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Old 31st October 2008, 02:56 PM   #271
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Add a third aluminium panel only if it's needed for chassis structure, otherwise reducing AC interference is not neccessary, I've built amps with chips right beside toroids and all was quiet.

It's better to keep DC connections short and AC as required.

Your setup looks good.
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Old 31st October 2008, 03:23 PM   #272
AndrewT is offline AndrewT  Scotland
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check your chip temperature once you have it running.
Leave space for a bigger (wider + deeper) sink in case it runs too hot, or consider adding back the CPU fan (on 7Vdc to keep it quieter).
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Old 31st October 2008, 05:39 PM   #273
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I cant decide which kit to buy

I am using a set of Klipsch RB-81s that have a efficiency of 97db so the 3875 would work fine.

Which would sound better using a tube pre.

Premium 3875 or the 4780?

I plan on building two mono amps
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Old 31st October 2008, 10:15 PM   #274
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Default Rnfb premium kit question.

Hello all,

This question is for anyone who has built Peter's premium 3875 kit.

It seems there are multiple options to mount the Rnfb resistor on the board. I can place the caddock in the spot marked "Rf" on the pcb or it seems I can mount one leg on the tiny hole by pin eight and solder the other leg to pin 3.

What is the preferred method?

Thanks!
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Old 31st October 2008, 10:53 PM   #275
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There might not be much difference in mounting methods, but installing it directly on chip pins is preferred.
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Old 2nd November 2008, 02:02 AM   #276
mikje is offline mikje  United States
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Default Wiring the transformer???

I'm building my first AudioSector LM3875 Dual Mono Classic Amp. I believe it's a version B. I'll be using an Avel Lindberg Y236750.
http://www.parts-express.com/pe/show...number=122-640
I looked at the spec sheet and that didn't help.

I'm a bit unsure about wiring the primary. It's got two pairs of wires. I'm in the States, so I'll be running off 115VAC. Do I only use one pair and does it matter which one? If I need to use both pairs, how do I wire them?

Secondly, Is there an advantage to using two different rectifier boards, or should I run both amps off one board? It appears that both rectifier boards can supply two channels of the needed voltage.

Thanks.
Mike
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Old 2nd November 2008, 03:19 PM   #277
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Default Re: Wiring the transformer???

Quote:
Originally posted by mikje
I'm building my first AudioSector LM3875 Dual Mono Classic Amp. I believe it's a version B. I'll be using an Avel Lindberg Y236750.
http://www.parts-express.com/pe/show...number=122-640
I looked at the spec sheet and that didn't help.

I'm a bit unsure about wiring the primary. It's got two pairs of wires. I'm in the States, so I'll be running off 115VAC. Do I only use one pair and does it matter which one? If I need to use both pairs, how do I wire them?

Secondly, Is there an advantage to using two different rectifier boards, or should I run both amps off one board? It appears that both rectifier boards can supply two channels of the needed voltage.
In States you need to wire primaries in parallel (115V operation); it's been explained on page 5 of specs sheet: http://www.partsexpress.com/pdf/avelspecs.pdf (blue/violet wires together and gray/brown together).

When using single transformer I always recommend a single rectifier board.
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Old 2nd November 2008, 04:07 PM   #278
mikje is offline mikje  United States
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Thanks Peter,
What about the secondaries? It shows them in parallel too; however, I'm thinking I run one pair to one rectifier and the other pair to the other rectifier.

Sorry if this seems like a no-brainer of a question, but since this has to do with where the power is being applied I want to make sure I do it correctly for obvious reasons.

My other question was about the rectifier boards. It appears they both have two rectified outputs. Do I need to use both boards or should I run both power outputs off one board? Since I'm using a dual output transformer, do I treat it as though it is two transformers and use the jumpers as you mention on the first page of this forum?

One more question; are the LM3875s insulated or do I need the mica pieces between them and the heatsink?

Thanks again for your help and for this project.

Mike
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Old 2nd November 2008, 04:33 PM   #279
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Quote:
Originally posted by mikje

What about the secondaries? It shows them in parallel too; however, I'm thinking I run one pair to one rectifier and the other pair to the other rectifier.

Sorry if this seems like a no-brainer of a question, but since this has to do with where the power is being applied I want to make sure I do it correctly for obvious reasons.

My other question was about the rectifier boards. It appears they both have two rectified outputs. Do I need to use both boards or should I run both power outputs off one board? Since I'm using a dual output transformer, do I treat it as though it is two transformers and use the jumpers as you mention on the first page of this forum?

One more question; are the LM3875s insulated or do I need the mica pieces between them and the heatsink?
The secondaries should be used separately, as you mentioned.
And indeed, you run power to two amp boards off a single rectifier board (as it provides pads for dual outputs)

Although transformer has dual secondaries, you cannot treat them as dual ouputs as the amp uses symmetrical power supply (+/- V) which makes it single transformer. Connection diagram as here: http://www.diyaudio.com/forums/attac...amp=1210694958

The LM3875 that come with my kits are insulated, so no mica pieces needed (only thermal grease).
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Old 2nd November 2008, 05:10 PM   #280
mikje is offline mikje  United States
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Thanks so much Peter!
It's great to be able to get one of your kits (I got it from diyAudio member gychang after he bought it and decided against building it) and then be able to get such great support.
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