OK-- last go 'round, I hope.
I'm trying to leverage aesthetics with a desire for a short signal / wiring path, so I did as suggested with the cap-n-rectifier swap, but I couldn't quite realize the center-of-the-amp presentation for the OPT and 300b.
Anyway, I think this marries a reasonably good look with an allowance for a short wiring path. As long as everthing looks hunky dory with the transformer orientation, I think this will work.
Have a look:
I'm trying to leverage aesthetics with a desire for a short signal / wiring path, so I did as suggested with the cap-n-rectifier swap, but I couldn't quite realize the center-of-the-amp presentation for the OPT and 300b.
Anyway, I think this marries a reasonably good look with an allowance for a short wiring path. As long as everthing looks hunky dory with the transformer orientation, I think this will work.
Have a look:
Attachments
garbage said:
Will do! Thanks!
Kofi
The Lundahl piece is no doubt a fine unit, but if you really have a tight budget, it may not be an essential item. That choke serves two purposes; filtering 120Hz ripple and some reduction of common mode noise (which comes for free, because it has two identical coils). I would think the almost all of the common mode noise will be higher frequency stuff, which could go right through that choke anyway. Experts should weigh in here, but I suppose you could add a low value (cheap) CMC right before the input cap. But this isn't a common sight, probably for a reason - you don't really need it?
Sheldon
Sheldon
I agree with Sheldon. If money is no object…
I have 2 DRD amps based on Jack Elliano’s design and I am working on a parafeed version. The best one use’s a choke input filter of conventional design. The other use’s a cap input to get the voltage I need and sounds damn good as well, they are different enough so I cant say it’s the filter.
What you might try is two conventional 8-10 H chokes, one on the B+ the other on the return. But not common mode. I think one ~10 H choke on the B+ line will sound great.
as to the layout. the 274 rectifier in operation is something to behold, it’s prettier then my mesh plate 300b’s. If you can find a way to move it to the front, you will not regret it …John
I have 2 DRD amps based on Jack Elliano’s design and I am working on a parafeed version. The best one use’s a choke input filter of conventional design. The other use’s a cap input to get the voltage I need and sounds damn good as well, they are different enough so I cant say it’s the filter.
What you might try is two conventional 8-10 H chokes, one on the B+ the other on the return. But not common mode. I think one ~10 H choke on the B+ line will sound great.
as to the layout. the 274 rectifier in operation is something to behold, it’s prettier then my mesh plate 300b’s. If you can find a way to move it to the front, you will not regret it …John
The choke has two coils and it could be wire for common mode service, but I don't believe the designer intended that. I think it is wired as a conventional choke (do we call that differential mode?) with half of the windings in the negative (ground) lead.
In theory, if the two windings have perfect coupling between them then the choke is invisible to common mode signals (except for the DCR of the windings which happens to be very small in the Lundahls anyway.) In reality, the windings are not perfectly coupled. At low frequencies they are pretty well coupled so the choke functions mainly in the conventional way. As you go up in frequency the coupling becomes weaker so you do get some common mode rejection at higher frequencies. Of course this comes at the expense of conventional (differential mode) inductance at higher frequencies. Nothing is free.
In the end, I agree that these particular units are not a necessary part of the design. I don't want to minimize the importance of a good ps to the sound of an amp, but there are many good approaches to ps design. I think the Lundahl could be replaced with an ordinary single winding choke (of good quality) with less inductance and still get good results. Maybe better results, maybe not, I don't know.
Whatever you do, make sure the 4uF first cap is an oiler (but don't make it bigger than 4uF.) It is subject to very high ripple currents. Motor run caps are cheap even if they are bigger physically. I'd use motor runs everywhere in the supply, but there are other opinions...
-- Dave
2wo said:
Yeah, the TJ 274s have been removed from consideration due to price. I am using the Valve Art 274B (it's the one on the right in the picture). At $18 a pop, its priced to beat the band.
I'll probably leave the layout as is, although I wish I could compact it more. I just got a 12" x 24" piece of aluminum sheet to play with and realized how huge this motherfather is! To put it in perspective, it's going to be twelve inches (one foot / 30.48 centimeters) by twenty-four inches (two feet / 60.96 centimeters).
If you made a scaled-down drawing of the distance from the Earth to the Sun such that this distance was one foot in the model, then the length of my amplifier would equal twice the distance from the Earth to the Sun! For ONE CHANNEL!!!
Holy cow!
Actually, I've gone 'round and 'round about this before. I can honestly say that if the designer were here with us today, he'd say that the two section Lundahl choke acts as a 20H differential choke (which has much better ripple rejection than an 8H one) which helps significantly in keeping mains crud out of the (audio) circuit and that it is entirely intended.
Not looking to push back here, and you can be sure I don't really understand all of the above statement (see any prior postings from Kofi for evidence of dumb-assedness). Just wanted to state that, at least from a design perspective, this is what was intended.
Kofi
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