norb said:
Just realised that this is not true, i built the standard F5T without cascode.
Nelson Pass said:
Maybe i should try the cascoded version then, would not have to replace transformers. Thanks for this information.
A75 running since yesterday evening, no hint of crackling noises or other problems.
The origin of the noise remains unclear, anyway i´m happy it´s gone.
Looking forward to the next 13 years. Sorry, F5T ...
Thanks to everyone for help !
The origin of the noise remains unclear, anyway i´m happy it´s gone.
Looking forward to the next 13 years. Sorry, F5T ...
Thanks to everyone for help !
Help Needed with F5 Turbo V3 Monoblock Bias Issue on Startup
In that thread 'audiosan' explains why one should get rid of the diodes.
In that thread 'audiosan' explains why one should get rid of the diodes.
Thank you Andersonix for information on F5 problem.
Nevertheless my A75 is producing noises again after working flawlessly until a week ago.
I had DVMs on the outputs all the time to monitor DC, and after 5 min warm-up it always was about -30 to +50 mV.
When the crackle on the right channel came back, the output DC read about 3,3V.
Checked output section and front-end separately, everything works as it should. Output MOSFET bias currents, VGS-voltages etc. same as last time. I keep an .xls-file on all measurements now ...
Of course i could swap semiconductors one by one, but my design is not that service-friendly, and i would like to listen to some music again before the end of the year ...
So i will start by swapping input channels (DC-coupled preamp with Salas DCB1), just to make sure that noise+DC-offset don´t come from there.
Next thing would be swapping frontend-PCBs of A75. After that i would replace either all outputs or frontend MOSFETs. 🙁
But if anybody here knows some trick or whatever to shorten this procedure, i would be very happy to know of ...
Norb
Nevertheless my A75 is producing noises again after working flawlessly until a week ago.
I had DVMs on the outputs all the time to monitor DC, and after 5 min warm-up it always was about -30 to +50 mV.
When the crackle on the right channel came back, the output DC read about 3,3V.
Checked output section and front-end separately, everything works as it should. Output MOSFET bias currents, VGS-voltages etc. same as last time. I keep an .xls-file on all measurements now ...
Of course i could swap semiconductors one by one, but my design is not that service-friendly, and i would like to listen to some music again before the end of the year ...
So i will start by swapping input channels (DC-coupled preamp with Salas DCB1), just to make sure that noise+DC-offset don´t come from there.
Next thing would be swapping frontend-PCBs of A75. After that i would replace either all outputs or frontend MOSFETs. 🙁
But if anybody here knows some trick or whatever to shorten this procedure, i would be very happy to know of ...
Norb
So ... after a year of normal operation the left channel failed (softly) again, heatsinks and transformer got quite hot, music still playing but again with crackling noise.
After last problem i double-checked everything again, but with no result. Now on the left channel one N-FET measured 1,6 - 2,8 kOhms between any terminal. The measured resistance varies, it goes up, then down, then up again ... funny.
The 50 pcs. IRF630 i ordered for the A75 were by ST Micro, but 2 different batches with slightly different TO220-packages marked CHN502 and PHL431. All N-FETs on the left channel are CHN502, of which 3 have failed so far. All N-FETs on right channel are PHL431, of which none has failed up to now. Also the problems always occured during warm seasons, so it seems the CHN502-ST-FETs were operating on some thermal limit, explaining their somewhat erratic behavior.
Going to replace all STs with IRs now. I only wonder if i should replace all output P-FETs as well, to not mix used and new devices.
I´ll be very happy for some advice or experience on this.
p.s.: anybody have a spare A75 for me in the meantime ?
After last problem i double-checked everything again, but with no result. Now on the left channel one N-FET measured 1,6 - 2,8 kOhms between any terminal. The measured resistance varies, it goes up, then down, then up again ... funny.
The 50 pcs. IRF630 i ordered for the A75 were by ST Micro, but 2 different batches with slightly different TO220-packages marked CHN502 and PHL431. All N-FETs on the left channel are CHN502, of which 3 have failed so far. All N-FETs on right channel are PHL431, of which none has failed up to now. Also the problems always occured during warm seasons, so it seems the CHN502-ST-FETs were operating on some thermal limit, explaining their somewhat erratic behavior.
Going to replace all STs with IRs now. I only wonder if i should replace all output P-FETs as well, to not mix used and new devices.
I´ll be very happy for some advice or experience on this.
p.s.: anybody have a spare A75 for me in the meantime ?
Damn .... always thought it was OPLRF.
On TO247: Half number of devices with double power dissipation / half RthJ-C should lead to basically same chip temperature as with TO220, and maybe because i´m too lazy for complete rework i again will ignore your friendly expertise-backed suggestion.
I trust ST China for bad copying of devices from ST Philippines 😉, and if the new IR-IRF630 last another 13 years, rework design will be ready then.
On TO247: Half number of devices with double power dissipation / half RthJ-C should lead to basically same chip temperature as with TO220, and maybe because i´m too lazy for complete rework i again will ignore your friendly expertise-backed suggestion.
I trust ST China for bad copying of devices from ST Philippines 😉, and if the new IR-IRF630 last another 13 years, rework design will be ready then.
