Alternative Acoustics preamp

[CJ]

somebody brought in a garage sale item,  a phono pramp and switch box hand made by Dave  Herren, alias Stereo Dave,

http://www.stereodaves.com/dave.php

uses 4 Mullard 12AX7a's, DC heaters, and monster wire to hook it all up,

power supply>

 

[CJ]

coupling caps are all  nonpolarized jobs from Southern Electronics and IMP along with some .47 uf orange drops

amp section>

 

[CJ]

front plate, the knobs weigh about 10 lbs each but sit on 1/4" shafts,

i believe this was a prototype as there are no other face  plates like this for the other preamps,

 

[CJ]

monster cables for heaters tacked right on to the sockets, don't now what kind of first stage cap that is,

precision resistors all around, output voltages match up real good,

 

[Tubetec]

Wow ,serious psu on that,
transformer ,three chokes and some very big caps per channel,
Monster speaker cable to supply the juice too ,
Does it sound any good ?

 

[CJ]

have not had a listen yest, owner says it sounds nice, very good waveforms,

5 v and 6.3 V winds in series feed bridge and 7812 regs,  nice buss bar style gound, output gnd is brought to the rear and grounded to pwr supply buss,

 

[Tubetec]

I know those grey precission resistors ,there ex army stock ,

 

[Tubetec]

looks like theres enough juice in the psu to run power amps ,never mind the few mA that ecc83's use

 

[CJ]

he likes to parallel 3 different types of caps,

 

[CJ]

no schematics anywhere, had to hardwire our own, pwr supp>

 

[Tubetec]

He dont do things by half, Dave, bit of a charachter by the looks

 

[Tubetec]

Tiny caps on the Ht after the rectifier, its a handy way to dump excess voltage .

 

[CJ]

tons of NFB into the first stage as evidenced by the low output,

plenty of headroom,

amplifier section>

 

[Tubetec]

Ive used multiple chokes on some ht supplies too ,lovely and simple ,and they can do the job really well ,Im a fan of the 'Dave'
style

 

[Tubetec]

So totally passive line input section then ?
I see the last section of the second triode is unused

 

[CJ]

here is an SIMetrix sim of the feedback network for the phono preamp,

RIAA playback is supposed to increase bass, wtf?  doh, that's inverse feedback, so it will increase bass as the output curve s/b the inverse, right/

 

[CJ]

RIAA curve

 

[PRR]

> SIMetrix sim

R3 may be 1K, not 1Meg.

 

[CJ]

your right, feeding cathode, not grid, 

 

[CJ]

new graph