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Old 3rd October 2002, 09:21 PM   #11
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Default PSU

Aaron,

You won't find me arguing with Ultranalog that easily.
So,that's a choke input from me too.

Dunno about Gordon Rankin, but Sakuma and Kondo seem to have a taste for the overly soft,suave kind of presentation of sound.
Matter of cuisine,I'ld say.
You're "ze chef".

Cheers,
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Old 4th October 2002, 12:27 AM   #12
arnach is offline arnach  United States
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First, the new schematic. How's it looking now?
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Old 4th October 2002, 12:30 AM   #13
arnach is offline arnach  United States
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Default psu

Choke input it is! Now, the power supply for the B+ and the A+, B+ is taken at 60mA (~320V), A+ is taken at 20mA (~190V)

Transformer is the Tango MX-175. Chokes are the Tango LC-5-250D and the Tango LC-15-150D cut-cores.

The first two caps you see will be Black Gate WKZ. The third cap has to be Elna Cerafine unless I win the lottery.

How's it look?
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Old 4th October 2002, 01:44 AM   #14
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Hey Aaron,

Supply looks pretty good. I ran it through PSUD and found that I got 210V for the driver. Upping the series R to 6700 put it spot on 190V.

I also tried stepping the load on both current sources to half and double the quiescent values, and it was stable, so a big signal input won't send it into wild oscillations.

If you haven't bought the Blackgates yet, don't, find some PP in oil metal can caps or some Solens in similar or larger values. Will probably be cheaper than the BGs and maybe even the Elnas. PP PSU caps are much nicer sounding. To my ears there seems to be a drop in the background hash, and a general increase in resolution I have difficulty describing.

Also, if you haven't bought the chokes yet, look into the Lundahls. They are exceptional and very cheap for the quality. All 4 should be around $US250 in the States. Just checked at www.kandkaudio.com and they're $US66 ea. I'd get 4 x LL1673/15H . I have some of these and the 20H versions as well and I'm very pleased with them. Only negative is they're not pretty, but they are small so you can mount under the top plate.

I'd recommend the Lundahls for the OPTs as well.

Cheers
Brett
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Old 4th October 2002, 02:19 AM   #15
arnach is offline arnach  United States
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Strange, that schematic came straight from PSU designer..

Anyway, I'll look for the PP in oil caps. The Solens would actually be cheaper then the Black Gates.

Finally, I like Tango iron. I would use a Tamura F-5001 as the output transformer, but I have heard the Tribute is just as good, and is half the price. I believe the Lundahl would be a compromise in this area.
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Old 4th October 2002, 09:04 AM   #16
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Default Re: psu

Quote:
How's it look?
Well, not bad for starters, but I would like to point out a few things:

I try to avoid using same LC values in subsequent sections to avoid ringing and motorboating. Simulating with PSUD, at the start you already see about a 10 Hz ringing, which corresponds to the L and C used. Furthermore, I'd use small C's up front and larger C's to the back. This reduces rectifier peak currents again. And after all, it's only the last C that feeds the amplifier. The voltage after the first choke is determined by the tranny and the choke, changing C does nearly nothing for voltage there.

I raised chokes to 10H. Usually these have a little more DCR, which is good to dampen the LC response. I try to aim for critical dampening (Q=0.5, 4% overshoot).

Here's a pic of the sim. I've stepped up the tranny voltage a bit.

The 5k6 in the voltage line is a tad high, but if you bias the driver deep into class A it won't matter too much. Still I prefer separate driver stage supplies, I find it reduces intermodulation distortion a lot, which gives you that open, seemingly effortless sound.

Regards,
Remco
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Old 8th October 2002, 09:51 PM   #17
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Default 437a or 6900

While I can still optimize for a particular tube, would you guys recommend going for the Western Electric 437A or the 6900...?

They're similar in expense.

Thanks,

Aaron
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Old 10th October 2002, 06:38 PM   #18
dice45 is offline dice45  Germany
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Aaron,

6900 is a HIQ version of the 5687, not of the 417A.

both 417A and even more 437A have higher transconductance. They may be tricky to tame in this application. And as both have way higher , your bias will be maybe too low and you have no headroom for the input swing.
Can sound good, can sound awful.

The 6900 if properly applied is one of the best tubes for audio. Sonically.
You have a of 18, bias should be somewhere between -7 and minus 12.5 V, depending whether your plate voltage is rather 180 or 250V.

I would choose the 6900. No Q.
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Old 10th October 2002, 07:50 PM   #19
arnach is offline arnach  United States
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Word. Let me go buy a pair then. I suppose I should pay extra for the gold pin version?
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Old 11th October 2002, 03:21 PM   #20
john is offline john  Philippines
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Look for the Bendix 6900...

I used 5687 on my 2A3 amp. I am still sourcing for this Bendix 6900... Any body knows the sonic signature for this tube on a 2A3 SET amp?

The monoplate RCA 2A3 is the best recommended! Balloon 45's are eyecathing and with depths.

I would be glad to know the listening impressions you have with this amp...

Thank You and Good Luck,

John
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