SolaSound - Tone Bender MK1.5  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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sinner
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Post by sinner »

Wtf is impex?

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Post by mictester »

Torries wrote:Additionally I used a Rainbow LED and I can hear the colour change within the signal. Any advice?
Filter the LED supply - put an electrolytic capacitor in parallel with the LED. Try 10µ at 16V (or more volts). This should help a lot. Also, your LED will appear to fade out as you switch it off!
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Post by Dirk_Hendrik »

sinner wrote:Wtf is impex?
Apparently the brand of the transistors. Had to use google to find that out.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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beedotman
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Post by beedotman »

Yup, these transistors seems to be pretty rare. I now that at least one more MK1.5 and one MKII are existing, pics are somewhere on DAM forum.
Here is pic from pigdog transistor porn session:
Image

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Post by beedotman »

hyhy, sorry, orginal pic is to big..
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impex.JPG

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nightraven
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Post by nightraven »

They were used quite a bit in Marshall Supafuzzes. Statistically it would not be unlikely for one of Mictester's alleged two basement-find Sola Sound made Supafuzzes to have those Impex transistors inside.

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Electric Warrior
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Post by Electric Warrior »

In Voxes and a couple of Sola Sound MKIIs as well. They're quite common in that circuit. If you ever see one with unmarked metal can transistors, they're most likely Impex S3-1Ts.
Rather rare for MK1.5s though.

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Post by ljn »

Hi, everyone. I ended up building one of these mk.1.5 tone benders and I think they're great. I built mine from a fuzzcentral schematic and used a couple of AC128 transistors. I be live the hfe on them was in the 60-80 range. It's pretty bright and cleans up quite nicely. I used a pot on Q2's collector. It has a great Neil Young tone.

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Post by ivan H »

Hi, I know this thread has been inactive for a while but I'd like to revive it rather than start a new one. So anyway I've put together a test circuit (Vero board) with trimpots for both q1 & 2 so I can trial transistors. I started with 2 OC75's that came from Smallbear as a mk1 set that had worked in the mk1, though I ended up using q2 from the set as q1 in my mk1 build, along with 2 AC125's for best results. So, I tried the remaining 2 in this, q1 hfe 70, leakage 210uA, q2 hfe 100, leakage 289. This worked ok, but only with the attack turned above around 30~35%. It was really gated & would only pass signal when strings were struck hard & quit well before the string vibration did. Trying to dial it in with the trimpots didn't really fix. I also tried adding the 43k pulldown resistor & 10nf pulldown cap as in the DAM coppertop which made it worse, needed the attack above 50% to work. I tried a few different transistors, OC77 & AC125 for q1 & AC125 for q2, several combinations, with not much better results. Then I tried the same 2 OC75's that I had first tried, but this time I swapped their positions. Q1 hfe 100, leakage 289uA, Q2 hfe 70, leakage 210uA. This time it works no matter where the attack is set, from min to max. Its not perfect & could do with some dialling in, but it is working. I was wondering if anyone had any tips on doing this. I noticed on page 4 of this thread someone has posted transistor voltages from an original Mk 1.5, but have not mentioned the position of the attack pot when voltages were taken, which I have noticed matters. I also have a set of AC125's matched for a fuzz face on the way to try in it. So, any tips anyone?? Cheers

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Post by ivan H »

Hi again, I just wanted to clear up that its only really gated & not passing a proper signal when the attack pot is below 35%, (or 50% with other combinations of transistors). Oh, & the voltages were posted (by Electric Warrior) on page 3, not 4. I'll post back with results of trying a "fuzz face" set of AC125's. Cheers

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Post by Bret608 »

That is interesting--it sounds like it might want the leakier transistor to be in Q1. Let us hear about your results for sure! I've been thinking about doing one of these too.

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Post by ivan H »

Yes, it does seem to like the leakier transistor in the 1st position. One thing, the weather here where I live is usually quite warm to hot, even during the day in winter (now), & was when I first threw this together. Since I tried this configuration though, it has been raining & cool. Yesterday I was experimenting with the trimpots & found that, no matter the position of the trim on q1's collector, q2 is best with the stock value of 8k2. I have a 100k trim on q1's collector it best when it is set up near 100k. Any thoughts on this anyone. Cheers

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Post by ivan H »

Ok, so a "fuzz face" matched set of AC125's arrived an hour ago. Numbers are q1 hfe 87, leakage 133uA, q2 hfe 137, leakage 267uA. Plugged straight in, stock values its as experienced with other combinations. With attack set below 30% its extremely gated & not sustaining properly at all. With attack above 30% it works fine. With q1's collector resistor at 100k it works throughout the entire sweep of the attack pot. Now I have noticed that some reissue fuzz face's (equipped with AC128's) use a 27k resistor in this position, while others use 100k. So maybe I'll just use the 100k resistor, & pick the better sounding transistors, OC75s or AC125s. Cheers

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Post by Electric Warrior »

I wouldn't call that a matched set. Looks like they're mismatched on purpose. The degree of matching or mismatching and which hfe/leakage should be higher depends on your personal preference. I like to start out with a closely matched set (especially when the gains are low) and then substitute transistors and listen to the difference it made.
Keep in mind that with germanium, the voltages depend a lot more and leakage than on hfe.

Q1's collector resistor sets the collector voltages for both, Q1 and Q2. When you're using transistors with low leakage, you can make up for it by using a larger resistor to bring Q1C down and Q2C up.

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ivan H
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Post by ivan H »

Hi & thanks Electric Warrior, I was kinda hoping you'd chime in. I have a small stash of a few different types of germanium's so will take your advice, try & find pairs that closely match each other & go from there. Cheers

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Post by ivan H »

Oh, just quickly, where I said the AC125's were matched, I really should have said " matched to fuzz face requirements" which was how they were advertised. Cheers

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Post by Electric Warrior »

Auditioning transistors sure is the best thing you can do. Shouldn't be all that hard either. :thumbsup

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Post by Bret608 »

I will be especially curious to hear what sounds good to you and gets in the ballpark of the voltages on vintage units. Chromesphere (DIY guitar pedals) did a comparison of a bunch of different Fuzz Face sets on his YouTube channel. He did variations of the 70/120 "conventional wisdom" type of combination, then tried it where Q1 and Q2 were the same gains. This sounded better to me in almost every case! I would have liked to know the voltages in those situations. I bet Mk1.5s sound better with them closer in gain as well.

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Post by ivan H »

DIY guitar pedals is where I've been getting the AC125's from. I'll try some closer matched ones today & post results. Cheers

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Post by jalmonsalmon »

I put this circuit on my breadboard and can sit there all day tweaking it and I always get great fuzz tones out of it. Tone bender 1.5 is my favorite. I tried lots of transistors but settled with OC84s for my pedal and all of the caps and resistors are stock 1.5 values except I have a bias pot because where I live... 100 degrees or more outside lol

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