Acoustic 150 Question

[gridcurrent]

The first proto 150 amplifier was a great HiFi amp and it was "BAD SOUNDING" not enough" MUSICAL SOUND" many other colorful descriptions from marketing.

would like to see that hi-fi design.
on the topic of interstage solid state amplifiers,
while usually associated with germanium output devices,
the topology was indeed later paired with silicon.
some notable examples, both germanium and silicon:
hi-fi:  Fisher including the Electra series which used tubes in input/voltage drive,
hi-fi:  Acoustic Research, elegant styling and  desirable, nearly 50 years later,
upper end hi-fi:  short lived Mattes (pun clearly intended).  photo and description in Tremaine 2nd edition.
musical instrument:  Leslie.
high power pa:  Hill DX1500.
the interstage transformer concept as applied to solid state amplification has (imho) sonic merit.

 

[PRR]

Are we forgetting THE transformer driven music amp?

Early versions of the Rhodes piano used a design right out of the old Delco serving suggestions.

 

[PRR]

Not a one I was thinking of but similar.

We recognize the small transistors as a (NPN) FuzzFace(!), except it has NFB and about 50X the current in stage 2. The transformer with dots proving CJ was right, the phase flips. Big Ge PNP were cheap and rugged even at the 60V 8r level. Bipolar supply. Output centering via resistances not NFB.

The Acoustic is similar in the output. Acoustic driver uses two polarities of transistors. The Rhodes drawing makes the Base-area relationships clearer. (But Acoustic was not selling tutorials.)

 

[CJ]

hacking up an old Fender in the lab which is rumored to be like the Rhodes power amp,
that is two solid state amps this week with a driver xfmr,  could be a conspiracy, 

thanks Grid current for that schemo!  that Triad xfmr is almost exactly like the one in the Acoustic save the split primary,

going to change the gap thickness to 1mil, eyballed at 2 but you could see thru it so it might be 1, don't know why they bother as the natural gap is 3 times as thick,

thanks Duke for correcting the error, will get on that,

Question: what would be the max voltage swing going into that transformer primary?

 

[PRR]

> what would be the max voltage swing going into that transformer primary?

Likely 90+% of the supply voltage, 25V or 40V, so it may matter.

For design/check, 40V is probably your number.

 

[CJ]

rev 2 print, change wire from 28 to 27, added ohms, feet, copper wt, changed flux levels to match 40 volts rms and corrected RCA transistor #m changed gap to .001 paper and changed steel to non orientated M19