Got my PCBs from the manufacturer. Will try to have 1 channel ready this weekend...
Mellowman,
Wonderful work....... how is the bass and treble on this amp? Do vocals 'engage', touching your heart?
Low parts amp this one, and very good use of an opamp!
Hugh
Wonderful work....... how is the bass and treble on this amp? Do vocals 'engage', touching your heart?
Low parts amp this one, and very good use of an opamp!
Hugh
Hi Hugh,
tonal balance of this amp is very nice maybe leaning a bit to V shape with mids slightly recessed. But overall it’s very musical with lots of nuance in treble and firm bass at the same time 🙂 or maybe this is how my speakers are…
Łukasz
Sorry mate, I will not, because you don’t hear what I do 😉 I built original Alpha (20w) and Alpha Nirvana with a twist (with 2sa1381). Have not heard OG
I completed assembly and testing of both channels today. No problems whatsoever. Everything worked perfectly from the beginning.
My build is done according to 2nd schematic from post #93. 20V rails, 2.36A current. IRFP outputs. TL071 op-amp. CCS: MPSA92.
Output DC offsets are 5.4mV and 0.9mV.
Photos say it all. I'm working on the chassis now.. Haven't tried different op-amps yet.
My build is done according to 2nd schematic from post #93. 20V rails, 2.36A current. IRFP outputs. TL071 op-amp. CCS: MPSA92.
Output DC offsets are 5.4mV and 0.9mV.
Photos say it all. I'm working on the chassis now.. Haven't tried different op-amps yet.
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Very nice opamp driven AN, Minek. The square wave is textbook, but in truth the sawtooth waveform tells us it is extremely linear, there is absolutely no deviation from a straight line, and in my experience this is a telling result, indicating the amp will have almost zero distortion. Using the 1056A IC?
Do you have any subjective results vis a vis the discrete AN? I would expect it to be quieter and better offset control, and possibly better bass since the shunt electro is not used (C5 linked?).
HD
Do you have any subjective results vis a vis the discrete AN? I would expect it to be quieter and better offset control, and possibly better bass since the shunt electro is not used (C5 linked?).
HD
Using LT071. Will try other op-amps later on.
Working on a proper chassis now. Can't run both channels from my bench PSU - not enough Ampers 🙂
Also my cooling system with bucket of water and alu plate is not adequate for longer tests.
It seems that Kapton tape is not conducting heat very well (definitely not recommended for class A amp)- but it'll do for a quick test.
Will try playing music once chassis with proper PSU and (active) cooling is ready (next weekend?).
As for comparison with AN - it used to be necessary to fiddle with LPT current AND with offset (vas current) - 2 resistors - and as far
as I remember from the sim, these two things were dependent on each other, so it always took some time to get it right.
Now, there is no adjustment needed at all, which is a big plus.
Feedback shunt cap is shorted, as you noticed - I was expecting this to be case, but left space for it on on the PCB, just in case....
Output DC offset is minimal, and it goes to virtually zero very quickly after starting the amp.
At 36Vpp it was not clipping yet, and then my PSU runs out of juice, so I'll have to test clipping once it's all finished with chassis
and proper PSU (2*20V, 6A).
This exact schematic - as built - with these exact components:
As far as I can tell - selection of transistors is not critical at all. CCS will work with pretty much any small PNP.
Q1 - any decent small PNP will do. For VAS (Q2) I would either use KSC3503 or Toshiba TTC004B or NTE374 or KSC2690.
Working on a proper chassis now. Can't run both channels from my bench PSU - not enough Ampers 🙂
Also my cooling system with bucket of water and alu plate is not adequate for longer tests.
It seems that Kapton tape is not conducting heat very well (definitely not recommended for class A amp)- but it'll do for a quick test.
Will try playing music once chassis with proper PSU and (active) cooling is ready (next weekend?).
As for comparison with AN - it used to be necessary to fiddle with LPT current AND with offset (vas current) - 2 resistors - and as far
as I remember from the sim, these two things were dependent on each other, so it always took some time to get it right.
Now, there is no adjustment needed at all, which is a big plus.
Feedback shunt cap is shorted, as you noticed - I was expecting this to be case, but left space for it on on the PCB, just in case....
Output DC offset is minimal, and it goes to virtually zero very quickly after starting the amp.
At 36Vpp it was not clipping yet, and then my PSU runs out of juice, so I'll have to test clipping once it's all finished with chassis
and proper PSU (2*20V, 6A).
This exact schematic - as built - with these exact components:
As far as I can tell - selection of transistors is not critical at all. CCS will work with pretty much any small PNP.
Q1 - any decent small PNP will do. For VAS (Q2) I would either use KSC3503 or Toshiba TTC004B or NTE374 or KSC2690.
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All in all - this amp has excellent parameters, small parts count, small size, rock solid stability, and it's extremely easy (and cheap) to
build and get it running. No adjustments needed.
🙂🙂🙂
build and get it running. No adjustments needed.
🙂🙂🙂
Nice! I like your prototyping cooling with a bucket of water! 🙂
Could you run some distortion measurements? I would be interested in 1k and multitone FFT, both at maybe 3V and near max output.
Could you run some distortion measurements? I would be interested in 1k and multitone FFT, both at maybe 3V and near max output.
Hi Hugh,
the amp indeed touches my heart 🙂 settled on LT1056 but tried TL071 and TLE2071. That one let me crank up the volume more than others without fatigue and that tells something.
Łukasz
Chassis is ready. As usual, it's a 'naked' amp, on 1 inch thick aluminum slab, with active cooling (2 Noctua fans on HP heatsinks).
The smaller box below it - it's a PSU.
Works, plays music, sounds good.
I have to remind myself - no more class A amps. They run hot!
Every time I built class A amp, I say to myself - this is the last one, no point in building something that runs so hot.
So hopefully, this is the last one 🙂
IRFP outputs are running at little bit over 60 degrees Celsius (measured by 2 different thermometers, one by contact, one infrared).
Also the 0.15 Ohm resistors running damn hot. Note for future - keep them far away from other components on the next PCB.
The smaller box below it - it's a PSU.
Works, plays music, sounds good.
I have to remind myself - no more class A amps. They run hot!
Every time I built class A amp, I say to myself - this is the last one, no point in building something that runs so hot.
So hopefully, this is the last one 🙂
IRFP outputs are running at little bit over 60 degrees Celsius (measured by 2 different thermometers, one by contact, one infrared).
Also the 0.15 Ohm resistors running damn hot. Note for future - keep them far away from other components on the next PCB.
Haven't done extensive music testing yet, perhaps tomorrow.
IRFPs running at little over 70 degrees C (not low 60s as previously reported) measured right at the transistor case.
Fans are nicely blowing; getting breezy in here 🙂
IRFPs running at little over 70 degrees C (not low 60s as previously reported) measured right at the transistor case.
Fans are nicely blowing; getting breezy in here 🙂
Very nicely made....... naked construction makes it difficult to have the active cooling directly connected to the output devices unless you use flexible leads, but yes, the heat of these amps is a bit irritating after a few weeks when the novelty wires off and the weather starts to hot up.
Beautifully pcb work and wiring, Minek, great project, thank you for gracing the AN with such an innovative opamp input stage.
Hugh
Beautifully pcb work and wiring, Minek, great project, thank you for gracing the AN with such an innovative opamp input stage.
Hugh
I like the 'naked' style amps! 🙂
Maybe you could direct the air from the fans down towards the PCB's to cool the resistors and caps next to them? It might even help cool the 'slab' the transistors are mounted to when you get some airflow over it.
Maybe you could direct the air from the fans down towards the PCB's to cool the resistors and caps next to them? It might even help cool the 'slab' the transistors are mounted to when you get some airflow over it.
