Distortion pedal with Fender 5F6-A type EQ

[sffwy]

Hello.

The first image is close to what I want to do.



I will be using an Electra Distortion for [A] and a Fender 5F6-A type EQ for the EQ.









My first question is, does the EQ work with the output impedance of the Electra?
I believe [A] is an impedance and level adjustment.


[These values are from a Fender Tone Stack which is made to run off of a source impedance of 30-80k ohm.]

https://www.diystompboxes.com/smfforum/index.php?topic=103977.0


I found something close to the answer within this page.
( however, I am not able to calculate the output impedance of the Electra).

My second question is, can I remove [B ] and use another booster with a larger output, or connect from the DI to the mic preamp after the EQ section?


Sorry if my English is not clear.
Thanks for reading.

[antonis]

however, I am not able to calculate the output impedance of the Electra

Just consider its Collector resistor value..

can I remove [B ] and use another booster with a larger output

Just copy Mig Muff Π last stage..

P.S.
It should be helpful to post the Tonestack (with items values) you intend to build..
(its impedance should stipulate A output and B input impedances..)

edit: And of course, Welcome...!!

[PRR]

The Fender stack is fairly un-fussy about source impedance from under 1K to over 200K, except loss increases as source impedance gets very large.

https://www.guitarscience.net/tsc/info.htm
https://www.duncanamps.com/tsc/  (Windows software)

[sffwy]

Just consider its Collector resistor value..

Just copy Mig Muff Π last stage..

P.S.
It should be helpful to post the Tonestack (with items values) you intend to build..
(its impedance should stipulate A output and B input impedances..)

edit: And of course, Welcome...!!

I have searched for the formula for Collector resistor value.
It seems I need to proceed without the use of my left brain and rely only on my ears.


After trying Big Muff, I will try other circuits.


I thought the third image was a tone stack, but am I missing some necessary information?
I have also prepared the next image, although I have cropped it due to its size in PDF.





The note said the following.
[5F6-A Bassman amps left the factory with a 100k tone slope resistor and .1uF bass cap even though the schematic and layout show 56k and .02uF.]



Waiting for your advice. Thank you.

[sffwy]

The Fender stack is fairly un-fussy about source impedance from under 1K to over 200K, except loss increases as source impedance gets very large.

https://www.guitarscience.net/tsc/info.htm
https://www.duncanamps.com/tsc/  (Windows software)

The link also had the 5F6-A circuit.
Thanks for the great answer and link.

[antonis]

I have searched for the formula for Collector resistor value.
It seems I need to proceed without the use of my left brain and rely only on my ears.

I'm afraid you didn't get me..

Output impedance of a CE amplifier IS the value of its Collector resistor..
(4k7 for your 2^nd image..)

As Paul said above, that impedance should cause no Tonestack driving issues..

IMHO, the impedance (mis)matching issue will appear at the last stage..
That's the reason for JFET Source follower used in your 1^st image..
Of course, there are solutions, like bootstrapping (stage A) if you wish to stay bipolar..

[sffwy]

I'm afraid you didn't get me..

Output impedance of a CE amplifier IS the value of its Collector resistor..
(4k7 for your 2^nd image..)

As Paul said above, that impedance should cause no Tonestack driving issues..

IMHO, the impedance (mis)matching issue will appear at the last stage..
That's the reason for JFET Source follower used in your 1^st image..
Of course, there are solutions, like bootstrapping (stage A) if you wish to stay bipolar..

Are you saying that I was trying to calculate from scratch something that already had the answer written on it?

As you know, I can solder the same as the layout, but have little understanding of what each component does.
I should have told you this when I first asked the question.

If my understanding of your advice is correct,

Electra / Output -> Input / EQ /

I think we are good to go so far.

Next step.

(EQ) / Output -> Input / Boost (Muff) / Output ->

Is there anything I need to do here? (add components, etc.)

Any more help would be appreciated.
Thank you.

[Rob Strand]

Is there anything I need to do here? (add components, etc.)

The tone control loads down the output of the preceding amplifier.  It does this on a tube amp and it does this on you circuit.   To make a faithful emulation of an amplifier your circuit needs to do the same as an amp.

The output impedance of a triode stage is around 60k,
https://www.aikenamps.com/index.php/designing-common-cathode-triode-amplifiers

The output of a common emitter transistor amp (without feedback) is approximately the value of the collector resistor;  actually less due to the transistor Early effect.

You have two choices:
- design the transistor amp with a 60k collector resistor and use the tube amp values for the tone control.
- leave the transistor amp with 10k collector resistor then impedance scale the tone control by a factor of 10/60 = 1/6.   So all caps increase by a factor of 6 and all resistors and pots decrease by a factor of 6.

For transistor stage the second method usually ends up with less noise.  As high valued resistors are a source of noise.

[sffwy]

Is there anything I need to do here? (add components, etc.)

The tone control loads down the output of the preceding amplifier.  It does this on a tube amp and it does this on you circuit.  To make a faithful emulation of an amplifier your circuit needs to do the same as an amp.

The output impedance of a triode stage is around 60k,
https://www.aikenamps.com/index.php/designing-common-cathode-triode-amplifiers

The output of a common emitter transistor amp (without feedback) is approximately the value of the collector resistor;  actually less due to the transistor Early effect.

You have two choices:
- design the transistor amp with a 60k collector resistor and use the tube amp values for the tone control.
- leave the transistor amp with 10k collector resistor then impedance scale the tone control by a factor of 10/60 = 1/6.  So all caps increase by a factor of 6 and all resistors and pots decrease by a factor of 6.

For transistor stage the second method usually ends up with less noise.  As high valued resistors are a source of noise.

Thanks for the great advice and links.
It still seems to be a difficult method for me right now.
For now I will try to amplify the signal by placing some sort of simple clean booster after the EQ.
But I will remember your advice when I take the next step.

Thank you.

[antonis]

I'd follow Rob's suggestion for retaining Tonestack original values..
(in case you experience noise issues, scale down EQ and Q1 Collector & Emitter resistors by a factor of 10 and scale up EQ caps values respectively..)

[sffwy]

I'd follow Rob's suggestion for retaining Tonestack original values..
(in case you experience noise issues, scale down EQ and Q1 Collector & Emitter resistors by a factor of 10 and scale up EQ caps values respectively..)

Thank you for preparing the schematic.
Is this the second of the choices Rob suggested?

You have two choices:
- design the transistor amp with a 60k collector resistor and use the tube amp values for the tone control.
- leave the transistor amp with 10k collector resistor then impedance scale the tone control by a factor of 10/60 = 1/6.  So all caps increase by a factor of 6 and all resistors and pots decrease by a factor of 6.

For transistor stage the second method usually ends up with less noise.  As high valued resistors are a source of noise.

I am not sure how much I understand it now, but I am sure it will be important to me in the future.

Thank you very much.

[antonis]

Is this the second of the choices Rob suggested?

No, it's the first one..
(the one which contributes about 60k Q1 output impedance, retainig "original" EQ values..)

For noise issues prevention, make Q1 Collector & Emitter resistors 5k6 & 1k2 respectively..
(Rob's 2^nd suggestion..)

Q2 is an output "recovery" stage and its gain could be set according to Tonestack losses..
(as it is, the whole configuration can compensate for about 28dB loss - meaning Vin amplitude = Vout amplitude..)

47k & 10μF in both stages serve for inputs impedance "immunity"..
(they bootstrap bias configurations making them look like much higher than their actual value..)

[PRR]

The thread says 5F6-A but people keep saying 60K.

The 5F6-A specifically has a cathode follower and the Rsource is like 1.3k.

Most Fenders drive the tonestack from a 12AX7 plate with a 100k load resistor and the Rsource is about 40k (100k || 60k =~ 40k +/-20%).

But it is very unfussy. Mostly a loss of extreme treble. And there is a knob for that. It really is OK to just build it and ear it.

The prime tool for "noise" (hiss) here is having just enough gain (amplification, not fuzz) in front of the tonestack. Lower impedance throughout the tonestack helps but slowly, square-root of impedance. (Also the film caps get fat.)

[Rob Strand]

The thread says 5F6-A but people keep saying 60K.

You're right, it's the Bassman, low Z driving the tone stack.   In retrospect posting a link to the original schematic might have helped.

The original 10k collector resistor might be OK.   

I definitely would not be dropping the collector load on the first stage to 1.2k  - that will make the first stage noisy when fed with a guitar pickup.   You might be able to squeeze it down to 4.7k.  However, if you *really* want to go so far as to drive the stack with a low impedance perhaps add a buffer after the first stage - just like the original circuit.

As far a noise goes you can tweak the current of the first stage transistor.  And you really should be using lower valued resistors on the tone stack.   Lower tone stack resistors and means using a buffer after the first stage.  If you dropped the tone stack resistor values by a factor of 10 then it technically needs to be fed by a 100 ohm impedance.

[PRR]

If this comes from the guitar, control of gain does more for noise than changing impedance or operating current. As you say, 1/10X impedance is a stupid low source impedance and only nets 10dB less hiss.

[Rob Strand]

Something else, making the first stage variable gain via the emitter resistor isn't going to maintain a good/high input impedance.   At high gain settings the bootstrap probably won't be able keep the input impedance high.   Even if you raise the 10k base bias resistor the reflected impedance from the emitter through to the base is going to be low-ish.   Sometimes the devil is in the details of this stuff but RE*hFE = 1k * 300 = 300k looks borderline.

[PRR]

Well, vacuum tubes ARE better than transistors. But that compromise seems to be already decided.

[sffwy]

Is this the second of the choices Rob suggested?

No, it's the first one..
(the one which contributes about 60k Q1 output impedance, retainig "original" EQ values..)

For noise issues prevention, make Q1 Collector & Emitter resistors 5k6 & 1k2 respectively..
(Rob's 2^nd suggestion..)

Q2 is an output "recovery" stage and its gain could be set according to Tonestack losses..
(as it is, the whole configuration can compensate for about 28dB loss - meaning Vin amplitude = Vout amplitude..)

47k & 10μF in both stages serve for inputs impedance "immunity"..
(they bootstrap bias configurations making them look like much higher than their actual value..)

Thanks for the detailed explanation.
I need to learn more.

[sffwy]

The thread says 5F6-A but people keep saying 60K.

The 5F6-A specifically has a cathode follower and the Rsource is like 1.3k.

Most Fenders drive the tonestack from a 12AX7 plate with a 100k load resistor and the Rsource is about 40k (100k || 60k =~ 40k +/-20%).

But it is very unfussy. Mostly a loss of extreme treble. And there is a knob for that. It really is OK to just build it and ear it.

The prime tool for "noise" (hiss) here is having just enough gain (amplification, not fuzz) in front of the tonestack. Lower impedance throughout the tonestack helps but slowly, square-root of impedance. (Also the film caps get fat.)

thanks for the advice.

The thread says 5F6-A but people keep saying 60K.

You're right, it's the Bassman, low Z driving the tone stack.  In retrospect posting a link to the original schematic might might have helped.

I may be too late, but I posted the schematic.








Going back to my first post, what I want to do is add a tone stack to the Distortion Pedal as shown in the 1st image.
I will be using the Electra in the 2nd image and the Fender 5F6-A type EQ in the 3rd image.
To summarize what I think I can do with the advice of antonis, PRR, and Rob so far,


Electra / Output ->
need sufficient signal level, impedance is ok

The prime tool for "noise" (hiss) here is having just enough gain (amplification, not fuzz) in front of the tonestack. Lower impedance throughout the tonestack helps but slowly, square-root of impedance. (Also the film caps get fat.)

The Fender stack is fairly un-fussy about source impedance from under 1K to over 200K, except loss increases as source impedance gets very large.

As Paul said above, that impedance should cause no Tonestack driving issues..

-> Input / EQ / Output ->
I can't say I completely understand the detailed explanations given by all three of them.
Is there any part of the 2nd image values that should be changed?


-> Input / Boost (Recovery) / Output ->
I will be using Big Muff for boost.

can I remove [B ] and use another booster with a larger output

Just copy Mig Muff Π last stage..

The circuit will be the one in the next image.





Is there anything I am understanding the advice incorrectly?

[GibsonGM]

You're not showing the Electra, Sffwy.  This is the Electra.




Because it has clipping diodes, the output signal is going to be lower than one might expect. You could try sticking the tone stack after it with Muff recovery stage, as an experiment (which might have a lot of noise and leave a lot to be desired),

OR

Make the 2 transistor driver/recovery circuit that Antonis posted above, and put the tone stack inside it where it says "EQ", which is what I recommend.  If you are doing this on breadboard it shouldn't take much time to try it both ways, esp. since you'll want to build the Electra and the tone stack anyway. 


EDIT: Now I see you want to use the Muffer up front?  Same sort of deal.  What the others are saying is to use the last stage of the 'real' Big Muff Pi circuit to recover the level lost in the tone stack.  The 2 transistor circuit Antonis posted will do this fine - I would literally build what he presented and consider it all the 'tone stack', placing Electro or Muffer before it.