Need some help with this custom amp

[Floti]

Hi guys!

This is my first post here, but I've been reading for some time and I've learned a lot from this forums.

I'm not completely new to the amp building thing, I've done some kits and read a lot, but I'm also no expert, as you will see.

The thing is that I'm planning to build a new amp with the Sound City 50 Plus preamp (I love that tone controls) and was thinking about changing it's power stage with the one used by the Ceriatone Creme Brulee.

My question is: Where exactly do preamp and power amp meet each other? Do I have to use the phase inverter of the Ceriatone build or the original from the SC50+? Do I have to make other changes to the circuit than just changing the power amp for another?

I'd apreciatte your answers!! Right now I'm finishing the SC50+ Layout drawing and I'd like to start with my next step soon!

Thanks in advance!

[txstrat]

You could change one power stage for the other. The preamp ends and the power amp starts right at the cap before the PI. In the Sound City schem that would be C23. I'd start with the value of the cap at .01 and see if it sounds ok. If not you could decrease that value to .005 or .001 or in between.
Keep an eye on the voltages. EL34 can stand almost three times the voltage that an EL84 can and I believe you don't want to blow up the latter with too high voltages.

[Floti]

Thank you so much for your answer!

Now that I know this I can finish my layout, which is a big first step!

If I'm using exactly the same setup for the power amp that the ceriatone amp uses, will the voltages be a problem? Or will it just work fine without making any adjustments to the circuit?

[txstrat]

Well, changing the voltage surely changes the tone to some degree but having a look at the Sound City schem, the first filter cap (totem pole) is made of two 200v caps i.e. a total rating of 400vdc. I assume the B+ is somewhat less. I further assume - the voltages of the Ceriatone are at +/- 390V - 290x1.41 minus the voltage drop of the GZ34 - you wouldn't have a problem with them in your build. You might have to change the dropping resistors (two 22k) to get the voltages more to the Sound City values but even that is not too big of a problem (+/- 10% is OK IMHO).

[Floti]

Hi!

I finished my amp and I'm having some problems with it.

The thing is that it sounds, but really LOW and a bit too farty (if that's a word). When I play lower notes it really makes that fart sound, but when I play higher notes it sounds almost normal, though really really low.

The voltages are more or less OK. I get 400 V at the B+ and the preamp tubes are a little hotter that they should, but the change in sound is dramatic compared to that changes.

Do you guys know what's possible failing?

I could post some pics if you want.

Thanks in advance!!

[loudthud]

From your description I'd first be looking for wiring errors. But tell us exactly what pieces from each amp you used. Did you use the Master and Cut controls from the Creme Brulee? What is the bias point of the output tubes? What are the voltages around the phase inverter?