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Zerozone class A dc offset adjustment?
Zerozone class A dc offset adjustment?
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Old 12th July 2019, 06:08 AM   #51
ubergeeknz is offline ubergeeknz  New Zealand
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Quote:
Originally Posted by N101N View Post
Mona, are you a lady if I may ask?
What difference would it make?
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Old 12th July 2019, 06:44 AM   #52
N101N is offline N101N
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Maybe I would flirt with her...
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Old 12th July 2019, 08:27 AM   #53
mjona is offline mjona  New Zealand
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Originally Posted by Rallyfinnen View Post
OK, now the magic smoke is out of one of the amps.. Put in a potentiometer to adjust the current, but forgot to check the setting on the potentiometer before I connected power.

Suggestions on other class a kits to buy cheap, same supply voltage..? I'm pretty tired of this one now..
I built a new enclosure but have only one channel to put in it.
I have done a simulation of this amplifier using similar IRF MOSFET devices and the circuit should work without extreme alterations assuming the matching is close - which they are claimed to be. A dc output of 100 mV is not good enough and the only way around this would be to buy a selection of devices as replacement and match them yourself.

Futurlec is a surplus components supplier who have IRF9610 listed for $US0.70 a piece you could buy a couple of dozen for not much outlay.
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Old 12th July 2019, 08:53 AM   #54
Ketje is offline Ketje  Belgium
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Quote:
Originally Posted by mjona View Post
A dc output of 100 mV is not good enough and the only way around this would be to buy a selection of devices as replacement and match them yourself.
Even with matched Q4-Q5 you will have an offset.It is because the different currents in those fet's.
And 100mV out is no big deal.
@N101N, no luck, no lady here
Mona
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Old 12th July 2019, 04:00 PM   #55
mjona is offline mjona  New Zealand
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Originally Posted by Ketje View Post
Even with matched Q4-Q5 you will have an offset.It is because the different currents in those fet's.
And 100mV out is no big deal.

Mona
The simulation gives 9 mV with R1 value changed to 220R, R11 changed to 1k, and R3 changed to 39k - all standard values.

The CCS current is 25 mA and there is a difference in the drain currents for Q4 and Q5 of 1 mA. Output stage Iq is set at 2A with +/- 18V rails.

The substitute MOSFET's in the simulation are IRF9640 and IRFP240. Q5 and Q7 are 2N5210.
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Old 14th July 2019, 06:20 AM   #56
Rallyfinnen is offline Rallyfinnen  Sweden
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I actually made an order for these to see if I can get the faulty board working:
IRFP240PBF TO-247AC N-ch 200V 20A 2
IRF9610PBF TO-220 P-ch 200V 1.8A 2
BC550C TO-92 NPN 45V 100mA 2
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Old 14th July 2019, 10:51 PM   #57
mjona is offline mjona  New Zealand
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Quote:
Originally Posted by Rallyfinnen View Post
I actually made an order for these to see if I can get the faulty board working:
IRFP240PBF TO-247AC N-ch 200V 20A 2
IRF9610PBF TO-220 P-ch 200V 1.8A 2
BC550C TO-92 NPN 45V 100mA 2
You may be lucky to get a match with just one pair of IRF9610.
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Old 15th July 2019, 05:16 AM   #58
Rallyfinnen is offline Rallyfinnen  Sweden
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It seems to me that matching them is a drop in the ocean compared to the rest of the circuit, since swapping them did close to nothing to the offset, and they are not matched now. I think it's only one power fet and possibly the 550 transistor that needs replacing, just ordered some extras just in case.
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Old 16th July 2019, 03:36 AM   #59
N101N is offline N101N
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What is the purpose / advantage of this output stage configuration?
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Old 17th July 2019, 07:02 AM   #60
Rallyfinnen is offline Rallyfinnen  Sweden
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I did a half-hearted attempt to bring the burned channel to life, but now I'm tired of it.. The boards are not so great any more with all the drilling and soldering and cutting traces, and the dc-offset is a bit annoying too.
Looking to buy another class a amp to drive my 4ohm tweeters. Only a couple of watts should do it I think.
Hope for suggestions, and hopefully I can use the 18V bricks for the next ones too.

Here are a few I looked at on ebay (europe)
V18 PNP Sanken 2SA1216 JLH1969 Class A Power Amp Kit 10W+10W Amplifier Kit | eBay
DIY PNP A1216 JLH1969 class A power amp kit 10W+10W amplifier board kit | eBay
PA-05 amp PASS ACA 5W Single-ended Class A FET + MOS amplifier kit 5W+5W | eBay
Assembled Hifi A30 Pure Class A High-current FET Amplifier Board 30W+30W | eBay
HIFI PASS A3 Single-ended Class A Power Amplifier Kit 30W+30W AMP ( 2 Channel) | eBay

Hoping for some input from all the gathered experience here. Which ones are considered good sounding, reliable etc?
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