DCAudioDIY.com

Is this thing still on?

So, not waning to be boring, I recently built a direct coupled PP amp This one actually doesn't look too bad, as it's built on an old Jolida integrated amp chassis. This amp will probably be back to being an integrated at some point, and will likely be going to a friend in Front Royal... The power supply is pretty much the untouched Jolida supply, but the output transformers are vintage HK from a receiver that used 7355s for outputs.

Schematic, some of you may notice a similarity to an Acrosound amp of years gone by:

Parts list:


Note that since the B+ is a bit higher than I'd hoped it would come out, I'm curerntly running 6550s rather than the 5881s specified in the parts list. With a suitable power supply providing a B+ of more like 425V, the 5881s would be a good alternative. El34s would probably be fine at this B+, but I don't have any to try...
pic (not my pic) can be seen here:
http://4.bp.blogspot.com/-PDyyhNoLrEo/V ... 00/006.JPG

Sound is quite interesting so far, very immediate, and dead quiet. Now that it's had a chance to break in a bit, I'm gonna have to get serious about comparing it to the other amps I have available. I may build a pair of mono-blocks on this design, I have a pair of UTC LS-61s just dying for some work

I've also designed, but not built yet, a direct coupled screen driven SE amp that I'll post details on sometime tomorrow...

So, is anyone else actually building anything?!?!?

Roscoe

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I can explain it to you, but I can’t understand it for you.

currently restoring a passel of integrateds I need to get done, afterwards I hope to do some amps...

Building anything? A new race car. It will probably sound pretty good but not good in the way we think of around here.

Is this the first time you've tried the "Pearl" Triode" circuit?
Have you heard it used on other amps before?

http://www.t-linespeakers.org/tubes/triode-trick.html

Well, Roscoe, I'm building something but not what you mean.

I'm so far behind on my phono amp that I'm planning to build an op-amp phono amp so I can listen to music in the mean time. Suggestions accepted: I'm thinking of splitting the RIAA inversion between two gain stages and using a pair of 9V batteries as power supplies.

I have ideas for a couple power amps and a power sequencer to apply and remove power from circuits, but Life keeps interfering! I'm glad that doesnt happen to anyone else!

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- Guy

You might look at this one: http://phonoclone.com/diy-pho5.html

Also, if you're going to do battery power, bite the bullet and get two 8xAA battery holders, that'll give you +/- 12V, and about 50x the battery life... If you use 9V batteries, the first time you forget and leave it on over night (but, you'd never do that, right?), you'll need to replace the batteries.

Roscoe

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I can explain it to you, but I can’t understand it for you.

Well..... I'm in the middle of taking an old time tube radio repair class which has been fun and has given me the courage to work on an old Fisher 500B that I inherited from a family friend. I've fixed a couple of old radios along the way which has been fun. To bad there isn't more interesting stuff on the AM band.

I'm also fiddling with a PP 845 amp. With 700 - 750 volts on the plates looks like I can get 30 -40 watts without trying to hard. Driver stage isn't as hard as it would be with a higher power amp and 700 volts doesn't scare me quite as much as 1200. Got a lot of experimenting to do though. I was hoping that with a PP amp you could use AC on the filaments and it would cancel out if you wire it in phase but it doesn't work as well as I hoped, sigh...... I'll have to talk with Dave B. about that RF filament supply.

Charlie

I have a home built phono preamp that has inputs for both MC and MM. The MC stage uses OP37 OP AMPs and the MM stage uses OP27 OP AMPs. It also has an output level control. You are welcome to use it until yours is done.

Tom

Nice looking project! I like the gold valve train, you need transparent plastic valve covers to show that off.

I have a MM/MC Roksan phono pre with outboard PS that you are welcome to use until you get something built up.

Plus, the 9V batteries are much more expensive than other choices....