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Old 5th December 2001, 09:53 PM   #21
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Koy, I have two questions

How do you measure 400mV PER 0.47 Ohm? (Or is it simulation?)

Did you consider putting an parallel 0.47 Ohm for each source resistor in your ALEPH30? (This would mean 6 extra resistors in parallel to the existing source resistors of both the current source and gain stage FET's) Or you could simply swap the 6 0.47 for 6 0.22 Ohm)

Either option would roughly double your quiescent current without changing R17,R19(1.5k and 47.5k)

Dissipation of heat will surely double as well. So provide for more heathsinking!!

I don't think it is a good solution, because your FETS will dissipate twice as much heat. Hence, each IRF244 will have to get rid of roughly 35 Watts. This I regard as little to much for a single device. But this is only my opinion.
I hope your supply (transformer, capacitors) can handle the extra current demand as well. This of course without the famous hum penalty.

Regards



[Edited by rtirion on 12-05-2001 at 05:00 PM]
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Old 6th December 2001, 05:11 PM   #22
Koy is offline Koy  Czech Republic
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AD measuring: With multimeter. On 0.47ohm resistor ( on both sides). It is true that resistors differ a little (I was not able to match IRFP) from 0.35 to 0.56 ohm to get equal current (without signal of course).
My heatsinks are able to cool more power ( and transformer to supply - it has 5OOVA).I would like to go to about 1.5A per trans(more will be too much).I considered to use 0.33ohm instead of 0.47.
With simulation I noticed interesting thing - using 0.33 ohm with 4k7 and cca 33k ( instead of 47K or 22Ok) lowers significantly distorsion.I try to find datasheets of IRFP244 (to know where on the curve it works).
Unfortunatelly I have no possibility to measure the distorsion. Sound is not bad but I still feel significant "instability" on the backround or lack of "quiet and clarity " in the sound. Any suggestions? I dont know.
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Old 9th December 2001, 10:09 AM   #23
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Koy,

Sorry for the late reply but here it is:

I do not understand how you can measure a voltage on each source resistor in the ALEPH30. As I mentioned earlier I think all three resistors 0.47 Ohm are parallel connected. So an in-circuit measurement of a voltage accross a single 0.47 ohm is not possible. Or am I missing something here?
However you could measure the current through each by diconnecting one side of the resistor and putting an amp meter in. But this it not so easy.

I think your 0.33 Ohm idea is the way to go if you are looking for the proper way to increase the quiescent current.

On sound quality, my ALEPH 3 is very quiet with good clarity. There is almost no harshness in the mid's and high's. As you probably know, in a lot of amps, this harshness is regarded as clarity or detail.
Listen to voices pronouncing strong K's, T's, P's and of cource S's.

Did you hook up an oscilloscoop to find any (small) oscillations?

Regards
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Old 9th December 2001, 11:49 AM   #24
Koy is offline Koy  Czech Republic
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Sorry, but there is only one(!) 0.47 resistor connected to each source of each IRFP. Not three paralelly. Circuit is the same as A3 has but one transistor ( ad 0.47) is added. That why I can measure the voltage - between source and drain of contralateral transistor (Q106 and Q108 as A3 has).
Osciloscope is good idea.I try to find somebody who has it.I was thinking about some exact measurements for a check.
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Old 9th December 2001, 06:33 PM   #25
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I guess you are right, looking at the simplified schematic of the ALPEH30.
If all sources were connected and the 0.47 resistors were parallel connected, the sharing of the quiescent current would not be evenly distributed among the IRF244's and the 0.47's.
The X3 for each assembly R28,Q6,R34 pointed me in the wrong direction. It is something to be carefull with in other schematics.

Regards
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Old 1st April 2002, 07:21 AM   #26
Koy is offline Koy  Czech Republic
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I am experimenting with A30, I have to say I turned back from A30 to better sounding old A3.
Does anybody tried to remove R113? Another question ( maybe silly).Sound seems to me to have a little pronounced hights. Whats is the value of C104 - "0.001" means 1nF?
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Old 1st April 2002, 08:25 AM   #27
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Yes, 0.001 means 1nF. It keeps things a little more stable.
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Old 1st April 2002, 09:12 AM   #28
Koy is offline Koy  Czech Republic
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Thanks.Yes this cap limits gain on higher frequencies.Only think I dont know is why A30 uses ordinary RC feedback ( and 10pF instead of 1n) and A3 only this cap in position where increases input capacitance. Do you have any experience with omiting resistor R113?
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Old 1st April 2002, 08:57 PM   #29
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No, I do not have experience removing R113.

But AC wise you loose a litlle local loop around Q105. I think this will have some but minor effect on the complete CS.
DC wise you could say removing R113 is the same as increasing R113 to a very high value. As you know above 220K the bias is not changing anymore. Lower values of R113 will rob Q105 base current. I still do not think this is such a good idea. I have done some sims and measurement showing results that confirm this.

Hope this helps a little
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Old 1st April 2002, 09:51 PM   #30
Koy is offline Koy  Czech Republic
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I got the same results by simulations.Now I am very bussy to do it on the board. I only wanted to know other oppinion.
Anyway.I would like to now why Mr. Pass uses that "strange" values.
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