This is my silicon version of the Tone Bender MKI.
I tried it to be as original as possible, except for some minor and necessary changes.
The input buffer has the same Z-In, since 4m7//1m2=1m
The second stage has a smaller cap because the fuzz pot does not need to go to 1k8 as in the germ version because of the bigger emiter-base voltage drop. Since there is a minimum 22k I reduced the 22u cap to 2u2.
The third stage has a trimmer at the base to set the voltage of Q3.
If you stick to hfe near 70 it should work with no further tweaks.
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=48760&g2_serialNumber=1)
Enjoy!
mac
This looks cool! Thanks for sharing!
I had been messing around with the original circuit on the breadboard without much luck. I was getting terrible noise during note decay. I can't wait to give this one a try!!!
Bless your heart, Mac!
I have a fat sack of low-gain Silicons
NOW, for the Mk II, por favor!
Please note that even for Si, bias are highly dependent on hfe because the emiter is grounded.
Let me know your experiences.
QuoteNOW, for the Mk II, por favor!
jaja ok!
The TB Silicon Trilogy ;D
mac
Hi. I've tried the circuit but got a problem. When hitting the strings hard the sound was very compressed and dark at first but as the notes ring it opens up and gets louder. I don't notice it when lowering the guitar volume or playing softer. I really want to know what's wrong and how to fix it.
I used transistors with hfe 60-70 in Q1 (e 2v) and Q3 (c 8.5v) and hfe 90-100 in Q2 (c 8.5v-5.8v).
Thanks for sharing the circuit!
Can I get one of you guys who are furiously soldering these together to try my idea of adding leakage by soldering a reverse biased germanium junction across the collector-base of a silicon transistor?
I *think* this provides the leakage of a germanium transistor equal to the leakage of the diode. This is then amplified by the transistor, etc, etc. I'm up to my eyeballs in other stuff and can't try it out in any real way right now.
Subbed for sound samples. My germanium MKI is noisy and annoying.
QuoteHi. I've tried the circuit but got a problem. When hitting the strings hard the sound was very compressed and dark at first but as the notes ring it opens up and gets louder. I don't notice it when lowering the guitar volume or playing softer. I really want to know what's wrong and how to fix it.
I used transistors with hfe 60-70 in Q1 (e 2v) and Q3 (c 8.5v) and hfe 90-100 in Q2 (c 8.5v-5.8v).
Maybe it is the 2.2uf cap interacting with the fuzz pot path. Make it smaller, say 0.22uf.
Or set Q3 collector a little lower.
mac
Quote
Can I get one of you guys who are furiously soldering these together to try my idea of adding leakage by soldering a reverse biased germanium junction across the collector-base of a silicon transistor?
I *think* this provides the leakage of a germanium transistor equal to the leakage of the diode. This is then amplified by the transistor, etc, etc. I'm up to my eyeballs in other stuff and can't try it out in any real way right now.
RG,
I have nothing to do the rest of the year except going to the beach, so I'll try your idea ;D
Since this circuit calls for leaky germs I think that new germ diodes have little leakage for it, most likely it will work with old ones.
BTW, a reversed diode and its leakage current can be considered like a big mega ohm resistor from B to C?
mac
Quote from: mac on March 04, 2013, 01:24:27 PM
I have nothing to do the rest of the year except going to the beach, so I'll try your idea ;D
Go ahead, rub my face in it. :icon_lol:
QuoteSince this circuit calls for leaky germs I think that new germ diodes have little leakage for it, most likely it will work with old ones.
BTW, a reversed diode and its leakage current can be considered like a big mega ohm resistor from B to C?
Taking the question first: no, not quite. A reversed diode acts more like a constant current source (or leak) than it does a resistor. The leakage on a reverse biased semiconductor junction rises over a small-ish few volts of reverse bias, then flattens out a LOT. It's not perfectly flat, but the leakage remains reasonably constant, not rising linearly with reverse voltage like a large resistor would. It was this idea that actually kicked off the Millenium Bypass. It's very, very difficult to get resistors that are consistent to any degree, and much larger than 1M, which is what the Millenium circuit needed.
That being the case, going to an external device to supply "appropriate" :icon_lol: leakage is much simpler. You can choose diodes for leakage, using old unsuitable germanium devices for their collector base or base-emitter junction. You can use two (or more) modern germanium diodes with low leakage for germanium, but still 1000x the leakage of silicon til you get the leakage your circuit likes.
This offers a degree of freedom in using transistors that picking among old germaniums does not.
In combination with piggybacking to lower gain, it may well be possible to trim in a generic silicon transistor to sound like an old, low gain and leaky germanium.
Wow. Who'd have ever thought that there would be a use for deliberately making things worse. :icon_lol:
Quote from: R.G. on March 03, 2013, 06:49:06 PM
Can I get one of you guys who are furiously soldering these together to try my idea of adding leakage by soldering a reverse biased germanium junction across the collector-base of a silicon transistor?
after doing that, can we still use your test to get accurate results?
http://www.geofex.com/FX_images/xstrtest.gif
Actually, yes. That test measures the current flowing in the collector in two conditions: (1) with only the transistor's internal leakage into the base, and (2) with an added external bias current added.
If there was a semi-internal leakage current added to the device under test from base to collector, it acts the same as an internal leakage, in that it funnels charge carriers into the base region.
There are probably micro-differences where this is not exactly the same, but I speculate that it will pick up much of the effect, just like piggybacking does a good job of lowering the effective gain.
I've just discovered that the C2, C6, C4, C7 and C5 are a positive feedback path, and/or in combination with the resistors to gnd they are much like an oscillator. :icon_redface:
Updating the schematic to avoid potencial oscillations or motorboating. Removing C6 and C7 an adding a cap across 47k (R12) to gnd.
Or making R12 a 50kB pot, and a cap between the wiper and gnd, as variable treble cut.
mac
That would be very odd if the rest of the circuit is right. The big difference in size with C6 and C7 and the others makes it unlikely to oscillate unless there is something else helping it.
Is it grounded correctly, and is the power supply bypassed correctly?
Quote from: mac on March 04, 2013, 01:11:03 PM
QuoteHi. I've tried the circuit but got a problem. When hitting the strings hard the sound was very compressed and dark at first but as the notes ring it opens up and gets louder. I don't notice it when lowering the guitar volume or playing softer. I really want to know what's wrong and how to fix it.
I used transistors with hfe 60-70 in Q1 (e 2v) and Q3 (c 8.5v) and hfe 90-100 in Q2 (c 8.5v-5.8v).
Maybe it is the 2.2uf cap interacting with the fuzz pot path. Make it smaller, say 0.22uf.
Or set Q3 collector a little lower.
mac
Thanks, will try this when I've got some time for myself. The sound of fuzz pedal debugging is not appreciated by everyone.
Stinky,
I tried hard playing, which I rarely do :), and lowering the cap helps, loosing lows.
The problem is not the cap but Q2 hitting Q3 too hard. I added a 4k7 resistor between them and it works a lot better IMO.
This pedal has the sound of misbiased transistors ;D
QuoteThat would be very odd if the rest of the circuit is right. The big difference in size with C6 and C7 and the others makes it unlikely to oscillate unless there is something else helping it.
Is it grounded correctly, and is the power supply bypassed correctly?
RG,
I did everything to get oscillations but you were right.
I only had problems when I put the metal cover under the breadboard, but oscillations stopped when I grounded the cover.
No need to remove the rool off caps.
mac
Adding a resistor after Q2 helped. I'm thinking a pre-gain would be a good addition to this circuit.
Now I want to try it with germ diodes as RG suggested and wonder if I got it right.
Is this how you simulate a leaky, low gain transistor?
(http://dl.dropbox.com/u/68780779/germsub.PNG)
Quote from: stinky on March 07, 2013, 03:50:07 PM
Is this how you simulate a leaky, low gain transistor?
(http://dl.dropbox.com/u/68780779/germsub.PNG)
That's the first iteration, OK.
Mac reports that the distortion changes on a first attempt. There will probably be some tinkering with bias as the leakage from the diode affects the bias point - as it's supposed to.
I have tried a germ diode instead of the extra resistor with Q3. I can't get Q3s collector voltage low enough, it's 9.2v (power supply 9.4v) and stays there even if I change diode. When measured according to http://www.geofex.com/Article_Folders/ffselect.htm the leakage varied from 100-300 uA with different diodes and a hfe 100 transistor. A germ transistor I tried (hfe 110, leakage 300) gave me collector voltage 8.5v. It feels like I've missed something.
Quote from: stinky on March 08, 2013, 02:58:12 PM
I have tried a germ diode instead of the extra resistor with Q3. I can't get Q3s collector voltage low enough, it's 9.2v (power supply 9.4v) and stays there even if I change diode. When measured according to http://www.geofex.com/Article_Folders/ffselect.htm the leakage varied from 100-300 uA with different diodes and a hfe 100 transistor. A germ transistor I tried (hfe 110, leakage 300) gave me collector voltage 8.5v. It feels like I've missed something.
just curious...what happens if you use the ge transistor that gave you 8.5V as the diode (eb or bc) ?
Quote from: LucifersTrip on March 08, 2013, 04:20:17 PM
just curious...what happens if you use the ge transistor that gave you 8.5V as the diode (eb or bc) ?
That gave me 9.1V, but went up to 9.2 as it got back to room temperature.
I tried higher hfe transistors, which gave a much higher leakage, and still 9.2V.
(1) is there some other problem with your circuit, not just the added "leakage diode"?
(2) Can you provide us with the other voltages in the circuit, not just the collector of Q3?
I'm using mac's schematic except for Q3. With a germ transistor in Q3 there is fuzz and omitting the Q3 stage gives a boost/ overdrive sound. I can't get any sound with silicon and a germ diode. So it feels like Q3 is the only problem, and the only part I've experimented with...
Both germ and silicon transistors had e: 0 V and b: 0.03 V.
It feels like the parts are broken but I have probably just stared myself blind at the breadboard.
Quote from: stinky on March 09, 2013, 04:06:28 PM
I'm using mac's schematic except for Q3. With a germ transistor in Q3 there is fuzz and omitting the Q3 stage gives a boost/ overdrive sound. I can't get any sound with silicon and a germ diode. So it feels like Q3 is the only problem, and the only part I've experimented with...
Both germ and silicon transistors had e: 0 V and b: 0.03 V.
It feels like the parts are broken but I have probably just stared myself blind at the breadboard.
That's one issue, and a good illustration of why to measure all the pins. The silicon won't start at all until its base is up at about 0.45V.
The idea of using a germanium diode to fake germanium leakage may make silicon leakage-bias-ABLE but it won't get the base-emitter junction voltage down to the same as if the base-emitter of the transistor itself is germanium.
Is it possible for you to measure all three pin voltages of all three transistors? That will tell me a very large amount about what's happening.
Did you use the 82K and 8.2K for the biasing on Q3? It is possible that there is a problem with the 50K pot wiring, and that a germanium is being entirely leakage biased there. It shouldn't be. And any specific leakage diode from base to collector on Q3 may not be enough to match the leakage of a specific germanium subbed it.
This is still a very experimental idea, so it may or may not work out. Thank you for being willing to experiment.
Stinky,
Just curious, what range of voltages do you get at Q3 with your silicons as you vary the trimmer?
QuoteAdding a resistor after Q2 helped. I'm thinking a pre-gain would be a good addition to this circuit.
I think this circuit needs inter-stage resistors, 4k7 - 10k.
If i'm not wrong, Q2 and Q3 have very low Z-in, and are driven from higher Z-out sources, Q1 and Q2.
From a msg I sent to RG,
RG,
Sorry for the late response.
I experimented a little more, and the big picture is this:
All the diode's leakage has to feed the transistor's base.
For example, if you want a mpsa42, hfe: 100, to sit at 4.5v with a 10k at the collector, you need a base current of 4.5v/10k/100=0.0045ma. This is what the diode must leak. When this happens it sounds great.
Or if the diode leaks a little more than 0.0045ma, adding a B to Gnd resistor to send excess leakage to gnd helps.
Unfortunately, I got a "shhhhhhh" noise with some old diodes
I did not try with a resistor feeding the base yet, only in "self leakage bias" mode
mac
Should I still use a resistor from power supply + to base, even with a germ diode?
Much strange stuff happening on my breadboard now, or at least to me. Q1's voltages is c: 9.4 V, b: 2.0 V and e: 2.4 V, shouldn't b be higher than e?
With the germanium transistor in Q3, the voltages changed as I turned the fuzz knob. So when Q2 collector was around 6 V, Q3 c was around 8 V but when Q2 c was 8 V Q3 c went down to 2 V. Tried a bunch of different caps between Q2 and Q3 but still the same interaction, lifted the cap and Q3 c went back to 8.5 V. If I remember right Q2 base voltage was 0.8 V.
And somehow I've managed to kill a couple of my very few low gain transistors (old bc107a) with my messing.
I can't understand in what ways I'm messing things up, but I'm hoping to learn from it.
Thanks for your time!
QuoteShould I still use a resistor from power supply + to base, even with a germ diode?
Only if diode's leakage is tiny.
QuoteMuch strange stuff happening on my breadboard now, or at least to me. Q1's voltages is c: 9.4 V, b: 2.0 V and e: 2.4 V, shouldn't b be higher than e?
Yes, VB=VE+0.6/0.7v.
What transistors are you using? Check pinout.
QuoteWith the germanium transistor in Q3, the voltages changed as I turned the fuzz knob. So when Q2 collector was around 6 V, Q3 c was around 8 V but when Q2 c was 8 V Q3 c went down to 2 V. Tried a bunch of different caps between Q2 and Q3 but still the same interaction, lifted the cap and Q3 c went back to 8.5 V. If I remember right Q2 base voltage was 0.8 V.
And somehow I've managed to kill a couple of my very few low gain transistors (old bc107a) with my messing.
I can't understand in what ways I'm messing things up, but I'm hoping to learn from it.
Thanks for your time!
Q3 voltage is independent of Q2, you should not have changes in Q3 while you vary the fuzz pot, and viceversa.
Check pinout and connections. Sometimes it is better to start over, put together Q1 and test voltages. Then Q2 and connect to Q1 with the coupling cap. Same for Q3.
If you use 2N and then change to BC you have to flip them.
One minute silence for those dead BC107s. :icon_cry:
It is not rare killing transistors while messing in a live breadboard and when the transistor is emiter grounded. I killed a lot of devices this way.
mac
I recorded two crappy samples today, guitar to breaboard to laney lc30 clean to laptop
Min settings (http://www.aronnelson.com/gallery/main.php/v/mac/sound+demos+of+my+circuits/tbmki+min+min.mp3.html)
q2 and q3 near vcc
Max settings (http://www.aronnelson.com/gallery/main.php/v/mac/sound+demos+of+my+circuits/tbmki+max+max.mp3.html)
q2 and q3 biased lower
mac
Sounds good! I think I prefer the Min settings sample. Sounds less "metal" on power chords.
Agreed! It has a lot of the right kind of sizzle at the low gain setting.
Getting really close, Mac!
Sounds great mac. I've got a lc30 to, what settings did you use and what kind of guitar?
Quote from: mac on March 10, 2013, 05:57:33 PM
Q3 voltage is independent of Q2, you should not have changes in Q3 while you vary the fuzz pot, and viceversa.
Check pinout and connections. Sometimes it is better to start over, put together Q1 and test voltages. Then Q2 and connect to Q1 with the coupling cap. Same for Q3.
If you use 2N and then change to BC you have to flip them.
One minute silence for those dead BC107s. :icon_cry:
It is not rare killing transistors while messing in a live breadboard and when the transistor is emiter grounded. I killed a lot of devices this way.
mac
All the transistors I've used got the same pinout so that's not the issue, probably something even simpler.
I think start over is the best way to go. Gonna clear the breadboard, test some other circuit and then come back to this one in a couple of days or so with a clear mind.
QuoteAgreed! It has a lot of the right kind of sizzle at the low gain setting.
Sounds good! I think I prefer the Min settings sample. Sounds less "metal" on power chords.
I agree. I prefer at least one transistor close to vcc.
QuoteSounds great mac. I've got a lc30 to, what settings did you use and what kind of guitar?
The clean channel tone control is fixed at B5, M3 and T5 since the day I bought it ;D
Volume at 4, no bright sw.
My model has the HH 12", JJs, no mods and no scratches :)
Guitar is a stock Yamaha 721, pseudo-single coil bridge mic.
mac
Man, those sound samples sound great! Personally I like the max setting! ;D
If I didn't have 6 boards semi-done and boxed, this would be my next to-do!
Mac, love it, love it.
I updated the schematic a bit.
It has now three 4k7 interstage resistor to balance impedances and to avoid hitting the next stage too hard.
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=48826&g2_serialNumber=1)
mac
What a cool thread!
Just what I was looking for :-)
Stay tuned, Silicon Tonebender Trilogy coming soon :)
mac
Fantastic!
(Is it the MkII coming up this time?)
I've listened to the sound clips, and I think that they are quite close to a GE Mk1 8)
Did you, or anyone else, get this "diode simulating leakage thing" working?
Quote(Is it the MkII coming up this time?)
1,2 and 3 in a single pdf :)
QuoteDid you, or anyone else, get this "diode simulating leakage thing" working?
Yes. BUt there is no magic "formula".
I'm trying with Schottky now because they leak just right and they are less noisy.
I'll dig deeper and open a new thread.
mac
I'm REALLY looking forward to be able to learn from your experience!
Thanks :-)
Any updates on this?
Quote from: polifemo on April 11, 2014, 12:16:05 PM
Any updates on this?
(http://greenido.files.wordpress.com/2011/10/screen-shot-2011-10-30-at-11-26-24-am.png)
;D
mac
Hi, hopefully this thread is not too dusty now... I just found it recently when looking for info about piggybacking. Wow! Awesome stuff! :icon_twisted:
I did my own science experiment starting from the last schematic that mac posted. Instead of using low-gain Si transistors, which I don't have any of, I built it using only 2N3904's, but piggybacked them for Q2 and Q3. In the buffer stage I don't think that the actual part for Q1 is very important, in fact if I remember my textbook correctly, the higher gain the better to reduce the output impedance of the buffer stage. Anyway, I just used a single 2N3904 there.
In addition to the piggybacking, I also used the B-E junctions of some OC44's to provide leakage. I tried some 1N34A's and 1N60s that I have, but they didn't leak much at all, and really had no effect. The OC44's both had hFE of about 40 (using R.G.'s measuring technique).
I found that piggybacking two 2N3904s, using an OC44 for leakage, and a 15K resistor between the emitters of the 2N3904s gave me an equivalent hFE of about 95 - 105. This was measured just plugging straight into the multimeter.
The only adjustment I made to the overall circuit was to change R6 to 24K, because the collector voltage on "Q2" was over 9V when the Fuzz pot was at a minimum. This swap dropped the collector voltage on "Q2" to 8.56V.
I really like the sound a lot! Not having ever heard an actual MkI Tonebender, I have no real reference to compare to, but it sounds like I'd expect a late 60s fuzz to sound. Thanks for all your work mac!
QuoteIn addition to the piggybacking, I also used the B-E junctions of some OC44's to provide leakage. I tried some 1N34A's and 1N60s that I have, but they didn't leak much at all, and really had no effect. The OC44's both had hFE of about 40 (using R.G.'s measuring technique).
If you have germs, build the real thing! ;D
Interesting what you did, RG suggested to use a reversed biased germ diode from C to B to simulate leakage. I experimented a bit and it works fine, but the problem is to find a diode with the exact amount of leakage for a given transistor gain.
mac
QuoteIf you have germs, build the real thing!
Ha, yes, I got the irony of using a Ge transistor to simulate a Ge transistor. :) But in this case, the hFE of the OC44's is too low for them to work well in a fuzz circuit, and I don't have any leaky Ge diodes. (Unsure where to procure such a thing since I don't have an old stash of parts lying around.)
Apologies for bringing this thread back from the dead.. Has anyone got any tips with this, i've been trying this circuit with slightly higher gain transistors but with no luck what so ever. I have ordered some BD175s so hopefully i'll have better luck with that. The circuit seems to work - just haven't really got a distorted sound. I've been looking at the FZ1 diagram mac posted also.
I've spent the last few days fiddling with this, just recieved some low gain silicon transistors what work great in this project! can't seem to get much control with the attack knob but it sounds massive. Very good sound!
Edit: So I attempted to make a vero layout of this, not sure if it works but here it is if anyone is interested.
(https://i.postimg.cc/zH8M2Rr0/Tone-bender-si-tagboard.png)
I just read your last 2 posts.
Glad to read you made it work.
Just for the record, can you post transistors and hfe?
mac
When testing I used 2n2369a's for q1 - 3 but when I soldered it to tagboard I accidentally used a bc108 for q2 (no idea of the hfe) but the hfe for the 2n2369a's was around 90. I'm using a 50k pot in place of the 25k and getting the effect cutting out on when the pot is at one extreme and then a high frequency roll off on the other extreme, in the middle the pot works well, adjusting the bias of q2. I will continue breadboarding the circuit, got some bd175 and bd237s so will try them in the circuit also, I was thinking about incorporating an additional fuzz control on the base - ground of q3 like you did on your fz1 silicon conversion, have been trying to think of ways to ads additional controls, perhaps controlling q3 collector? In all honesty I'm pretty new to electronics and pedal building so been trying to absorb as much information as possible.
You can control Q3 collector with a 25k pot from Base to Gnd.
A fixed 100k to 220k from Vcc to Base can do it, IIRC.
If you want the FZ-1 slow attack I posted some months ago try this:
1. No interstage resistors
2. 22uf before T2,3
3. Use whatever booster or clean disto you have instead of the BMP input stage I added to the Maestro.
mac
Just revived the thread because I couldn't play the sound samples... :icon_mrgreen:
Reminds me of my "why does a TB mkI sounds good" stuff. The main conclusion was high pass filtering effect in the third stage, making the unit arguably the first transistor based distortion rather than fuzz.
Any transistor clipping with the fitting filtering would come close.
Silicon transistors usually have higher internal resistance, so any device with the same hfe might have higher input impedance than a germ one.
Said that, a look in this light at the last circuit brings the conclusion the high pass effect before the clipping q3 will be less. Especially with R16 in play. This will result in less treble boosted tone the original has. Lowering the 8k2 resistor will give higher cut off point.
Siliconising germanium circuits is nice. My favourite Fuzz Face is a silicon one.
hello all
I've been working on this version of the mkI and I don't know if I'm there or if I still need to tweak the values a bit.
here's a quick demo on my girlfriend's vox AC4, standard E tuning and drop A tuning.
https://youtu.be/FXaZXsIRXJI
what do you people think?
cheers
Quote from: Frances Rhodes on July 23, 2021, 09:41:14 AM
hello all
I've been working on this version of the mkI and I don't know if I'm there or if I still need to tweak the values a bit.
here's a quick demo on my girlfriend's vox AC4, standard E tuning and drop A tuning.
https://youtu.be/FXaZXsIRXJI
what do you people think?
cheers
Sounds great beyond the gating. Probably a finetuning thing of the bias in each stage. How did you build the stages? Collector - base resistor?
Sorry for the necrobump - just curious if anyone happens to have the schematics for this project? The image links seem to be lost to time.
Thanks!
Quote from: R.G. on March 04, 2013, 01:42:54 PM
Quote from: mac on March 04, 2013, 01:24:27 PM
I have nothing to do the rest of the year except going to the beach, so I'll try your idea ;D
Go ahead, rub my face in it. :icon_lol:
QuoteSince this circuit calls for leaky germs I think that new germ diodes have little leakage for it, most likely it will work with old ones.
BTW, a reversed diode and its leakage current can be considered like a big mega ohm resistor from B to C?
Taking the question first: no, not quite. A reversed diode acts more like a constant current source (or leak) than it does a resistor. The leakage on a reverse biased semiconductor junction rises over a small-ish few volts of reverse bias, then flattens out a LOT. It's not perfectly flat, but the leakage remains reasonably constant, not rising linearly with reverse voltage like a large resistor would. It was this idea that actually kicked off the Millenium Bypass. It's very, very difficult to get resistors that are consistent to any degree, and much larger than 1M, which is what the Millenium circuit needed.
That being the case, going to an external device to supply "appropriate" :icon_lol: leakage is much simpler. You can choose diodes for leakage, using old unsuitable germanium devices for their collector base or base-emitter junction. You can use two (or more) modern germanium diodes with low leakage for germanium, but still 1000x the leakage of silicon til you get the leakage your circuit likes.
This offers a degree of freedom in using transistors that picking among old germaniums does not.
In combination with piggybacking to lower gain, it may well be possible to trim in a generic silicon transistor to sound like an old, low gain and leaky germanium.
Wow. Who'd have ever thought that there would be a use for deliberately making things worse. :icon_lol:
How much leakage do you like to see RG?
Quote from: mdcmdcmdc on August 21, 2023, 11:58:07 AM
Sorry for the necrobump - just curious if anyone happens to have the schematics for this project? The image links seem to be lost to time.
Thanks!
(https://i.postimg.cc/sQCC9z38/Silicon-MKI-Tonebender.png) (https://postimg.cc/sQCC9z38)
Btw, I ditched the interstage resistors and left out the C-B caps on Q2/3. I used Si transitors that had similar hfe to my Ge version. Sounds great- maybe a touch darker and a little more drive than the Ge.
Quote from: bmsiddall on August 21, 2023, 09:25:57 PM
Btw, I ditched the interstage resistors and left out the C-B caps on Q2/3. I used Si transitors that had similar hfe to my Ge version. Sounds great- maybe a touch darker and a little more drive than the Ge.
Glad you like it.
And thanks for adding a link to the circuit.
mac
Thank you both!
Quote from: bmsiddall on August 21, 2023, 09:25:57 PM
Btw, I ditched the interstage resistors and left out the C-B caps on Q2/3. I used Si transitors that had similar hfe to my Ge version. Sounds great- maybe a touch darker and a little more drive than the Ge.
The original MkI last stage's circuit determines a lot of the EQ and sound which is far less "flabby" than most vintage fuzzes. It is the most driven stage and has the lowest input impedance which interacts with the 0.1uF cap.
In the germanium one we have a Re of about 25 ohms, which means the impedance at the base is about a couple of kohms with a hFE of 100 on average.
Any change in hFE (esp. higher) or swapping to silicon which might have higher internal Re might raise the input impedance enough to lower the corner frequency. The stage is less "hampered" in the lows. This means more low mids get amplified and driven which sounds to me like as described.
Lowering the 8k2 resistor might compensate.
Transistors hfe and internal capacitance make a lot of difference.
I have some 2N2369 that are very fuzzy, but others from Motorola sound different.
BD237/175/139 and TIP31/41 have high internal capacitance.
MPSA42 and 2SC1213 are my workhorses for old 60s fuzzes experiments --> hfe: 100-150, cheap, available.
I won't use any Si above hfe:150 like 2N3904 (*) because of bias and too much gain for my taste. But if super gain is what you like try BC550C or 2N5088 (adjust R5 and R8+R9)
(*) maybe a high gain at Q1 ??
mac
Quote from: mac on August 24, 2023, 10:28:17 AM
I won't use any Si above hfe:150 like 2N3904 (*) because of bias and too much gain for my taste. But if super gain is what you like try BC550C or 2N5088 (adjust R5 and R8+R9)
As I said, that would make for wooly fuzzy IMHO.
Lowering the hFE (esp on Q3) works let's say a bit like rolling back the volume on a Fuzz Face :icon_mrgreen:.
I'm not in this thread yet. well, now I am. I've breadered mac's version, using med power drivers AY-6115 's w/ hFE's 68/50/62, and I get more bursting nasty tizz decay oscillation than I care for. I've been trying to bypass the collector resistors [100nF across the 2k2 works, but affects the top end], as well as the 100pF B-C caps. I'll have another go tomoz w/ the added 4k7's and see if they help.
also not much impressed by the attack/fuzz pot range - might set that at maxx and use interstage level control instead.
Quote from: duck_arse on September 11, 2023, 11:57:18 AM
I'm not in this thread yet. well, now I am. I've breadered mac's version, using med power drivers AY-6115 's w/ hFE's 68/50/62, and I get more bursting nasty tizz decay oscillation than I care for. I've been trying to bypass the collector resistors [100nF across the 2k2 works, but affects the top end], as well as the 100pF B-C caps. I'll have another go tomoz w/ the added 4k7's and see if they help.
also not much impressed by the attack/fuzz pot range - might set that at maxx and use interstage level control instead.
Did you ever make germ mkI?
yes, indeedy, some many years ago, with japanese transistors. I remember nothing at all about the tone.
as for my current bb, the in and out stopper resistors on Q2 [2k2 at base, 1k at collector] along w/ the 100pF pair and 6n8 across the 2k2 collector resistor has tamed mostly all of the fringe-ing oscillation junk. Q3 adjusted to the quiet zone helps. overall, I'm not sure this is the circuit I'm looking for.
well, transistors, who'd a thunk it? it seems my selected transistors are far too hissy for the first stage config, tho they are fine in other circuits. odd results with low noise transistors being very much more hissy than low hFE parts.
I tried a pnp TT800 power/driver at Q1, it was as silent as I could get. will build a Heath 28 instead.
Do you like it now?
the silicon TB mkI is an ok sounding thing, if you sort your transistors for hissy fit. but - I couldn't get it to produce any variation in tone with my tested transistors and the fuzz pot setup as standard, or as a collector-base bias vario. so not worth my building as is, with the very limited palette of parts I have in mind for a particular build style.