Hi,
I am back with the Hybrid amplifier
I have made a lot of test with Rev. 5 and was never able to run correctly the MOSFET SRPPI have made a big mistake on the PCB because the 2SK1058 and 2SJ162 have a different pimout than other MOSFET : the middle pin and the flange is the source and not the drain !!! (https://www.renesas.com/us/en/doc/products/transistor/003/rej03g0847_2sj160ds.pdf & https://www.renesas.com/in/en/doc/products/transistor/003/rej03g0906_2sk1056ds.pdf)
Any way, after crossing the legs it still didn't play music, I found that there was no gain in the input stage
Now I have decided to build the other version of the hybrid amplifier Rev. 5 HD, this is a version suggested by Hugh Dean which use a mu-follower stage made by Alan Kimmel instead of the SRPP. This time the input circuitry is working well and with about 1 V signal I have 10 V on C6 and C7
Helas, when I put the power on the semiconductor part of the amplifier M1 (2SK1058) become immediately very hot (I burn my finger when I just touched it)
I don't understand what happen, I have only +30 V and -30 V, which is less than the 50 V specified and the 2SJ162 didn't become so hot ? Since the output stage is straightforward I don't see what can be wrong ? If you have some solution for this amplifier to play music, I will be happy...
Rgds,
Marc
Laterals do oscillate easely, a small cap does stop it, connect between drain and gate of top fet or both. Maybe the idle is to high or thermal contact with heatsink not oke.
regards
OK, I can listen the music
Finally it was not a problem with the MOSFET or even the Hybrid amplifier Rev. 5 HD, it was a strange behavior of the Main Soft Start for Toroïdal Transformer ( Sjostrom Audio - SST03 Softstart for toroidal transformers ) I found that when I see that my power supply didn't start always or some time shut down without any reason, why this has the effect of increasing the temperature of the 2SK1058 MOSFET, I don't know ?
Now with +/- 45 V the transistors are only at 30°C, DC offset is about -20 mV but I am at the maximum of the trimmer, may be this is because I -46 V and only + 44.5 V !
The amplifier has a lot of bass, too much and a strange background noise, no hum more like a white noise, I will change the 12AX7 which is an old used Toshiba tube...
Rgds,
Marc
Finally it was not a problem with the MOSFET or even the Hybrid amplifier Rev. 5 HD, it was a strange behavior of the Main Soft Start for Toroïdal Transformer ( Sjostrom Audio - SST03 Softstart for toroidal transformers ) I found that when I see that my power supply didn't start always or some time shut down without any reason, why this has the effect of increasing the temperature of the 2SK1058 MOSFET, I don't know ?
Now with +/- 45 V the transistors are only at 30°C
, DC offset is about -20 mV but I am at the maximum of the trimmer, may be this is because I -46 V and only + 44.5 V !The amplifier has a lot of bass, too much and a strange background noise, no hum more like a white noise, I will change the 12AX7 which is an old used Toshiba tube...
Rgds,
Marc
I changed the tube with a brand new JJ ECC82 but it did not change anything
However during more test I have found the solution : I had to reduce the high voltage from 250 V to 200 V and the amplifier sound now very well, no more background noise and not too much bass but enough
I think that the input stage was saturated with too much voltage ? Now it is playing non stop since 4 hours and the MOSFET temperature is stable at 32.5 °C
There was an error on my previous post : the Toshiba tube was a 12AU7 which is equivalent to the European ECC82...
Since the amplifier is now very quite I can hear a small mechanical vibration noise from the Talema 300 VA power transformer ( 55174-P1S2 TALEMA - Transformateur: toroidal | TME - Composants electroniques ), it not fixed in a chassis yet but in the future I may look for an other manufacturer or use R-Core transformer ? Did you have any suggestion ?
Cheers,
Marc
However during more test I have found the solution : I had to reduce the high voltage from 250 V to 200 V and the amplifier sound now very well, no more background noise and not too much bass but enough
I think that the input stage was saturated with too much voltage ? Now it is playing non stop since 4 hours and the MOSFET temperature is stable at 32.5 °C
There was an error on my previous post : the Toshiba tube was a 12AU7 which is equivalent to the European ECC82...
Since the amplifier is now very quite I can hear a small mechanical vibration noise from the Talema 300 VA power transformer ( 55174-P1S2 TALEMA - Transformateur: toroidal | TME - Composants electroniques ), it not fixed in a chassis yet but in the future I may look for an other manufacturer or use R-Core transformer ? Did you have any suggestion ?
Cheers,
Marc
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