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Old 24th March 2007, 02:32 PM   #1
la1209 is offline la1209  Hong Kong
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Default Any comment on Vacuum State dpa300b??

Dear All,

Anyone used Vacuum State dpa300B power amp before?
Any comment on it?
I'm now consider to buy this power amp.

Thanks a lot!

Best Regards
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Old 20th April 2007, 04:21 AM   #2
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Default Re: Any comment on Vacuum State dpa300b??

Quote:
Originally posted by la1209
Anyone used Vacuum State dpa300B power amp before?
Any comment on it?
I am about to start building a pair of these amps. At the moment I am busy building Allen Wright's RTP3D preamps.

Are you considering building a kit, or are you going to be buying the DPA-300B amps ready built?
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Old 22nd April 2007, 12:13 PM   #3
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In theory the DPA300B should be one of the finest amps availble. I based my current amp design on the differential aspects of this amp. I also built a version of the FTP5 preamp and the sonic characture of this preamp is very pure. I would guess that the DPA300B is probably the nearest to wire with gain that its possible to get in the field of Valves.

Shoog
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Old 22nd April 2007, 12:53 PM   #4
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Quote:
Originally posted by Shoog
I would guess that the DPA300B is probably the nearest to wire with gain that its possible to get in the field of Valves.
It may be. One of the misgivings I have about the design is that it is actually too good. It promises to be an amp that can really deliver what has been very difficult in practice: an amp that can preserve all that important delicate detail, isn't fatiguing to listen to, but isn't thin in the bass like many SE amps are.

But what about all those juicy harmonics? To borrow Allen Wright's metaphor, maybe I do want chocolate sauce on everything. I mean, what is the point of building a valve amp where the valves are so tightly bootstrapped? It's sort of like not letting valves be themselves, in a manner of speaking.

But it's worth doing, because for me the alternative is trying to build Lynn Olson's Karna amp, which would mean sourcing every component myself, and having to set up a small workshop to make a chassis, and I really don't want to do that.
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Old 22nd April 2007, 06:03 PM   #5
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Funny you should mention the Karna amp. My current amp uses the differential aspects of the dpa300B, and the interstage phase splitting of the Karna.

I know what you mean about wanting a bit of distortion - but to be honest my experience is that valves are intrinsically the least distorted amplifiers of the lot and its only poor design that allows distortion in.

PP is definately the way to go. Its not so much that the bass is thin in SE designs, more that its woolley and indestinct. I think that a design like the Karna or dpa300B will produce the type of midrange detail of a SE, but without the high frequency roll off which makes it sound to smooth for my taste.
The woolley bass of SE can also be attributed to a lack of ultrasonic detail which has the effect of adding the snap into bass passages.

Shoog
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Old 22nd April 2007, 06:30 PM   #6
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Snap. That's the word I was looking for. It's reassuring to hear that the DPA-300B could deliver the midrange I'm after. I sure hope so, because kit or no kit, these things are by no means that easy to put together. Well, not the RTP3D preamp, anyway. Because of the latest design change, the component count has crept up, and things are getting rather crowded.

I've seen a discussion on a forum somewhere contrasting Allen's and Lynn's design philosophy; interstage transformer coupling contrasted with RC. In some ways I like Lynn's design more. There's an irony in taking a 1930s Western Electric design and combining it with technology unavailable at the time -- SS-based constant current sources. It's making some kind of statement about being true to proven designs but across a long timespan.
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Old 22nd April 2007, 06:39 PM   #7
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From my reading - anyone who has heard interstage transformer phase splitting would never ever go back to RC coupling. Unfortunately these transformers as very expensive and need serious drivers to get them to give of their true potential. Beyond the the scope of most single build DIYers.

Most bottleheads seem to avoid CCS because they think they want that distorted sound. I use CCS where ever I can put them. Even a triode based CCS brings benefits, and its the lowest performing one of the lot (you would already know that from your preamp build).

Shoog
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Old 22nd April 2007, 06:48 PM   #8
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Hi Shoog

Quote:
My current amp uses the differential aspects of the dpa300B, and the interstage phase splitting of the Karna.
I think you are referring to the amplifier with the ECL82 and 6AS7, that, if I remember well, was trafo coupled between ECL's pentode and 6AS7? Other thing I remember is that you were using individual LM317's per triode of the 6AS7. Do you still use individual, or are you using one single LM317 configured for 200mA CCS? (I imagine that one single LM317 would be more like the DPA300B.)

Erik
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Old 22nd April 2007, 06:53 PM   #9
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Quote:
Originally posted by Shoog
My current amp uses the differential aspects of the dpa300B, and the interstage phase splitting of the Karna.
Is it the final stage of your amp that resembles that of the DPA-300B? If so, why?
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Old 22nd April 2007, 10:21 PM   #10
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Quote:
Originally posted by Martin Hayes
contrasting Allen's and Lynn's design philosophy
I know Allen has great respect for Lynn... him and Lynn were sharing hotel space at the last VSAC, Allen was traveling on foot and wasn't able to bring his amp when he came to visit. My buddy Chris did hear it, it caused a lot of ripples for those that heard it.

When we are considering building PP amps this design always serves as one of our reference designs ... one of these days i hope to build one.

dave
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