Hi Friends,
Here is one more update.
My listening choice is without any tone-control between the player and the amplifier.
But for all the friends who like to add a tone-control, I tested the amplifier with Apex TB3 (By Mile) with all quality tested components. The coupling capacitors were removed. The opamps were replaced by extremely low distortion LM4562.
The listening experience is just out of this world.
I tested it from
1. Self made RPI4 + Kali Re-clocker + Allo Piano DAC + special audio grade power supply which is rated very high.
2. Sony Bluray player to play CDs
3. Fisher record player
For media files, anything above 24bit 48khz is sounding just wonderful. DSDs are sounding ultimate.
Even the compressed Youtube music is sounding great.
I have one more DAC ie Fiio FQ1222. It comes with extremely low noise OPA series opamps. I shall also test the amp with it and update.
Ganesh
Here is one more update.
My listening choice is without any tone-control between the player and the amplifier.
But for all the friends who like to add a tone-control, I tested the amplifier with Apex TB3 (By Mile) with all quality tested components. The coupling capacitors were removed. The opamps were replaced by extremely low distortion LM4562.
The listening experience is just out of this world.
I tested it from
1. Self made RPI4 + Kali Re-clocker + Allo Piano DAC + special audio grade power supply which is rated very high.
2. Sony Bluray player to play CDs
3. Fisher record player
For media files, anything above 24bit 48khz is sounding just wonderful. DSDs are sounding ultimate.
Even the compressed Youtube music is sounding great.
I have one more DAC ie Fiio FQ1222. It comes with extremely low noise OPA series opamps. I shall also test the amp with it and update.
Ganesh
As mentioned before, we have now built the BJT front end version exactly according to data book.
We shall build the all FET version, thoroughly test both, and release details in a new thread when ready.
We shall stick to the original as much as possible, and make no attempts to "improve" the original circuits.
Patrick
.
We shall build the all FET version, thoroughly test both, and release details in a new thread when ready.
We shall stick to the original as much as possible, and make no attempts to "improve" the original circuits.
Patrick
.
Attachments
The circuit doesn't belong to us.
So we shall release everything, including Gerber files, in due course, in the above mentioned separate thread.
Will take some time. Please be patient.
Patrick
So we shall release everything, including Gerber files, in due course, in the above mentioned separate thread.
Will take some time. Please be patient.
Patrick
One piece of advice: in comparison to fixed resistors, those 20-turn trimmers have poor Tempco. This means that your bias level will vary according to temperature... The performance seen on the bench / when cold, will not be mirrored in the listening room. Secondly, I am not suggesting that you have used a cheap brand of pot, but I have seen (don't use 'Suntan' for anything) lesser makes of the same trimmer jump wildly in value in the field... This could potentially create a catastrophic amount of heat. My tip is to adjust bias via a dummy load, taking into account your size of heatsink, finding a sweetspot on the bench, while the amp is relatively cold. I would then replace the trimmer with a pair of fixed resistors that have been chosen for good Tempco.
NB - your amp is identical to the one in this thread https://www.diyaudio.com/community/threads/maplin-mosfet-amplifier-ga28f-construction-thread.257488/
The all-FET one is a different beast and I look forward to reading about the results. My suspicion is that it will not outperform the Maplin-style one you've got here. If you look at Hitachi's later designs, where they changed the front end to FET, they give much the same THD spec, but are slightly noisier. The 2SA872 BJTs are extremely quiet. You will have to get up early in the morning to find quieter front end BJTs.
NB - your amp is identical to the one in this thread https://www.diyaudio.com/community/threads/maplin-mosfet-amplifier-ga28f-construction-thread.257488/
The all-FET one is a different beast and I look forward to reading about the results. My suspicion is that it will not outperform the Maplin-style one you've got here. If you look at Hitachi's later designs, where they changed the front end to FET, they give much the same THD spec, but are slightly noisier. The 2SA872 BJTs are extremely quiet. You will have to get up early in the morning to find quieter front end BJTs.
If you would follow my previous projects, you would know that I almost never use trimpots.
The one in the photo is only for setup.
Once it is finally installed in the final heatsink case, the trimpot will be replaced with fixed resistors, as I always do.
The PCB is designed to take both.
Patrick
The one in the photo is only for setup.
Once it is finally installed in the final heatsink case, the trimpot will be replaced with fixed resistors, as I always do.
The PCB is designed to take both.
Patrick
The all FET version is working last night.
The front end uses, in my version, 2SK372.
It is probably the quietest JFET around, as measured by the late Scott Wurcer.
www.diyaudio.com/community/threads/more-fet-noise-measurements-for-euvl.175040/
I like how FET amp sounds.
But that's just me.
Patrick
Please accept my sincerest apologies for making the suggestion.
Note to self: must try harder...
NB - I made that amp in 1987.
👍
The advise is a real good one, for all others who don't understand why I use fixed resistors for trimming, especially in SMD.
Best regards,
Patrick
