteallums mod to my pedal, and I was just cleaning up the work inside since I've gotten better. So then I wanted to implement some of the Keeley mods, and I read about those MPSA18's, and I had just taken some out of a dynacomp, so I thought, "cool"

I've only got two transistors on mine, I think because it's the true-bypass Maxon OD-9. They are circled below:


Can anyone tell me the model or pinout of the transistors I had there, because I was tired, and dropped one of them in the carpet, and I can't remember what I did to the other one. :

Also, that cap isn't in the signal path, is it?

I appreciate any help.

[Suhnton]

The transistors I used in mine are 2N3904's.
The pinouts are (with the flat side facing to the right): C-B-E top to bottom.
The GenaralGuitarGadgets (GGG) schematic uses 2SC1815's. I think they are the same pinout configuration.