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Old 10th October 2011, 10:17 PM   #1
jdubs is offline jdubs  United States
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Default Hypex UCD180 Gain Change?

Guys, I read here:

http://www.hypex.nl/docs/appnotes/gain_appnote.pdf

that adjusting the gain for the 180HG is as simple as changing out the R14 resistor. Question I have is, which one is R14? I don't see it on the main board anywhere.

I'm thinking about possible inserting a stepped attenuator in its place.

Thanks,
Jim
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Old 9th June 2014, 10:26 AM   #2
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Hi,

I know this is such an old thread, but I have the same problem. Did you ever find an answer?

Thanks,
Matt
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Old 9th June 2014, 03:19 PM   #3
Julf is offline Julf  Europe
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Quote:
Originally Posted by mattiscat2 View Post
I know this is such an old thread, but I have the same problem. Did you ever find an answer?
Do you want to change the resistor to change gain, or replace it with an attenuator? The latter is a bad idea, as you don't want to make the cables any longer than they are - they are in the direct feedback path.
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Old 9th June 2014, 03:38 PM   #4
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Hi Julf,

Ok thanks, I guess I just want to change the resistor then. I have UCD180ST's in bi-amped speakers.

I am trying to match a woofer with 86dB sensitivity to a tweeter with 91.5dB sensitivity. So I'm trying to reduce the gain on the tweeter UCD180 so that the tweeter and woofer match in level.

I have found the 3 resistors that Hypex mention in the PDF...

R10 (Rg) which seems to have 1201 written on it.
R11 (Rf) has 2201
R12 (Rf) has 1022


These numbers seem to differ to what Hypex say they should be.
The resistor numbers aren't really next to the resistors, so it's a bit confusing which is which.

I'm not sure how I calculate the value of Rg that I need, and what type of resistor I need to replace it with.

Thanks,
Matt
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Old 9th June 2014, 03:44 PM   #5
Julf is offline Julf  Europe
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See this Hypex application note

R10 is the one to change for a UcD180ST. Go for a 1% smd resistor of the same physical size.
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Old 9th June 2014, 04:39 PM   #6
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Hi Julf,

Thanks for the info regarding the resistor type, much appreciated!
Thanks for the link as well. I have read that document but I have a couple of problems.

The first is it's actually hard to tell which one is R10 because R10 R11 R12 are all close to each other - it's not clear which is which.

Secondly I don't how what value to change the resistor to.

I know that the tweeter is 5.5 dB more sensitive (so needs to be attenuated) than the woofer, but I don't know how to translate this into a resistor value.
The equation in the application note you linked to, seems to only give the amount of amplification (the modules default are set at 20 [26dB] times by default).

Anyone that can offer any insight, would be much appreciated.

Many thanks,
Matt
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Old 9th June 2014, 05:00 PM   #7
Julf is offline Julf  Europe
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Quote:
Originally Posted by mattiscat2 View Post
The first is it's actually hard to tell which one is R10 because R10 R11 R12 are all close to each other - it's not clear which is which.
Can't help you there, as I only have nc400's - different layout, but it should be the one with the 1201 on it.

Quote:
I know that the tweeter is 5.5 dB more sensitive (so needs to be attenuated) than the woofer, but I don't know how to translate this into a resistor value.
Thus you need 5.5 dB less amplification. 5.5 dB is a ratio of 1.9, so you need to scale down the amplification by a factor of 1.9.

Quote:
The equation in the application note you linked to, seems to only give the amount of amplification (the modules default are set at 20 [26dB] times by default).
Right, so what you want is to change the amplification from 20 to 10.6 (20/1.9). Using Bruno's formula suggest that changing Rg (R10) from 1.2k to 3.3k (nearest E24 value) gives a gain of 10.5, close enough (this is assuming the values of 2.2k and 1.2k for Rf and Rg respectively, as indicated by the 1201 and 2201 numbers).
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Old 9th June 2014, 05:50 PM   #8
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Quote:
Can't help you there, as I only have nc400's - different layout, but it should be the one with the 1201 on it.
No worries, thanks anyway. That's the thing - my values are different to the Hypex App notes. I've attached a picture - maybe I'm just not reading it right.

Click the image to open in full size.

Quote:
Thus you need 5.5 dB less amplification. 5.5 dB is a ratio of 1.9, so you need to scale down the amplification by a factor of 1.9.
Thanks! Just for my future reference, how do you get to the ratio 1.9? Is it a power ratio thing, as I thought double the power was equal to 3db?

Quote:
Right, so what you want is to change the amplification from 20 to 10.6 (20/1.9). Using Bruno's formula suggest that changing Rg (R10) from 1.2k to 3.3k (nearest E24 value) gives a gain of 10.5, close enough (this is assuming the values of 2.2k and 1.2k for Rf and Rg respectively, as indicated by the 1201 and 2201 numbers).
Thanks, that all makes sense now. Much appreciated. I'm just uncertain how you find the ratio in the first place.

Many thanks,
Matt
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Old 9th June 2014, 06:52 PM   #9
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Quote:
Can't help you there, as I only have nc400's - different layout, but it should be the one with the 1201 on it.
Ok my fault. The smd values are correct, I was reading up side down - quite hard to tell as the 2's look the same both ways.

R10 = 1.2k as it should be.

I understand using the forumla, but still trying to understand where 1.9 comes from.

Just to throw a spanner in the works, what if i decided to do this the other way round? Increasing the gain of the woofer to match the tweeter?

Thanks,
Matt
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Old 9th June 2014, 07:08 PM   #10
Julf is offline Julf  Europe
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Quote:
Originally Posted by mattiscat2 View Post
No worries, thanks anyway. That's the thing - my values are different to the Hypex App notes. I've attached a picture - maybe I'm just not reading it right.
As I read it, R12 is on the top, 2201 (2.2k), R10 (Rg) is below that, 1201 (1.2k), R11 below those in a vertical orientation (another 2201 - 2.2k).

Quote:
Thanks! Just for my future reference, how do you get to the ratio 1.9? Is it a power ratio thing, as I thought double the power was equal to 3db?
For power, 3 dB is a factor of 2, but here we are talking about amplitude ratios, so a factor of 2 corresponds to 6 dB (or 20*log10(x), to be accurate). A doubling of amplitude results in a quadrupling of power (both voltage and current doubles), so the result is 3+3 dB.
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