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Old 14th July 2013, 07:50 AM   #11
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The Grounded Grid preamp kit from Transcendent Sound is well worth a look. I use one with both SS and valve amps and I'm more than happy with it. For guys like me who aren't much good at design but are ok with a kit then this fits the bill nicely.
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Old 14th July 2013, 01:27 PM   #12
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Quote:
The Grounded Grid preamp kit from Transcendent Sound is well worth a look.
Simon, Rozenblit's chassis is decent and the circuitry is OK. However, the OP wants a full function preamp and finding a complete kit for that is not easy.

James, please give us a feel for your skill level. Design is not an issue, as the members can point you at all sorts of reasonable options. Can you do a bit more than "follow the dots"?
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Old 14th July 2013, 03:10 PM   #13
Loren42 is offline Loren42  United States
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Originally Posted by ChrisA View Post
Most of the "sound" is where the gain is. In other words a tube running at a gain of 1.0 adds almost nothing. You can't hear it that there is even a tub in the chain. If the tube is providing gain, that it will add something you can hear.

So the only use of tubes, other then for decoration and bragging rights is when it will actually do amplification. That would be either (1) in the power amp or (2) in the phono preamp. But NOT in a line level low or no gain section.

I think you will find that tube equipment is so darn simply you don't need a kit. point to point ott turret board contruction is better than using printed circuits too. You can cut aluminum chasses with hand tools if needs be. It is pretty easy.
I agree.

I really would not go the preamp route unless it is simply something that you want to do to fulfill a bucket list. The sound quality will only be as good as a good solid state preamp, but no better and likely less.

The tube power amp acts as a current drive amp, which behaves differently than a solid state amp (voltage drive amp).

That means the changing impedance of the speaker over the audio spectrum affects the true SPL differently depending on the type of amp.

I contend the "tube sound" of an undistorted amplifier has more to do with this behavior than anything else.

When a solid state amp drives a higher impedance load the power produced goes down. Most speakers have higher impedances at the low end resonance point of the woofer and increasing impedance as frequency goes up with a tweeter. So, solid state amps tend to loose audio SPL and sound a little duller and lacking bass because of that when compared to a valve amp.

The valve amp, with its lower negative feedback, operates closer to a current driven amp and provides more power as speaker impedance rises, providing a somewhat brighter and bassier response compared to a solid state amp that has lots of feedback.

The downside is lower damping with the valve amp. However, when you factor in a passive crossover, that loss is not that significant.

Last edited by Loren42; 14th July 2013 at 03:13 PM.
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Old 14th July 2013, 04:16 PM   #14
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Speakers and amps form integrated wholes. The OP has B&W N804 speakers, which exhibit 1 or more nasty dips in the impedance curve. With few exceptions, those speakers should be mated to SS power amplification. A Harman/Kardon Cit. 2 refurbished ala Jim McShane is an exception and would work well, with the N804s connected to the 4 Ω taps.

As I read it, reality is a tweaked Hafler DH500 driving the N804s. A full function (phono and line) tubed preamp that gets the most out of what's downstream is what the situation requires. Lots of good options are available and I hope other members will make suggestions. Of course, I'll grind my own axe and suggest designs I'm associated with, but they are far from "the only game in town".

I've uploaded schematics for a tweaked RCA phono section and a 12B4 line stage. That pair would do the job quite nicely. A PSU that provides for the needs of both sections would have to be worked out, but that's NBD.
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Old 14th July 2013, 07:07 PM   #15
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The graphics got "lost". I'll try again.
Attached Images
File Type: jpg Full Tweaked RCA Phono Stage.jpg (45.4 KB, 115 views)
File Type: jpg 12B4 Line Stage.jpg (24.4 KB, 114 views)
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Old 15th July 2013, 12:52 AM   #16
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Quote:
Originally Posted by Loren42 View Post
I contend ...
Please take your contention to a thread that cares.

OP asked for something specific and you've waded in with flame bait.

That's not going to help the OP at all.
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Old 15th July 2013, 01:09 AM   #17
Loren42 is offline Loren42  United States
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Originally Posted by thoglette View Post
Please take your contention to a thread that cares.

OP asked for something specific and you've waded in with flame bait.

That's not going to help the OP at all.
Thanks, but I think you are badly mistaken.

Actually, my opinion is that he is not going to get what he wants by pursuing the route he outlined.

Your opinion may differ, and that is well, fine and probably appreciated; but you will not find me telling you where to go because I see things differently.

So, in the interest of diversity, it may serve Jhm007 better to hear a wider spectrum of opinions than simply what you feel is appropriate. Would you agree with that?
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Old 15th July 2013, 01:59 AM   #18
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Originally Posted by Eli Duttman View Post
However, the OP wants a full function preamp and finding a complete kit for that is not easy.
Making it a bit easier is that the Hafler has a 47Kohm input impedance according to the manual

I've seen input SS amp impedances well below 10K which makes driving them properly without an output transformer rather difficult. So the KK kits would be overkill. They're not cheap either.

But neither are the Audio Note kits.
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Old 15th July 2013, 02:17 AM   #19
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Quote:
Making it a bit easier is that the Hafler has a 47Kohm input impedance according to the manual
47 KOhms is an absolute "piece of cake" for the 12B4 line stage. It was designed to cope with the nasty IHF "standard" 10 KOhm load. A really good CCS is needed when dealing with 10 KOhm I/P equipment. For the DH500, a 10M45S rates to be satisfactory.
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Old 15th July 2013, 02:26 AM   #20
Magz is offline Magz  United States
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If you truly want Full Function, then you could start with the Bent Audio TAP OEM parts. You get autoformer VCs which can double as outputs if you parafeed, remote control with balance, mute, tape loop and input select (6 inputs), and LCD displays. You then build your preamp around it, as I did with my 26 pre.

It sounds astounding. If you're in NJ let me know and you can stop by and hear it.

PS: It's mated to a 1st rate SS power amp now...at least until the 833C monos are done.


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File Type: jpg 26 Preamp and PS.jpg (410.0 KB, 99 views)

Last edited by Magz; 15th July 2013 at 02:31 AM.
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