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Old 23rd March 2010, 03:21 PM   #1
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Default Removing input caps and pot

Hi,

I've just bought the Topping TP20 mk2 2020 amp and the plan was to use it on a second system with a Squeezebox Touch - when it's released.

I will be attempting to build new power supplies for both in the near future, but in the meantime I have a couple of questions:-

a) As I will be using the line out of the Squeezebox is it OK to remove the input caps altogether and DC couple the amp?

b) Also, can I just remove the volume pot and use the the volume control on the Squeezebox instead? If so, do I just replace the pot with some straps or do I need to use a resistor?

Many thanks.
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Old 23rd March 2010, 07:26 PM   #2
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Quote:
Originally Posted by Stanphink View Post
Hi,

I've just bought the Topping TP20 mk2 2020 amp and the plan was to use it on a second system with a Squeezebox Touch - when it's released.

I will be attempting to build new power supplies for both in the near future, but in the meantime I have a couple of questions:-

a) As I will be using the line out of the Squeezebox is it OK to remove the input caps altogether and DC couple the amp?

b) Also, can I just remove the volume pot and use the the volume control on the Squeezebox instead? If so, do I just replace the pot with some straps or do I need to use a resistor?

Many thanks.
a) As the input is DC coupled it wont make any sound at all if you remove the input caps and worse still the amp and/or Squeezebox most likely wont survive the experience either.

b) Sure, you can remove the input pot as long as you're certain that you get the correct input impedance, remember though that without a suitable input impedance, ie. from removing all resistors, your Squeezebox will be toast. That's a guarentee. I certainly wouldn't remove it without knowing the output voltage of the Squeezebox first, and you can bet big money that the Squeezebox volume control is a LOT worse than the Alps pot in the Topping amp.

Anyways, go by the DIY axiom: Listen, then mod.
Instead your approach of: Mod, then poof.

Last edited by Saturnus; 23rd March 2010 at 07:36 PM.
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Old 24th March 2010, 12:00 AM   #3
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Saturnus, thanks for the wise advice - I think I'll go and do a bit more reading before attacking things with a soldering iron .

You're quite right about listening first and then modding, so I've decided to go and practice on my doorbell - that way I can only blow up the postman and not my new Squeezebox .
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Old 24th March 2010, 04:35 PM   #4
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I've done a bit more reading and just in case someone else was considering doing something similar, there is a good explanation here.
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Old 24th March 2010, 05:37 PM   #5
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Quote:
Originally Posted by Stanphink View Post
I've done a bit more reading and just in case someone else was considering doing something similar, there is a good explanation here.
Well, that really doesn't descibe what is the actual problem here though.

The input is DC coupled meaning there's a DC voltage directly on the input caps of usually -2.5V. Removing the caps means this voltage goes directly to the output of the connected source potentially damaging it. And a signal directly connected on the chip input pins is certainly enough to fry the chip althogether. Removing the cap also means the input will not get a negatively loaded signal so it wont make any sound at all.

Secondly, if you accidentally connected a much too low input resistor, or removed it entirely, the Squeeze box will try to provide a few watts of output power to it's output, most likely frying the output circuit. Although it's probably equiped with a short-circuit protection to save you but in any case it wont make any sound.
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