I am tracing through the pre amp and finding that the signal stops at IC5 SSM2012a. I could  be wrong about this but it looks like this chip is bad. Since these are long unavailable what are people doing for a substitute?

The schematic is :
https://www.prowessamplifiers.com/schematics/images/Coliseum_300_11_x_17.pdf

Quote from: saturated on August 27, 2026, 07:13:35 PMSo I looked at the data sheet and found this but I think this is something different

Furthermore, the device incorporates an original
(and patented) short-circuit protection system
comprising an arrangement for automatically
limiting the dissipated power so as to keep the
operating point of the output transistors within
their safe operating range.

That is something different and internal to the TDA2030.  The 2 diodes are external and are mentioned in table 5 (page 10 of datasheet pdf).

I noticed in one of your photos, on your circuit board there are 2 diodes D9 and D10.  They have the zener symbol marked on the board underneath them.  As there is no such thing shown on the 10XL schematic, I guess it does not match your unit.  Yours probably has zeners for the +/-15V supplies.

Quote from: saturated on August 26, 2026, 10:08:29 PMI was reading about this today and became very interested in it.  Some old posts one of the big dogs here was fussing about fender saying they don't know how to make distortion all they do is diode clipping.  So I immediately took notice and said hey I definitely want to check this out  Also it's right there with the other stuff I have been doing 

So I was at work and I wanted to know how to make a sin wave with the points chopped off like a sin wave with flat peaks

I always have old books at work to look at and of course I easily could have looked it up online....but I said why don't you try to come up with something based on what you have been doing and learning 

And honestly I didn't have much

About the best I could do was maybe use zener diodes in parallel maybe but I figured there was a way using ordinary diodes

I also figured it would help to get some capacitors involved but honestly my head is still spinning from trying to grasp all that they do 

So I thought about the diode limiter experiment I did and thought well you just need some voltage remaining so you'll have some peaks and then maybe have the diodes in parallel so I get the positive and negative and yes I was pretty much guessing like well I'll build it and see what happens

So I got off work and had to go mow and pick up two bags of pine needles  got back and even before showering thought dude just try it so guess what

Input

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And output

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And yeah it's pretty ugly I wanted some nice peaks with the tips cut flat.

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I think the resistors are 10k maybe I can try different values but I think it actually works   

But idk here are the two channels together

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Regular diodes still clip somewhat rounded, try Zeners, tose are more flat topped, more angular and harsher.

Somebody might on a boring rainy Sunday afternoon.
I would but am in the middle of moving 
But expect only MINOR differences, exact same circuit, only maybe effects loop added or an extra CD/AUX input to play along, stuff like that.
It sounds very good as-is, by using a GOOD speaker,

Please post pictures of your mystery Argentine speaker. I might know it.

Yes Those are to protect chipamp from speaker flyback voltage when amp is clipping.

SCG means Sequential Cascaded Gain and is a fancy name for plain old distortion.
Marketing guy has to earn his salary 

When G1 said that I was like oh hell yeah of course it does 

Then later on I was "hmm I wonder what that means in English?"   

So I looked at the data sheet and found this but I think this is something different

Furthermore, the device incorporates an original
(and patented) short-circuit protection system
comprising an arrangement for automatically
limiting the dissipated power so as to keep the
operating point of the output transistors within
their safe operating range.

So I said well just make a diagram and try to figure it out so here goes 



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Hope I didn't get it backwards my mind gets turned around trying to figure out those diodes

If someone could compare those two schemstics, I'd be really thankful, since all I know about this stuff is that electricity comes from kites.

Thanks for the clarification G1.

The diodes D6 and D7 are for 'protection against output voltage spikes' and are included in the datasheet circuit (attached).
If the output swings more than approx. 0.7V above or below the supply rails, they conduct and clamp the output to the rail voltage.
D8 and D9 on 10XL schematic appear to be clipping diodes that are switchable for whatever "SCG" stands for.

If you want more amplitude before clipping, add more diodes in series. 
Also, try just clipping the top alone (or bottom), which is what you might find in some tube amp stages.  We don't always get a nice symmetrical waveform, nor do we always want it.