V341 mods

Hey,

can anyone tell me, if it is possible and easy to implement some modifications to these preamps?
I'm thinking about high pass filter, maybe line switch and is it possible to get a bit more gain out of it?

Maybe change the 1k resistor at pin 7 from  input transformer? For more gain.

hey 3nity, thanks for the suggestion! Will try that.
Can you explain what this 1k resistor does?
Does anyone know, what the 1meg variable resistor is good for?
And does someone know the input impedance of this amplifier?
I assume the output impedance is 300 Ohm?

I just revisited this preamp and fully recapped it.
By looking at the schematics I'm a bit puzzled about the gain switch and it's resistors...
The actual resistors on the unit vary a bit from the ones in the schematic. Also why did they choose these values?
The resistors are in parallel, right?
I get the following values from lowest gain to full gain:
5040
1777.77
3733.33
888.88
406.34
273
180.32
133.33

Calculating the values from the schematic gives me the following values:
6092.59
1800
3733.33
666.66
440.42
280.57
214.11
121.22

Can someone maybe explain these values to me?

Also still puzzled about the 1M trimmer. What does it do?

Does the 1M apply negative feedback from the output to the base of SF132?

I think it takes a friction of the output and feeds it to the input of that stage.
The SF132 works in Common emitter and so it flips the polarity of the signal.
So the signal feed to the base of the SF132 is reverse polarity to its input signal at that point.

Murdock said:

I assume the output impedance is 300 Ohm?

Click to expand...

Do you know the ratio of the output transformer?

DerEber said:

Does the 1M apply negative feedback from the output to the base of SF132?

I think it takes a friction of the output and feeds it to the input of that stage.
The SF132 works in Common emitter and so it flips the polarity of the signal.
So the signal feed to the base of the SF132 is reverse polarity to its input signal at that point.

Click to expand...

Hmm, what would be the benefit of this reversed polarity?

I will inject a signal with a generator and look at the output with an oscilloscope and see what effect the 1M trimmer has.

No, I don't know the ratio of the output transformer. I will measure it.
According to this site: https://www.radiomuseum.org/r/lorenziv_studioverstaerker_v341_1.html
the input Impedance is more than 10 kΩ and output impedance is less than 40 Ω...
10k input impedance seems rather high... It's probably a typo and it is 1k I would think.