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Old 11th June 2008, 12:24 PM   #1
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Default reducing system gain

hi all ive got way to much gain from my cd player to pre and poweramp which means i can only use the first qaurter of my volume control on my pre is there an easy way i can reduce the gain from my cd player into my preamp to make my volume control more usable maybe with some resistors in my cd to pre interconnects or something .i dont want to do anything that will degrade the signal
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Old 11th June 2008, 12:31 PM   #2
rabbitz is offline rabbitz  Australia
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A common problem. Try some Rothwell Attenuators.

http://www.decibelhifi.com.au/prod475.htm
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Old 11th June 2008, 01:57 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
what are the gains of the pre and the power amp and what is the sensitivity of the speakers?
Presumably the output of the CDP is between 1.9Vac and 2.5Vac @ 0dBfs?
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Old 11th June 2008, 05:10 PM   #4
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You could insert 2 resistors as a voltage divider, or even a variable resistor (volume control).
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Old 11th June 2008, 11:57 PM   #5
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hi all the pre is a metaxas opulence and i cant find any info on the gain.. the cd player is a opera audio reference 2.2 linear and its output is 2.35 v .im using anthony e holtons nx400 synergy modules that i have made into monoblocks ill get some info on the gain from him today thankyou to all for any help /advice .also the speakers are troels gravesen ekta grande and i would say there sensitivity is 90+
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Old 12th June 2008, 03:01 AM   #6
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hi all my amp gain is 40 to 1 so 1v in and 40v out
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Old 12th June 2008, 03:37 AM   #7
CBS240 is offline CBS240  United States
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Quote:
Originally posted by myhrrhleine
You could insert 2 resistors as a voltage divider, or even a variable resistor (volume control).

Yes. Metal film.....or you could spend more I'm sure.
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Old 12th June 2008, 09:42 AM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by slr 5000
hi all my amp gain is 40 to 1 so 1v in and 40v out
ask Anthony H. if you can reduce the gain of the power amps to below 30times. From +32dB to + 28dB or +29dB.
And what needs altering in the compensation to let this happen?

What is the gain in the pre-amp?
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Old 12th June 2008, 12:46 PM   #9
VHF man is offline VHF man  Australia
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Advice from Andrew T is on the money but I'm willing to bet that changes to compensation values will not be recommended by the designer. There are various parameters to consider such as 20KHz OL voltage gain, noise figure, and slew limiting. A voltage gain of 40 is actually about 6dB above the average and your metaxas preamp is probably designed to drive a wide range of power amps, and may have a voltage gain of about 5. This assumes 15V rails and 2Vrms as a designed input signal. This means that your total av is near 200 which is probably 20dB too much. Padding the output of the preamp seems sensible but you may unavoidably load the preamp with a lower than intended load resistance or feed the power amplifier from a higher than intended source impedance, and actually it's likely to be a combination of the two, so although the voltage gain will be corrected there may be some bandwidth limiting at one or both ends of the audio spectrum. This is because the power amplifier will have an input filter with pole f calculated from approx 100 ohms source impedance (very typical) and the preamp will expect to be seeing 10k ohms or greater at the PA input so if there's an output capacitor it will not be sufficiently large to prevent LF roll-off. However, if your Metaxas preamp can really drive 1K ohm without problems then the simple solution is an L pad with starting values of 1K in series and 200 ohms to ground. This will keep the output impedance low (150 ohms) without overloading the preamp and the gain will be reduced by about 16dB.

Hope this makes sense.
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Old 12th June 2008, 11:48 PM   #10
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hi all i spoke to anthony the amp designer and he said the amp gain could be reduced but he does not recciomend it as it may affect the sound .im very interested in your solution vhf man can you explain firther about how i would make your changes to my pre like where do the connect to and maybe a simple schematic any further help you could give me would be very much appreciated . for the meantime ive purchased some rothwell attentuaters which i should recieve next week but im worried they may affect my sound quality and would prefer to use another way if possible
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