Trans Amp LZ Schematic

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

china_dude

New member
Joined
Aug 26, 2011
Messages
3
Location
NY, USA
This is the real Trans amp LZ schematic (all seeing eye - pyramid block), licensed from Paul Buff of Alison Research & Valley People, as manufactured by a USA console manufacturer (now defunct), during the best days of creating great sounding stuff.
 

Attachments

  • Trans Amp Block Schematic.pdf
    128.9 KB · Views: 212
Thanks China-Dude!

Just may have to build one to see if it really does sound as good as I remember

Cheers

tc
 
That looks close enough...

I would suggest replacing the Q1, Q2, and Q3,Q4, with a pair of modern low noise devices. Paul used two devices in parallel to get the input noise voltage down, but modern parts can beat those old soldiers using only one per.

My go-to part was a 2sb737s but these are obsolete now, so a good part that is still made (I think) is 2sa1083e (-e is the higher beta option, but -d should still be OK). 

The note say's match for Vbe. The circuit will work without selecting these, but the gain pot will be scratchy at high gain end if DC offset is large.

JR
 
Hi All,

2sb737s are more recent. Also 2sa970.
I have had very good performance from Zetex ZTX550, 750. The Zetex parts are a small package, large geometry, 1A collector, made for switching, but the 1/f & other noise is very low. The transistor matching is for DC shift while turning the gain pot, as pointed out, but also to maintain equal currents & voltages in the different legs of the circuit.
The more equal everything is, the less problems you will have.

The Trans Amp LZ implementation has a DC shift trim, but it is dependent on speed of gain pot rotation & temperature drift. Turn faster, more thump.

I have used these gain blocks as dual (stereo) phono preamps with passive EQ networks. The Trans Amps are flat gain make-up only. They sound unbelieveable.

Best to All
 
china_dude said:
Hi All,

2sb737s are more recent. Also 2sa970.
I have had very good performance from Zetex ZTX550, 750. The Zetex parts are a small package, large geometry, 1A collector, made for switching, but the 1/f & other noise is very low. The transistor matching is for DC shift while turning the gain pot, as pointed out, but also to maintain equal currents & voltages in the different legs of the circuit.
The more equal everything is, the less problems you will have.

The Trans Amp LZ implementation has a DC shift trim, but it is dependent on speed of gain pot rotation & temperature drift. Turn faster, more thump.

I have used these gain blocks as dual (stereo) phono preamps with passive EQ networks. The Trans Amps are flat gain make-up only. They sound unbelieveable.

Best to All

Coincidentally, I too used this topology in a phono preamp I published as a kit back in 1980.  I used the 2sb737 in a moving coil version (in fact what those devices were designed for). My moving magnet preamp used JFETs for input devices since the higher source impedance of a MM cartridge is not optimal with those low noise bipolars.

The original transamp was based on some medium power transistors to get low Rbb for low noise, but back in the day processes weren't as clean as today so they had to be screened for 1/F noise, etc. The later devices designed for low noise at low impedance (and high beta) work well in that topology.

JR

 
Back
Top