OK, so put in the screen control resistors, which I stupidly forgot to install and nothing changed. I addes 100uf to the power supply and hum was cut in half!! So, going to add another choke and more capacitance, its weird because the hum sounds like 60hz not 120, but I dont have a scope to check. Amp does sound amazing! Will post pics when I get a chance. This sounds much much better than my OTL amp. Gain isnt super high, but it is high enough. I do have an issue with the volume pot not tracking equally during low volumes (its a cheapo pot) - it will get changed out in due time for something better.
I have a preamp drawing 150mA in total (two channels) and my PSU needed 3 caps of 220uF and I think needs more...
I believe you are right, I'm going to put in at least 300uf more. And another choke.
I was thining about something strange; without the screen resistors installed on the 71a, I thought the amp sounded better. What would happen if I omitted them altogether? I noticed no ill effects without them installed.
Gonna redo this from scratch
OK, this amp sounds good, but there is a low level hum that I just cant deal with anymore; I am going to rebuild this and I am going to go all out and use as a preamp/headphone amp combo.
Im looking at going 01a with filament bias and rod coleman regulator interstage coupled with Lundahl LL1660 to 71a with coleman regulator on the 71a then using the LL2765 for the output for preamp with a tap for 300-600 ohm headphones. going to build this in two seperate chassis.
Power supply is going to be LCLC with shunt regulators from K&K audio.
OK, this amp sounds good, but there is a low level hum that I just cant deal with anymore; I am going to rebuild this and I am going to go all out and use as a preamp/headphone amp combo.
Im looking at going 01a with filament bias and rod coleman regulator interstage coupled with Lundahl LL1660 to 71a with coleman regulator on the 71a then using the LL2765 for the output for preamp with a tap for 300-600 ohm headphones. going to build this in two seperate chassis.
Power supply is going to be LCLC with shunt regulators from K&K audio.
Do you need 700mW at those impedances? The lower noise floor gained by using a 5K:8 transformer for headphone use can be extremely useful with DHTs.
There is no 8ohm tap. The options on the LL2765 are 150/300/600 if I remember correctly (need to redownload the datasheet). I have it wired 3:1 currently.
You might want to consider a different transformer to remove some of the stress of getting an amp like that nice and quiet.
I’m not sure if you’re talking about building the audio and power sections in separate chassis, or each gain stage. Whatever you end up going with, know that 01a is very sensitive, so a great preamp tube but requires some design and layout consideration.
The raw filament supplies will be in a seperate chassis as will the power supply. I built a couple preamps with 26/01a/112a and they were all fairly quiet; the only tube I had a hard time getting quiet was the 27 IDHT. I will probably end up with four seperate chassis LOL😱
hold your horses.. be sure you pinpoint hum source, from which stage it is coming.
my two stage stax amp has a quite gain, but now finally it is dead quiet
everything can be fixed
Honestly, the hum wasnt that bad and was probably because I did not elevate the 56 heaters; I really just want an excuse to rebuild 😀
Hi! I'm planning a R120 SE amp for my Hifiman headphones. Using the Lundahl LL2765. PSU will be FET regulated for the input tubes (400 Volt), and CLC for R120 output tubes. Any comments are welcome.
all good, but i´d rather go with fet gyrator instead.
better results than triode follower
http://peteslab.blogspot.com/2015/11/stax-2a3-se-amplifier.html
the latest jfet version is absolut detail hammer
better results than triode follower
http://peteslab.blogspot.com/2015/11/stax-2a3-se-amplifier.html
the latest jfet version is absolut detail hammer
Hello,
I'm also planning to get this output transformers, because on the secondary, I can run low and high impedance cans also.
My problem with it, it is BIG. I can not believe this core size is needed for any dinamic headphone. Still, I probably get this one, but I would need a plan with "normal" tubes like 5687, not 2A3. I have 2A3 in the room PSE amp, but in the headphone amp I want something smaller.
Can you guys help?
Thanks,
JG
I'm also planning to get this output transformers, because on the secondary, I can run low and high impedance cans also.
My problem with it, it is BIG. I can not believe this core size is needed for any dinamic headphone. Still, I probably get this one, but I would need a plan with "normal" tubes like 5687, not 2A3. I have 2A3 in the room PSE amp, but in the headphone amp I want something smaller.
Can you guys help?
Thanks,
JG