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Hi-end GM70 amplifier with only 2 stages

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andrzej1959

Member
Joined 2010
I dont like interstage transformers.

Im tested LEGENDARY amplifier CARY CAD 805 300B good quality Sophia Royal with interstage driving 845 Unison Research or 211 tube too.

My design Gm70 or 813 sound much better then testing CARY.

Many peoples like choke or resistive loaded driving output tube with good CAP.

Nicholas' GM70 SE Amp

Audio note ONGAKU KONDO design no interstage driving output tube.
One is the best tube amplifier with silver output transformer.

Andrew polskihiend Guru in Poland EU.
 
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45

Account Closed
Joined 2008
andrzej1959 said:
I dont like interstage transformers.

Im tested LEGENDARY amplifier CARY CAD 805 300B good quality Sophia Royal with interstage driving 845 Unison Research or 211 tube too.

My design Gm70 or 813 sound much better then testing CARY.

Many peoples like choke or resistive loaded driving output tube with good CAP.

Nicholas' GM70 SE Amp

Audio note ONGAKU KONDO design no interstage driving output tube.
One is the best tube amplifier with silver output transformer.

Andrew polskihiend Guru in Poland EU.
Click to expand...

You can like anything but for sure that resonant circuit is still a bad design. The reason why LC coupling gained some popularity some years back was the lack of availability of interstage transformers (the excellent and expensive Japanese transformers were basically the only ones). I used LC coupling once while I was waiting for a Tango NC-20 to be delivered and of course the Tango was and is FAR better than any choke and capacitor. Transformer coupling also doesn't cause blocking distortion which is there once there is a cap.
I forgot to say that the good Lundahl LL2756 costs 150 euro tax included while the Sowter anode choke costs 130 GBP (i.e. almost 170 euro)! Still need to buy grid choke and capacitor.

andrzej1959 said:
Audio note ONGAKU KONDO design no interstage driving output tube.
One is the best tube amplifier with silver output transformer.

Andrew polskihiend Guru in Poland EU.
Click to expand...

What is the point of calling the Ongaku into cause? Do you think I don't know it? That is completely different amplifier and has nothing to do with the subject of this discussion. Nothing to do with your badly designed resonant circuit because there is no resonance. It has no transformers and no chokes. It has an active loaded voltage amplifier RC coupled to a cathode follower driver. The cathode follower is DC coupled to the power tube. So there is no cap between the driver and the power tube as well. No blocking distortion in this case as well. Mr Kondo would be offended to see his amplifier compared to a guru amplifier......
 
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45

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Joined 2008
andrzej1959 said:
Please show me speakers works from 8Hz or Output transformers maybe lundahl....Tango, Tamura, Hashimoto, Magnaqest, Audio Note....

who the people hear 8Hz 0,00000001 percent people population.
Click to expand...

I think I have already explained what LC coupling does. Even worse if there is a grid choke. It is not about what your hear at 8Hz but what it does to the bass frequency range. Easily up to 80-100Hz. Measure the driver at full swing at 30Hz, 50 Hz, 100Hz and compare to 1KHz. Then see which frequency have 30, 50 and 100Hz harmonics and you can see audible effects do fall where 99.9999999% of population can hear them. Do the same with a proper interstage or any other properly designed non-resonant circuit.
 
kevinkr

kevinkr

Administrator
Joined 2004
kta-hifi.net
Paid Member
Confessing to being in the interstage camp and can corroborate the issues with LF resonances with grid chokes in particular and lots of phase shift well into the audio band unless the resonance is below a couple of Hz.
Regular choke loaded drivers work quite well too depending on the design requirements.

I can recommend interstage transformers from Monolith Magnetics. (what I am using.)

Edit: IMO I wouldn't consider anything designed by Cary to be "legendary" nor a standout from the background noise of their competition. (Obviously just the opinion of another diy nobody..)
 
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andrzej1959

Member
Joined 2010
I like the sound natural , such as concert live . It is not a sound perfectly fine , many harmonic distortion. Distilled water is absolutely chemically cleen and pure but no one is drinking. Transistor amplifier have a ideal parameters but sound no good tube SOUND much better.


WHY....

I posted a couple of schemes to assess members Diy i posted a couple of schemes to members DIY .

I showed my portfolio, PLEASE give pictures Yours good BEST sound amplfier and best circuit.
Im Waiting

My amplifier sound very good ACOUSTIC LIVE.
B. Regards

polskihiend
 
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pieter t

Disabled Account
Joined 2009
tribute-audio.nl
What a nonsense :D
Natural sound is what we all prefer, and it is perfectly possible with solid state as well as tube electronics.
Your generalizations and comparisons have no clue, and have been everlasting subjects on this forum; pointless :mad:
As long as you accurately express your opinion we know how serious we have to take them :rolleyes:
It seems better to come up with some solid technical backing of your arguments.

And last but not least: a moderator's opinion is not more valid because it's a moderator's opinion .....
 
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djn

djn

Member
Joined 2004
Hey 45, I might be getting confused here and this is all very important to me because I finally have all the parts for my amp using Nicholas' GM70 schematic.

When you talk about LC coupling, are you talking about the plate choke going to the driver tube and the cap going from the driver tube to the GM70?

If so, would the inter-stage replace both of them?

Also, and this is out of pure confusion, but when you say an amp resonates at 23hz, will that matter if my speakers don't go down that low?
 
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45

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djn said:
Hey 45, I might be getting confused here and this is all very important to me because I finally have all the parts for my amp using Nicholas' GM70 schematic.

When you talk about LC coupling, are you talking about the plate choke going to the driver tube and the cap going from the driver tube to the GM70?

If so, would the inter-stage replace both of them?

Also, and this is out of pure confusion, but when you say an amp resonates at 23hz, will that matter if my speakers don't go down that low?
Click to expand...

Yes it replaces both choke and cap an possibly grid resistor which you might not need with the transformer.
Having a resonance at 23 Hz means that for the full bass range the driver will work into a rather reactive load and distortion is made of higher frequency harmonics. It matters. At least you should check it doesn't distort too much (I doubt it) and use a bigger capacitor to make sure you get resonance as low as possible and good damping.
Also with transformer you don't have blocking distortion caused by grid current which is particularly relevant for tubes like GM70, 211 etc...
Nowadays there are good affordable transformers. I don't see any reason for using LC coupling anymore.
 
djn

djn

Member
Joined 2004
Thanks 45. I have all the parts and will do it with the choke and cap first. The schematic calls for a .47 coupling cap but I plan on using a 1.5uf PIO Siemens for the coupling cap.

I might need help with how to measure for distortion when it is done and can make changes as needed.

p.s., how do I size an interstage xformer?
 
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