I ordered FQA36P15 from Polida 2008, however, I received what appear to be fake parts from their distributor. It took them 3 weeks to ship, which also indicates they were fabricating the counterfeits before shipping. No need to clog up this thread further on the topic, but wanted to share my experience and show what I received for awareness. Polida is willing to take them back at cost of shipping, but the process of shipping them back is a complicated mess with both cost and customs.
https://www.diyaudio.com/community/...haring-experiences-thread.412771/post-7710169
https://www.diyaudio.com/community/...haring-experiences-thread.412771/post-7710169
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Congratulations myleftear, nice and interesting build.
Last week I was playing with distortion and feedback. First, I lowered the gain of my HGF to value Acl = 5 because there is no need for a big gain factor when using a preamp with 6dB. Following changes of feedback resistors were made:
RF2 = 15k
RF3 = 180k
RF4 = 68k
The feedback level is maintained the same β = 0.25.
The measurements have shown that there is no ringing in step response when using OPA551 (CH1 is HGF, CH2 - generator). Unfortunately, there was some waving in step response with OPA604 I was preferred before.
So OPA551 has found its highly valued place in my HGF again.
The next step will be a non-GBF configuration with the same gain level.
Last week I was playing with distortion and feedback. First, I lowered the gain of my HGF to value Acl = 5 because there is no need for a big gain factor when using a preamp with 6dB. Following changes of feedback resistors were made:
RF2 = 15k
RF3 = 180k
RF4 = 68k
The feedback level is maintained the same β = 0.25.
The measurements have shown that there is no ringing in step response when using OPA551 (CH1 is HGF, CH2 - generator). Unfortunately, there was some waving in step response with OPA604 I was preferred before.
So OPA551 has found its highly valued place in my HGF again.
The next step will be a non-GBF configuration with the same gain level.
Attachments
As you may have read, my amp gets quite warm, about 30° above room temp. Gianluca says his specs are good, so I'd have a 0.28§C/W HS per channel...
Just a question out of insecurity (and curiosity, and ignorance): What would be my options to run the HGF closer to its lower limit, temperature-wise? Lower the bias, and down to where approx?
(or lower voltage at the 25V-ish PSU?)
Just a question out of insecurity (and curiosity, and ignorance): What would be my options to run the HGF closer to its lower limit, temperature-wise? Lower the bias, and down to where approx?
(or lower voltage at the 25V-ish PSU?)
@myleftear
Looks like you biased it just as the design doc had recommended, i.e. 1.25A at +/-25V which is roughly 62.5watts of dissipation. Try a lower bias current for lower dissipation. For example, instead of 137mV across R1 or R2, try 110mV. I am assuming you have 0.11 ohms for R1 and R2. This will give you a bias of I = V/R which is 0.110/0.11 ohms = 1A approximately. That will be 50 watts of dissipation which should cool your heatsinks a bit.
Other options are using a fan (Baby Sitter), and of course lowering your rail voltages.
At these dissipation levels your Mosfets are not being overloaded in anyway.
Best,
Anand.
Looks like you biased it just as the design doc had recommended, i.e. 1.25A at +/-25V which is roughly 62.5watts of dissipation. Try a lower bias current for lower dissipation. For example, instead of 137mV across R1 or R2, try 110mV. I am assuming you have 0.11 ohms for R1 and R2. This will give you a bias of I = V/R which is 0.110/0.11 ohms = 1A approximately. That will be 50 watts of dissipation which should cool your heatsinks a bit.
Other options are using a fan (Baby Sitter), and of course lowering your rail voltages.
At these dissipation levels your Mosfets are not being overloaded in anyway.
Best,
Anand.
@lhquam
From what I understand, Modushop's heatsink ratings are based on an 85 degree C rise above ambient. See here. As such, any rating I see with regards to a Modushop heatsink for my purpose, I multiply that rating by 1.4.
In example, in post #635, member myleftear states the rating he was told was 0.28 degC/watt. Multiply by 1.4, you get 0.392. So with 62.5watts dissipation with two FETs in your design with 1.25A bias @+/-25V, we have a 25 degree C rise above ambient...which is pretty close to what member myleftear is getting.
Best,
Anand.
From what I understand, Modushop's heatsink ratings are based on an 85 degree C rise above ambient. See here. As such, any rating I see with regards to a Modushop heatsink for my purpose, I multiply that rating by 1.4.
In example, in post #635, member myleftear states the rating he was told was 0.28 degC/watt. Multiply by 1.4, you get 0.392. So with 62.5watts dissipation with two FETs in your design with 1.25A bias @+/-25V, we have a 25 degree C rise above ambient...which is pretty close to what member myleftear is getting.
Best,
Anand.
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These observations by Albert written back in September 2023 when he was reworking his Aleph 2 build has some info. Since then I've been using a "fudge factor" of 1.4 with Modushop's heatsink ratings.
Other than using a 1.4 "fudge factor" and empirical measurements of the heatsinks in my own builds (most are 4U/300 and 5U/400), that's about all I have done to confirm. But the numbers are much closer to theoretical than they used to be using the original Modushop heatsink data.
Best,
Anand.
Other than using a 1.4 "fudge factor" and empirical measurements of the heatsinks in my own builds (most are 4U/300 and 5U/400), that's about all I have done to confirm. But the numbers are much closer to theoretical than they used to be using the original Modushop heatsink data.
Best,
Anand.
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