Q3c Bias Point - RDV Silicon MkII

[Big Monk]

Anyone happen to know what the Q3c target bias voltage for the silicon TB MkII was? I'm trying to understand the bias changes required for the silicon circuit and knowing the target for that schematic will help in my calcs.

[iainpunk]

its the same as a Si FF Q2 bias point.

cheers, Iain

[Big Monk]

its the same as a Si FF Q2 bias point.

cheers, Iain

I'm wondering if that was by design or if it just took the info from the Fuzz Central stuff. I didn't bond with my Si Tonebender and that might have been why.

[Big Monk]

Goofing around a bit with the circuit, it seems like the split load resistors on Q3c would have to have a much lower series resistance to get the collector current up into the 7-8 V range. I also don't see any way to get the Q2c voltage down lower than 1.3 V, although I'm not sure how much an effect that has one the tone.

I may need to build another one of these with the more common TB collector voltages and see how it works out.

[PRR]

The collector point, relative to the supply voltage, is picked for a psycho-musical happy zone of asymmetry. The in-built voltages of Ge and Si are different but not-really compared to 9V swings. So what works for Ge should be a real good starting point for Si.

What varies is the Vbe and Vrb of the first transistor in the compound, meaning different value for Re of the second transistor in the compound. Or since Re normally must be a standard pot value, change Rc to suit.

No, you can not change the Vc of the first transistor in the compound, and collector current can vary over a wide range. 

[Big Monk]

The collector point, relative to the supply voltage, is picked for a psycho-musical happy zone of asymmetry. The in-built voltages of Ge and Si are different but not-really compared to 9V swings. So what works for Ge should be a real good starting point for Si.

What varies is the Vbe and Vrb of the first transistor in the compound, meaning different value for Re of the second transistor in the compound. Or since Re normally must be a standard pot value, change Rc to suit.

No, you can not change the Vc of the first transistor in the compound, and collector current can vary over a wide range.

In the spirit of candidness, I have never been that strong on microelectronics theory. I trained in EE but my concentration (and ultimately my career direction) was focused on electro mechanics and electric power engineer (I'm a utility protection engineer).

With that said, experimentation and trial and error has always been my go to for circuits work. I have become very familiar with the Ge Tonebender MkII circuit, so my initial goofing around was centered on upping the Q3c collector voltage to the 8 V range. I'm used to seeing Q1c close to the source voltage, Q2c in the 0.0x range and Q3c up near 8 V in my Ge version. Tweaking Q2c works well for getting Q3c voltage up, and I think I need to adjust to the fact that due to the inherit differences between Si and Ge, Q2c won't be as low as the Ge version.

Ive been using the Fuzz Face bias calculator to give me reasonable approximations of the Q2 and Q3 setup in the TB, but my lack of transistor current flow and voltage theory isn't allowing me to derive the equations used.

I'll keep goofing with it. I need to understand the voltage and circuit relationships better for my own personal benefit anyway.

[Gus]

Two threads that might help

reply 16
https://www.diystompboxes.com/smfforum/index.php?topic=92104.0

https://www.diystompboxes.com/smfforum/index.php?topic=114210.msg1059856#msg1059856

[Big Monk]

Two threads that might help

reply 16
https://www.diystompboxes.com/smfforum/index.php?topic=92104.0

https://www.diystompboxes.com/smfforum/index.php?topic=114210.msg1059856#msg1059856

Thank you. Electric Warrior has been very helpful in getting me up to speed on the many facets of the Ge version and I was reading through the thread of yours just a few minutes ago. It shows me I was definitely on the right track, although with lower gain transistors.

Appreciate the response!

Side note: I should reacquaint myself with some sort of Spice simulation. Would be helpful to model the circuit and see how voltage and current moves around with component swaps.

[Mark Hammer]

Is the RDV for the late Ricky Don Vance?  Just thought I'd ask since there are many who joined here well after his untimely passing.  Just a tip o' the hat to a nice guy, enthusiastic and diligent about his distortion.

[Big Monk]

Is the RDV for the late Ricky Don Vance?  Just thought I'd ask since there are many who joined here well after his untimely passing.  Just a tip o' the hat to a nice guy, enthusiastic and diligent about his distortion.

Yeah. I first heard of him in regards to the HiWatt Ruby mods from RoG. Everyone who interacted with him had a similar high opinion.

[Big Monk]

After have some frustration on the breadboard this weekend with an OC75 Bender, I decided to give the Silicon version another spin with an eye toward the real Tonebender voltages.

I kept the stock RDV Bender circuit but tweaked Q1b from 100k to 51k and Q3c from 5.6k to 1k. I also added a 220 pf from B to C on Q2 and a 100 pf from B to C on Q3.

Initial, and very low volume, testing was promising. I will crank it up tomorrow and report back.

[Big Monk]

I cranked this up today and WOW! Much different (and better) than I remember my previous stock version. Very close to the Germanium MK II versions I've built so far but with less noise.

[Rob Strand]

Side note: I should reacquaint myself with some sort of Spice simulation. Would be helpful to model the circuit and see how voltage and current moves around with component swaps.

Get the germanium models posted by Gert in reply 15.   You would be hard pressed finding something better.   I did some sims and they look representative.     Be aware that models with low VAF parameters can look like they have higher gains than you might think from the gain (BF) parameters.

https://www.diystompboxes.com/smfforum/index.php?topic=78932.0

[Gus]

Try Si power transistors
I have built treble booster and fuzz circuits with Si power transistors and posted about using Si power transistors for sometime at this forum

[Big Monk]

Try Si power transistors
I have built treble booster and fuzz circuits with Si power transistors and posted about using Si power transistors for sometime at this forum

I'm using this:



I reworked the voltage divider on Q3 to 470 ohm and 1k ohm to increase the Q3c to 8 vDC. I swapped the 2N5089 for a 2N5088. I changed the Q1 base resistor to 51k ohm which increased voltage on Q1c to 8.1 vDC. Finally, I dropped the output cap to 0.01 uf, added a 220 pf cap across the B-C on Q2 and added a 100 pf cap across B-C on Q3.

With these mods I'm very happy with how it sounds. I built it stock before but it was not that great and the Attack pot was almost useless. Upping the voltages makes it sound like its namesake.

[Big Monk]

Here are a few clips:

[iainpunk]

Try Si power transistors
I have built treble booster and fuzz circuits with Si power transistors and posted about using Si power transistors for sometime at this forum

people might be sick of hearing this line coming from me:
"I recommend the BD139/BD140 power transistors", they sound really good to my ears, in most low gain discrete circuits, it has something just magic going on.
they have gains from 25 to 150, so checking the gain is crucial, you can opt for buying a bulk and sorting them in gain ranges yourself

cheers

[DCVeffects]

I still hAVE all his precious service savers, bias points and collector voltages for most everything he contributed in.....man its hardish following his layouts lol