| Sherman |
I am accumulating the parts for my GC system and have a couple of questions regarding the layout of the power supply.
I am using cigar boxes as chassis, 2 for the monoblocs, 1 for the passive controller (volume, input selection) and 1 for the PS. I have some aluminum tape I plan to use to line all the boxes as shielding.
I'm using two of those $10 40VCT transformers from PE, one per channel. The box for my PS is *just* large enough to place both trafos side by side if I overlap the mounting lugs on the inside. I will have 1/2" of space behind the trafos and about 1" in front and 1" on the sides.
There is sufficient space to mount my DPST switch and a panel mount fuse holder at one end of the box. Inside there will be space for the rectifiers as well. It will be close but none of the parts will physically touch any of the others except the trafo mounting lug overlap. I am debating what to use for feeding power out to the amps but will probably use Speakon connectors.
Questions-
1- I've always been told to mount transfromers that must be in close proximity at right angles. I don't have room to do it that way if I want to have the PS for both channels contained in one box. Will it be a problem to mount the trafos side by side with one lug of each over lapping?
2- Would there be any advantage to mounting the transformers in the PS box but mounting the rectifiers in the amp boxes? (Intuition tells me I'd be better off not running AC between the PS and amps but my intuition sucks.)
3- Would there be any advantage in building *two* PS boxes, one for each channel? I think I'd rather have one box but I'm open to ideas.
Whew!!! Thanks for reading all that and any ideas are welcome.
Sherman |
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| Ropie |
Hi Sherman,
Q1. I'm not too sure, but I would think it is best to keep magnetic fields at right angles to avoid direct inteference with one another.
Q2. No problem having your bridges in either box. I had an amp with the rectifiers right next to the chips and the transformers in a separate box and it was absolutely fine. Just make sure you use good quality mains cable (not more than a cople of feet) to make your umbilical leads from the psu to the amp/bridges.
Q3. Again, I have had two transformers in two boxes and two in one box and have not had any problems with either. I would say two boxes give you more flexibilty when it comes to positioning but you will need more plugs/cables/sockets lying about and do you want that? Then again, using two boxes for two transformers may well solve your problem in Q1.
Sonically, I cannot say which of any of the above methods will sound best as it depends on so many other factors also. The key is to try things and keep an open mind.
:) |
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| Sherman |
Thanks for your reply! I think I will put the entire power supply including rectifiers in one box and just run the DC to the amps. It just seems "cleaner" that way. I think I'll still mount the caps in the amp boxes though to keep that end of things close.
I played with the layout a little more and found that I can put them at right angles in a "V" shape configuration or by bending up one mounting tab on one of them I could get them into a "T" formation.
However, I may have to change my plans. Today I toasted one of the transformers and I only had two. (It fell three feet to a concrete floor :bawling: and upon firing it up for testing all the magic smoke came out.)
Since it doesn't appear that PE has any more of the $10 transformers I may just get the Avel-Lindburg toroidal and go with one transformer for both channels. I was really hoping to use these other transformers because they fit in the cigar box I'm planning to use for the power supply and the Avel won't fit.
PE does have some 48VCT 3A transformers for $23 that would work and the cost for two would equal the Avel so that's a possibility.
Sherman |
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| Ropie |
| Shame about your transformer, but you can still run a great stereo amp from just one transformer (make sure you still use two bridges though). Infact I prefer the one-transformer sound (160VA). Yes, keep the caps and power ground as close to the chips as is humanly possible. |
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| Sherman |
| quote: | Originally posted by Ropie
... you can still run a great stereo amp from just one transformer (make sure you still use two bridges though). In fact I prefer the one-transformer sound (160VA).... |
I thought about just using the one transformer and I will probably give it a shot. The problem is that while the specs at PE said it was 200VA some others here said they thought it was really more like 100VA so it may be a little lacking in power.
I do agree with you regarding 160VA being sufficient. My main system uses a 9 watt (~4.5 RMS) tube amp and my speakers are efficient. I'm not worried about not getting the rated 56 watts from the 3875.
Tomorrow I'll build the ps with the single transformer (solves all my issues about orientation!). I can use a smaller box as well.
Sherman |
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| Sherman |
| quote: | Originally posted by Ropie
... you can still run a great stereo amp from just one transformer (make sure you still use two bridges though). Infact I prefer the one-transformer sound (160VA)... |
Since my transformer is a 40VCT would this be the right approach to a single transformer PS? |
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| Ropie |
| Though I'm not familiar with the 40VCT rating you mention, with that layout 20-0-20V secondaries should give you approx +/- 30 VDC after rectification, which is fine. :) |
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| Sherman |
I was thinking about 28VDC so at least its close. I should have it built today! I also won an auction for a pair of 44VCT toroidal transformers as well so I will have an option for more power if this one doesn't quite do it.
Thanks for your help on this. I'm excited about getting this amp built!
Sherman |
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| Ropie |
| Good luck with it and don't forget to post some pictures when it is done! ;) BTW, are you building an inverted or non-inverted circuit? |
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| Sherman |
| quote: | Originally posted by Ropie
Good luck with it and don't forget to post some pictures when it is done! ;) BTW, are you building an inverted or non-inverted circuit? |
I have been planning a non-inverted version this time around. I will definitely post pics when I have it complete. I'm still deciding on a couple of other components. (Monoblocks vs. all in one box, separate passive control unit or put the volume control and selector in the same box.)
Sherman |
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