Hello,
I have a Marshall 5275, which has some problems:
It is a transistor amplifier (75 W Reverb) which was manufactured in 1985(or before).
The problem is that there is distortion in the highs if the input signal is too strong.
The guitar is a Gibson Sg-x (the microphone is a 500-T, which has a high level of output).
Would somebody have an idea from where that can come? (I am ready to repair it)
picture: http://images.google.fr/images?q=tbn:DA0nOgjGyrwJ:sites.uol.com.br/lucas_ortiz/marshall75.jpg
schematic🙂p): http://www.drtube.com/schematics/marshall/5275.gif
PS: I've readed http://www.diyaudio.com/forums/showthread.php?s=&threadid=30887&highlight= : is it the same problem?
sorry for my bad english 🙁
I have a Marshall 5275, which has some problems:
It is a transistor amplifier (75 W Reverb) which was manufactured in 1985(or before).
The problem is that there is distortion in the highs if the input signal is too strong.
The guitar is a Gibson Sg-x (the microphone is a 500-T, which has a high level of output).
Would somebody have an idea from where that can come? (I am ready to repair it)
picture: http://images.google.fr/images?q=tbn:DA0nOgjGyrwJ:sites.uol.com.br/lucas_ortiz/marshall75.jpg
schematic🙂p): http://www.drtube.com/schematics/marshall/5275.gif
PS: I've readed http://www.diyaudio.com/forums/showthread.php?s=&threadid=30887&highlight= : is it the same problem?
sorry for my bad english 🙁
Has this distortion always been there, or is it a new problem? Have you recently changed guitar to the SG?
From the schematic, the amp has a high gain input stage (x10) so with a high output guitar pickup, this could be driving the amp too hard. Is there a gain control? If so try turning it to the minimum.
From the schematic, the amp has a high gain input stage (x10) so with a high output guitar pickup, this could be driving the amp too hard. Is there a gain control? If so try turning it to the minimum.
Hello,
No, this is a second hand amplifier, and it always did that with the SG.
indeed, when I lower gain(normal volume?), saturation drops a little, but it is always there...
Is this typical of Marshall??
Thank you
No, this is a second hand amplifier, and it always did that with the SG.
indeed, when I lower gain(normal volume?), saturation drops a little, but it is always there...
Is this typical of Marshall??
Thank you
sorry,
i am araid that you have to turn off the volume in your guitar.
sg has extremely high output and from the schematic i could guess that the full output from 1 stage may be over +-15V (10Xgain 2 V input = 20Vpp)
i am araid that you have to turn off the volume in your guitar.
sg has extremely high output and from the schematic i could guess that the full output from 1 stage may be over +-15V (10Xgain 2 V input = 20Vpp)
Thanks for your replies,
so I think that I will have to create an attenuator between the guitar and the preamp...🙁
A kind of de-premplifier
so I think that I will have to create an attenuator between the guitar and the preamp...🙁
A kind of de-premplifier
If you just change the 1M resistor (R3) on the input opamp to a lower value, you'll get lower amplification and lower noise. Start with maybe 220k. That'll give you ~1/5 of the gain you have now.
Rune
Rune
You said R3? I will test that.
In the worst case, I will not use any more the distortion, or it will be a little more "bluesy"😉
Thanks!!
In the worst case, I will not use any more the distortion, or it will be a little more "bluesy"😉
Thanks!!
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