Sola Sound - Tone Bender Mark I (1965)

blanik · Post by **blanik** » 08 Mar 2009, 06:44

i managed to get mine working but it sounds all muffled, no highs... i was wondering if the 2M resistor at the end might kill highs... and anyway, why the hell is there a 2M2 reistor there?? (in series with the pot?)

leeyoungun · Post by **leeyoungun** » 08 Mar 2009, 14:52

blanik wrote:i managed to get mine working but it sounds all muffled, no highs... i was wondering if the 2M resistor at the end might kill highs... and anyway, why the hell is there a 2M2 reistor there?? (in series with the pot?)

The 2M2 shouldn't be killing the highs. Can't offer any other advice.

Solidhex · Post by **Solidhex** » 08 Mar 2009, 21:36

blanik wrote:i managed to get mine working but it sounds all muffled, no highs... i was wondering if the 2M resistor at the end might kill highs... and anyway, why the hell is there a 2M2 reistor there?? (in series with the pot?)

If you have an audio probe you should listen to the output of the q3 collector. Then you'll know what impact the components following it are having on the top end. I don't see much of a point to having anything but an output cap and a volume control myself.

--Brad

Fuzzer · Post by **Fuzzer** » 09 Mar 2009, 08:00

That particualr resistor is not a pulldown.

The purpose of pulldown resistors is to have a path to ground so the coupling capacitors can discharge and avoid the nasty pops when switching an effect in and out.

They can be put on both ends, but when there's a volume control at the output as in the tonebender shown, you don't need one, because the volume pot is already pulling to ground.

Solidhex · Post by **Solidhex** » 09 Mar 2009, 08:13

Yo

I think that whole post q3 arrangement can be puzzling. I tend to consider what happens in the clipping stages to be way more important. I like to try out the stock circuit first but I think the more frequency response related decisions are personal taste city.

--Brad

RnFR · Post by **RnFR** » 16 Apr 2009, 17:45

i've become intrigued with this circuit after hearing a great clip over at the DAM forum. so, while trying to not fall asleep when doing sound for a conference on turkish medical tourism, i designed a vero layout-

with vintage mojo!

as of yet unverified, but it looks good to me. i did the Hurst version, but it can easily be modded to original specs. haven't decided which version i'm going to do yet, that's what the breadboard is for. i'll mark it verified after i build it up. unless someone else beats me to it!

jrod · Post by **jrod** » 16 Apr 2009, 19:11

NICE! Looks great...and suitable for framing. Thanks, RnFR!

RnFR · Post by **RnFR** » 23 Apr 2009, 06:11

so i finally just got around to breadboarding this thing. i used some trans tek 2n1307s that were rather high gain. didn't measure the leakage, just used my ears. i just swapped out a couple of trannies until enjoyed what i heard. when removing the resistor configuration at the end of the circuit, i got some oscillation and raspyness when using my bridge pickup, so i put it back on, but instead of the 2M2 i used a 1M and now there is plenty of boost to be had and no rasp. i'm diggin it. it's giving exactly what a MK1 should be!

next up is the vero!

RnFR · Post by **RnFR** » 23 Apr 2009, 10:07

VERO IS VERIFIED.

graemey · Post by **graemey** » 06 Jul 2009, 16:47

RnFR wrote:VERO IS VERIFIED.

Hang on...

Shouldn't C3 be 0.1uf, not 25uf?

I built this circuit two days ago using my own vero layout.
SAVAGE sounding fuzz but Im getting a loud howling (like a Fuzz Factory) if I turn the attack (fuzz) control up above minimum setting?

I used an OC75 for q1 and two AC125's for q2 and 3.

Any ideas please guys? I really want to get this one working right!

RnFR · Post by **RnFR** » 06 Jul 2009, 16:59

there are a couple of versions. this is the Gary Hurst Mk1 from Dave Main's schematic.

https://www.freestompboxes.org/viewtopic ... 6&start=60

sonicvi · Post by **sonicvi** » 06 Jul 2009, 18:38

graemey wrote:
RnFR wrote:VERO IS VERIFIED.
I built this circuit two days ago using my own vero layout.
SAVAGE sounding fuzz but Im getting a loud howling (like a Fuzz Factory) if I turn the attack (fuzz) control up above minimum setting?

I used an OC75 for q1 and two AC125's for q2 and 3.

Any ideas please guys? I really want to get this one working right!

I would start by rechecking your layout and your wiring. In my experience even high gain and high leakage won't result in howling or oscillation. Can you post your layout here?

sonicvi · Post by **sonicvi** » 06 Jul 2009, 18:43

I finished another MK1 last week.

graemey · Post by **graemey** » 06 Jul 2009, 19:35

sonicvi wrote:
I would start by rechecking your layout and your wiring. In my experience even high gain and high leakage won't result in howling or oscillation. Can you post your layout here?

I would, but it's just a pencil scribble that won't make much sense to anyone other than myself

I will certainly triple check my layout, wiring etc and let you know if I find anything.
I used the DAM schematic for the Mk1 that appears earlier in this thread. It is the original Mk1, not the Gary Hurst version above.
JUST REMEMBERED!!! I used a 22uf electrolytic as I didn't have a 25uf. Would that cause the oscillation perhaps??

Thanks for your reply btw!

sonicvi · Post by **sonicvi** » 06 Jul 2009, 20:23

graemey wrote:
sonicvi wrote:
I would start by rechecking your layout and your wiring. In my experience even high gain and high leakage won't result in howling or oscillation. Can you post your layout here?

I would, but it's just a pencil scribble that won't make much sense to anyone other than myself

I will certainly triple check my layout, wiring etc and let you know if I find anything.
I used the DAM schematic for the Mk1 that appears earlier in this thread. It is the original Mk1, not the Gary Hurst version above.
JUST REMEMBERED!!! I used a 22uf electrolytic as I didn't have a 25uf. Would that cause the oscillation perhaps??

Thanks for your reply btw!

Nope, that woudn't matter. Have you tried any other transistors? Post some photos of your board for us if you'd like some additional pairs of eyes.

graemey · Post by **graemey** » 06 Jul 2009, 21:18

sonicvi wrote:
Nope, that woudn't matter. Have you tried any other transistors? Post some photos of your board for us if you'd like some additional pairs of eyes.

Hi Sonicvi!

Just checked my wiring and found an error on the vol pot. Now that is correct.

The high-pitched screech was still present: it turned out to be the light on my work-bench! When I covered the board with the bottom of the enclosure, the screech went away.
Seems that the OC75 at q1 is the culprit. I tried a few (I have 6 to choose from) and some are noisier than others.

Next, I subbed q1 (OC75) and q2 (AC125) for some NKT 213's. Much less noise and very nice sound. Is the problem leakage? biasing? hmmm?

Im getting closer. The overall fuzz effect is a little bassy. Perhaps I could try another input cap?

Oh, and I have just used cheap ceramics for my caps. This is a kind of test build, I will get some nice 'mojo' components soon and build another.

It's good fun all the same!

sonicvi · Post by **sonicvi** » 06 Jul 2009, 22:13

It's really hard to say where noise is coming from. Audio probing the circuit could help narrow it down. When I had my latest build on the breadboard I was getting all kinds of high frequency noise and sizzle at certain settings of the attack pot. Having read about how the originals are from Dave and Graham in the DAM forum I just chalked it up to normal behavior of the circuit and those TI transistors. When I assembled the final build all of that noise was gone. I don't know if it's because of the shielding from the enclosure or the shielded wire I used or if there's stray capacitance in the breadboard or what.

You can try smaller in/out caps for less low end. The Zonk Machine had .001uF for the input and .047uF for the output and has a bit less low end.

Scruffie · Post by **Scruffie** » 06 Jul 2009, 23:06

I know it's not Mojo to add things to an old circuit but a tinyyy cap from the 9v to ground might help I use 47pF if I ever have an issue with noise and that normally sort things out but aslong as it was in the pF range it would probably be alright.

Just my £0.01

RnFR · Post by **RnFR** » 07 Jul 2009, 00:02

it very well could be those ceramics. they are known to be microphonic at times, and that sounds a lot like howling and screeching.

graemey · Post by **graemey** » 07 Jul 2009, 05:49

Excellent advice guys

I thank you all!

I will keep tinkering til Im happy. Im 95% there with it now

Sola Sound - Tone Bender Mark I (1965) [schematic]