Aleph-X builder's thread. - Page 201

SGregory · 14th November 2010, 03:41 PM

In post 1995, is that your calculated bias or the bias actually measured on both sides of the amp across the source resistors?

JBL4435 · 14th November 2010, 05:11 PM

Quote:

Originally Posted by SGregory

In post 1995, is that your calculated bias or the bias actually measured on both sides of the amp across the source resistors?

Measured Bias

SGregory · 14th November 2010, 05:16 PM

Good. As before would be interesting to see the output of the diff pair.

JBL4435 · 14th November 2010, 05:26 PM

Quote:

Originally Posted by SGregory

Good. As before would be interesting to see the output of the diff pair.

First of all thank you for trying to help me. I can check the output of the diff pair only tomorrow. It would be nice if you can return

Just for thinking about it meanwhile, do you have an idea what could be the problem?

SGregory · 14th November 2010, 05:32 PM

Since your bias is correct, offset both absolute and relative is within range, I would suspect that the fault lies within the drive portion of the circuit. Look for unmatched feedback or ac gain.
Distortion is apparrent in all three of your traces above but becomes obvious at the higher power levels.

Zen Mod · 14th November 2010, 05:33 PM

gain is shelving down with frequency ;

it's possibly coincided with output mosfet's capacitance ......

what's current through input LTP ?

SGregory · 14th November 2010, 05:44 PM

Very good point ZEN. That would be another point to check.

JBL4435 · 14th November 2010, 05:48 PM

Quote:

Originally Posted by Zen Mod

gain is shelving down with frequency ;

it's possibly coincided with output mosfet's capacitance ......

what's current through input LTP ?

Zen, can you explain this "LTP" I'm not good in abbreviations.

Do you mean it's a given that the power output decrease with rising frequency?
We are talking about 20kHz, not 100 or 200.

SGregory · 14th November 2010, 06:00 PM

LTP = Long Tailed Pair. What ZEN is pointing at is that the current should be measured on the FETS in the LTP. If the current is too low, the capacitance presented by the output devices would attenuate the high frequecy. The attenuation would get worse as the frequecy increases.
Could you point me to the correct schematic for the "Green" boards. It has been several years since I built my x100's. (Like in 2004).

IIRC Mine is built with IRP244's

JBL4435 · 14th November 2010, 06:10 PM

Quote:

Originally Posted by SGregory

LTP = Long Tailed Pair. What ZEN is pointing at is that the current should be measured on the FETS in the LTP.

I'm no novice but how do I measure this?

Quote:

Originally Posted by SGregory

Could you point me to the correct schematic for the "Green" boards. It has been several years since I built my x100's. (Like in 2004).

I use the boards used here

Aleph-X 100w Amplifier Construction Notes

Schematic
http://www.facstaff.bucknell.edu/esa...es/axschem.jpg

Board
http://www.facstaff.bucknell.edu/esa...es/pcb-ext.jpg

14th November 2010, 03:41 PM	#2001
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	In post 1995, is that your calculated bias or the bias actually measured on both sides of the amp across the source resistors? __________________ Living Life Doing the Waltz in 4/4 meter.

14th November 2010, 05:16 PM	#2003
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	Good. As before would be interesting to see the output of the diff pair. __________________ Living Life Doing the Waltz in 4/4 meter.

14th November 2010, 05:32 PM	#2005
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	Since your bias is correct, offset both absolute and relative is within range, I would suspect that the fault lies within the drive portion of the circuit. Look for unmatched feedback or ac gain. Distortion is apparrent in all three of your traces above but becomes obvious at the higher power levels. __________________ Living Life Doing the Waltz in 4/4 meter.

14th November 2010, 05:33 PM	#2006
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	gain is shelving down with frequency ; it's possibly coincided with output mosfet's capacitance ...... what's current through input LTP ? __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; Mighty ZM's Bloggg;I'm dumb

14th November 2010, 05:44 PM	#2007
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	Very good point ZEN. That would be another point to check. __________________ Living Life Doing the Waltz in 4/4 meter.


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14th November 2010, 06:00 PM	#2009
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	LTP = Long Tailed Pair. What ZEN is pointing at is that the current should be measured on the FETS in the LTP. If the current is too low, the capacitance presented by the output devices would attenuate the high frequecy. The attenuation would get worse as the frequecy increases. Could you point me to the correct schematic for the "Green" boards. It has been several years since I built my x100's. (Like in 2004). IIRC Mine is built with IRP244's __________________ Living Life Doing the Waltz in 4/4 meter.

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