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trancy 26th February 2004 09:50 AM

tube preamp...opinions
 
2 Attachment(s)
what do you think about this preamp??...Iam pretty new arround tubes, but i want tube pream on my zen amp...any suggestions??

hvala (thanks)

fscarpa58 26th February 2004 10:40 AM

hi

where have you planned to put the volume pot?

what is the input res of your Zen amp?

Do you need so much gain?

If you don't need gain the simplest solution
is a buffer , eg. cathode follower.
(lower distortion for the same output, lower output res)


Federico

trancy 26th February 2004 11:11 AM

Quote:

Originally posted by fscarpa58
hi

where have you planned to put the volume pot?

what is the input res of your Zen amp?

Do you need so much gain?

If you don't need gain the simplest solution
is a buffer , eg. cathode follower.
(lower distortion for the same output, lower output res)


Federico


1)i dont need a volume pot...its separate (ir controled)...
2)input res on zen is 4,75k, gain is about 8,5dB, it must be driven with 3,5V and 700uA....
3) how much is so much??
4)how cathode follower looks like?

hvala (thanks)

trancy 27th February 2004 09:53 AM

anyone?

Ropie 27th February 2004 09:58 AM

2 Attachment(s)
This is a cathode follower for a gainclone chip amp, if it's any help...

:)

trancy 27th February 2004 10:09 AM

i know that one, but im interested to make preamp with a little bit more gain....

fscarpa58 27th February 2004 10:41 AM

2 Attachment(s)
Quote:

1)i dont need a volume pot...its separate (ir controled)...
2)input res on zen is 4,75k, gain is about 8,5dB, it must be driven with 3,5V and 700uA....
3) how much is so much??
4)how cathode follower looks like?
Hi

1) no matter. Is the volume planned before or after the above
pre stage?. I asked this because this pre will be saturated
if the input signal is greater of about 1Vrms. So I hope the
volume is before.
2) o.k. 4.7k is rather small. you will need low output impedance
and good current capabily.

3) As is ( loaded by 4.7k) the circuit has a gain of 24.5 db,
that is 16.8x but it is at -3db at 40 Hz. The out cap has to be
at least 4u and the bypass cap 300u. This happens
because the output res is too high, greater of 2k, in respect
to the load.
4) a CF is a very simple buffer. It has no gain but is is not
relevant if you utilize, for example, a CD player as source
since you have usually 2Vrms at your disposal.
it looks like the following.

Federico

fscarpa58 27th February 2004 11:05 AM

2 Attachment(s)
I see

If you want gain then you can have
it by placing a common cathode in
fron of the CF.

gain 24.9 db
Rout <200 Ohm if freq >500 Hz

If 165 Volts is not a constraint then things
can be done better.

Federico

trancy 27th February 2004 01:11 PM

thanks a lot federico.....

165 volts is not constrain...please, show me better....

fscarpa58 27th February 2004 01:50 PM

2 Attachment(s)
Rout <150 Ohm if freq >500 Hz

THD <0.1% for Vout = 10 Vrms

ciao

Federico


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