Hi,
Has anyone build this amp what audiodesign proposed ?
I would like to read second opinion about sound quality.
I'm not an expert but simplicity of this circuit is something what focused my attention ;-) I would like to try this amp since I'm constantly struggling with matching speakers to my tube amps ;-)
Has anyone build this amp what audiodesign proposed ?
I would like to read second opinion about sound quality.
I'm not an expert but simplicity of this circuit is something what focused my attention ;-) I would like to try this amp since I'm constantly struggling with matching speakers to my tube amps ;-)
Lundahl can produce a LL1671/20mA instead of LL1671/30mA, ask for the 20mA model.
Some update: Amplifier End by Andrea Ciuffoli
Some update: Amplifier End by Andrea Ciuffoli
Final measurements and other photos
Amplifier End by Andrea Ciuffoli
bias 2 x 42V 0.9A
output 50W on 8ohm
Amplifier End by Andrea Ciuffoli
bias 2 x 42V 0.9A
output 50W on 8ohm
In the Circlotron there are no crossover or switching distortions and "the amplifier behaves sonically like a class A amplifier but with much lower power consumption.
from:
6moons audio reviews: Thorens TEM 3200
from:
6moons audio reviews: Thorens TEM 3200
For the output stage is possible to use only capacitors (22000uF) without choke (CLC) and also in this case there is no output noise.
For the driver stage is possible to use a virtual battery and a LM317 like my PF2007 to reduce the cost:
PF2007: the system
For the driver stage is possible to use a virtual battery and a LM317 like my PF2007 to reduce the cost:
PF2007: the system
That applies for Frank Blohbaum's TEM3200 concept, which has a circlotron output stage, but does it apply for all circlotron output stages?
In other words, do you claim that your amplifier is on par with the TEM3200?
This is a known property of Circlotrons. In the EV Wiggins Circlotron, the amp was operated class B as the there were no magnetic field collapse issues with the output transformer.
In an OTL, the issue is similar, there is almost nothing in the way of crossover issues to be concerned about. The main thing you loose by running less bias current is a little bit of low-level authority.
In solid state embodiments the output impedance is usually so low that this is not much of a concern.
IOW, if the design is done properly, distortion will become unmeasurable as the output power goes to zero.
Andrea's design has a damping factor of about 12 (output resistance 630mOhm) with the Exicon fets.
That's comparable with a good tube amplifier.
Sorry guys, I am not convinced at all.
Circlotrons are no more than one species of push-pull amplifiers, with all matters related.
They also don't work different in the class A, A/B department from the more standard types of push pull amplifiers (wether they are tubes or SS).
Don't agree?
Then read what Broskie wrote about circlotrons, and come back with hard technical arguments why he is wrong.
For the time being my vote goes to John Broskie.
This does not imply that excellent circlotron amplifiers could not be made; it is just that it is one of many possible topologies, not an inherently better one.
Circlotrons are no more than one species of push-pull amplifiers, with all matters related.
They also don't work different in the class A, A/B department from the more standard types of push pull amplifiers (wether they are tubes or SS).
Don't agree?
Then read what Broskie wrote about circlotrons, and come back with hard technical arguments why he is wrong.
For the time being my vote goes to John Broskie.
This does not imply that excellent circlotron amplifiers could not be made; it is just that it is one of many possible topologies, not an inherently better one.
A normal 300B amplifier have a higher output impedance
Zout = (Ra / (Primary/Secondary)) = (700 / (3500/8)) = (700 / 437) = 1.6ohm
some Sakuma amp. and my 300B SE use 5600 Primary to get
Zout = (Ra / (Primary/Secondary)) = (700 / (5600/8)) = (700 / 700) = 1ohm
so 630mohm is between a solid state amplifier and a single-ended vacuum tube amp.
Zout = (Ra / (Primary/Secondary)) = (700 / (3500/8)) = (700 / 437) = 1.6ohm
some Sakuma amp. and my 300B SE use 5600 Primary to get
Zout = (Ra / (Primary/Secondary)) = (700 / (5600/8)) = (700 / 700) = 1ohm
so 630mohm is between a solid state amplifier and a single-ended vacuum tube amp.
Don't forget secondary DC resistance of the output transformer; in less than top quality transformers it might easily add 0.5 ohms or more to the total output resistance.
You will agree it is very much closer to vacuum tube amp than the standard quality solid state amp.
The difference is that small that I don't see it as a real advantage (choice of loudspeaker remains important as in the SE tube amp case).
In my opinion the most elegant aspect of your design is the simplicity (but at the same time I think a comparison with for instance the Moskido, also a very popular hybrid design when I check this forum, might be interesting. This one does not need the two floating power supplies).
OK I'll bite. IMO Broskie has been a powerful source of misinformation about Circlotrons for some time, despite the rather obvious fact of how smart and informed he is. I suspect that this comes from not actually having used them or played with them to any great degree- IOW most of his comments don't seem to be based on experience, from where I see it.
IOW, he's not one that you can quote and convince me of at the same time- I just don't buy it.
Build a Circlotron up for yourself and then see if this crossover issue is real or not. That will be the best way to know. I've been playing with them for about 40 years (and gotten awards for them in the audio press) and tried a lot of different things with them, including measurement
I based my prior comments on that experience, having built class A OTLs (something Broskie says can't be done, which is bulls**t), class AB OTLs that operate AB1 and AB2, and also class A2. IME you don't have crossover issues with any of them unless the problem is originating in the driver, which does not count
According to the Audio Cyclopedia, the Wiggins was indeed immune to crossover issues related to collapse of the magnetic field in the transformer, which is why the amp was made class B.
You should (once more) read Broskie's "Cars, Planes and Circlotrons" - october 2003.
I quote:
"....How true are these formulas to reality? I don't know, as I don't have examples of the two amplifiers to test, but I know it is accurate regarding my own pair of Atma-Sphere M-60s
Build a Circlotron up for yourself and then see if this crossover issue is real or not. That will be the best way to know. I've been playing with them for about 40 years (and gotten awards for them in the audio press) and tried a lot of different things with them, including measurement
My point is the class A issue.
No matter the possible benign character of the crossover (by bringing this up you admit we talk class B...) it is suggested here that this particular (?) crossover behaviour "stretches" the class A operation (meaning class A "sound quality"), which IMO it does not.
Broskie never said that class A OTL's can't be done.
I'd say clean up your glasses and read Broskie.
He clearly points out that with the operating points applied the Atma-Sphere MA60 will not supply 60 watts class A (which it wrongly claims....claimed?), but no more than....well you know you have the experience so you will know...
Reminds me of the unity coupling transformers of McIntosh which hit the market at about the same time.
I would not be surprised if a sober and comparative look at both configurations would show them being not very different.
To the best of our knowledge, he never had any such thing (Our customers tend to have very close contact with us). I think its obvious that it was useful to say he did though.