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Old 15th December 2006, 02:23 PM   #1491
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If you install transformer in a same enclosure as the amp, it's a good idea to isolate it mechanically. Some people suggest not to use magnetic bolts to mount the transformer, but I didn't experiment with that yet.

As to the amp section itself, it's really hard to say if it's better to use soft pads or rigid support. I tent to prefer the hard support, usually with brass cones. I also use bronze standoffs for the amp boards.

A good example of that approach is the amp described here: http://www.diyaudio.com/forums/showt...156#post879156 I'm using soft rubber to support one end, but there is still a cone that allows a mechanical single point contact with a mechanical ground.

I tried soft suspentions all around, but it never sounded right to me.

Too much damping for the chip is not good either. I used to use a copper clamps to attach chip to the heatsink, but later found out that the sound becomes "too dead" and not airy enough, so now only a single screw is being used. I also prefer the isolated chip package as it seems to be less bright than non isolated package (in that case damping seems to be beneficial). If I mount the chip like in a picture here: http://www.diyaudio.com/forums/showt...565#post636565 I'm still using 2 washers under the copper bar, to isolate main chip body from the bar (so the pressure is only at the screw sides)

I'm not sure about advantage of dual transformers over a single one. If I build for myself, I usually choose dual mono, but I never found a single transformer powering two channels to be lacking in any way, so both approaches are fine, depending on how complicated you want it to be. But use a single rectifier board in that case one transformer is used, as it's reported to sound better than two boards powered from a single trafo.
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Old 15th December 2006, 06:22 PM   #1492
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You are using brass for the heatsink right, but bronze plates for mounting (fancy)?

I guess I might have to think about a few ideas to hard-mount the heat sinks (I planned on suspended via heatskin amp boards, or should they be mounted to the board as well?) like some sort of isloation pad between the transformer piece of the board and amplification piece.

I doubt induced magnatism from a transformer, on a bolt going through it, could actually make the bolt cause an effect that reaches out past the transformer... I suppose maybe it could have an effect on the transformer itself though.
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Old 15th December 2006, 07:00 PM   #1493
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Oh yeah I had planned on using good hardmount cones for the board itself, it was that I was thinking of Deflex washers just for the heatsink which the chip and amp board would be mounted, was the original thought.

After some reading I think I will go with copper bus bar though.
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Old 15th December 2006, 07:03 PM   #1494
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The heatsink is from bronze as well. The choice of standoffs was coincidential, as I found them in a local surplus store.

However, I would not recommend bronze for heatsink: it's too expensive with very poor thermal conductivity. You should be probably better off with copper. As to the influence of the material itself on the sound, well, that is another matter.

Proximity of transformer to amp board does not present a problem and any special shielding is not really required.

The best is to experiment with different setups and choose best sounding option.
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Old 15th December 2006, 07:27 PM   #1495
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I do not get to expermint with this one...

What do you think of a ground tap on the copper heatsink?

I was originally going to use a small piece of copper bus bar with a ground tap to shield the amp side from the transformer. If shielding is a non-existant issue than I can skip it I suppose. I have no idea how much influence beyond the transformer itself, can it produce.
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Old 15th December 2006, 08:29 PM   #1496
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I'm not sure about copper heatsink working as ground tap. I do it the way described here: http://www.diyaudio.com/forums/showt...773#post787773
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Old 15th December 2006, 10:15 PM   #1497
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Perhaps that is a bad description... (every one on this board goes back and forth on electrical and electronic, then a bunch of made up language all the time)

An earth ground straight to the bus bar. Then no grounding to the earth ground except for this, and perhaps two two million ohm resistors to bleed off the capacitors intead of into the speakers when the amplifier is turned off?

My idea is to keep this huge (relative) copper bar from getting too much induced signals from the outside right up next to the 3875 chip itself.

When you say ground it appears in most of your stuff you are talking about the negative, or common, and you are tieing it all together to make it easy to work with an umbilical cord, or fancy wiring scheme, from what I understand.
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Old 15th December 2006, 10:21 PM   #1498
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Peter said:

Quote:
I'm not sure about advantage of dual transformers over a single one. If I build for myself, I usually choose dual mono, but I never found a single transformer powering two channels to be lacking in any way, so both approaches are fine, depending on how complicated you want it to be. But use a single rectifier board in that case one transformer is used, as it's reported to sound better than two boards powered from a single trafo.
Peter, does this apply to transformers with dual secondaries? That is, I have a Plitron with dual 20V secondaries and was going to wire the boards (when they arrive) as dual mono. Are you recommending against this?

Thanks.

Aengus
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Old 15th December 2006, 11:04 PM   #1499
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Dual secondaries are needed per channel ( as power supply is symmetrical). If you want to got true dual mono from a single transformer you need quadruple secondaries.
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Old 15th December 2006, 11:09 PM   #1500
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Quote:
Originally posted by Destroyer OS.
Perhaps that is a bad description... (every one on this board goes back and forth on electrical and electronic, then a bunch of made up language all the time)

An earth ground straight to the bus bar. Then no grounding to the earth ground except for this, and perhaps two two million ohm resistors to bleed off the capacitors intead of into the speakers when the amplifier is turned off?

My idea is to keep this huge (relative) copper bar from getting too much induced signals from the outside right up next to the 3875 chip itself.

When you say ground it appears in most of your stuff you are talking about the negative, or common, and you are tieing it all together to make it easy to work with an umbilical cord, or fancy wiring scheme, from what I understand.
Since my PS is separate, I'm not connecting earth ground to the amp (ground or chassis). The chassis is grounded off the output ground.
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