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Schematics and Layouts / Re: Variable resistor on marshall scheme
« Last post by Jazz P Bass on March 17, 2019, 11:59:01 PM »
That symbol is trying to indicate that the wiper (the middle leg) gets attached to either the left or the right leg.
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Schematics and Layouts / Re: Operational Amplifier in Marshall 5010 scheme
« Last post by Jazz P Bass on March 17, 2019, 11:48:21 PM »
The + of the bridge rectifier is marked 'A'.
The - is marked 'D'.
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Schematics and Layouts / Variable resistor on marshall scheme
« Last post by Szcz on March 17, 2019, 11:03:34 PM »
Hi,
I'm trying to figure out how variable resistor on this scheme should be connected to it, cause I've never seen vr symbol like this before. On this scheme is Mid and Bass resistors. Can anyone explain how to do that with the actual potentiometer, cause there are just 2 pins on the scheme instead of 3 like on the Gain. Thanks
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Schematics and Layouts / Re: Operational Amplifier in Marshall 5010 scheme
« Last post by Szcz on March 17, 2019, 10:15:28 PM »
Yes thanks, when you wrote it, I almost finished scheme in kicad, but if you can, do you know where is the plus of the bridge? Cause it's a little bit confusing here and I don't know did I did it right.
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Schematics and Layouts / Re: Operational Amplifier in Marshall 5010 scheme
« Last post by Dino Boreanaz on March 17, 2019, 09:13:52 PM »
In the top-right corner of the schematic it specifies that IC1 is an MC1458.  This is a dual op amp that provides the two gain stages shown in the schematic as IC1a and IC1b.  Pin 8 connects to the positive rail as shown and Pin 4 (not labelled on the op amp) connects to the negative rail as shown below R7 in the schematic.  This is the same op amp application used in many solid state Marshall amps of this era.

As suggested, this circuit can use a variety of dual op amps.  I've read about people trying many different dual op amps in these applications.

I've been considering building this amp too, and would be interested to follow your progress.
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Schematics and Layouts / Re: Operational Amplifier in Marshall 5010 scheme
« Last post by Szcz on March 17, 2019, 04:39:39 PM »
Oh, and if there are two op amps on the scheme and they are mono(?), then shold I use one TL072, or two TL072?

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Schematics and Layouts / Re: Operational Amplifier in Marshall 5010 scheme
« Last post by Szcz on March 17, 2019, 04:35:22 PM »
So the only thing that will mater here is that op amp should be dual? Ok, thanks
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Schematics and Layouts / Re: Operational Amplifier in Marshall 5010 scheme
« Last post by tonyharker on March 17, 2019, 04:17:08 PM »
It doesnt really matter. Any dual op amp eg TL072, NE5532, JRC4558 etc will work.
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Schematics and Layouts / Operational Amplifier in Marshall 5010 scheme
« Last post by Szcz on March 17, 2019, 03:43:51 PM »
Hi,
I found a scheme for a Marshall 5010 ss amplifier, that I'd want to make. There is a problem, that I don't know which operational amplifier should exactly be according to this scheme. There are two of them and both of them aren't named. Does anybody know what should it be?
Thanks
P.S. If I wrote anything wrong and you don't understand the question, write me about it and I'll write it again. English isn't my 1st language.
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Amplifier Discussion / Re: HELP Marshall 5203 Master Reverb 30
« Last post by g1 on March 10, 2019, 09:32:40 PM »
Yep.  Notice the 5205 schematic still has 25V caps?  Not possible if that were really a 21-0-21 secondary.
This may sound crazy, but some companies label the transformer or schematics with what the rectified DC voltage will be.  (Roland?)
That must be the case with this 5205 schematic.  So a 15-0-15 secondary like Phil mentioned will give a rectified +/-21V which will drop a little bit under full load and give the 12W at 16ohms that the 5205 specs. 

The 5203 is completely designed around a certain voltage supply.  If you change it, even though you put in higher voltage caps, you would need to adjust the dropping resistors R35 & R36 so that the 15V zeners don't burn.  Then you will probably have to increase the size of the heatsink, which was spec'd for 30W output.  Now you can hope that the power transistors can handle the extra current, and that the speaker can handle the extra power.  :D
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