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|11th May 2008, 06:09 PM||#1|
Join Date: May 2004
My opinion on Audio Note M10 schematic - Japan version
Recently I find myself have more interest on Audit note's product, particularly their line amp.
I bought a pair of line stage EI core transformer for their kit series namely L3, and when I refer to their web site, they said that this model can fit for their future product M10 ( because the date of catalog page is year 2006)
I was full of exciting to use this tran. to make a M10 machine based on the Japanese ver. as posted in the internet. The result is very horrible and sounds like a pocketable and housed with plastic box transistors made radio receiver !!!!
I then turn to make the L3 and everything smooth and ok. The sound is good to me at least, but as compared to my friend's C - core with ultra high "B" version, still got difference. Any way, the margin to me is very acceptable and I don't want to pay 4 times money to buy the C-core ultra high "B" to improve the 20% margin appproximately.
Actually, I didn't and never listen the sound produced by M10 and just based on the rumors and its legend !!! Although I am unsuccessful to clone a M10, I still want to try again, because I do like the sound generated from the combination of 6072 and 5687.
After a further investigation of the schematic, I find something very strange and try to figure out the finding whether I am correct or not:
1) 6072 connected as SRPP and direct couple to the grid of a paralleled 5687 which is config. as common cathode circuit.
This seems no problem at all and I accept the paralleled 5687 even it looks unnecessary.
2) Both the 6072 and 5687 is using the same B+ supply, this causes me very curious that in case of direct couple, 5687 must increase the cathode to ground voltage to balance out the positive DCV imposed on the grid of 5687 from previous stage - 6072 by way of increase of the resistor value of the cathod resistor. Provided 5687 is self - bias and it is.
Then what ? If using the same value of B+ for these two tubes, the net plate DCV of 5678 will be very low if under the arrangement above and I don't think this is linear operating point for 5687.
Just based on a roughly estimation, the DCV passed from the 6072 to the grid of 5687 will be probably 110 DCV or above. Based on the B+ is 230 DCV. The 5687 will now only have 230V (the B+) - 110V (the voltage across the paralleled 33K) - 11V (the voltage bias) = 109DCV.
But the M3 or L3 is feeding a 260 DCV to the output transformer's HT point, after the winding resistance, at least 230 DCV or above. Is this arrangement for M10 correct ? I think 5687 will be easily saturated before 6072 !!! We are making tube amp., not semi-conductor, man !!! Only higher plate tension can play dynamic but detail and soft sound !!!
3) If 5687 is really in parallel connection, then the L3's output transformer is still valid for this arrangement ? Ignore the tolerance of the current pass through, the primary resistance of output still valid for a parallel connection ? I don't think so !!! Did you see a paralleled 300B SE using a 3k to 5K output transformer ? If this is true, what is the purpose ? aim to increase lineraility of a single 300B ? Not even to consider the miller effect arises from a paralleled triode ?
If someday I was tired of the sound from this L3, I have to make the following arrangement:
1) only one side of the 5687 used or both sides for two channels.
2) using four regulated power supply for mono block, one is 230 DCV and one is 260 DCV, so that's why there are four, then housed with a seperated chasis. This will cause not two much if under the condition of DIY, because the parts involved should not be expensive except using well known power tran. and black gate cap. for filter.
What do you think, folks ? I absolutely suspect the correctness and feasibility of M10 schematic that "swimming" in the internet world !!!!
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