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Post by Clive on Jun 23, 2020 11:38:38 GMT
There's a trend in very cost effective DACs with preamp - these often have balanced outputs. I was thinking about valve power amps to match such DAC/preamps.
With P-P valve amps I've always liked the sound with interstage transformers but is this because such designs remove the phase splitter valve? This train of thought leads me to wonder about a fully balanced P-P amp with no phase splitter/interstage Tx. Is this how it works and are there any good circuits out there?
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Post by MartinT on Jun 23, 2020 12:18:34 GMT
Because of transformers, most P-P valve designs are single-rail and use single-ended inputs.
An OTL design might get away with direct coupling using split power rails but it would be a dangerous beast (aren't they all?) and even then may not have balanced inputs.
Not really my area so others will need to chip in.
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Post by John on Jun 23, 2020 15:25:02 GMT
I used to have the SAC Glowmaster 88 which was able to be run fully balanced. But I got rid of it because it would go through a set of Tubes every 9 months.
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Post by Clive on Jun 23, 2020 15:48:12 GMT
It looks like the Glowmaster is fully balanced end-to-end. Burning out the 88s I suppose is down to their being driven too hard.
I wonder if there’s a halfway house. Balanced front end to remove the phase splitter but a single rail output stage. Ok there won’t be any CM rejection but removing the phase splitter could be useful. Probably this is just idle curiosity....or it could be something to play with when I retire (again). OTL does indeed look to be an option.
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Post by Eduardo Wobblechops on Jun 24, 2020 11:50:49 GMT
Not bought Pinnacles yet Clive? :-)
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Post by Clive on Jun 24, 2020 12:53:56 GMT
Not bought Pinnacles yet Clive? :-) It's the mortgage required for 8 x 300B.....and I have 4 amps currently unused... Must stop Must stop Must stop Must stop Must stop |
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Post by Eduardo Wobblechops on Jul 8, 2020 5:59:40 GMT
Yes, that’s is a downside. In a related matter, have bought a Masterpiece which I will pick up at the weekend.
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Post by Firebottle on Jul 8, 2020 6:29:58 GMT
It's an excellent observation Clive and an approach that should work really well. I haven't come across any published circuits.
A split supply isn't required or necessary as there isn't a 'P' type valve.
A traditional amp with phase splitter could be reworked to provide + and - inputs fairly easily, perhaps one of your 4 unused amps?
What are they, I could have a look at the circuits and advise.
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Post by Clive on Jul 8, 2020 9:14:08 GMT
It's an excellent observation Clive and an approach that should work really well. I haven't come across any published circuits. A split supply isn't required or necessary as there isn't a 'P' type valve. A traditional amp with phase splitter could be reworked to provide + and - inputs fairly easily, perhaps one of your 4 unused amps? What are they, I could have a look at the circuits and advise. Hi Alan, Thanks for your offer. I don't have a valve P-P amp currently so I'd need to build one. I have just two valve amps - a 300B SE and your EL84 PSE :-) When I say unused, they are wheeled out when I fancy a change. Actually the EL84 is darned good into my 100db open baffles. This project is a slow-burn, probably a winter project. I'm thinking a P-P using 45, 2A3, EL84 or EL34. EL34 is tempting as it has "character", 2A3 would be the cleaner more accurate alternative, EL84 would be the most economic. The streamer/DAC/pre I use in the Lindemann Source, the balanced output is up to 5V. I expect getting the gain right will be an aspect to consider when deleting the phase splitter. I'll keep an eye open for a 2nd and World Design KEL84...if that is suitable. |
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Post by Firebottle on Jul 9, 2020 6:26:52 GMT
The KEL84 could be done, changing the input/splitter valve for a twin triode.
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