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Old 13th February 2009, 10:13 PM   #1
tfboy is offline tfboy  United Kingdom
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Default How to volume control for mini UcD180 project?

Apologies if this is a bit of a noob question. I've had a search but can't seem to find something really relevant.

I'm thinking about building a small stereo amp based on a pair of UcD180 units. But I want to make it as small and light as possible.

It will be used as a low powered PA kind of system with just a pair of speakers. There only needs to be one input and it will be an unbalanced line level output of a consumer CD player (for example). or possibly the audio out of a laptop.

What is the simplest / easiest way of getting some volume control? I would have hoped that a single dual-channel variable pot would be OK, but realist it may be too coarse or the input may be too low for the amps to work well enough.

I really want to keep it to one physical box. If a kind of "preamp" is a must have, it must be small enough to fit inside the main unit which will only consist of a pair of UcD180 and a SMPS.

Suggestions?

Thanks
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Old 15th February 2009, 07:14 PM   #2
Javin5 is offline Javin5  Switzerland
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The input impedance of the UcD180 is 100K, so a dual pot of about 25K should be just fine. This yields an input impedance between 20k and 25K, no problem for a CD-player. You don't really need any gain, a cd-player is able to drive the UcD180 to full power. I'm less sure in regard to your laptop; you would have to consult the specs there.
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Old 15th February 2009, 10:13 PM   #3
tfboy is offline tfboy  United Kingdom
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Thanks.

Next question I guess is what 25k pot would be suited for the application. I read a lot about different "grades" of pot, and people have personal preferences and all that.

I don't want to spend a lot of money on this, bearing in mind the final application for it. So a TKD is probably a bit overkill.

I'd also need to find something that can be sourced in the UK so US-based merchants like percy audio probably aren't a viable solution.
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Old 15th February 2009, 11:17 PM   #4
Javin5 is offline Javin5  Switzerland
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Take any reasonable quality log pot, no need to go overboard price wise. Check the specs for tracking error. If you want one with remote control, that will of course cost more.
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Old 18th February 2009, 04:13 AM   #5
col is offline col  Australia
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do a search in these forums for "jaycar pot" or Taiwan Alpha. There is a very good quality cheap and small dual-gang pot that is ideal. I use them all the time.

:edit: try this:

"Silver-Carbon" Pot ex Tawan - Photo - & ignore my ugly Pinky!

:edit again: oh yeah and this:

http://www.diyclassd.com/cables.htm

for how to wire the pot.

col.
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Old 28th April 2009, 02:18 PM   #6
tfboy is offline tfboy  United Kingdom
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Quote:
Originally posted by col
do a search in these forums for "jaycar pot" or Taiwan Alpha. There is a very good quality cheap and small dual-gang pot that is ideal. I use them all the time.

:edit: try this:

"Silver-Carbon" Pot ex Tawan - Photo - & ignore my ugly Pinky!

:edit again: oh yeah and this:

http://www.diyclassd.com/cables.htm

for how to wire the pot.

col.
Hi Col. Thanks (and sorry for the belated reply!)

I've now ordered a set. In the meantime, can you specify what diameter the hole in the case needs to be? I'm guessing the "9mm" is the length of the square body and not the shaft diameter?

Thanks!
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Old 28th April 2009, 11:16 PM   #7
col is offline col  Australia
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I think the splined shaft (threaded bit) is 7mm. If you need knobs for them, guitar spare parts stores have heaps.

Here is one of my projects sporting a pair off a Fender Telecaster

Click the image to open in full size.


col.
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Old 29th April 2009, 06:33 AM   #8
tfboy is offline tfboy  United Kingdom
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Quote:
Originally posted by col
I think the splined shaft (threaded bit) is 7mm. If you need knobs for them, guitar spare parts stores have heaps.

Here is one of my projects sporting a pair off a Fender Telecaster

Click the image to open in full size.


col.
Hehe, looks neat

I'm building my list of parts to buy from CPC / Farnell. 4mm binding posts, volume knobs, phono connectors, etc. I'm hoping to get a custom made box to house it all - and it should look neat as it'll be professionally made by some metal workers, laser cut and all.

But your Aiwa box is and trendy
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