Nominal heat of the input dif.pair in Aleph

[marjan]

Hi peple!

Anyone mesured the temperature on IRF9610 haatsinks (input dif. pair and 1QA5(A2) on aleph`s)?

Does enyone have the expirience of geting any - like the bad ground conectin - noise from the speaker when amp is bounced a little. It hapened to me whwn I acidantly tuched the amp with my leg litle harder. I chacked out all soldered and screwed conections. Nois stoped after a second and music was playing on without any interuption.

Any idea?

regards Marijan

 

[Nelson Pass]

Normally they are a few degrees above ambient. You
can run them without sinks.

The other sounds like a loose connection nevertheless,

 

[marijan]

N.P.

What can be a problem then. I`m reading 9,5V acros the Z9 foloving Q1A5 and 3,5 betwin drain and source, of diferencial pair and Q1A5. There is 4,5V acros R24 (392ohm betwin drains of input pair) - all values from the schematic are in limits of nominal values. But my IRF9610 all three of them (Q1A1, Q1A2, Q1A5) are runing extremly hot even with heatsinks(I shoud say tuching the heatsink there is at least 70°C, and allready after let say 10 minutes. No hum, no interferences, sound OK. What should I check out or can it be normal. Amps are runing about 4 ours per day, side heatsinks are reaching 61°C since I comleted chasis, bias 2,8 - 2,9A on output total, dc ofset on output, 15mV.
???????????? Don` get it.

Thanks for reply
regards Marijan

 

[Nelson Pass]

The diff pair are running about 1/2 watt each, and the
current source about a watt. They should be fine with
sinks rated for 2-3 watts or so.

You can always check the voltage across the Source to
v+ resistor to see if you are running about 25 mA through
the current source.

 

[marijan]

Hi!

Like you sugested, I mesured the curent on Q3. I `m reading 6V acros source resisor (R11 in aleph2 220ohm) on V+. So I`m geting aproks. 27-28mA of bias. Zener is allso litle higher 9,5V instade of 9V. Coud there be a problem?
Voltage on source of dif input is 3.5 and not 4V like in the shematic. Othervise R14 (392ohm) on the drains of dif input to output devices, does produce 4,25V as it should be. Frend of mine sugested me to replace my no name zeners with the more quality one or lover the value of the zener. What would be your sugestion to decrease bias if nececary?

rgds Marijan

 

[mefinnis]

Gee ..... I feel really at home in this thread

Hi Marijan,

1. My 9610s are all quite warm to the touch, probably around 50-60C. Remember this is much less of a problem because the power dissipation is so much lower as Nelson has stated.

From the datasheet, max Rt junction-to-case is 6.5C/W ..... so if we are dissipating 1W, the junction temp is still < 70C ..... no problemo

This is quite a different proposition to the output stage.

2. My new Aleph5 has some intermittent static in the right channel. Disappears once the amp gets warm and all measures/works perfectly. Been over the thing with a proverbial "tooth-comb" ....... these things can be very hard to find

I'll track the blood thing down, though .... even if I have to completely rebuild the right channel .... GRRRR !

cheers, mark

 

[Peter Daniel]

I have some hum in one channel of my Aleph5 which disappears when the amp is warmed up. No idea where it comes from.

 

[Jens]

Marijan,

Just measured the temperature of Q1-3 in my Aleph 2 clone (without sinks/on the top of the MOSFETs):
Q1 = 140° C
Q2 = 82° C
Q3 = 124° C

BTW: Q1 delivers 26ma CS

 

[marijan]

Mark my man!

thanks for reply. Looking the results of Jens`s mesuring of his IRF9610I`ll sleep like the baby.
I succesfuly repared the bump problem. It was a bad conestion after all like Nelson said.
I had a hum on left and right chanal using preamp on RCA conection without shortin plugs. On XLR or directly conected CD player hum of the toroid disapered.
You`ll make it work I know. Such a beatifull amp.

Jens

Thank you for your results. I`m peaceful now.

all the best Marijan

 

[Nelson Pass]

Generally the noise improves as the amp warms up,
mostly becuase the devices inrease in gain as they
warm up, and the extra gain becomes feedback to
improve the PSRR.