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Old 13th September 2005, 11:02 PM   #1
mr.lex is offline mr.lex  Sweden
diyAudio Member
Join Date: Sep 2005
Unhappy Amp construction?!

Why is it big different between channels???
Sorry for my bad english.
I have 4 Macrom synthesis1000 evolution amps, which I can adjust in an independent way. I have big difference in the channels. The left channel has more power, which the right channel has not. I mean the difference between left and right is about 3dB and it is a big difference. I know all amps have a little difference between gains but not 3dB! When I adjust the left channel about 11 o'clock and the right channel about 2 o'clock then I have the same power. All my 4 amps have exactly the same problems, which the left channel, have more power and right channel have less power. This amps have a switch in circuit witch I can disactivate preamp and crossover and in this mode the amp is driven with a fixed sensitivity of 1.1V and the phase rotates 180' only right channel. (This mode because the sound quality will be the same as really home hifi amps) Therefore is important the right speaker output connection must be inverted. Now, I have no control over my input sensitivity gain adjustment and crossover. Both channel have the same output power. Which in this case it is correct. But I don't got it, when I have the switch on built-in preamp which in this case I activated input sensitivity gain and crossover the channels is different... This amps cost $1500 each and are very expensive. Now, Macrom say it is normal because into the pre-amp section there is an inverter circuit between channels, this circuit allows the mono configuration into the output speakers which I have very difficult to believe.
Thanks alot if some guys kan help me.
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Old 14th September 2005, 03:14 AM   #2
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Is there an imbalance if you use a y-cable to feed both channels exactly the same signal?

If so, there is a defect in the amplifier. An amplifier company that can not get the gain to match in the inverter circuit wouldn't be able to get anything to work properly. There's a chance that there was a mix-up on the assembly line and one part (probably a resistor) is wrong in all 4 amps.

If I were you, I'd bug them until they replace or repair the amplifiers.

If you have a test tone CD, play a tone near 60Hz (non 'true RMS' meters are more accurate at frequencies of ~20-400hz) and measure the voltage on both channels. Use a y-cable when doing this to assure that the signal is precisely the same for both channels. Set the gains all of the way up or all of the way down (to make sure that they are in precisely the same position). Set the level so that you have the best resolution (most digits right of the decimal point). For many meters, it's going to be in the range of 3 volts.

Make and record as many measurements as you can with the switches in various positions. If you give them hard numbers and you show that you know what you're talking about, you're more likely to get results.
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Old 14th September 2005, 03:56 AM   #3
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Try swapping your left and right signal cables. If the problem moves to the other channel, then there is a problem with your source.
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Old 15th September 2005, 12:05 AM   #4
mr.lex is offline mr.lex  Sweden
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Join Date: Sep 2005
thanks a lot guys,
my first reaction was my source but it's not.
Mr Perry Iím coming tested whith Y-cable as you told me and I come back to you soon after test result.
I had contact with amplifier company Macrom many times and he was very helpful. He wants replace me the new one if I want and he promise me the new one are the same and he sad it's not any wrong whith this amps.
I had tested this amps whitout Y-cable before I contact you and it is very strange when I mix-up to maximal I have same power out puts between channels. More I mix down more differences I have between channels! Why the factory built or chooses strange way to designed this amp. Something is wrong with the design, which the manufacture wont acknowledged their mistake, or what they sad about into the pre-amp section there is an inverter circuit between channels, this circuit allows the mono configuration into the output speakers as he told me is maybe true!
This amps design, which I can drive, output 2 channels in mono (both L mono and R mono) or ST or only left mono (bridged) or trimode etc.

I have service Manuel over (preamplifier) and there is an inverter circuit if you want se that.
Iím very sorry for my bad English:-)
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Old 15th September 2005, 12:54 AM   #5
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Virtually all amplifiers have an inverted channel. That's what makes them bridgeable. There is nothing about the inverter that will reduce the level of the signal. It simply flips the waveform (when the normal signal is going positive, the inverted signal is going negative). The amplitude of each will be the same.

If you perform the tests I suggested, please post the results?

If you have the schematic for the preamp section, post it. If you are concerned that macrom may object, email it to me.
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Old 21st September 2005, 06:24 PM   #6
mr.lex is offline mr.lex  Sweden
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Join Date: Sep 2005
Default Thanks a lot,

Mr Perry I have send you email the test result and the schematic for the preamp and amp section.
thank you very much for everything.
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