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PostPosted: 08 Mar 2014, 19:42 
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mwhouston wrote:
The power tranni I put aside for this is a 275-0-275. I'll have to see what else I have or order again.
I just went back and looked at my notes. I actually got about +314 before my dropping resistor. As the B+ only needs to be about 272v you may well be just fine with the 275-0-275 transformer. You'll also have a much lower peak plate current with the low value capacitor so your rectifier drop will be less. You might just prototype it with a fixed load and see how it does.

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PostPosted: 08 Mar 2014, 20:07 
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Suncalc wrote:
mwhouston wrote:
The power tranni I put aside for this is a 275-0-275. I'll have to see what else I have or order again.
I just went back and looked at my notes. I actually got about +314 before my dropping resistor. As the B+ only needs to be about 272v you may well be just fine with the 275-0-275 transformer. You'll also have a much lower peak plate current with the low value capacitor so your rectifier drop will be less. You might just prototype it with a fixed load and see how it does.

I'd rather not pay for another tranni, I'm trying to reduce components but I think they are breeding in the dark places of my out-of-control computer room. I was thinking split PS from after the first 4uf cap. And thinking dual 5H 50mA Hammond chokes for a total of four chokes, two per split rail. The next two filter caps 100uf each. By this I'm hoping the amp will image really well and be really quiet.

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PostPosted: 08 Mar 2014, 22:48 
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If you really want channel separation then you could wire your PS like this:
Attachment:
PS.jpg

This is based on your suggestion of two 5H chokes per rail. The first 5H choke / 100µf capacitor (≈ 46dBv ripple reduction) gives the primary filtering for each channel, then the power stages get another 5H choke / 100µf capacitor (≈ 46dBv ripple reduction) filter stage and the driver gets a 5kΩ / 33µf capacitor (≈ 40dBv ripple reduction) filter stage. This puts total ripple reduction for the drivers at 86dBv and the power stages get 91dBv. Channel separation should (theoretically) be well over 100dB.

Even with the relatively small first cap this should be an insanely quiet power supply. What do you think?


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PostPosted: 09 Mar 2014, 00:44 
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Hey, thanks. Not how I planned it but very do-able. I would love to mount the chokes and caps on a piece of vero-brd (strip brd), one for each channel. But if that is not possible mount all the chokes (4 of) on the top plate under a suitable cover and wire them into the cap brds. underneath. Two days from now I will pull out the chassis and see what is possible. We have Labor Day tomorrow which is a public holiday so the good lady wife is home. I try not to do DIY stuff who she is home. Thanks again Matt, I see you may have an interest in this build. I should do us both proud. I have a few tricks up my sleeve.

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PostPosted: 09 Mar 2014, 23:41 
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Matt: I have been tossing around in my head (plenty or room up there) your PS design. Where I think the driver tube is the most noise and hum sensitivity part of the amp you have the least filtration. Personally I would have thought you would pick-off the driver tube HT from the last choke, then trough the limiting resistor and onto the last storage cap?

Am I missing something?

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PostPosted: 09 Mar 2014, 23:48 
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If you pick up the driver B+ after the second choke, then variations in B+ at that point due to the heavy load of the power stage get inserted back into the driver. And because the power stage load is highly inductive, i-v phase offsets can cause all kinds of headaches to the driver stage. In the manner I drew the schematic, the second choke also provides very important isolation between the power stage B+ and the driver B+. Also, the driver has about 11 dB of PSRR but the power stage has very little. As such, even though it looks like the driver gets less filtration, it is actually better off due to its inherent PSRR.

I think the double legged filter should work well for a SE Class A1 amp.

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PostPosted: 09 Mar 2014, 23:54 
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I'm sold. I'll do it your may. All makes sense now. Tomorrow I will hopefully do the layout, drill and prime. Better stock the fridge, it's going to be a long day. Also I need at asses whether I can mount the chokes on the PS cct. brd. (my preferred way) or mount them remote. A lot to consider, a lot to do. Now I'm excited.

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PostPosted: 18 Mar 2014, 17:51 
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Finally a layout. Top plate now marked for drilling.
Attachment:
P3182728.JPG
Attachment:
P3182729.JPG
Attachment:
P3182730.JPG
Attachment:
P3182731.JPG


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PostPosted: 19 Mar 2014, 02:08 
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Look nice! Aren't inputs close to PT? You can rotate OTs to 90 deg., IMO, coils of PT and OT are close, irons are parallel.

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PostPosted: 19 Mar 2014, 02:13 
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azazello wrote:
Look nice! Aren't inputs close to PT? You can rotate OTs to 90 deg., IMO, coils of PT and OT are close, irons are parallel.

Great idea but that wouldn't look as good. I have had no problems in the past with this type of layout.

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