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The MONGREL (supersym II)
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Old 15th August 2010, 11:33 PM   #301
ostripper is offline ostripper  United States
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Quote:
Originally Posted by AndrewT View Post
r16=4k7 for +-70Vdc????
R18=4k7?
Works perfect ...Andrew. The ones I have now are 2.7/2.7K , exact circuit , 45-0-45V. To keep the 7ma VAS standing current , the 4.7K's are needed. (See below 75-0-75VDC / 4.7k)

Edit - I see the error R17-18 are the 4.7k's

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Last edited by ostripper; 15th August 2010 at 11:40 PM.
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Old 17th August 2010, 10:17 AM   #302
ostripper is offline ostripper  United States
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At it again , after a break. (Pix 1) is the NEW PB60LP low profile for those with "IDI BIDI" amplifier cases , it will be done tomorrow. Also for tomorrow , I should have the NEW IMPROVED PB60 / PB250 done. NOTHING was wrong with the last ones.But after testing , research , and discussion... 2 ground points are the best for these boards.

And here is why .... PMA pointed out that large rail caps on the main board increase noise and foul up the star with their "filthy" current pulses. I LIKE big onboard rail caps for the simple reason that they negate the effects of the FUSE!! (yes, the fuse is a resistor) and they add a noticable "edge" to the sound. SO , why not just have their ground separate and feed that individually back to the main star of the amp's power supply. IT works , On the "supersym" , it halved my already low noise floor ... a worthwhile design change.

Andrew T. advised on "guard rings" and taking negative feedback in the most pure form back to the differential. This is now the "standard" (a shielded cable with the shield at the same potential as the NFB signal) coming direct from the inductor to the voltage boards NFB input.

And , the "biggie" Greg erksine informed me of the miswired "doug self magic resistor" on the onboard Vbe. This has been corrected. Anybody that has made the PB250/60 could just jumper (omit) that resistor anyways. BELOW are all 3 boards with all 3 "fixes". Tomorrow night they will be all ZIPPED and ready to go.

G1 and G2 - G1 is the "dirty ground" ,accepts loudspeaker return and goes back to the main PS star with 12 or 14 ga. wire. G2 is the "clean" ground , it is only a reference for the C/R/C filter - capacitance multiplier as well as the voltage board ground. IT only needs a 18 Ga. wire returned to the PS main star.

ALL BOARDS color code .. GREEN = both grounds/ RED=V+ / BLUE=V- /YELLOW= signal paths /ORANGE=positive drive / Light BLUE= neg. drive...

ALSO , next to come is the PB200M , which will be a quasi MOSFET 4 device masterpiece to round out the power board lineup. (last pix)

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File Type: gif PB60LP_overview.gif (79.5 KB, 496 views)
File Type: gif PB60_overview.gif (144.0 KB, 482 views)
File Type: gif PB250_PCB_overview.gif (113.4 KB, 467 views)
File Type: gif PB200M.gif (24.1 KB, 472 views)
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Old 17th August 2010, 10:30 AM   #303
AndrewT is offline AndrewT  Scotland
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post302,
careful with the use of "magic" for that extra Vbe multiplier resistor.

There is another paper (can't remember the Author) on introducing a "magic" resistor into the topology to improve the sound quality. It is quite different from the multiplier's extra resistor.

R80 is still in the wrong place.
The driver is tapped into the bottom of R80 adjacent to the Vbe transistor's collector.
As a result the capacitor must now be moved to the VAS side of the multiplier. C86 connects the collector of Q8 (VAS) to the collector of Q10 (CCS)
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Last edited by AndrewT; 17th August 2010 at 10:35 AM.
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Old 17th August 2010, 10:55 AM   #304
keantoken is offline keantoken  United States
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What is C85 for?

- keantoken
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Old 17th August 2010, 11:10 AM   #305
keantoken is offline keantoken  United States
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And to help compensate for the capacitance of the lower outputs, how about trying a small cap parallel to R88, equal to the capacitance seen by Q99?

Also the MJE3x0 drivers seem a little low-Fi...? Especially since everything else is high-tech japanese devices?

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Old 17th August 2010, 01:26 PM   #306
ostripper is offline ostripper  United States
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Quote:
Originally Posted by AndrewT View Post
post302,
careful with the use of "magic" for that extra Vbe multiplier resistor.

There is another paper (can't remember the Author) on introducing a "magic" resistor into the topology to improve the sound quality. It is quite different from the multiplier's extra resistor.

R80 is still in the wrong place.
The driver is tapped into the bottom of R80 adjacent to the Vbe transistor's collector.
As a result the capacitor must now be moved to the VAS side of the multiplier. C86 connects the collector of Q8 (VAS) to the collector of Q10 (CCS)
I did not update the schema , the boards reflect the change, although. I get the hard part first (the boards), then go back do "cleanup" (match BOM , schema, parts overview...). Also , I reuse previous simulator builds to make new ones...

"Magic resistor" AHHHH 1

I almost forgot, To eliminate or reduce the "memory effect" the french dude put them between active and cascode trannies. (a GX amp update ). Link is here : Memory Distortion Philosophies - Part 5 : Circuits, continued

Quote:
By keentoken - And to help compensate for the capacitance of the lower outputs, how about trying a small cap parallel to R88, equal to the capacitance seen by Q99?

Also the MJE3x0 drivers seem a little low-Fi...? Especially since everything else is high-tech japanese devices?

You don't like MJE340/350's .... those poor , poor devices , nobody likes them .. except tube guys Would you suggest the KSA/KSC's , so the IRF's could "sing" better at 4 mhz ?? I will try Q99..


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Old 17th August 2010, 01:31 PM   #307
AndrewT is offline AndrewT  Scotland
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you're forgiven.
Nobody can do everything at the same time.
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Old 17th August 2010, 01:32 PM   #308
ostripper is offline ostripper  United States
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What is C85 for?

- keantoken
At 20k , C85 improves stability of the Vbe , reducing Xover point deviation to under 1mV on all the PB's. Still researching WHY?
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Old 17th August 2010, 01:36 PM   #309
ostripper is offline ostripper  United States
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you're forgiven.
Nobody can do everything at the same time.
Just to lay it to rest.. is this (pix) the correct way. (reflects the boards)

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Old 17th August 2010, 01:38 PM   #310
AndrewT is offline AndrewT  Scotland
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c89 is in the wrong place.
It should be between the VAS and it's load (the CCS or bootstrap)

I wonder if that accounts for the very high current in the cap when the sim modeled behaviour?
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Last edited by AndrewT; 17th August 2010 at 01:41 PM.
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