There is a switched potentiometer (or whatever you call a dial that turns on and off  ) for the overdrive gain

I thought maybe I could check the + and - voltage of each 4558DD with the gain off and on

But I got the same reading with it off or on it appears they are powered up at all times 

Then I checked the rectifier diodes and looks like we have a bipolar power supply 

Whose voltages show up on the TDA

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I think I may look at these diodes I'm curious I always think these clear colored diodes are zeners but sometimes they are (switching?) diodes idk

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But looking at the schematic for the 10xl and 15xl kindly provided by G1 they look like ordinary diodes

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So might be time for a look at the TDA and see why it needs diodes around it 

Seems like this is gonna be a good project I thank you for your help 

These integrated circuits op amps chips etc must be revolutionary because it occurred to me there is not one transistor in this amp 

I wanted to have an amp chassis I could put on the bench and maybe accomplish a few sorely needed achievements
-be able to look at any component and identity it moreover locate it on the schematic
-identify the components of the power supply
-determine the route of the signal path
-do some signal tracing

The amp works I tried it a while back it is missing a speaker

Beautiful ain't it

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Well that didn't take long (I had to be careful not to scratch the Tolex)

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And inside on the bench

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Doesnt look too intimidating but it just occurred to me that TDA 2040 or whatever it is may eliminate quite a few components

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Maybe this is the bridge rectifier

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That white cable is some type of three wire cable I just attached for makeshift speaker wire

Also I see an 8 DIP wondering what that is but all good in the hood because I get to find out 
EDIT: They are two 4558DD

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They must be for the cheese that goes CRUNCH

As far as the signal path well at least I think it begins at the input jack and ends at the speaker 

Quote from: g1 on August 25, 2026, 04:06:22 PMHere is the pdf schematic package that has yours on the last 2 pages.  So I think we can safely say that PR 241 is EC1912 drawings.

Thx!.
What would that mean (being EC1912 drawings)?.

Quote from: Chorch Cluni on August 24, 2026, 07:31:32 PMMine is:
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Here is the pdf schematic package that has yours on the last 2 pages.  So I think we can safely say that PR 241 is EC1912 drawings.

Quote from: dmeek on August 14, 2026, 09:11:12 PMThis one is PR495  You cannot view this attachment.

Mine is:

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Lateral (audio) Mosfets are hard to drive, require over 6Vgs to reach 7-8 A drain current, so a 10V extra rail is enough, any higher is overkill.

Profusion PLC Exicon 10N20, one of the few remaining Audio MosFets

Now it's time to flip the diode around

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Now I'm adding positive DC to the input and about all I can get on the output is about 0.72V at 15.5V input

Ok now for a sin wave input

During a positive iteration the diode should conduct and Vout should be near ground maybe showing Vf

During a negative iteration the diode should be cut off and Vin reflected on Vout

Well here goes

Hey alright I got lucky

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You have to excuse me enjoying this because once I start adding a capacitor stuffs gonna get real 

Okay now it's time to try to input a sin wave and see what happens

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So.....

During the positive iteration of the sin wave (well we already know what's gonna happen from above)

During the negative iteration the diode will be forward biased and conduct so I'm guessing no voltage (maybe Vf?) will be seen

Ok I just did this and sure enough

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I'm really liking these circuits because they are simple 

Lots of excitement here tonight 

Wondering if I predicted this correctly

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I wanted to make the circuit with the diode pointing each direction ⬇️⬆️

And you know me I'm gonna start out with DC first

I better get this right 

I'm gonna add DC to Vin and since the diode is reverse biased the Vout will show voltage

Here goes

And...it does 

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Yes sir thanks I tried a 1.5M resistor and that took too long to bleed down

I replaced with a 10k and that worked pretty good I could see the voltage bleed down whenever it was turned on or I increased

After that I put the meter and probes away and stuck an LED between resistor and ground and I had a visual indicator

The power supply side reaches a steady state and holds constant

But if the DC is increased there is a period where the other side of the capacitor shows the increase and then bleeds off