Still finishing designing this circuit. Any ideas, critique or opinons?

[swever]

So I've finished designing this circuit yesterday. Any critique or opinions?

It started as an Elektra distortion style thing. I wanted to see how that would sound with one of the higher gain npn germanium transistors. Then I tried adding a second one and put a tonestack between them. Then I and added another tonestack and a jfet gain stage at the end with yet another (bypassable) set of clipping diodes.

I'm really loving the result. I'm not sure if that's me being biased now but I think it's the most amp like sounding circuit I've heard yet. It offers a very wide range of timbres and works great with my very clean tsa-15h tube head. I believe may also work great plugged into return of a dirtier amp. It loves a booster or a fuzz in front of it too.

I have no training in electrical engineering and pretty much just cobbled this thing together. I would appreciate if you great people who know more than me would have a look and say if you see any obvious errors or potentially problematic parts.

[thermionix]

Looks like it should work, as you have already confirmed.  Some odd components that would prevent most of us from breadboarding it.  So if you get a chance to post a sound clip or video, we'd love to hear it.

[antonis]

If you really love the result, there shouldn't be any error (obvious or potentional..) 

I'm not familiar with your Brilliance circuit but it seems to me it creates a 10Hz LOW pass filter with 33nF and 500k pot wiper set to GND..

Also, 22nF input cap creates a 1.4kHz HIGH pass filter togheter with about 5k input impedance..

But if you love it, keep going...!!! 

[diffeq]

Some odd components that would prevent most of us from breadboarding it.  So if you get a chance to post a sound clip or video, we'd love to hear it.

КП303А - JFET with Vgs(off) 0.5-3V and Idss of 0.5-2mA. 2N3819 comes to mind as a substitute. ГТ404Е - generic n-p-n Germanium, gain of 60-150. So something like AC176 or 2SD127 is equivalent. Rare subs, but not unobtainium.

Some odd components that would prevent most of us from breadboarding it.  So if you get a chance to post a sound clip or video, we'd love to hear it.

Second this request.   

[swever]

Looks like it should work, as you have already confirmed.  Some odd components that would prevent most of us from breadboarding it.  So if you get a chance to post a sound clip or video, we'd love to hear it.

КП303А - JFET with Vgs(off) 0.5-3V and Idss of 0.5-2mA. 2N3819 comes to mind as a substitute. ГТ404Е - generic n-p-n Germanium, gain of 60-150. So something like AC176 or 2SD127 is equivalent. Rare subs, but not unobtainium.

I've experimented with different type of transistors and diodoes (for many long evenings) and came up with this configuration. I most liked the sound of it with q1 being a si with ~400 hfe and a ~150 hfe ge q2, schottky diodes in the first stage and a combination of ge a si diodes in the second stage. However, it works very well with other bjt's, jfet's and diodes.

[swever]

It sounds like punk/garage rock/post-rock at max gain to my ears. Rough and grainy and "bubbly", with tight articulate dynamics. Using either guitar volume control or gain control a whole range of mid-gain tones is acheivable, each method givng a noticeably diffrent colour and texture.

Here's a little sample of one of the circuit's earlier iterations: http://picosong.com/wfFwd/
This is before I added gain control. I may have swaped the transistors and diodes after recording this.

Will record more samples later.

[swever]

If you really love the result, there shouldn't be any error (obvious or potentional..) 

I'm not familiar with your Brilliance circuit but it seems to me it creates a 10Hz LOW pass filter with 33nF and 500k pot wiper set to GND..

Also, 22nF input cap creates a 1.4kHz HIGH pass filter togheter with about 5k input impedance..

The brilliance control is a Moonlight tonestack I filched from here. My version has a switch to choose between two capacitor values 

And that impedance thing may be the reason why it is so interactive with guitar volume control. I get a very full bassy sound when it's at max, and it quickly becomes very bright when I roll it down. I really really like this behaviour, but I'd also love to hear how it sounds if I make it "right". How do I go about increasing input impedance?

[duck_arse]

I don't understand how Q3 biases with the diode connected to the gate as shown.

[swever]

I don't understand how Q3 biases with the diode connected to the gate as shown.

TBH I dont understand it either 
The idea with the diode comes from here. In fact the whole stage does.

[duck_arse]

I don't understand how Q3 biases with the diode connected to the gate as shown.

TBH I dont understand it either 
The idea with the diode comes from here. In fact the whole stage does. The only change I did was change the drain resistor. IIRR I aimed for 4.5V at drain, but maybe not haha.

indeed - but see how the diode has the pull-up resistor connected to its anode? this will bias the jfet gate and forward bias the diode, whereas your dia shows the jfet gate hard-to the diode anode, with no source of voltage connected.

[swever]

indeed - but see how the diode has the pull-up resistor connected to its anode? this will bias the jfet gate and forward bias the diode, whereas your dia shows the jfet gate hard-to the diode anode, with no source of voltage connected.

You mean the 10m to +V? Mine has that too.

[duck_arse]

ahhhhh, sorry, I was misreading your schem. I see now, I thought the resistor was crossing over the diode, now I see "no dots" notation. sorry, carry on, all is clear now.

[swever]

No probs, hehe. Sorry for the missing dots. I knew I *should* put them, but then I thought it's readable like that. I'm gonna redraw the schematic anyway soon once I start designing a pcb/perf layout for this.

[Jeema]

КП303А - JFET with Vgs(off) 0.5-3V and Idss of 0.5-2mA. 2N3819 comes to mind as a substitute.

If I am reading this Google-translated datasheet correctly, it looks like КП303А has a transconductance of 1-3mmhos at 10V.  In that case 2N5457 may be an even closer match...

[swever]

Also, 22nF input cap creates a 1.4kHz HIGH pass filter togheter with about 5k input impedance..

Just tried using larger value caps. Ended up leaving this at 22n. Gives a fast type of feel at higher gain settings.
I think I am one of those who like cutting lows before clipping  If I understand correctly, it must be a 6db/octave high pass. Not too steep.

[antonis]

How do I go about increasing input impedance?

Easiest way is to omit 22μF big can cap..
It shouldn't (drammatically) lower Q1 gain due to NFB topology of 500K+47k gain set..

With NFB gain setting, you can't increase input impedance more than [547k/(1+Gain)] // (h_FEx R_E), 'cause lowering Gain pot setting also decrease total NFB loop resistance so you are only able to increase Emitter resistor or use a higher gain transistor (or both)..

Or place a simple buffer before it to find if it should be worth the trouble..

If I understand correctly, it must be a 6db/octave high pass. Not too steep.

"Steepnes" is a matter of taste, of course.. 
(12dB at 350Hz, 18dB at 175Hz and 24dB at 88Hz might be considered steep..)

[swever]

Thanks for the info and advice, Antonis. That's something I will experiment with for sure.

I'd really prefer keep the emitter bypass cap. It's really one of the integral parts of the tone.

Btw, this cap. It measures about the correct value (+/- a percent or so iirc) with both my multimeter and component tester. But there is significant difference it tone between this one an a regular electrlytic of the same value and similar ESR. This is the first time I actually hear a difference between different capacitor types. Could it be that mojo is not totally a myth? Or it could be some other parameter that makes the difference. Leakage?

The capacitor is a К53-14 - said to be solid electrolytic (oxide solid state, aluminum).

[antonis]

Could it be that mojo is not totally a myth?

Can't say for sure.. 

What I CAN say is: If you need to replace that cap you'll ruin your circuit's performance.. 

To be more serious: The combination of actual capacitance, ESR, Voltage rating and leakage difference could result in significant tone alter..

[swever]

I tried putting a jfet buffer in front of it and sounds better than ever before.



The only issue is that gain control has much less range now.

[anotherjim]

The low output impedance of the new buffer may be shunting out more of the NFB coming back via the "gain" pot?
Maybe it could be better with some resistor inserted before the coupling cap from the buffer?

I always find voltage NFB gain control on discrete stages hard to get right. I'd rather put the gain pot in series with the emitter bypass cap.