Tubes4HiFi SP-6 preamp

[BWentler]

I'm looking at building this pre-amp to drive a pair of Audio Sector LM3875 Amplifier Kit (non-inverting) amps. I have no idea if this is a good design or not. Could any of the tube engineers on this forum please take a look at this and give some feed back.

http://www.tubes4hifi.com/pre3.htm

VTA SP6 preamp specs:

PHONO STAGE
Gain +43dB
Input Impedance 47k ohm
Output Impedance <1k ohm
RIAA Response +/-1dB from 25Hz to 25kHz
Bandwidth (-3dB) 15Hz to 30kHz
Distortion 0.02% @1kHz
SNR 75dB ref 5mV A-weighted
Overload 250mV @1kHz

LINE STAGE
Gain +15dB
Input Impedance 100k
Output Impedance 3k ohm
Bandwidth (-3dB) 10Hz to 100kHz
Distortion 0.08% @1kHz @1Vrms
SNR 83dB A-weighted
Phase Inverted

 

[Geek]

....Output Impedance 3k ohm

A little high, but should still be able to drive it.

 

[fdegrove]

Hi,

THis is a classic example of an old, not even particularly good by current standards, preamp being mated with something designed to be current driven.

While it's technically not impossible to drive the amp as it is you'll never hear neither preamp nor amp in full glory that way.
In order to do that the SP6 should have an outputstage with a Zout in the order of a tenth of what it is now and capable of delivering some current into a lowish Zin.

Not impossible to do with tubes but it will require a return to the drawingboard.

Cheers, 😉

 

[Geek]

If you look elsewhere in this forum (in the SEWA thread, IIRC), I posted a modified White CF that has an output impedance of 100 ohms. Place that between this preamp you speak of and the chipamp and you'll drive it OK 😉