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Old 10th February 2006, 08:07 AM   #771
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[QUOTE]Originally posted by Peter Daniel
[B]2 x 25V, 300VA transformer will work fine (providing the speakers are easy load). It is my observation that the higher the voltage, the better the sound.

Peter, many thanks for your response. Now i'm more secure.

My friend have build one GC with this transformer and the speakers to 8 ohm. When he increase nearly to max of the volume, one channel enter in mute for one or two seconds!!
Why??
What do you think ??
It can be the voltage of the transformer ?

Giuseppe
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Old 10th February 2006, 10:57 AM   #772
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Peter, I still ask to you, if i want to build a perfect your dual mono LM3875 Kit with two transformers, what voltage and VA you suggest me?

Thank...thank you!!

i'm afraid, but you are my point of reference
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Old 10th February 2006, 02:27 PM   #773
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Well, I'm just about finished with my lm3875 amps and should be starting the all-in-one dac kit in the next week or two.
The new buffer boards caught my eye, as have TVC's and AVC's.
If I wanted to use the buffers between the dac and gainclone, would something like intact audio's AVC work well at the input of the buffer?

I also had a question about heatsinking.

With an 18V-0-18V 160VA transformer per channel, would a 4" long 1 1/2" square aluminum bar work for both shielding and heatsinking?

Thanks
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Old 10th February 2006, 03:09 PM   #774
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Quote:
Originally posted by mcamolin
My friend have build one GC with this transformer and the speakers to 8 ohm. When he increase nearly to max of the volume, one channel enter in mute for one or two seconds!!
Why??
What do you think ??
It can be the voltage of the transformer ?
[/B]
Maybe he is overloading the amp's input. Without more info on source equipment it's really hard to comment.


Quote:
Originally posted by mcamolin
Peter, I still ask to you, if i want to build a perfect your dual mono LM3875 Kit with two transformers, what voltage and VA you suggest me?
The choice of transformer depends on the speakers. If they are easy, 8 ohm load, 2 x 25V will work fine. I'd rather prefer 2 x 24V but it's harder to find trafos with that rating. Personally, I'm using 2 x 22V, 300VA toroids, as this gives me better compatibility with most setups.


Quote:
Originally posted by sdedalus
Well, I'm just about finished with my lm3875 amps and should be starting the all-in-one dac kit in the next week or two.
The new buffer boards caught my eye, as have TVC's and AVC's.
If I wanted to use the buffers between the dac and gainclone, would something like intact audio's AVC work well at the input of the buffer?

I also had a question about heatsinking.

With an 18V-0-18V 160VA transformer per channel, would a 4" long 1 1/2" square aluminum bar work for both shielding and heatsinking?
Such bar seems a bit small, even for one channel, but if speakers are easy to handle it may be still OK. However, a square tubing of that size would be more efficient in heat dissipation. Unless the bar is connected to other, metal, chassis parts.

Regarding buffer, I'm not familiar with intact AVC, but I find that the buffer works very well at the DAC's output and resistive attenuator directly at amps input. I think that it may be equally suitable to replace resistors attenuator with TVC or AVC.

I don't really feel like I need a buffer after the attenuator. The buffer has 6 ohm output resistance and improves substantially driving capabilities of any source.

I will soon have all the required semiconductors and buffer kits will become available.
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Old 10th February 2006, 03:14 PM   #775
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I'm also working on an attenuator project that will complement the buffer for a nice line stage: http://www.diyaudio.com/forums/showt...425#post839425
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Old 10th February 2006, 03:41 PM   #776
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quote:

I will soon have all the required semiconductors and buffer kits will become available.


sweet and i have the case to complement it marble.
didnt work out as a se tube amp wife left it on fried the transformer.

she is now banned from going in my room
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Old 10th February 2006, 04:59 PM   #777
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Quote:
Originally posted by safetyman


Peter, thanks for your response. Actually, my casing will be aluminum on all 4 sides. The left and right side where the amp is going to be attached to is 4" (H) X 8.5" (D) X 0.5" (thick), and the front and back is 4" (H) X 11.5" (W) X 0.25" (thick). I would rather not add fins if possible. The bottom will be a piece of wood off a nice chopping board and to show your beautiful PCB, the top will probably be acrylic.

My speakers are a pair of Epos ES11 which I believe they are about 87-88 dB sensitivity. No idea on impedance though, but I guess it will depend on the music played too.
peter, could you please give your thoughts on the above. Thanks.
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Old 10th February 2006, 05:23 PM   #778
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If you ensure good thermal transfer between all those panels (angles or bars, or proper contact surface) I don't think you would experience any problems.
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Old 10th February 2006, 05:26 PM   #779
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Peter, you are the man. I believe a friend of mine had just placed an order for some LM3875 boards and I had lumped into that order. Looking forward to that too.

BTW, what value resistors do you use to short the binding post for the burn in period. Could you kindly share?
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Old 10th February 2006, 05:29 PM   #780
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I don't do that with resistors, I enjoy the amps right from the start, connecting the speakers.

But I think 10R should be fine as long as the wattage is appropriate.
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