I do not thik we can critise youmig-ru said:
by your choice of TUBES
I think you have got just about the best Tubes there!!
Now , what is left is a good circuit,
preferably without transformator
in the signal chain.
So, give this boy a better circuit
PLEASE
I know you all can do it .....
/halo - can't do it
...Some quick initial observations..
Hi,
I've just been through looking at how best to drive and bias a 2A3 for a design of my own and I thought I throw down some thoughts on the beast...
1) It's a great little valve and great prices for good examples e.g. Golden Dragon or Sovtek...
2) it has (like all DHTs) quite a lot of capacitance associated with the grid and therefore needs quite a lot of current to prevent the onset of slew rate limiting...
I calculated that I needed +/- 7.5mA of current drive for 3dB headroom at 25kHz. Your driver circuit would not provide that as shown without lots of distortion. I'll look at it later no time now...
3) My favorite operating point for the Sovtek 2A3 is 275Volts Va-c and -48 Volts Vg-c and about 55mA Ia. That would give you a cathode resistor of 870R.
Some people like different operating points and I'm sure we'll see some different recommendations...
Try them all if you can. It's fun!
Ciao
James D.
Hi,
I've just been through looking at how best to drive and bias a 2A3 for a design of my own and I thought I throw down some thoughts on the beast...
1) It's a great little valve and great prices for good examples e.g. Golden Dragon or Sovtek...
2) it has (like all DHTs) quite a lot of capacitance associated with the grid and therefore needs quite a lot of current to prevent the onset of slew rate limiting...
I calculated that I needed +/- 7.5mA of current drive for 3dB headroom at 25kHz. Your driver circuit would not provide that as shown without lots of distortion. I'll look at it later no time now...
3) My favorite operating point for the Sovtek 2A3 is 275Volts Va-c and -48 Volts Vg-c and about 55mA Ia. That would give you a cathode resistor of 870R.
Some people like different operating points and I'm sure we'll see some different recommendations...
Try them all if you can. It's fun!
Ciao
James D.
Re-worked design....
I have taken the liberty of re-working the design over lunch to illustrate my advice. As commented above I believe the driver was a little under spec. on current delivery and I have chosen to use an ECC99 driver valve. This valve is designed specifically for driving DHT and, in particular, with 2A3 and 300B in mind. It generates lower distortion under high current delivery conditions than most other alternatives.
How to set it up?
Current demand +/- 7.5mA therefore bias driver for over twice that current for good linear performance i.e. >14mA. ECC99 is specified at 18mA Ia so choose that. Grid bias is -6V therefore cathode resistor is 330R. Anode resistor for Va 150volts at 18mA is 8k1. Stage gain is about 17 times.
2A3 is as per my previous message so the circuit looks like the one below.
Hope this helps, I believe it will sound much cleaner than your circuit. Haven't build it but might do one day....
Ciao James D.
I have taken the liberty of re-working the design over lunch to illustrate my advice. As commented above I believe the driver was a little under spec. on current delivery and I have chosen to use an ECC99 driver valve. This valve is designed specifically for driving DHT and, in particular, with 2A3 and 300B in mind. It generates lower distortion under high current delivery conditions than most other alternatives.
How to set it up?
Current demand +/- 7.5mA therefore bias driver for over twice that current for good linear performance i.e. >14mA. ECC99 is specified at 18mA Ia so choose that. Grid bias is -6V therefore cathode resistor is 330R. Anode resistor for Va 150volts at 18mA is 8k1. Stage gain is about 17 times.
2A3 is as per my previous message so the circuit looks like the one below.
Hope this helps, I believe it will sound much cleaner than your circuit. Haven't build it but might do one day....
Ciao James D.
Attachments
James,
MUCH better. I agree that DHTs need a lot of grunt to sound any good, or else they sound all 'tubey' and gutless.
In the last week I've been playing with my PP813, and although an ECC99 should <i>theoretically</i> drive it satisfactorily, adding a power tube as a driver makes a world of difference to how it sounds. I tried EL84's, Sylvania 807 and Svet KT88 (all trioded), and the 807, running at 300V/60mA was incredible. I'll sub a 2A3 in as driver later. [ ECC99 - IT - 807 - IT - 813 all stages differential]
Paul Joppa (amongst others) has made someposts at AA in the past stating that in his experience when a factor of 5x the min theoretical drive current neccessary to slew the outputs is available in the driver, that's when the tubes really come alive and their characteristic signature becomes trivial. The more I experiement the more this seems to bear out, and annoys me because of all the expense it can entail. I've also lost the elegance of a simple two stage design. Oh, well, the sonic benefits are so outstanding it's worth it.
MUCH better. I agree that DHTs need a lot of grunt to sound any good, or else they sound all 'tubey' and gutless.
In the last week I've been playing with my PP813, and although an ECC99 should <i>theoretically</i> drive it satisfactorily, adding a power tube as a driver makes a world of difference to how it sounds. I tried EL84's, Sylvania 807 and Svet KT88 (all trioded), and the 807, running at 300V/60mA was incredible. I'll sub a 2A3 in as driver later. [ ECC99 - IT - 807 - IT - 813 all stages differential]
Paul Joppa (amongst others) has made someposts at AA in the past stating that in his experience when a factor of 5x the min theoretical drive current neccessary to slew the outputs is available in the driver, that's when the tubes really come alive and their characteristic signature becomes trivial. The more I experiement the more this seems to bear out, and annoys me because of all the expense it can entail. I've also lost the elegance of a simple two stage design. Oh, well, the sonic benefits are so outstanding it's worth it.
...more power...
but in the driver stage!
I've not used DHTs until recently but I'm learning real fast that they like current drive...
I spent years getting ss amplifiers to sound as good as possible, and found out that getting the driver stage right was one of the big contributors to how they sounded. It seems that DHTs are the same.
I can relate to Paul Joppas remarks as with sand devices I ended up going for the same i.e. 5 times calculated current. Must be related to the detectable onset of slew rate limiting with complex music signals....
I really like the sound (!) of what you are doing! And the IT definitly sounds best to me too. If I was starting a 2A3 SE from scratch I would use an interstage or at least anode and grid chokes a la Thorsten... And I would probably choose a 6C45 to drive it but for a first amp. that's a bit hairy so the ECC99 is a great second choice...
Ciao
James D
but in the driver stage!
I've not used DHTs until recently but I'm learning real fast that they like current drive...
I spent years getting ss amplifiers to sound as good as possible, and found out that getting the driver stage right was one of the big contributors to how they sounded. It seems that DHTs are the same.
I can relate to Paul Joppas remarks as with sand devices I ended up going for the same i.e. 5 times calculated current. Must be related to the detectable onset of slew rate limiting with complex music signals....
I really like the sound (!) of what you are doing! And the IT definitly sounds best to me too. If I was starting a 2A3 SE from scratch I would use an interstage or at least anode and grid chokes a la Thorsten... And I would probably choose a 6C45 to drive it but for a first amp. that's a bit hairy so the ECC99 is a great second choice...
Ciao
James D
Brett, James, et al,
I have used a high mu driver (6F5) with a plate current of a puny 0.9mA to drive a 71-A, and granted, it may not be identical to a 2A3 or 300B in behavior, but....
do you have an explanation for why that amp sounded so clean, transparent, and dynamic? The same is true for my mono version, which uses an UX-201A with Ip of 3mA. Also, a "classic" like the WE91 uses a 6SJ7, etc, in all the updates I've seen - and that tube draws a few mA at best.
I have used a high mu driver (6F5) with a plate current of a puny 0.9mA to drive a 71-A, and granted, it may not be identical to a 2A3 or 300B in behavior, but....
do you have an explanation for why that amp sounded so clean, transparent, and dynamic? The same is true for my mono version, which uses an UX-201A with Ip of 3mA. Also, a "classic" like the WE91 uses a 6SJ7, etc, in all the updates I've seen - and that tube draws a few mA at best.
ET ALL REPLIES...
Hi Joel,
Just some info:
Posted by Lynn Olson (M) of Aloha Audio on June 03, 2002 at 11:37:45
In Reply to: Confessions of a plate choke convert & a few CCS questions (long) posted by Doug Flynn on June 03, 2002 at 02:41:03:
One of the traps people fall into is not realizing just how low DHT distortion really is ... and that DHT's need a not only a lot of voltage, but enough current to overcome a substantial amount of capacitance (this controls slew rate).
How low? Well, the Amity has no trouble putting out 16 PP watts at 0.3% distortion, and 1.6 watts at 0.07%. That's *including* the distortion of a PP 7119 driver. If you really went nuts on the driver and used something like another 300B (!) as a driver, I'd bet the distortion might fall even more, maybe down to 0.2% or less.
300B's need anything from 42 to 60V rms of extremely linear drive to realize their full potential. I doubt that most people have even heard what a 300B really sounds like ... many DHT amps have more driver distortion than the final stage, and the drivers have the additional disadvantage of not delivering enough current to the DHT grid.
Although bare-bones engineering indicates that only a few milliamps are needed for full power at 20kHz, it's easy to forget that slew distortion is merely the current equivalent of voltage clipping ... and we all know distortion doesn't just go from zero to full. Instead, distortion gradually falls with decreasing level. The same thing happens with *current* distortion - the less current demanded, the more linear the driver is. Well, we can't do much about the current demand of the 300B grid, but we can certainly increase the current running through the driver ... by several times if transformer, choke, or active loading is employed.
Improving the slew rate by several times doesn't sound like what you'd expect. People expect shimmery triangles and amazing transients, but that's not what you notice. Instead, there is a dramatic reduction in the "electronic" coloration of the sound - in fact, most of the "tubey" vintage aspect of the sound disappears.
Since slew distortion is greatest at the zero crossing of the waveform, anything we can do to remove even the slightest trace of slew distortion (which is a different animal than generic THD) will give an astonishing improvement in hearing subtle details in complex passages. After all, we can all live with some distortion on the signal peaks, but we *don't* want any distortion at all in the zero-crossing region.
Personally, I think it's impossible to overdesign a driver or power supply. You want the most linearity possible with lots of linear current available, and the power supply needs to deliver lots of peak current while isolating the audio circuits from rectifier switch-noise and AC line noise.
If you're tired of vintage sound, improve the driver. Go nuts. Aim for 3 to 6dB of headroom or more, at least 15-20 mA of operating current, and transformer, choke, or active loading. (And yes, they all sound different!)
Cheers,
Hi Joel,
Just some info:
Posted by Lynn Olson (M) of Aloha Audio on June 03, 2002 at 11:37:45
In Reply to: Confessions of a plate choke convert & a few CCS questions (long) posted by Doug Flynn on June 03, 2002 at 02:41:03:
One of the traps people fall into is not realizing just how low DHT distortion really is ... and that DHT's need a not only a lot of voltage, but enough current to overcome a substantial amount of capacitance (this controls slew rate).
How low? Well, the Amity has no trouble putting out 16 PP watts at 0.3% distortion, and 1.6 watts at 0.07%. That's *including* the distortion of a PP 7119 driver. If you really went nuts on the driver and used something like another 300B (!) as a driver, I'd bet the distortion might fall even more, maybe down to 0.2% or less.
300B's need anything from 42 to 60V rms of extremely linear drive to realize their full potential. I doubt that most people have even heard what a 300B really sounds like ... many DHT amps have more driver distortion than the final stage, and the drivers have the additional disadvantage of not delivering enough current to the DHT grid.
Although bare-bones engineering indicates that only a few milliamps are needed for full power at 20kHz, it's easy to forget that slew distortion is merely the current equivalent of voltage clipping ... and we all know distortion doesn't just go from zero to full. Instead, distortion gradually falls with decreasing level. The same thing happens with *current* distortion - the less current demanded, the more linear the driver is. Well, we can't do much about the current demand of the 300B grid, but we can certainly increase the current running through the driver ... by several times if transformer, choke, or active loading is employed.
Improving the slew rate by several times doesn't sound like what you'd expect. People expect shimmery triangles and amazing transients, but that's not what you notice. Instead, there is a dramatic reduction in the "electronic" coloration of the sound - in fact, most of the "tubey" vintage aspect of the sound disappears.
Since slew distortion is greatest at the zero crossing of the waveform, anything we can do to remove even the slightest trace of slew distortion (which is a different animal than generic THD) will give an astonishing improvement in hearing subtle details in complex passages. After all, we can all live with some distortion on the signal peaks, but we *don't* want any distortion at all in the zero-crossing region.
Personally, I think it's impossible to overdesign a driver or power supply. You want the most linearity possible with lots of linear current available, and the power supply needs to deliver lots of peak current while isolating the audio circuits from rectifier switch-noise and AC line noise.
If you're tired of vintage sound, improve the driver. Go nuts. Aim for 3 to 6dB of headroom or more, at least 15-20 mA of operating current, and transformer, choke, or active loading. (And yes, they all sound different!)
Cheers,
A 5687 will provide all of the current needs of a 2A3 and enough gain to do the job in one stage.
http://search.ebay.com/search/searc...=0&st=2&SortProperty=MetaEndSort&BasicSearch=
http://search.ebay.com/search/searc...=0&st=2&SortProperty=MetaEndSort&BasicSearch=
Frank, I can't verify if his facts are true or not at the moment, but I can tell you that I don't have "vintage", or "tubey" sound from any of my amps. In fact, I truly wonder what that is in the first place... it's bantered about alot by people who, 9 out of 10 times don't know a tube from a turkey baster. Usually they mean "warm"... which to me means rolled off highs and high distortion - symptoms of an old amp that hasn't been cared for for 50 years.
The cleanest amps I own, SS or tube, are my mono 71's. And they should sound the most "tubey" of all according to the gurus.
Brett, John, or James? I'm still eagerly waiting a reply.
The cleanest amps I own, SS or tube, are my mono 71's. And they should sound the most "tubey" of all according to the gurus.
Brett, John, or James? I'm still eagerly waiting a reply.
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