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Old 25th March 2013, 04:00 PM   #1
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Default Audio Note M7 line stage preaamp!

I have DIY one Audio Note M7 preamp, but now the problem I facing is the output gain is too high for my power amp, I hardly could turn the volume over 8-9 o'clock. Does anyone know what is happened and how to solve it, thanks.
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Old 26th March 2013, 08:54 AM   #2
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Remove the line stage...Your power amplifier probably has sufficient gain without having to use a line stage.
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Old 26th March 2013, 09:33 AM   #3
AJT is offline AJT  Philippines
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a passive preamp consisting of just a volume control helps...
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Old 26th March 2013, 10:50 AM   #4
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true, but since you've build M7, i guess you want to use it .. maybe examining internal gain structure of your power amp (maybe even your source) could it make possible to integrate your M7. ..or just rebuild it with tube that has lower gain.

in fact i was in the same situation. my M7 sounded great but what bothered me was that my SS power amp simply didn't need it. so i ended up adding a power section to the M7 and practically making a SET amp.
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Old 26th March 2013, 11:45 AM   #5
DF96 is offline DF96  England
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Add an attenuator (i.e. a pair of resistors forming a potential divider). As a start, set the attenuation equal to the gain of your line stage. Then you can relabel the line stage as a room heater!
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Old 26th March 2013, 11:49 AM   #6
john65b is offline john65b  United States
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What tube are you using?12AU7? 5687? There are many different M7's out there...
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Old 26th March 2013, 04:58 PM   #7
GoatGuy is offline GoatGuy  United States
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Wink Taming the Pre

Specifically - get the schematic listed, and I'm sure I (along with another dozen) DIYaudio members will make very specific recommendations as to how to "tame" the output.

The most trivial, of course, is just to use a resistive divider. It has the added benefit of synthetically lowering output impedance. And, its darn cheap. And it doesn't change the operating characteristic of the amplifier very much (if at all). And did I mention, its cheap? OK. Its cheap. And safe, and easy, and cheap. Cheap, cheap, cheap!

Other posters have identified "just get it out of the system" ... but you might like the colorizing it does to the signal. I would NOT however put an input attenuator on it - that just begs to increase noise overall.

Anyway, there you are.

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Old 26th March 2013, 06:50 PM   #8
piano3 is offline piano3  United Kingdom
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You could get rid of the upper triode in the input cascode, running that stage as a simple common cathode stage and then use the discarded triode section as the upper valve in a beta-follower before the final cathode follower output stage. If you are using 12ay7 as per the schematic then I don't suppose that the miller capacitance of the input stage would be too much of a problem.
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Old 26th March 2013, 06:53 PM   #9
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Quote:
Originally Posted by piano3 View Post
You could get rid of the upper triode in the input cascode, running that stage as a simple common cathode stage and then use the discarded triode section as the upper valve in a beta-follower before the final cathode follower output stage. If you are using 12ay7 as per the schematic then I don't suppose that the miller capacitance of the input stage would be too much of a problem.
i don't know about the variations but i had one with a single 5687.
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Old 26th March 2013, 07:10 PM   #10
piano3 is offline piano3  United Kingdom
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The original Japanese M7 was a 4 stage phono preamp using 12ay7(or, more accurately 6072WA) only. The stages were cascode followed by RIAA network, common cathode followed by selector, balance and volume controls, then common cathode direct coupled to output cathode follower. It therefore has potentially enormously high gain, somewhat lowered by unbypassed cathode resistors in stages 2 and 3.

I am sorry, I have just noticed that this is a line amp only. Was the schematic part of an Audionote UK kit?

Last edited by piano3; 26th March 2013 at 07:14 PM.
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