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Old 9th May 2012, 09:00 PM   #1461
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Quote:
Originally Posted by imix500 View Post
Ok, in that case how much lower do I want to go? Does a little go a long way?
What is the VGS required by your mosfets to conduct at around wanted current?

Set resistors for near enough and use pot to twidle
Keep pot influence to minimum is best IMO.
Take reading before you solder mosfets to board easy peasy and which way is clokwise in my particular pot question sorted + is my Jfet duda working question ansvered as well.
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Old 9th May 2012, 09:22 PM   #1462
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I will try to post Vgs vs Id curve for 12p20 tonight. I will add it to other curves of N channel fets. This should give folks an idea of what Vgs yields a given Id. This will help determine needed Id of jfets as BKsabbath suggested. Mine measured .5(sj74) and .6(sk170) across jfets Rs. This gava current needed to bia soutput fets to 1A. Reason you need more current for n channel jfet is higher Vth of P channel output fets. In this regard, FQA16n25c is closer match to Nchannel compliment than original 19n20c, by a smidge.
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Last edited by buzzforb; 9th May 2012 at 09:25 PM.
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Old 9th May 2012, 09:23 PM   #1463
imix500 is offline imix500  United States
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Hello all,
Ok thanks for the info. I have a mouser order going anyway, so I'll pick up some 10ohm 1W resistors to parallel as an option.

I don't have output devices yet and I'm not 100% on where they are coming from (more like 98%) so I would have to go by data sheet values.
I'd prefer not to have to desolder too many times, so the stuffing will continue with other components until outputs are finalized.
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Old 9th May 2012, 09:24 PM   #1464
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That would be great buzzforb.
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Old 9th May 2012, 09:51 PM   #1465
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Quote:
Originally Posted by imix500 View Post
Hello all,
Ok thanks for the info. I have a mouser order going anyway, so I'll pick up some 10ohm 1W resistors to parallel as an option.

I don't have output devices yet and I'm not 100% on where they are coming from (more like 98%) so I would have to go by data sheet values.
I'd prefer not to have to desolder too many times, so the stuffing will continue with other components until outputs are finalized.
Very soon!
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Old 9th May 2012, 11:04 PM   #1466
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Quote:
Originally Posted by imix500 View Post
in that case how much lower do I want to go?
Stop as soon as she starts giggling, otherwise you've gone too far.
Quote:
Does a little go a long way?
She will be the judge, and definitely let us know when you have results.
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Old 9th May 2012, 11:30 PM   #1467
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LMFAO!!
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Old 10th May 2012, 02:02 AM   #1468
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updated graph with P channel part. You can see why the extra current is need from the N channel Jfet. Hope to run more thorough test this weekend on Pass testing rig. May even try some distortion test with new emu0404.
Attached Files
File Type: doc FQA comparison.doc (51.0 KB, 57 views)
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Old 11th May 2012, 09:02 PM   #1469
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If we are looking down on the boards in the linked photo, as far as I can see Q5 and Q6 are still wrong. The double line is on the wrong side. The Emitter should point to the JFET's Drain and they don't. I had to draw them on a piece paper and turn it upside down to make sure.
I put them in according to the graphic on the board and had to unsolder them in the prototype V2 boards and turn them around.
Secondly there are not enough ground holes. The link hole has no open ground hole to link to. Input ground wire, power ground wire, Link to where? double wires in one hole?

One more thing, in this new version, where is the hole for the speaker output? All the O/P holes in the input board are full, you wouldn't want to take the speaker wire from the N or P boards. You should connect the speaker wire to where the N and P boards connect together, at the input board, right?.

Rush

Rush,

I believe you are correct regarding Q5 & Q6.
Let me double check again.

I'll revert back soon.

Andy
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Old 11th May 2012, 09:44 PM   #1470
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Originally Posted by UKToecutter View Post
Rush,

I believe you are correct regarding Q5 & Q6.
Let me double check again.

I'll revert back soon.

Andy
In regrds to the Link;

If using as SE you wire a link between 'Link' and Input Ground.
For balanced you wire a link between the two 'Link' terminals.

In regards to the Output and Ground Connections, the intention was that the Output connections are collected together at the chassis output terminals.
The Grounds are 'star' connected from the PSU.

If there is an error in my thinking I'm happy to be corrected.

Andy
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