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Old 9th October 2006, 09:08 AM   #1
iqbad is offline iqbad  Sweden
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Default Ucd180 and volumecontrol?

Hi!

I am planning to build an amplifier using the hypex ucd180 modules. I have never build something like this before, and I have a few questions.

I would like not to use a preamp for this amplifier, and therefore need to construct some kind of volume control.

Has anyone done this before?

What kind of pot did you use? Where did you buy it?

Where and how was it connected?

Regards, Eric, Sweden
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Old 9th October 2006, 10:21 PM   #2
Javin5 is offline Javin5  Switzerland
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The input impedance of the UcD180 is 100K, so if you are using a 25K pot, you should be ok. Use a logarithmic pot of good quality (e.g. Alps). If there is no dealer in your area, you can mailorder it.

For a stereo amp with two ucd180 modules, you will of course need a dual pot, one at the input of each channel. That's if you are using unbalanced inputs. For balance XLR inputs you would require a quad pot.

The wiring between the wiper and the module input should be as short as possible to minimize input capacitance; ie. locate the pot close to the module. High capacitance would yield undesirable phase shift and attenuation at high frequencies.

Kurt
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Old 10th October 2006, 10:11 AM   #3
iqbad is offline iqbad  Sweden
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Thank you for your answer Javin5!

Performancevise, is it better to skip the idea of a simple volumecontrol and build a small preamp instead?

Could anyone recommend a well performing DIY preamp?

/Eric
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Old 13th October 2006, 05:44 PM   #4
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Quote:
Originally posted by Javin5

The wiring between the wiper and the module input should be as short as possible to minimize input capacitance; ie. locate the pot close to the module. High capacitance would yield undesirable phase shift and attenuation at high frequencies.

Kurt [/B]

I wanted to do something similar with a remote POT, say, on a 5 to 10 foot cable. Will this cause a problem? What if I use heavy guage wire? Thanks!
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Old 13th October 2006, 07:16 PM   #5
Javin5 is offline Javin5  Switzerland
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Jringels:

Locating the pot in the poweramp is better, but you can of course use it remotely via a cable. In that case, the pot resistance and the cable capacitance will determine how your high frequencies are affected. A heavy wire gauge is only required for the speaker cables, not for the interconnect signals we are talking here. Normal shielded cable is all you need, but in your case it needs to be low capacitance.

- use a low capacitance interconnect cable, say 60 - 100 pf/m
- if your source can handle the load, use a 10K or 20K pot

With a 3m lenght, your cutoff frequency is then in the 200 KHz range, which is about an order of magnitude above the audio range.

Kurt
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