F4 power amplifier - Page 155

jleaman · 25th November 2007, 04:09 AM

Quote:

Originally posted by carpenter

Sure, I'd take a chance, but make a subtle change. If things work in your favor, continue--less chance of letting out the magic smoke.

No magic smoke, we don't want that.

carpenter · 25th November 2007, 04:20 AM

Dave, are you using proper anti-static techniques when handling your FETs?

It's freezing cold, where you're located, and that means static electricity abounds.

Just checking all the possibilities.....

Variac · 25th November 2007, 04:52 AM

Quote:

Which F4 version do you own?

6/4 Eleanor! (6/4/07 version) The PD boards. BUT it is in pieces at the moment, and with my schedule, will be until right before Christmas.

Magura was one of its midwives but he probably can't give you measurement info unfortunately..

carpenter · 25th November 2007, 05:06 AM

Quote:

Originally posted by Variac

6/4 Eleanor! (6/4/07 version) The PD boards. BUT it is in pieces at the moment, and with my schedule, will be until right before Christmas.

Magura was one of its midwives but he probably can't give you measurement info unfortunately..

Darn...

jacco vermeulen · 25th November 2007, 09:13 AM

Quote:

Originally posted by carpenter
quite the answer I wanted.

You can put a brick and a piece of metal on a scale and have static equilibrium, that doesn't mean they're the same but only on opposite sides.
Complementary wise, Mosfets are less well matching than Bipolars, and vertical Mosfets are worse than lateral devices.
The reason why some prefer quasi-complementary and Mr Hansen has to go the fully balanced symmetrical way to skip global NFB.

DaveM · 25th November 2007, 02:41 PM

About the static, I am aware and do my best. I make sure to touch ground before picking anything up. I would guess that if I had taken something out with static that it would not be passing a signal and making music. And the identical behavior between the two channels signals to me, in my limited experience, that everything is functioning properly, just that there is a mismatch or imbalance somewhere.

The diodes are correct. 1N4736.

Bias process is as described. Center P2, set P1 to zero. Power it up. Bring P1 up to adjust bias. Voltage across bias resistors to 200 mV per manual. Then adjust the DC offset with P2, measuring between ground and + out.

So far the smoke is still in. I hope to keep it that way.

carpenter · 25th November 2007, 04:11 PM

Quote:

Originally posted by DaveM

Bias process is as described. Center P2, set P1 to zero. Power it up. Bring P1 up to adjust bias. Voltage across bias resistors to 200 mV per manual. Then adjust the DC offset with P2, measuring between ground and + out.

Sounds good to me.

It's when you bring the bias measurement up to 200mV that the offset swings to 30 volts, yes? How far can you adjust the offset with P2?

Edit: how about a close-up pic of your pcb?

DaveM · 25th November 2007, 05:36 PM

The 30 V DC offset is with P2 turned to zero. When I start with it in the middle the offset in higher.

About the picture.... I intentionally left the leads long on all my changed parts. They are RS parts and I plan to change them out with Vishay's once I get it running and the values dialed in. Keeping the questionable components high off the boards makes them a whole lot easier to work with.

DaveM · 25th November 2007, 05:37 PM

Another pic

jleaman · 25th November 2007, 05:38 PM

Quote:

Originally posted by DaveM
Another pic

Pots are in backwards

25th November 2007, 04:20 AM	#1542
carpenter Paper mache horn fabricator diyAudio Member Join Date: Mar 2002 Location: Oregon City, Oregon	Dave, are you using proper anti-static techniques when handling your FETs? It's freezing cold, where you're located, and that means static electricity abounds. Just checking all the possibilities..... __________________ I enjoy audio so much that I constructed a web site. I share my ideas at: www.inlowsound.com

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25th November 2007, 02:41 PM	#1546
DaveM diyAudio Member Join Date: Feb 2003 Location: Vermont	About the static, I am aware and do my best. I make sure to touch ground before picking anything up. I would guess that if I had taken something out with static that it would not be passing a signal and making music. And the identical behavior between the two channels signals to me, in my limited experience, that everything is functioning properly, just that there is a mismatch or imbalance somewhere. The diodes are correct. 1N4736. Bias process is as described. Center P2, set P1 to zero. Power it up. Bring P1 up to adjust bias. Voltage across bias resistors to 200 mV per manual. Then adjust the DC offset with P2, measuring between ground and + out. So far the smoke is still in. I hope to keep it that way.