Silicon Chip ULD Mk3 amp - 0.0006% distortion

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Circlotron

Circlotron

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Joined 2002
July 2011 SC mag.
 

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lineup

lineup

Member
Joined 2005
The circuit has:
- PNP input with mirror output
- Darlington VAS
- MJE15030/31 drivers of
- 2 Thermal Trak pairs for output

All is pretty standard for getting high Open Loop Gain
in a blameless topology.
What is 'extra' is the Thermal Trak for good current control.
The amplifier's concept has been tested good many times before.
With a good power supply, I am sure this amplifier is worth the money :)
 
V

VHF man

Member
Joined 2007
lineup said:
The circuit has:
- PNP input with mirror output
- Darlington VAS
- MJE15030/31 drivers of
- 2 Thermal Trak pairs for output
Click to expand...



Changes from the mk2 version:

Only 2x thermaltrak diodes used
2 pole compensation
vbe multiplier and bias trim adjustment
really big cap in the fb network
lower pole frequency input filter

Adds up to - more consistent performance and low measured THD above 2kHz and below 50Hz.
 
MurphyUHF10

MurphyUHF10

Member
Joined 2010
Hi There,

Thanks for the heads-up :)

I'm a big fan of the MK 1 (stereo kit) which I converted to 'power amp only', and mono-block with custom aussie made transformers,, Sounds great!!

I have no personal experience with the MK 2, but feedback I've always heard is that MK 1 was far superior than the MK 2.. So it will be interesting to see (hear) how Mk 3 compares to MK 1 ??

Thanks
Murphy
 
W

wahab

Member
Joined 2009
J

jcx

Member
Joined 2003
match the high frequency loop gain curves as properly measured around the output devices, "inside" the TMC network and the stability properties are going to be very similar - for well understood engineering reasons...

you may notice several others in the Cordell Book TMC discussion thread made good cases for the essential similarity of 2-pole, TMC

also http://www.diy-audio-engineering.org/forum/index.php?topic=26.0 thread - but drawings, attachments not visible to non-members


the loop gain matching isn't done by simply rearranging the same valued compensation components between 2-pole, TMC
 
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V

VHF man

Member
Joined 2007
jcx said:
match the high frequency loop gain curves as properly measured around the output devices, "inside" the TMC network and the stability properties are going to be very similar - for well understood engineering reasons...
Click to expand...



You mean: you don't get something for nothing.
If you raise the olg above 20kHz by 20dB you are going to compromise stability regardless of method.

I have modified a mk2 version of the amp and it uses mostly TMC but also a bit of CMC. With an extra 20dB of 20kHz OLG thd is obviously very much reduced.

I favour TMC over TPC based on comparisons between the +ve slew rate - as well as my ears that tell me TMC sounds better with this design.
 
ostripper

ostripper

Member
Joined 2008
No longer impressed.

Is this amp 6 ppm THD20 ? At what output ? 6ppm is not hard to achieve these days. But can it "hold" that @ 100v p-p 20Khz ? 4R , anyone ? . If it's not a triple , highly doubtful ....
It does look like a nice build. Sporting those T-traks and using a real Vbe + 2 of the internal diodes must make for near perfect thermal response. :) Still , it is what it is. :D
PS - I can now beat TMC ... without TMC ( 2 designs).
OS
 
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W

wahab

Member
Joined 2009
jcx said:
match the high frequency loop gain curves as properly measured around the output devices, "inside" the TMC network and the stability properties are going to be very similar - for well understood engineering reasons...

the loop gain matching isn't done by simply rearranging the same valued compensation components between 2-pole, TMC
Click to expand...

Agree, but then most of the TPC advantages will be lost.
Although the result is better than classic miller comp THD wise,
it s inferior to TMC when looking at both THD and stability.
 
V

VHF man

Member
Joined 2007
ostripper said:
Is this amp 6 ppm THD20 ? At what output ? 6ppm is not hard to achieve these days. But can it "hold" that @ 100v p-p 20Khz ? 4R , anyone ? . If it's not a triple , highly doubtful ....
It does look like a nice build. Sporting those T-traks and using a real Vbe + 2 of the internal diodes must make for near perfect thermal response. :) Still , it is what it is. :D
PS - I can now beat TMC ... without TMC ( 2 designs).
OS
Click to expand...


Rated power, 8 ohms, 1kHz.

THD does degrade to 20ppm at 10 kHz but the reason is (apparently) due to minor limitation in the layout of the speaker traces. There will eventually be a mk4 to address it but we'll need to wait. However, there's nothing to stop constructors from routing the speaker earth return close to the rail feeds, and locating the output inductor further away from the vas.
 
P

prairiemystic

Member
Joined 2004
I read the mk2 had some blowup issues attributed to the VAS Q8 not being current-limited, SC added a 22k resistor on the (grounded) collector to fix. Scary that this mod and a few others don't appear on the SC website. Hopefully addressed in the mk3.
Looking forward to my issue arriving, postal strike here sucks.
 
W

wahab

Member
Joined 2009
prairiemystic said:
I read the mk2 had some blowup issues attributed to the VAS Q8 not being current-limited, SC added a 22k resistor on the (grounded) collector to fix. Scary that this mod and a few others don't appear on the SC website. Hopefully addressed in the mk3.
Looking forward to my issue arriving, postal strike here sucks.
Click to expand...

It had several non solved issues, dont know to what extent these
were solved in the current version..
 
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