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Old 21st November 2002, 03:42 PM   #21
Thomas is offline Thomas  Denmark
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Quote:
Originally posted by planet10
1/ How much heatsink do i need? The attached picture is a set of 4 i have. For reference they are sitting on a true 2x6. A ballpark calculation of 140 in^2 per sink. Can i live with 1, or do i need 2 per amp? Or is even that not enuff?
Hi Dave, I have calculated your heatsinks for you, and each heatsink should be around 1.6K/W. This should be enough if you use 2 per channel like I do. But, your heatsinks will be hot, and with the 18 V rails, this leaves little space to overclock... sorry biasing. You can probably get away with little over 1A but not much. The formula used is the one at Rod Elliot's homepage. 140 sqare inch is 903 sqare cm.

50 / sqr(cm^2) > 50 / sqr(903) = 1.66K/W
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Old 21st November 2002, 05:06 PM   #22
planet10 is offline planet10  Canada
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Quote:
Originally posted by Thomas
each heatsink should be around 1.6K/W. This should be enough if you use 2 per channel like I do.
Thanx. Guess i'll have to augment them by using plate aluminum for the top & bottom. That could supply some needed breathing room.

dave
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Old 22nd November 2002, 10:52 AM   #23
argo is offline argo  Estonia
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Mini - A building project update.
So, as Q4, Q5 and Q2 were mounted incorrectly in my amp board, everything I measured previously turned up wrong as well. Rewired the boards yesterday and now DC Voltages are closer to the goal.
Voltages across emitter - collector of Q4 and Q5: about 5 volts.
Same 5 volts across R4:
D1: still 9.25 V
R18 (0.33 ohm) - 0.49V = 1.5 A DC bias;
R19 (0.33 ohm) - 0.42V = 1.3 A DC bias
Bias on upper and lower part of output I think can be made more equal by increasing the value of R12 from 750 ohm to about 950 -970 ohms. Didnít try that out yet.
Capacitor multiplier power supply rails were kept pretty much equal by amp now - around 16.5 V.
The most important part Ė the sound: tiny bit less distortion but still unlistenable.
Current project status: put on hold. (till I develop as bright sense as Grey or Nelson or somebody else reports about his working amp)

Cheers
Argo
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Old 22nd November 2002, 01:16 PM   #24
Thomas is offline Thomas  Denmark
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Default Hey Argo!

NOOOOOOOOOOOOOO!!!!!!!!!!!!

Don't quit now, man!!!

Mine works fine. Look at: http://members.fortunecity.com/minialeph/

Try the Aleph 3 stock values instead. Power resistors= 0.47, R10=1.5K. Maby decreasing R11 to 33K if you get too high bias.
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Old 22nd November 2002, 01:53 PM   #25
argo is offline argo  Estonia
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Default Re: Hey Argo!

Quote:
Originally posted by Thomas
NOOOOOOOOOOOOOO!!!!!!!!!!!!

Don't quit now, man!!!

Mine works fine. Look at: http://members.fortunecity.com/minialeph/

Try the Aleph 3 stock values instead. Power resistors= 0.47, R10=1.5K. Maby decreasing R11 to 33K if you get too high bias.
R10=1.5k in my amp. I lowered R11 with several values and things got worst.
Wouldnít changing the power resistors affect lowering the DC bias current? I think I need even more current than this 1.5 A amp has now. But I cannot afford that because amp heat sinks are running on the limit already.
How can I describe the sound I am getting out of it? The sound is not just bad in audiophile sense - it is terrible for anyoneís ear. I got that same sound out from my JHL when constant current source fried - itís like broken 2W radio playing on maximum level.
I was starting to suspect some bad input fets. I got 6 of them, relatively cheap, also I didnít match them. Shall I buy another bigger set of them from different and more expensive source and match them - I havenít decided yet. But there is something very wrong with that amp right now but I can not figure out the actual cause yet. I have made tons of simulations with every kind of values and the amp should work in most cases. I will read through Nelsonís Zen variation 2 an 4 articles and aleph manual to get a grasp of the aleph current source circuit functioning. Thank you for suggesting to change these power resistors anyhow. Iíll try to change them tomorrow.

Argo
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Old 23rd November 2002, 10:04 AM   #26
Thomas is offline Thomas  Denmark
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Default Re: Re: Hey Argo!

Quote:
Originally posted by argo

Wouldnít changing the power resistors affect lowering the DC bias current? I think I need even more current than this 1.5 A amp has now. But I cannot afford that because amp heat sinks are running on the limit already.

Argo
Yes, changing the power resistors affects the bias. However, the sound should be just fine at 1.5A with 6 ohm speakers.

Matching the input pair Q1 and Q3 wont hurt and will probably do the sound good. I, for starters didn't match them and the amp still sounds very good. For quality of the fets used, I dont know what you got. I noticed you use BC 547, but did you turn it around because the pinout are different from the mpsa devices? I use the BC547C, but tried B version also - no difference to sound at all. You dont need to make new boards because of the BC devices, the mid pin are the same, so just turn the transistor on the board 180 degrees.

Good luck building.
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Old 23rd November 2002, 02:05 PM   #27
argo is offline argo  Estonia
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Default Re: Re: Re: Hey Argo!

Thomas,


Yes I did turn BC547B around. For now I have changed it for BC550A in. But those transistors should not alter any sound quality and can be generic type because they are there just to keep the reference voltage across source resistors as I understood. I must have some more major fault with the amps. Either it is bad fet, wrong device connection somewhere I canít see yet or I donít know what. One important thing I didnít report previously is that while other DC voltages seemed to mesure OK, DC offset is still about minus 1volt.
I donít have boards yet. I just soldered components on Veroboard using devise pins to connect them - very messy and time consuming imho, especially when you want to start modifying it with changing parts in and out. Thatís why I thought I will probably put it on the PSB sometimes and did the layout design (which is incorrect as I reported previously. Not only the BJTs are upside down but the input ccs fet is connected wrong. I asked webmaster to remove the picture put it's still there.).

What I plan to do is to put the amp under scope and check it step by step to find where the problem starts. This will take some time because I need to carry it to my friendís hose cause I donít have scope myself. Hopefully next weekend sometimes.



Argo
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Old 23rd November 2002, 09:51 PM   #28
Thomas is offline Thomas  Denmark
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Default Re: Hey Argo!

Quote:
Originally posted by argo
I asked webmaster to remove the picture put it's still there.).
I also asked webmaster to remove my dl files as they can be downloaded from my site. I know he has to pay for the bandwidth so i thourgt it could be a favour to him, but he didn't bother at all.

As for your troubble; keep working, it's well worth it.
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