DS-1 choking!

[Igor]

Hi.

Francisco Pena from Tonepad said that he was aware of the problem I'm having with the DS-1 and told me to ask you guys here, or direct the question to Joep Remkes.

So, here it is...

I have a few different schems of a DS-1. The one I decided to use is the same as the one provided on Tonepad.com but it has different component values (it also uses a TL072). It's values are for the Keeley DS-1 Ultra Mod. I've built that one and it worked fine, but it had a problem:

I could only turn the guitar volume up to about 5 and still have normal sound. If I turned it up all the way and hit the strings hard for some heavier riffs, the effect sounded "overloaded", the volume went down, the diodes wouldn't clip, like it choked. Then as the signal got weaker, after about 2 seconds, everything would return to normal, the distortion was there. It sounded like the signal from the guitar was too strong, I don't know how else to explain it. It was like trying to get heavy distortion from a small living room radio:) Like the speakers would fall apart:)

I then tried using the values from the Tonepad schematic. Again, it worked perfectly fine, but the problem remained. I tried with new 2N5088s, I tried with a new TL072, but with no success. I just don't understand! What could be the problem? I see that there are 2 build reports and they seem successful. My schematic is exactly the same and the values are correct, so I don't know why it's not working.

Could you help me? What could I try in order to fix this? The only thing I found different on those schematics is that the Keeley Mod with a TL072 has a 1k resistor from pin 7 to 9V and the Tonepad version doesn't have it.

I also have the original schematic and one drawn by Justin Philipott. But since these are working fine I'd like to debug them.

Thanks!

Igor Vihnanek

[aron]

Can you give us a link to the actual schematic you used?

[Joep]

Hi Igor,

I had a problem simular like you. It's due to a misbias of the second transistor. I used R3=100k and R4=470k. This fixed my problem.

Joep

[Igor]

Thanks Joep!

So, the 100K is between base and collector and the 470K resistor is from base to ground! I'll try it.

I also tried something else. I was talking about that 1K resistor from pin 7 to 9V, I tried using it and it seems that at least some of the problem is gone! I don't have my amp at home at the moment so I tried it out on a home stereo. It seemed fine! At least better than before.

Here's the link to that Ultra Mod schematic.
http://www.geocities.com/munkydiy/ds1ultralayout.jpg

You can see that resistor. It may be insignificant, I just noticed it . I used the schematic from Tonepad but I added the values from the Ultra Mod.

Igor