Preamp Project

[bcarso]

That's probably a good surmise regarding the emitter inductances. If you use the 'scope on signal trigger and just barely trigger on the noise peaks you will probably see something with a characteristic time constant and ringing. Note what that time constant is and it may lead you to the problem area upon reflection.

Does the Cohen thing exist only in preprint? What is the date?

 

[Samuel Groner]

Does the Cohen thing exist only in preprint? What is the date?

I think so, it's Nr. 2106.

Samuel

 

[Samuel Groner]

DW, I just noticed that C34 is way too small; at highest gain, you get a lof-freq. cut off @ 70 Hz. :? You need at least a 4700 uF.

BTW, do CM chokes like DC current flowing through them?

Samuel

 

[kvintus]

Does the Cohen thing exist only in preprint?

No it exists in my "c:\papers\electronics\" too...

If you mean if it's an AES journal article as well, then no.

What is the date?

August 1984


/Anders

 

[Samuel Groner]

I suspect it can be a bad PCB layout.

One typical pitfall is stray capacity from the gain control element which is usually mounted a few inches away from the rest of your electronics; try replacing the pot (or the rotary switch) with a resistor close to the board, just to see what happens.

Samuel

 

[designmaster]

[quote author="Samuel Groner"]BTW, do CM chokes like DC current flowing through them?
[/quote]
DC current is not an issue, since current is very small. But the max. current must be known. I have a friend doing the chokes for me, he has an own company for transformers.

Thanks for the hint on C34, I will place some caps in parallel.