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Old 17th September 2013, 08:58 PM   #581
6L6 is online now 6L6  United States
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Quote:
Originally Posted by PKI View Post
I say that you can go a bit higher for the case temp, like 70-75 maybe. It's just me though :-)

75C is 167F - That will burn you.

Plus if your heatsinks are that hot, your transistors are getting really hot, and that's just not a good idea.

The max you want to have is 65C transistors, 55C heatsinks
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Old 17th September 2013, 09:14 PM   #582
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Oh, I was talking about the transistors case, 2nd leg if you like. You are not going to touch it too often :-)
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Old 20th September 2013, 03:29 PM   #583
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I checked the temps this afternoon and had the following readings:-

Heatsinks 43C Mosfet cases 47C

Source resistor are at 53C whilst the schottky diodes are running at 56C.I think I'll fit bigger sinks on the schottkies or perhaps fit standard bridges or do folks think that 56C is out of the way?
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Old 20th September 2013, 03:34 PM   #584
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Look at the temperature ratings for the diodes you are using. (on the datasheet) My guess is that they are fine. Heatsinks never hurt, however...

Also - please take some photos of your amp and post them in the build guide thread!!
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Old 20th September 2013, 03:41 PM   #585
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Thanks Jim I'll post pics at some point but need to treat myself to a new camera first.
Forgot to say the diodes already have small sinks fitted.
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Old 22nd September 2013, 12:02 PM   #586
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I want to give some feedback about the bias adjustment of my aleph J with lateral toshibas.
At the end i have got R27=14.3K, R8=2k and R7=0.16K
Voltage drop near 450mV across the source resistors and offset below 1mV, after 1 hour.

So it was not necessary to change the source resistors, but bias is only adjustable with R27 and not with R8.
It was clear that the sound was getting a bit grainy with bias at 400mV.
The temperatur of the heatsinks is still high, but acceptable.

I like the sound being more relaxed and a bit nicer in the high frequency range than my Alephs with IRF mosfet input and output.

The comparison with F5 have to wait until i got an new Bass chassis for my Harbeth Monitor 30.1

There was a 2SJ109 dying at my first try of the amp, resulting in full voltage at the output, burning the chassis.
Its the first time in like 17 years of amplifier building and my punishment will be a huge bill.

I using my old self made speakers now, they sound nice and involving, but need more damping for the low frequencies and anyway, the Aleph J was planned to check out if it would sound even nicer with the harbeth, than the F5.

I was happy with the F5, but you know sometimes you just have to build something, driven by curiosity.
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Old 22nd September 2013, 09:25 PM   #587
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Quote:
Originally Posted by oliverniekamp View Post
It was clear that the sound was getting a bit grainy with bias at 400mV.
The temperatur of the heatsinks is still high, but acceptable.

I like the sound being more relaxed and a bit nicer in the high frequency range than my Alephs with IRF mosfet input and output.

The comparison with F5 have to wait until i got an new Bass chassis for my Harbeth Monitor 30.1

I was happy with the F5, but you know sometimes you just have to build something, driven by curiosity.
Thanks for the report. I love to see someone experimenting, traveling their own road. Enjoy.
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Old 11th October 2013, 09:43 AM   #588
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Quote:
Originally Posted by Zen Mod View Post
everything is pretty OK

after some time of enjoyment , check AC gain of Aleph CCS
Thanks Zen;how do I check AC gain?
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Old 11th October 2013, 10:29 AM   #589
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easy

Proper Current Source Adjustment


Quote:
Originally Posted by Nelson Pass View Post
I'm not sure that the quote addresses the question. I
interpret it as wanting to know how to set the current
gain of the Aleph current source, not the DC bias.

For the former, you generally want to set the gain so that
the AC variation of the current source is about 1/2 the output
current. It can be more or less, but 50% gives the optimal
energy efficiency figure.

You will note in the Aleph schematics that the Base of the NPN
transistor which controls the current source attaches to the
output of the amplifier through an RC network. The value for
C is set arbitrarily high so that it does not interfere with audio
frequencies, and it is the value of R which is the most convenient
spot to adjust the gain of the current source. For the purpose
of this discussion, I'll call it R0.

If you set the amplifier driving a sine wave into a load (let's say
16 Vrms into 8 ohms at 100 Hz), you can measure the current
variation of the gain N channel Mosfets (whose Sources attach
through power resistors to the - supply rail) with a cheap AC
voltmeter placed across one of these Source resistors. With
R0 taken out of the circuit, you will get one AC value across the
Source resistor (say 470 mV, for example). As you put a value
for R0 in the circuit, this will decline, and when it measures 1/2
the value without R0, you have reached 50%. If it measures
1/4 the value, the current gain of the Aleph source is 75%, and
this figure is too high for a standard Aleph. Most listeners like
the Alephs at 50% or lower, so I recommend between 50% and
100% of the AC voltage value compared with no R0.

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Last edited by Zen Mod; 11th October 2013 at 10:32 AM.
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Old 11th October 2013, 10:40 AM   #590
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Thank you.I guess I don't have enough test equipment
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