AE Europe got an excellent 1:1 interstage which i have tested and is one of the best I ever tried. It is also very cheap compared to performance.
Yesterday Mr. Bartolucci was in my house.
We hava compared the sound of the all Tango solution to the all Bartolucci set in the GM70 amplifier.
All the persons present have considered the Bartolucci result better than Tango.
We have also compared the sound of the my 2 stage GM70 to the amplifier used by Bartolucci in the last Hi-end meeting in Milano (Italy)
http://nuke.nonsoloaudiofili.com/Portals/0/Milano Hi-End 2009 B/175.jpg
This is a 3 stage amplifier using the 2A3 to drive the GM70 and separated vacuum tube power supply per each channel.
The my 2 stage has been considered better for many factors.
After these tests has been tested on this 845 amplifier a new prototype of interstage created with a different way (not two-wire and with a turn ratio 2:1).
The result is great, I have seen a flat frequency response in the range 20-20KHz.
Soon I will have the final version of these new interstage with a turn ratio 1.5:1.
We hava compared the sound of the all Tango solution to the all Bartolucci set in the GM70 amplifier.
All the persons present have considered the Bartolucci result better than Tango.
We have also compared the sound of the my 2 stage GM70 to the amplifier used by Bartolucci in the last Hi-end meeting in Milano (Italy)
http://nuke.nonsoloaudiofili.com/Portals/0/Milano Hi-End 2009 B/175.jpg
This is a 3 stage amplifier using the 2A3 to drive the GM70 and separated vacuum tube power supply per each channel.
The my 2 stage has been considered better for many factors.
After these tests has been tested on this 845 amplifier a new prototype of interstage created with a different way (not two-wire and with a turn ratio 2:1).
The result is great, I have seen a flat frequency response in the range 20-20KHz.
Soon I will have the final version of these new interstage with a turn ratio 1.5:1.
Hi Andrea
Later this year I’ll be doing an 845 SE.
Its to run into class A2: a small benefit of A2 is extra power, but I’ve heard a an SE class A2 on an 808 (radio transmitter tube) based amplifier with just modest parts in a seven way amplifier comparison. To my ears and one other, it was the best, on music I really like. http://www.tubelab.com/845SE.htm has some test results on A2 vs A1.
For prts - I already have some very good Tamura output trannies, and a very good high voltage toroidal power transformer.
I was going to do a three stage – but can imagine the benefit of only two stages.
With properly rated output transformers, etc, would your design (adapt to) run into class A2?
How far off recommendations or a partial kit are you?
In particular for a sweet spot on value interstages, the INT.XR-B, the INT8C NEW, a later INT8C or a newer one; or AE Europe?
Thank you
Later this year I’ll be doing an 845 SE.
Its to run into class A2: a small benefit of A2 is extra power, but I’ve heard a an SE class A2 on an 808 (radio transmitter tube) based amplifier with just modest parts in a seven way amplifier comparison. To my ears and one other, it was the best, on music I really like. http://www.tubelab.com/845SE.htm has some test results on A2 vs A1.
For prts - I already have some very good Tamura output trannies, and a very good high voltage toroidal power transformer.
I was going to do a three stage – but can imagine the benefit of only two stages.
With properly rated output transformers, etc, would your design (adapt to) run into class A2?
How far off recommendations or a partial kit are you?
In particular for a sweet spot on value interstages, the INT.XR-B, the INT8C NEW, a later INT8C or a newer one; or AE Europe?
Thank you
About the transation in A2 class there is a good article on:
http://www.geocities.com/bobdanielak/se_sv572.html
A2 class amplifier give a bad sound and it is necessary a feedback to compensate this problem.
Any A1 class amplifier can go in A2 class if the driver current is enough but if we keep in A1 the sound is better.
Using 1100v with these output tubes like the 845, 211 and GM70 it is possible get a very high power near to 20w and never go in A2 class.
In A2 class forget 1-2% thd without feedback.
Many years ago I have created a prototype amp. for the Aria company, they must use power supply voltage under 600v to keep the insurance rates low.
I have used SV811-3 driver by EL34 and 600v, the power was high going in A2 but the sound was terrible if compared to my 2A3 Reference PSE.
http://www.geocities.com/bobdanielak/se_sv572.html
A2 class amplifier give a bad sound and it is necessary a feedback to compensate this problem.
Any A1 class amplifier can go in A2 class if the driver current is enough but if we keep in A1 the sound is better.
Using 1100v with these output tubes like the 845, 211 and GM70 it is possible get a very high power near to 20w and never go in A2 class.
In A2 class forget 1-2% thd without feedback.
Many years ago I have created a prototype amp. for the Aria company, they must use power supply voltage under 600v to keep the insurance rates low.
I have used SV811-3 driver by EL34 and 600v, the power was high going in A2 but the sound was terrible if compared to my 2A3 Reference PSE.
I prefer increase the power supply voltage and keep in A1 class.
In any case this 2 stage design have enough current on driver to support some peak in A2 class.
The final interstage transformer is still in develop state and it will be a 1.5:1 so the 25mA will be 37.5mA on secondary.
Using the 6Hv4A there is enough voltage gain to use a 1.5:1 instead of 1:1 and the amplifier will need about 1Vrms to get 18-20w.
I hope to get these Bartolucci interstage very soon, probably in the next two weeks.
Also the output transformer can support many more power until 30w without increase the distortion.
In any case this 2 stage design have enough current on driver to support some peak in A2 class.
The final interstage transformer is still in develop state and it will be a 1.5:1 so the 25mA will be 37.5mA on secondary.
Using the 6Hv4A there is enough voltage gain to use a 1.5:1 instead of 1:1 and the amplifier will need about 1Vrms to get 18-20w.
I hope to get these Bartolucci interstage very soon, probably in the next two weeks.
Also the output transformer can support many more power until 30w without increase the distortion.
Hi Andrea
(Not really fair to compare an SV811-3 in A2 in a 2A3 Reference PSE . .)
Thank you for the link Bob Danielak’s article. I like the easily re-configurable circuits.
I interpreted Bob results summarised as:
“in Class A2 Grid Drive (Mode 1) sounds really powerful”. And “Mode 3 sounds very similar to Mode 1. . Warm and loud. Perfect for Rock-n-Roll. Does quieter stuff real well too”.
(That was also my distinct impression of an A2 amp).
And “If you like the "Single-Ended" sound usually associated with really nice 300B and 2A3” class A1 is the appropriate choice.
Bob implies the A1/ A2 choice is almost subjective and/ or depends on your favourite music.
Bob’s results differed to George’s (tubelab). Tubelab did 3 experiments to explore A2 operation, each with different current amplification. Have you read his reports?
Eg: “In normal operation the two amps sound similar until a sharp percussive transient occurs. The A1 amp will clip
The A2 amp does not. I find that the A2 amp does a much better job of recreating highly dynamic music which contains a lot of transients. Snare drums, rim shots, the sound of a cello being smacked sharply with the bow.”
Measured distortion is shown.
A better explanation of tubelab results with A2 starts half way down at http://www.tubelab.com/PDcookbook.htm
Eg: “Operation below 20 watts remains unchanged”
“A driver stage that can supply all the grid current the tube demands as the grid goes positive” for A2 is essential.
Though I personally believe a small amount of feedback is ok, tubelab apparently didn’t use it with any of the 3 options.
Most importantly “The distortion numbers improve at EVERY POWER LEVEL. So does the damping factor” referring to TubeCad simulations, verified with measurements and listening tests. Ie, class A2 can also be cleaner.
I’m looking forward to hearing the further refinement of your amp. How far into A2 would the current on your driver stage be likely to allow?
Thanks again
(Not really fair to compare an SV811-3 in A2 in a 2A3 Reference PSE . .)
Thank you for the link Bob Danielak’s article. I like the easily re-configurable circuits.
I interpreted Bob results summarised as:
“in Class A2 Grid Drive (Mode 1) sounds really powerful”. And “Mode 3 sounds very similar to Mode 1. . Warm and loud. Perfect for Rock-n-Roll. Does quieter stuff real well too”.
(That was also my distinct impression of an A2 amp).
And “If you like the "Single-Ended" sound usually associated with really nice 300B and 2A3” class A1 is the appropriate choice.
Bob implies the A1/ A2 choice is almost subjective and/ or depends on your favourite music.
Bob’s results differed to George’s (tubelab). Tubelab did 3 experiments to explore A2 operation, each with different current amplification. Have you read his reports?
Eg: “In normal operation the two amps sound similar until a sharp percussive transient occurs. The A1 amp will clip
The A2 amp does not. I find that the A2 amp does a much better job of recreating highly dynamic music which contains a lot of transients. Snare drums, rim shots, the sound of a cello being smacked sharply with the bow.”
Measured distortion is shown.
A better explanation of tubelab results with A2 starts half way down at http://www.tubelab.com/PDcookbook.htm
Eg: “Operation below 20 watts remains unchanged”
“A driver stage that can supply all the grid current the tube demands as the grid goes positive” for A2 is essential.
Though I personally believe a small amount of feedback is ok, tubelab apparently didn’t use it with any of the 3 options.
Most importantly “The distortion numbers improve at EVERY POWER LEVEL. So does the damping factor” referring to TubeCad simulations, verified with measurements and listening tests. Ie, class A2 can also be cleaner.
I’m looking forward to hearing the further refinement of your amp. How far into A2 would the current on your driver stage be likely to allow?
Thanks again
I want tell you that also using a strong driver with many current in A2 class we will get a higher distortion and lower damping factor at the same power.
A2 class need a global feedback to compansate these effects.
A2 class need a global feedback to compansate these effects.
First of all I think your work is very interesting but I wonder a little about your aversion against A2 operation which seems quite cathegorical.
Could you please elaborate this statement a little? How can a strong driver negatively affect the output stage damping factor? (or any driver for that matter) Also I wonder about the distortion statement since you cannot have the same output power in A1 and A2 for the same idle conditions and the same tube. If you stay in A1 territory I cannot see how a stronger driver could lead to higher distortion.
/Olof
audiodesign said:
Could you please elaborate this statement a little? How can a strong driver negatively affect the output stage damping factor? (or any driver for that matter) Also I wonder about the distortion statement since you cannot have the same output power in A1 and A2 for the same idle conditions and the same tube. If you stay in A1 territory I cannot see how a stronger driver could lead to higher distortion.
/Olof
If the driver stage have enough current it is possible driver the 845 in A2 class but it mean that the 845 grid will start to get current and the driver will change the dynamic characteristics so it will reduce the voltage gain for half of sine wave.
Using A2 tubes like 838 instead of 845 there are many problems because the Ra is more high (see plot) so the unique method to compensate this is add a local or global feedback.
Using A2 tubes like 838 instead of 845 there are many problems because the Ra is more high (see plot) so the unique method to compensate this is add a local or global feedback.
Attachments
Hi Andrea
I just want to say that I didn't mean to debate the merits of A2 in your thread, but just to see if - or how - A2 could be accommodated within your very interesting design
Cheers
🙂
I just want to say that I didn't mean to debate the merits of A2 in your thread, but just to see if - or how - A2 could be accommodated within your very interesting design
Cheers
🙂
Today I have tested a good socket for the 845.
It is an italian semi custom product in teflon with copper pins.
http://www.jakeband.it/
See the photo attached here.
Now I have requested also the model for GM70 and 813.
It is an italian semi custom product in teflon with copper pins.
http://www.jakeband.it/
See the photo attached here.
Now I have requested also the model for GM70 and 813.
Attachments
Finally is ready the transformer designed by Bartolucci for the 6HV5A with turn ratio 1:1
This is an unique design with this incredible parameters:
Lprim & Lsec=150H
RDCprim & RDCsec=440ohm
IDC=25-30mA
Here the measurements of the complete 845 amplifier using this interstage transformer (see ver. 4).
http://www.audiodesignguide.com/Claudio845/int3.html
Frequency band at -3db is about 10Hz - 30KHz
This is an unique design with this incredible parameters:
Lprim & Lsec=150H
RDCprim & RDCsec=440ohm
IDC=25-30mA
Here the measurements of the complete 845 amplifier using this interstage transformer (see ver. 4).
http://www.audiodesignguide.com/Claudio845/int3.html
Frequency band at -3db is about 10Hz - 30KHz
Thsi new interstage has beed created using a special isulated copper able to work until 5000Vdc
To get the best performances with the 6HV5A I have decided to develop with Bartolucci a new interstage with the turn ratio 2:1.
Using this new interstage is possible to drive the 845 in A2 because the 26-27mA in the 6HVA will be 50-54mA on 845 grid like a large power tube as 300b.
Here the incredible result of this solution:
http://www.audiodesignguide.com/Claudio845/intS65N5.html
26W on 8ohm with only 2% thd and output impedance less than 2ohm
The driver stage is able to give 115Vrms with only 0.2% thd
Using this new interstage is possible to drive the 845 in A2 because the 26-27mA in the 6HVA will be 50-54mA on 845 grid like a large power tube as 300b.
Here the incredible result of this solution:
http://www.audiodesignguide.com/Claudio845/intS65N5.html
26W on 8ohm with only 2% thd and output impedance less than 2ohm
The driver stage is able to give 115Vrms with only 0.2% thd
Using this new 2:1 interstage transformer it is necessary 1.4Vrms on input to get the max power so you must use a preampl. because the CD player output could be too low.