Hey,

I just looked at the recent schematics of my amp, and now I have one (probably simple) question: Would there be a difference between putting the treble peaker (in my case 470k||2n2) either BEFORE or AFTER the gain pot (which is bypassed by a 4n7 itself)? I've been thinking about making the amp switchable from JMP to #36, and that would be easier with the 470k||2n2 after gain 1. I believe it should be the same, but it wouldn't be the first time I was wrong

Cheers
Kilian

Hi Kilian

Can you post a schem of just the point you are talking about ... ? If it is the same resistor / poti circuit which can be found in MVs (470k || 500pF followed by 1M pot (gain) and whiper is going to grid of V1b) then it is a difference if you place the 470||500pF before the gain pot or after its whiper.

I have simulated exactly this circuit some days before - have to look up the output and post it, if you like. But first of all it is a difference because of the voltage division.

Regards, Stone

Hey,

I just looked at the recent schematics of my amp, and now I have one (probably simple) question: Would there be a difference between putting the treble peaker (in my case 470k||2n2) either BEFORE or AFTER the gain pot (which is bypassed by a 4n7 itself)? I've been thinking about making the amp switchable from JMP to #36, and that would be easier with the 470k||2n2 after gain 1. I believe it should be the same, but it wouldn't be the first time I was wrong

Cheers
Kilian

Yes you will hear a difference, keep the 2n2470k before the gain pot, I have done it switchable before, & i just took the signal from the coupling cap, just before the 2n2470k combo.

Anyways here is a new clip with a few tweaks, http://soundclick.com/share.cfm?id=10658172


Cheers

Nigel

Can you post a schem of just the point you are talking about ... ? If it is the same resistor / poti circuit which can be found in MVs (470k || 500pF followed by 1M pot (gain) and whiper is going to grid of V1b) then it is a difference if you place the 470||500pF before the gain pot or after its whiper.

Hey Stone,

yepp, it's the same circuit with just some other values. Dammit... 

Yes you will hear a difference, keep the 2n2470k before the gain pot, I have done it switchable before, & i just took the signal from the coupling cap, just before the 2n2470k combo.

Hey Nigel,

yes, that's what I planned first. But I thought I could maybe use the same pot for both of the modes. Well, then it's gonna be a stereo pot, I don't want too many holes in the front plate

Cheers
Kilian

Hi Kilian

It is a major difference in distortion / amplification and in frequency response. Maybe I 'll be back with the output of LTSpice this evening (to show it graphically).

Regards, Stone

Hi Kilian

I have attached a screenshot of both versions I think you had in mind; it does not matter, if it is exactly what you have realized in your amp, because it shows the principle.

I take off the signal right before the second tube at its grid.

As you can see, "vergleich02" shows an arrangement well known of the non-mv Marshalls treble input - values do vary (I know) but this does not matter, as stated before.

"vergleich01" shows an arrangement very similar to most mv-Marshalls - values do vary, too.

The resistors 900k/100k do simulate a 1M log gain pot which is turned up half.

What can be seen at first is the difference in frequency response because in the second arrangement the 470k resistor does act as a partially (frequency dependent) bypassed grid stopper.

At second you will notice a big difference in amplification at 100Hz and still at around 1kHz.

Regards, Stone

Hi Stone,

Thanks for the effort. But I guess there is a bug in the left circuit.
There you tap the signal at the input of the potentiometer, not at the wiper.
If connected this way, the potentiometer is only a hi cut but no volume control.

Peter

Hi Peter

You are right; I have to fix this, but this will only result in a more treble response of the circuit. The main difference is the "much more" gain and resulting distortion of the left one.

I thought of this arrangements some days ago, too and was wondering if there is pretty much current flowing to generate a remarkable voltage drop across the 470k in the left example. I came up with this simulation (I did not save it to disk so I redraw it yesterday) and was impressed - I think this is one of the reasons (and some other details which are overseen most times) which makes the treble circuit of the 1959 such a good rythmn channel

Regards, Stone

Hi

Again, sorry for posting a slightly wrong version / circuit.

Now I have corrected this and done some more simulations. First of all I simulated the circuits with the corrected tap of the gain pot; after that I removed the bypass cap of the gain pot, followed by removal of the 470pF cap (470k bypass cap) and at least I readded the gain bypass cap.

Regards, Stone

Hallo Stone,

kannst Du mal Deine aktuellste Version als Schaltplan hier einstellen ?

Baue auf der Basis gerade wieder einen........


Vielen Dank und bis Samstag.

Hallo Carlitz

Vom #39? Oder vom #36? Letzteren habe ich nicht mehr aufgebaut bzw weiter ausgebaut und die im Netz herumschwirrenden Pläne als Basis genutzt; müsste ich raussuchen (Link).

Gruß, Stone

#39 ist ok...

Ok, den wollte ich eh mal genau rauszeichnen (quasi als finale Version inkl der Loop). Mache ich heute Abend mal.

Gruß, Stone

Super, Danke.

ick freu mir...

Hallo Carlitz

Da es nicht ganz das Thema trifft, habe ich es mal in den Ursprungsthread gelegt ...

http://www.tube-town.de/ttforum/index.php/topic,13332.msg140125.html#msg140125

Gruß, Stone