My PSU voltage is +/- 63 VDC. R113 is 150 ohm.
One suggestion, get the bias down to about 35mA and check. Is the heatsink getting hot even under idle conditions (no music/signal playing)?
Hari
Hi Guys
Voltage around R113 is 1.27v
Driver vce 49.6v
Output vce 53.2v
DC offset 4mv
V emitter 0.22R = 17mV
What bias current for my 2 pair output do you recommend?
Heatsink more warm during music
Thanks again
Voltage around R113 is 1.27v
Driver vce 49.6v
Output vce 53.2v
DC offset 4mv
V emitter 0.22R = 17mV
What bias current for my 2 pair output do you recommend?
Heatsink more warm during music
Thanks again
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for 150r that tells you the drivers and the emitter resistor are passing ~0.0085A
That tells you the dissipation is ~0.42W
That tells you the output bias is 0.077A and when combined with the 53.2Vce you have a dissipation of ~4.1W
Your description of the heatsinked driver transistor does not fit with Driver "gets very hot to touch." (please excuse the typo corrections).
A 20C/W sink on a driver dissipating 0.42 Watt will give ~15C to 20C rise in temp above Ta. So Ts~ 25+20 = <45degrees C
Even a 30C/W sink will not go over 45degrees C
A bigger sink than 20C/W will run even cooler.
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Maybe your calculations are fine, i have not Measured the actually C/W for heatsink,Anyone know what it is?
I am also using a top perforated grill on amplifier maybe the heat can't out because driver heatsink get so hot?
I am using 120 ohm for R
An externally hosted image should be here but it was not working when we last tested it.
When you say the drivers are getting hot, how hot do you mean? Will you burn your hand on the heat sink, or is it just uncomfortable to touch?
I think the heatsink must be around 50 degrees because you can,t hold your finger on it but not burn your finger emiteably on it
No holes yet i could make a row each side with 5 to 6 holes size 5-6mm
Each on the bottom.
Then also 2-3 holes in the top above the driver heatsink where you see the bended alu to support the grill as in the picture?
Thanks
I would think some holes under the heatsink would be very helpful. Also be sure the amp is held high enough off the ground/shelf it sits on to allow good airflow into the bottom of the case.
Your chassis definitely would require an air intake in the bottom for convection cooling to work, but 50C driver temperature is okay. If don't actually burn yourself touching the heatsink the drivers are fine.
Kimschips, sorry for raising a fundamental doubt, but which heatsink is getting hot, the one on which the output pairs are mounted or the one on which Q107 and Q108 are mounted?
Secondly, the main heatsink needs to be oriented with the fins vertical to enable effective convection.
Hari
Secondly, the main heatsink needs to be oriented with the fins vertical to enable effective convection.
Hari
The main heatsinks are doing fine i have used them with my erlier amplifier modules with same power supply and output power.
It is the driver heatsink get to warm
An externally hosted image should be here but it was not working when we last tested it.
Can you highlight the driver and it's heatsink?
Have you recalculated the driver dissipation since you confirmed the driver emitter resistor value as 120r instead of 150r?
Have you recalculated the driver dissipation since you confirmed the driver emitter resistor value as 120r instead of 150r?
It is the aluminum 'bracket' in the photo in post 1996, near centre:
An externally hosted image should be here but it was not working when we last tested it.
It is used as the heat sink for the drivers.
If dissipation is too high then increasing R113 a little will reduce driver standing current and therefore reduce dissipation. The value of 150R is already up from early versions where 68R was specified, IIRC.
That's a big area of fairly thick aluminium.
I think he needs to recheck the voltages and currents through his drivers to try to identify the heat dissipation.
I think he needs to recheck the voltages and currents through his drivers to try to identify the heat dissipation.
Thanks for inputs i am keeping 120 ohm for now else I have to take whole amplifier apart.
But soon will drill some holes in the bottom to improve airflow in the amplifier and can already see it reduce heat on driver heatsink after drilling more holes in the bended alumium plate supporting the top plate (see post 2014)
I get back with more results☺
But soon will drill some holes in the bottom to improve airflow in the amplifier and can already see it reduce heat on driver heatsink after drilling more holes in the bended alumium plate supporting the top plate (see post 2014)
I get back with more results☺
Have any of you tested 2SC4883 or 2SC2837 as driver in a slewmaster or other amplifier?
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I tried 2sc2837 2sa1186, but it had to high vbe, I have a other pair somewhere around with lowest vbe.
Used onsemi after that with bias ok. Picked 6 with same vbe/hfe from 100 measured pairs.
Could it be better to use same transistors as output ones for pre-drivers all matched. Leave out the middle pair.
Lähetetty minun ONEPLUS A3003 laitteesta Tapatalkilla
Used onsemi after that with bias ok. Picked 6 with same vbe/hfe from 100 measured pairs.
Could it be better to use same transistors as output ones for pre-drivers all matched. Leave out the middle pair.
Lähetetty minun ONEPLUS A3003 laitteesta Tapatalkilla
How can Vbe be to high and compared to what?
Do not know with your last questions what result do you expect?
ignore last post.
You have it pretty good if music for a few hours is main problem.
You did not have this problem before putting this in enclosure?
With test tones and load was it stable before enclosure & "music" ?
Discribe your testing sequence would, and data for from before enclosure solve the issue as before driver changes it plays music for hour or two before hot indicates as stated problem but it plays. I would keep it.
Have any of you tested 2SC4883 or 2SC2837 as driver in a slewmaster or other amplifier?
To your question about drivers, [ELMAG] 2SC4883 2SA1859 tranzystory SANKEN 6 z? (6539032154) - Allegro.pl - Wi?cej ni? aukcje.
From iamp100 bom.
You have it pretty good if music for a few hours is main problem.
You did not have this problem before putting this in enclosure?
With test tones and load was it stable before enclosure & "music" ?
Discribe your testing sequence would, and data for from before enclosure solve the issue as before driver changes it plays music for hour or two before hot indicates as stated problem but it plays. I would keep it.
Have any of you tested 2SC4883 or 2SC2837 as driver in a slewmaster or other amplifier?
To your question about drivers, [ELMAG] 2SC4883 2SA1859 tranzystory SANKEN 6 z? (6539032154) - Allegro.pl - Wi?cej ni? aukcje.
From iamp100 bom.