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Chip Amps Amplifiers based on integrated circuits

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Old 4th March 2009, 04:45 PM   #331
troystg is offline troystg  United States
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Thanks for the link to the calculator.

That definitely explains it. I only use 22ga or larger for signal cable.

Usually my jumpers are made with the pieces of Silver plated copper from the excess of the input cabling.
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Old 5th March 2009, 07:33 AM   #332
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Quote:
Originally posted by AndrewT
having DC blocking caps in both the source and receiver is a complete waste.
You only need to block once.
I'm confused...isn't this exactly what I (and others) was saying a few posts ago that you so adamantly seemed to think was a terrible idea? or am I missing something?
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Old 5th March 2009, 08:51 AM   #333
AndrewT is offline AndrewT  Scotland
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You are missing something.
You need a DC blocking cap if the amplifier is AC coupled.

You only need to block the DC once.

If you know that ALL your sources are already fitted with a DC blocking cap then you can omit the extra cap at the input to the power amplifier.
This is the expensive way to do it.
Each Blocking cap needs to be of sufficient quality for that source and needs to be correctly sized for any power amp that it gets connected to.
The economic alternative is to fit the correctly sized DC blocking cap to suit the power amp, inside the power amp and make it of a quality that suits you.
Adding a DC bypass allows you to choose which input to connect any other source, whether it has a DC blocking cap or DC servo or none.
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Old 5th March 2009, 03:06 PM   #334
Tony X is offline Tony X  France
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Default Residual Hum

Hello again,

If I may pick your brains yet again, ------

Recall that after getting MyRef to work on both channels I had a serious hum.
This was reduced when joining transformer neutral outputs to ground.
Drastic further reduction was achieved by changing to monofilament wires between transformers and ampli and twisting them.

I thought that that had cured everything but in fact there is a residual hum that I could live with if necessary but I think you will understand that I would prefer to get rid of it completely.

Some observations:

A) The hum is very faint at normal volume settings and only increases perceptively in volume when the pot is turned right up way beyond normal listening setting.
B) Joining transformer neutral outputs to ground no longer has an effect. I can disconnect the ground and the hum stays but does not increase or decrease in volume.
C) If both interconnect cables Left and Right between CD player and ampli are disconnected, the hum disappears.
D) If the ampli input connections are then shorted, there is still no hum.
E) The hum is only present when both left and right channels are connected. If the left channel is disconnected, there is no longer any hum from either L or R speaker. Same if Right is disconnected.

Any suggestions ??
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Old 5th March 2009, 03:25 PM   #335
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Default Re: Residual Hum

Quote:
Originally posted by Tony X
Any suggestions ??
I've had a similar problem with a Gainclone.
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Old 5th March 2009, 04:15 PM   #336
billyk is offline billyk  United States
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Quote:
I thought that that had cured everything but in fact there is a residual hum that I could live with if necessary but I think you will understand that I would prefer to get rid of it completely.
Ground loop?
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Old 5th March 2009, 06:48 PM   #337
troystg is offline troystg  United States
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"D) If the ampli input connections are then shorted, there is still no hum.
E) The hum is only present when both left and right channels are connected. If the left channel is disconnected, there is no longer any hum from either L or R speaker. Same if Right is disconnected.

Any suggestions ??"

If shorting the inputs kills all hum it is not a AMP issue.

My suggestion is:

1) Tie the RCA grounds together at the source OR the amp.
2) Last resort is lift the cable ground on one channel and tie the AMP rca grounds together.

It is a ground loop of some sort.

Picture of the enclosure with rca inputs?
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Old 5th March 2009, 11:58 PM   #338
Bengali is offline Bengali  United States
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Default lm3886

Hi,

is it possible to bend the leads on the lm3886 chip
so that the pcb will also mount flush to the heatsink?

thinking making it modular and need to save space.

curious as to if this is possible.

thanks.
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Old 6th March 2009, 12:02 AM   #339
troystg is offline troystg  United States
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Carefully but yes you can.

They even have an LM3886 package that is set up for mounting that way.
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Old 6th March 2009, 12:03 AM   #340
Bengali is offline Bengali  United States
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Default DC Blocking Cap

Quote:
You only need to block the DC once.
Hi Andrew,

what you say makes sense. my question is regarding
the capacitor acutally being physcially close to the input
on the pcb vs. it on another unit. any affects?

electrically, audibly, it does not matter physically which
unit the dc blocking cap is on?

one high end cap on the output and a crappy cap on the input,
that is not good, so one cap makes sense.

thanks
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