BJFE - Emerald Green Distortion Machine  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.

Re: BJFE - Emerald Green Distortion Machine

Postby Manfred » 13 Jun 2018, 17:42

That wouldn’t reduce the gain much more, you’d be better off increasing the 2k resistor on q2’s emitter as well


I think there is a need for changing the gain of this stage, because the output level of it is limited by the clipping diodes.

After initial doubts about the AC128 stage of The Keeley Germaium Amplifier which has no base resistor,
but in that case the resistor is not needed because the biasing is achieved by the Emitter leakage current in combination with the Emitter resistor.

I still have my doubts as to the oparation without the 470k resistor.
I had thougts about and made some trials and found that the FET without the gate resistor acts as a voltage controlled resistor,
this explains why there is no stage gain in that case.
Manfred
Cap Cooler
 
Posts: 600
Joined: 05 Apr 2009, 00:42
Has thanked: 919 times
Have thanks: 458 times

Re: BJFE - Emerald Green Distortion Machine

Postby Seiche » 14 Jun 2018, 05:34

marshmellow wrote:Yes, at that point you can just take out the cap and resistor completely. To further reduce gain you can put in a series resistor with the 22µ on Q2 emitter or take it out as well. Like Belanger said increase the emitter resistor or increase the 47k in series with the potentiometer, which limits the gain range.

But would that not reduce the distortion? I want to keep the amount of distortion. The issue is turning up the gain increases the volume too much instead of just increasing distortion. I would expect the diode clipping to limit this. I have triple-checked my diodes are properly connected to GND.

Manfred wrote:I think there is a need for changing the gain of this stage, because the output level of it is limited by the clipping diodes.

Do you mean there is no need?

Belanger88 wrote:
Seiche wrote:[...]I have also upped the 2k to 20k, but I think it should be increased even more (maybe also the 8k2)

That wouldn’t reduce the gain much more[...]

why not?
User avatar
Seiche
Tube Twister
 
Posts: 2464
Joined: 01 Nov 2010, 01:16
Location: Germany
Has thanked: 234 times
Have thanks: 172 times

Re: BJFE - Emerald Green Distortion Machine

Postby Manfred » 14 Jun 2018, 09:27

Manfred wrote:
I think there is a need for changing the gain of this stage, because the output level of it is limited by the clipping diodes.

Do you mean there is no need?


I estimated the overall gain for the first two stages of 20 to 25, which is not much.
It was presupposed that the Drive pot is in maximum position and the 22uF capacitor is connected to ground by the Voice pot.
Could you remeasure this gain in the real circuit?

At the moment I can see no way forward at all to me, so I must reorder the FETs and build the circuit for myself.
Manfred
Cap Cooler
 
Posts: 600
Joined: 05 Apr 2009, 00:42
Has thanked: 919 times
Have thanks: 458 times

Re: BJFE - Emerald Green Distortion Machine

Postby Seiche » 14 Jun 2018, 17:27

marshmellow wrote:Yes, at that point you can just take out the cap and resistor completely. To further reduce gain you can put in a series resistor with the 22µ on Q2 emitter or take it out as well. Like Belanger said increase the emitter resistor or increase the 47k in series with the potentiometer, which limits the gain range.

I actually just bypassed everything after the clipping diodes and the 47n cap directly to the 50kA vol pot. Sounds great, and the gain is more manageable. So apparently the last transistor has to have negative gain (less than 1)? How does that make sense? The tone is not much different. So is it only an impedance thing?
User avatar
Seiche
Tube Twister
 
Posts: 2464
Joined: 01 Nov 2010, 01:16
Location: Germany
Has thanked: 234 times
Have thanks: 172 times

Re: BJFE - Emerald Green Distortion Machine

Postby Belanger88 » 15 Jun 2018, 00:19

I have a few NSC J202’s. I could send you a handful if your willing to put the work in like you always do :D

I appreciate what you do for the forum a lot,

Manfred wrote:
Manfred wrote:
I think there is a need for changing the gain of this stage, because the output level of it is limited by the clipping diodes.

Do you mean there is no need?


I estimated the overall gain for the first two stages of 20 to 25, which is not much.
It was presupposed that the Drive pot is in maximum position and the 22uF capacitor is connected to ground by the Voice pot.
Could you remeasure this gain in the real circuit?

At the moment I can see no way forward at all to me, so I must reorder the FETs and build the circuit for myself.
Success is no accident. It is hard work, perseverance, learning, studying, sacrifice and most of all, love of what you are doing or learning to do.
Belanger88
Breadboard Brother
 
Posts: 75
Joined: 15 Jul 2016, 23:28
Location: Canada
Has thanked: 104 times
Have thanks: 31 times

Re: BJFE - Emerald Green Distortion Machine

Postby Manfred » 15 Jun 2018, 16:14

I estimated the overall gain for the first two stages of 20 to 25, which is not much.


Sorry I was wrong, I calculated the 2nd Stage as FET-stage not as BJT-stage.
The BJT stage has a gain of ~100, therefor the maximum total gain could be ~ 250.
Manfred
Cap Cooler
 
Posts: 600
Joined: 05 Apr 2009, 00:42
Has thanked: 919 times
Have thanks: 458 times

Re: BJFE - Emerald Green Distortion Machine

Postby Manfred » 15 Jun 2018, 21:43

I have a few NSC J202’s. I could send you a handful if your willing to put the work in like you always do


Thanks for your offer but I already ordered 2N5952 FETs
Manfred
Cap Cooler
 
Posts: 600
Joined: 05 Apr 2009, 00:42
Has thanked: 919 times
Have thanks: 458 times

Re: BJFE - Emerald Green Distortion Machine

Postby Manfred » 28 Jun 2018, 13:49

I bought eigth 2N5952 transistor.
Here the data from the transitor with the average values:

N-Ch JFET
Vgs(off)=-2,23V at Id=5,3µA
Vgs(on)=-0,23V at Id=5,01mA
gfs=3,9mA/V at Id=3,0mA to 5,0mA
Idss=6,00mA at Vds=3,00V
Rds(on)=177,7Ω at Id=5,0mA and Vgs=0,0V

2N5952 ID_UD.jpg


2N5952 ID_UG.jpg
You do not have the required permissions to view the files attached to this post.

For this message the author Manfred has received thanks:
Seiche (03 Jul 2018, 13:13)
Manfred
Cap Cooler
 
Posts: 600
Joined: 05 Apr 2009, 00:42
Has thanked: 919 times
Have thanks: 458 times

Re: BJFE - Emerald Green Distortion Machine

Postby Seiche » 05 Jul 2018, 10:57

so if these are average values, what is the variance?
User avatar
Seiche
Tube Twister
 
Posts: 2464
Joined: 01 Nov 2010, 01:16
Location: Germany
Has thanked: 234 times
Have thanks: 172 times

Re: BJFE - Emerald Green Distortion Machine

Postby Manfred » 05 Jul 2018, 21:38

Seiche wrote:so if these are average values, what is the variance?

measurement results of eight pieces 2N5952
2N5952_Measured_Data.jpg
You do not have the required permissions to view the files attached to this post.

For this message the author Manfred has received thanks:
Seiche (06 Jul 2018, 05:48)
Manfred
Cap Cooler
 
Posts: 600
Joined: 05 Apr 2009, 00:42
Has thanked: 919 times
Have thanks: 458 times

Previous

Return to Boutique Stompboxes dissected...

Who is online

Users browsing this forum: astrondelta, vot and 28 guests