Speakers are 2 way based on audax drivers, amp is a LiFePO4 powered LM3875 amp that has seen off many contenders. The sound is very good, very dynamic, but smooth, and no harshness at all. A keeper.
More dynamic, and better (deeper) soundstage than before the coleman reg/filament bias/removing input cap.
More dynamic, and better (deeper) soundstage than before the coleman reg/filament bias/removing input cap.
when you are done with this and ready to move into 01a please let us know we will try to guide you through the build....remember it will not be easy. But if your amp and speakers are not at per the TT pre SQ may not be reflected properly.
Regards
Regards
I'm pretty confident of the amp and speakers - I've heard them in comparison to quite a few and they always fare well.
I have a few other projects, so it will be a while before I can start on the 01A stage. I need to gather parts for it anyway.
I have a few other projects, so it will be a while before I can start on the 01A stage. I need to gather parts for it anyway.
I have an oddball 211 amp here, it was a 1980s UK cottage industry product that was very short lived, and has an odd design, I think it has a 12au7 into a 5687 and then the 211. Its been a long time since I pulled it out of storage. Sounded good but I think the design means it doesn't shine at its best. It had a habit of blowing the rectifiers on the heaters - and in truth thats another one that could do with a coleman reg!
The other valve amps I have are all push pull
The other valve amps I have are all push pull
In fairness to it, its has been doing sterling service, while others like a rebuilt ST70, F5, an aikido type EL34, Croft EL84 etc all don't get a look in. A more conventionally powered LM3875 doesn't come close to it at all.
Your class D amp input impedance is 10K-22K. 3A5 plate output is not good enough to drive it properly. Same is true for 01A.
Regards
Regards
You can use a mu follower CCS cascade or Gyrator load to drive that impedance. Here's an example of a gyrator using the mu follower output.
https://www.diyaudio.com/forums/att...13-unholy-alliance-phono-amp-3a5phonotrim-jpg
Good suggestion from Sheldon.
and/ or
if 2.5x-3x gain is okay you can use line trans or parafeed.
Regards
and/ or
if 2.5x-3x gain is okay you can use line trans or parafeed.
Regards
OK, stupid question time. The input to the CCS shown in that schematic has a bias applied - where is that coming from?
Can I use a 2sk117 or 2sk170 instead of the LSK170? Any IDSS preferred?
Fran
https://www.diyaudio.com/forums/att...81365-unholy-alliance-phono-amp-3a5-phono-jpg
It's not entirely obvious, but there are two versions of the shunt supply for the amp. One adjusted for an output at 120 volts (second stage), the other 80 volts (input stage). They are shared for left and right. The bias is tapped from the PS 80 volt output.
Sheldon
It's not entirely obvious, but there are two versions of the shunt supply for the amp. One adjusted for an output at 120 volts (second stage), the other 80 volts (input stage). They are shared for left and right. The bias is tapped from the PS 80 volt output.
Sheldon
I don't know if it really applies here, but the IDSS of the upper JFET in a cascade should be higher than the lower JFET (Horowitz and Hill). I don't know about options for the LSK170, but I'm sure others on then forum do.
Sheldon
Sheldon
You can use cascode CCS from K&K
Other kits – K & K Audio
OR
You can use 10K:600 ohms line transformer in parafeed fashion. Easy and good sounding.
Regards
Other kits – K & K Audio
OR
You can use 10K:600 ohms line transformer in parafeed fashion. Easy and good sounding.
Regards
I put together a simple CCS using a 10m45s supplying 4mA to the plate - this gave quite a jump in sound quality..... which of course has me wondering what a cascode one would sound like!
I'll get some bits together to try out.... the sound quality is pretty outstanding.
As always, thank you all for the help, it is much appreciated.
I'll get some bits together to try out.... the sound quality is pretty outstanding.
As always, thank you all for the help, it is much appreciated.
Fran I recommend you to use the Moglia's hybrid mu-follower Hybrid Mu-follower (aka Gyrator) Rev08 PCB Update – Bartola(R) Valves
Felipe is right about Ale's Anode-Load - this is a very good implementation for horizontal load lines.
And with an anode current of 4mA, there is another reason to use it - it's difficult to build a cascoded depletion FET CCS that will work well at 4mA. It would need dissimilar FETs, with the lower part having an Idss much lower than the upper part.
Further explanation here:
Cascoded DN2540 CCS down to 0.3 mA
And with an anode current of 4mA, there is another reason to use it - it's difficult to build a cascoded depletion FET CCS that will work well at 4mA. It would need dissimilar FETs, with the lower part having an Idss much lower than the upper part.
Further explanation here:
Cascoded DN2540 CCS down to 0.3 mA