aleph/bls integrated?

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
I recently dismantled one of those great big Class -H monster receivers from the late 70's... Hitachi something or other (sounded horrible!). Anyway, I have a really big chassis with lots of great switches and knobs, and a monster toroidal power transformer. The panel by the line cord says 850 watts, 1150VA. I have dual 55 volt secondaries on the transfomer. So, my thoughts are this...
Since my budget isn't the highest right now, I would use the transformer to get a +/- 33 volt supply for each channel, and use this to power a balanced line stage preamp (running lower voltage) and an aleph 60 type power amp.
What do you think? Should I do away with the preamp stage in this chassis and build it seperately with the higher voltage for better performance, or should I just go for it with what I have?
 

paulb

Member
2001-06-01 4:53 pm
Calgary
So each of the 55 volt secondaries is centre-tapped, to give you the +/- 33 VDC? Wow.
Is there room in the box for a smaller transformer to power the line stage? That's what I would do if it's possible.
Another idea I had for revamping a friend's old amp would be to place the actual power amp in a new, separate box, and use the old amp for the preamp and its DC power supply. I would run the DC power through the speaker terminals (don't let your friends hook up your stereo!). I wasn't thinking of replacing the preamp in his case, but you could do that too.
Sounds like fun! I have an old Radio Shack receiver that has a good-sized (and heavy) transformer; I've been meaning to open up the case sometime to see what I could do with it. Big heatsinks in there too.
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
Thanks for the ideas. Actually, it is just two non center-tapped 55 volt secondaries. I was going to use two bridge packs and four banks of caps, and ground between the two sets of caps for a +/- supply. I didn't think that you had to have a center tapped transformer. Am I wrong? I've seen this done a lot in tube amps where you need higher voltage rated caps than are normally available.
I was thinking about adding another toroid for the preamp. The chassis is HUGE! It weighed at least 60 pounds when it was all together. I may just end up using the chassis for the preamp only, and steal the power tranny for a power amp. The only thing is the size. It really is big.
 

paulb

Member
2001-06-01 4:53 pm
Calgary
SteveG said:
I was going to use two bridge packs and four banks of caps, and ground between the two sets of caps for a +/- supply. I didn't think that you had to have a center tapped transformer.
It would work if you didn't try to sink or source any (well, much) current through the ground pin. You actually need a voltage splitter arrangement to do this, the caps won't perform very well even if you have resistors across them.
A voltage splitter is a definite possibility, though, I've done this. It depends on your amp circuit. But it may be easier to just use an amp that uses a single-ended power supply.
Yes, keep those transformers, you'll use them someday.
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
OK, I understand now. Since the tubes are such high impedance devices they don't run at high currents, and you can get away with it with balancing resistors. I'm glad that I found this out before spending the money for the caps! Maybe this will turn into a 6 channel balanced line stage for my SACD player. If I used a seperate active regulator for each channel, would it give me good isolation between channels, even though they would be sharing the same transformer? Thanks for all the info.
 

paulb

Member
2001-06-01 4:53 pm
Calgary
I had another idea, or actually an extension to the previous one. You could actually convert an amp's output stage to a voltage regulator.
I was looking at that Radio Shack receiver (it comes with a schematic!) and everything looks very modular. So if I keep the tuner boards, replace the preamp board, and convert the output stage to a voltage regulator I might have a great way to drive an external power amp, something like the Aleph or the hybrid X/Aleph that was being discussed here this week ("clamor, clamor"). You don't see voltage regulators used for high power audio very often, but if you have the transistors and heatsinks just sitting there, well...
And having a vintage Realistic receiver with the guts replaced appeals to my sense of whimsy.