Hi all. Last time I posted here was probably 5 years ago. Most of the time I come here to read. I can't find much info about the JLH 1969 MOSFET variant except one instance mentioned on the huge "JLH 10W" thread. Someone said this variant should have its own discussion thread but I can never find it. I am posting just to share my experience and not intend to "stir up" any dust.
One day I was browsing Aliexpress for something completely unrelated but then I noticed this board from China. They call it 1969M. I think M stands for MOSFET as output device. I read the description and it says to adjust Iq to 30mA and it will produce good sound. I have built a JLH 1996 dual rails many years ago (I think I posted it in this forum). Using MJ15003 as output and tested at different Iq, definitely bad sound if I set it at 30mA. However, curiosity set in. Paying less than $11 US shipped, I have nothing to lose and ordered them.
The boards came and I put them to test at the bench. Used a bench supply of 16VDC, I tested one board at a time. First board no problem set to 30mA and got sound on a test speaker. The second board's current adjustment was a bit challenging. The idle current oscillate. I short the input to ground and was able to adjust to 30mA and also got sound on the test speaker.
I then mounted them on an aluminum L bracket with a spacer at the bottom from the wooden board. The L bracket acts as the heat sink and front panel where the volume control is also mounted. I power the boards with a 24VDC LM723 analog regulated power supply. I also connect a ground wire to the L bracket so the boards will not become an AM radio. With the 24V supply, I have no problems setting the current to 30mA. 16VDC was probably too low.
I then connected them to my pair of JBL2800 which I am currently using. I didn't expect much but the initial listening impression is very promising. Afterwards, I replaced the input coupling caps with ERO MKT1813 2.2uF. After a day of two burn in for the caps (some of you disagree on coupling caps burn-in and I'm not going to stir up arguments here), the amplifier sounds really really good. The original input caps were not good, especially with piano music. The MKT1813 is way better for the job.
This amp sounds "liquid". I had another MOSFET amp years ago and this one reminds me of how MOSFET amp sounds. When I mean "liquid", it sounds like a very very small "reverb" effect is in place. The sound stage is wide and it fills from end to end of the room. The L bracket barely feels warm with a comfort volume level for a living room of about 15x15 ft. I have a tube-03 preamp with the Russian 6J1P-EV tube as the preamp of this amplifier. It seems to be the right mix for me. I know 30mA Iq definitely is not class-A but I have also not heard a solid state class AB amp that can sound this good so I take it. I do have tube amp and class D amps and I can say this amp is different. You know it is definitely not tube nor class-D but it is very comfortable to listen to. I can fall asleep while listening to this amp.....
[My source are modified (coupling cap) Sony CD player and Amazon Fire 7 streaming Pandora.]
One day I was browsing Aliexpress for something completely unrelated but then I noticed this board from China. They call it 1969M. I think M stands for MOSFET as output device. I read the description and it says to adjust Iq to 30mA and it will produce good sound. I have built a JLH 1996 dual rails many years ago (I think I posted it in this forum). Using MJ15003 as output and tested at different Iq, definitely bad sound if I set it at 30mA. However, curiosity set in. Paying less than $11 US shipped, I have nothing to lose and ordered them.
The boards came and I put them to test at the bench. Used a bench supply of 16VDC, I tested one board at a time. First board no problem set to 30mA and got sound on a test speaker. The second board's current adjustment was a bit challenging. The idle current oscillate. I short the input to ground and was able to adjust to 30mA and also got sound on the test speaker.
I then mounted them on an aluminum L bracket with a spacer at the bottom from the wooden board. The L bracket acts as the heat sink and front panel where the volume control is also mounted. I power the boards with a 24VDC LM723 analog regulated power supply. I also connect a ground wire to the L bracket so the boards will not become an AM radio. With the 24V supply, I have no problems setting the current to 30mA. 16VDC was probably too low.
I then connected them to my pair of JBL2800 which I am currently using. I didn't expect much but the initial listening impression is very promising. Afterwards, I replaced the input coupling caps with ERO MKT1813 2.2uF. After a day of two burn in for the caps (some of you disagree on coupling caps burn-in and I'm not going to stir up arguments here), the amplifier sounds really really good. The original input caps were not good, especially with piano music. The MKT1813 is way better for the job.
This amp sounds "liquid". I had another MOSFET amp years ago and this one reminds me of how MOSFET amp sounds. When I mean "liquid", it sounds like a very very small "reverb" effect is in place. The sound stage is wide and it fills from end to end of the room. The L bracket barely feels warm with a comfort volume level for a living room of about 15x15 ft. I have a tube-03 preamp with the Russian 6J1P-EV tube as the preamp of this amplifier. It seems to be the right mix for me. I know 30mA Iq definitely is not class-A but I have also not heard a solid state class AB amp that can sound this good so I take it. I do have tube amp and class D amps and I can say this amp is different. You know it is definitely not tube nor class-D but it is very comfortable to listen to. I can fall asleep while listening to this amp.....
[My source are modified (coupling cap) Sony CD player and Amazon Fire 7 streaming Pandora.]
