On peaks the final is drawing grid current, to be delivered by the interstage transformer. While delivering current, for maintaining the original voltage it must lower impedance. The driving valve must be able to fall four times in impedance (N<super>2</super>) while maintaining amplification. See the difficulty?
The easier solution is to use a penthode for voltage amplification and run some feedback from end to start of the amplifier to overcome the penthode distortion product. Post tubes are very fine tubes for this duty indeed.
The easier solution is to use a penthode for voltage amplification and run some feedback from end to start of the amplifier to overcome the penthode distortion product. Post tubes are very fine tubes for this duty indeed.
I think there is some misunderstanding here - I'm not using an interstage between driver and output stage. The driver stage uses a plate choke and coupling cap. I'm talking about a step-up on the input to the driver stage. As in this whole thread, I've been debating the choice between an op-amp or a step-up transformer.
I may investigate a pentode at some time in the future, but it's far from a priority and global feedback is out of the question - been there and didn't like it at all. This is a project for triodes, DHT or indirectly heated, with some added gain at the input of the whole 2 stage amplifier. I'd be quite happy with a DAC that put out 5 or 6 volts. It's basically an exercise in getting to that point by different means.
Lets's be clear here, this isn't about conventional thinking of a 300b amp - use a pentode or hi-mu pentode in triode and feed it with 2v from a DAC or preamp. I've studied numerous conventional 300b circuits for many years and built a few that I was never totally happy with. This is going back to the drawing board and saying "let's assume we put 5 or 6 volts or whatever is needed into a 2 stage amp. What does this give us in possibilities?"
I already have a solution built which sounds very nice to me, and has been my main system for a couple of months. NE5534 stage into 46 with plate choke into 300b. The 300b is a constant. I'm now playing around with the driver stage to see what alternatives there are, and the gain of this stage then asks questions about what's feeding it.
There are plenty of guys on this thread with considerably greater knowledge of electronics than me, since I'm self-taught, and I've been gratefully taking detailed notes and trying out suggestions. The feedback I've received has been great, and helped me try out the EL84/EL33/6V6 which opened my eyes about indirectly heated valves. I take all advice seriously and love increasing my knowledge through building up new projects and variations on what I have.
What I do have in my favour is 12 years experience of building many, many valve amplifiers and preamps on a modular basis, plus i have large stocks of valves and components. What I also have is a lifetime of working as a professional musician - I know the sound of acoustic instruments intimately over a lifetime of listening to them close up or playing them myself, so I know exactly what I'm trying to achieve in terms of tonality and realism. I'm not in any way saying the being a musician is an advantage, some would say the exact opposite, but I do know what I'm designing for.
I may investigate a pentode at some time in the future, but it's far from a priority and global feedback is out of the question - been there and didn't like it at all. This is a project for triodes, DHT or indirectly heated, with some added gain at the input of the whole 2 stage amplifier. I'd be quite happy with a DAC that put out 5 or 6 volts. It's basically an exercise in getting to that point by different means.
Lets's be clear here, this isn't about conventional thinking of a 300b amp - use a pentode or hi-mu pentode in triode and feed it with 2v from a DAC or preamp. I've studied numerous conventional 300b circuits for many years and built a few that I was never totally happy with. This is going back to the drawing board and saying "let's assume we put 5 or 6 volts or whatever is needed into a 2 stage amp. What does this give us in possibilities?"
I already have a solution built which sounds very nice to me, and has been my main system for a couple of months. NE5534 stage into 46 with plate choke into 300b. The 300b is a constant. I'm now playing around with the driver stage to see what alternatives there are, and the gain of this stage then asks questions about what's feeding it.
There are plenty of guys on this thread with considerably greater knowledge of electronics than me, since I'm self-taught, and I've been gratefully taking detailed notes and trying out suggestions. The feedback I've received has been great, and helped me try out the EL84/EL33/6V6 which opened my eyes about indirectly heated valves. I take all advice seriously and love increasing my knowledge through building up new projects and variations on what I have.
What I do have in my favour is 12 years experience of building many, many valve amplifiers and preamps on a modular basis, plus i have large stocks of valves and components. What I also have is a lifetime of working as a professional musician - I know the sound of acoustic instruments intimately over a lifetime of listening to them close up or playing them myself, so I know exactly what I'm trying to achieve in terms of tonality and realism. I'm not in any way saying the being a musician is an advantage, some would say the exact opposite, but I do know what I'm designing for.
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Ah, comme ca. If you have the opportunity of bringing suitable amplification to the amplifier input (and hence leave out the input transformer) that would be optimal.
So, you are looking for 20 times amplification with a voltage output of around 160Vpp? Vaic EML 30B can take you there if you are prepared to shake your moneymaker 😉
So, you are looking for 20 times amplification with a voltage output of around 160Vpp? Vaic EML 30B can take you there if you are prepared to shake your moneymaker 😉
When winding an input step up transformer, one must aim for high permeability cores to minimize primary turns as low as possible. Some great modern material choices are high mu nanocrystalline torroids. Huge permeability of course means less resistance to DC currents.
Parasitics to watch out are secondary lumped capacitance and overall leakage inductance.
The sum of capacitances (secondary + driving stage) will be reflected squared to the primary.
Parasitics to watch out are secondary lumped capacitance and overall leakage inductance.
The sum of capacitances (secondary + driving stage) will be reflected squared to the primary.
Yes, exactly this. If we make the assumption that we're putting at least 5-6 volts into the amplifier then we don't need pentode drivers. That would be a solution to a problem which didn't exist, or would only exist with a conventional 2v input. This was never meant to be a thread about conventional 300b amps - there's an abundance of threads about that already.
You could also say it's a thread about high output DACs and more of a solid state problem. That could also be true. What it is, in fact, is a thread about what goes between a DAC and a 2 stage amp to add gain. It's about where and how you add the gain. "Comme ca", like you say.
Suggestion:
As you are already into opamps with satisfying results, turn your opamp stage into one with balanced outputs.
Example(s) here: Balanced Transmitter and Receiver II
Then use something like a 6H6 double triode.
Couple this stage to your 300B through your LL1635 (balanced to SE).
Don't be afraid of something "balanced" in your amp....you might be surprised.
As you are already into opamps with satisfying results, turn your opamp stage into one with balanced outputs.
Example(s) here: Balanced Transmitter and Receiver II
Then use something like a 6H6 double triode.
Couple this stage to your 300B through your LL1635 (balanced to SE).
Don't be afraid of something "balanced" in your amp....you might be surprised.
The mention of "balanced" led me to revisit Lynn Olsen's original account of how he conceived the Amity amp. Very interesting reading.
The Amity, Raven, and Aurora
http://www.nutshellhifi.com/IT-Triode-Amp.gif schematic
This isn't SE, but he makes a number of points relevant to this thread:
- The Amity is a 2 stage design which then asks for a gain stage in front of it. The original design has a ECC99 driver tube, mu 22.
- The best preamp Lynn found initially was a Jeff Roland Consonance design using op-amps - "I appreciated the elegance (and boldness) of transformer-coupling a high-speed opamp in a preamp, thus keeping the solid-state electronics happy by filtering off ultrasonics from the CD source."
- He had a lot of trouble with an initial tube stage. "Most tube preamps, in fact, were downright dull and flat-sounding".
- The driver/input tubes he was happiest with were the "space-age family" (5687, 7044, 7119) and "radio-age family" (27, 37, 56, 76, 6P5). For the radio age family I'd add the trioded EL33, PEN 6P25/6, KT61, 6V6 etc. from the '30s.
- His choice of driver tubes were low Ra ones with "very high impedance load relative to the plate impedance ... preferably more than ten times higher".
- He uses teflon caps in critical positions (I use FT-2 coupling caps).
- When he re-designed this as the Karna he used DHTs as drivers (45, 2a3...) or a 6W6 in triode.
http://www.nutshellhifi.com/Karna.gif
i always liked Lynn Olsen's way of thinking - he analysed what he saw as problems and came up with solutions directly out of the problem set, ignoring conventional thinking (e.g. 12a*7 tubes, 2v input, no op-amps, Williamson type circuits).
The Amity, Raven, and Aurora
http://www.nutshellhifi.com/IT-Triode-Amp.gif schematic
This isn't SE, but he makes a number of points relevant to this thread:
- The Amity is a 2 stage design which then asks for a gain stage in front of it. The original design has a ECC99 driver tube, mu 22.
- The best preamp Lynn found initially was a Jeff Roland Consonance design using op-amps - "I appreciated the elegance (and boldness) of transformer-coupling a high-speed opamp in a preamp, thus keeping the solid-state electronics happy by filtering off ultrasonics from the CD source."
- He had a lot of trouble with an initial tube stage. "Most tube preamps, in fact, were downright dull and flat-sounding".
- The driver/input tubes he was happiest with were the "space-age family" (5687, 7044, 7119) and "radio-age family" (27, 37, 56, 76, 6P5). For the radio age family I'd add the trioded EL33, PEN 6P25/6, KT61, 6V6 etc. from the '30s.
- His choice of driver tubes were low Ra ones with "very high impedance load relative to the plate impedance ... preferably more than ten times higher".
- He uses teflon caps in critical positions (I use FT-2 coupling caps).
- When he re-designed this as the Karna he used DHTs as drivers (45, 2a3...) or a 6W6 in triode.
http://www.nutshellhifi.com/Karna.gif
i always liked Lynn Olsen's way of thinking - he analysed what he saw as problems and came up with solutions directly out of the problem set, ignoring conventional thinking (e.g. 12a*7 tubes, 2v input, no op-amps, Williamson type circuits).
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Quick update. I did some A-B tests today between my 46 driver stage and my new EL33 driver stage. To my surprise I preferred the EL33 - more focussed and really good tonality top to bottom. So I've been re-wiring my equipment through the day. The 46 stage is now on the shelf.
I still want to eliminate some other driver choices like the 6V6, E80L and 6197 which I have, and I may get some 6P25 if the price is right, but it's starting to look like the EL33 is the driver of choice here. So now I have too much gain from the x5.5 NE5534 stage so I could look at revising that. No special rush, since the whole system is sounding very nice as it is. Changes the title of the thread, though! This whole project has been very educational and where I've ended up isn't where I thought it would be.
I still want to eliminate some other driver choices like the 6V6, E80L and 6197 which I have, and I may get some 6P25 if the price is right, but it's starting to look like the EL33 is the driver of choice here. So now I have too much gain from the x5.5 NE5534 stage so I could look at revising that. No special rush, since the whole system is sounding very nice as it is. Changes the title of the thread, though! This whole project has been very educational and where I've ended up isn't where I thought it would be.
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Good to hear you like your EL33. Perhaps it may be interesting to revise the 46 implementation. I do love my D3a driver, but have to admit when I switch to 47 it had the DHT detail I was slightly missing. 46 and 47 aren’t easy to implement as it is the 45. Filament bias isn’t an option and to get the best out of them in my opinion needs a mu-follower stage and ideally a SUT to get the gain levels you want. Of course the OpAmp can remove the SUT, however it’s not my preferred choice from a sound point of view.
Keep posting your feedback on IHT drivers! No need to change the thread!
Cheers
Ale
Keep posting your feedback on IHT drivers! No need to change the thread!
Cheers
Ale
Hello Ale! Yes, I was thinking exactly what you say about the 46. It wasn't proper A-B comparison since the EL33 had a LL1660/18 plate choke and the 46 had a NP amorphous plate choke, which I would have actually thought was better from past experiments. But as you say I should try the 46 with a gyrator before ruling it out. So many variables to play around with.
The EL33 doesn't lack detail - far from it, it's very detailed. But as you say it isn't a DHT. I know just what you mean about DHTs - Lynn Olsen calls it "vitality". I'd maybe call it "vividness" or "clarity" or "timbre" or any combination of those.
I have a LL1554 to try out on the input. When I get round to wiring it up that should be informative - it's close to what RajkoM uses (LL1544A) and I have huge respect for him.
The EL33 doesn't lack detail - far from it, it's very detailed. But as you say it isn't a DHT. I know just what you mean about DHTs - Lynn Olsen calls it "vitality". I'd maybe call it "vividness" or "clarity" or "timbre" or any combination of those.
I have a LL1554 to try out on the input. When I get round to wiring it up that should be informative - it's close to what RajkoM uses (LL1544A) and I have huge respect for him.
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I have wondered about a solution like this. I would prefer to use the balanced outputs of a DAC to do the phase splitting. Recombining in an IT is a nice way to get common-mode distortion cancellation (from the DAC output), and breaking the ground-path from DAC to monoblocks is no bad thing.
Hi Ale , I am using the 45 driving the 300B tube.
Between the two is a Lundahl LL1671.
Can I calculate the plate resistance that the primary of the LL1671 in Kohm delivers to the anode of the 45?
With the grid resistor can I control it ?
Santiago.
Attachments
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"With the grid resistor can I control it ?"
The LL ITs tend to hump at few tens of kHz, the second side load smoothing it, and achieve proper load on the primary side.
The LL ITs tend to hump at few tens of kHz, the second side load smoothing it, and achieve proper load on the primary side.
DAC 5v balanced out into TVC
For several years I've been driving a two stage SE power amp: E182cc anode loaded with a 1:1 IT driving a 300B with Tent 5v & -ve bias boards, with a silk TVC (Transformer Volume Control) driven by the 5v balanced output of a Master 7 DAC. Speakers are Vitavox Thunderbolts (photo in last link) all works very well with plenty of volume available 🙂
SAC Thailand
???响
Audio Asylum Thread Printer
For several years I've been driving a two stage SE power amp: E182cc anode loaded with a 1:1 IT driving a 300B with Tent 5v & -ve bias boards, with a silk TVC (Transformer Volume Control) driven by the 5v balanced output of a Master 7 DAC. Speakers are Vitavox Thunderbolts (photo in last link) all works very well with plenty of volume available 🙂
SAC Thailand
???响
Audio Asylum Thread Printer
Contrary to the title of the thread I've been trying out a number of indirectly heated drivers. I've already mentioned the EL33, but I have a new contender, the RSD EL12n. Available new in box and quite cheaply from several European dealers. Kind of the 4P1L of indirectly heated tubes. It has a Y8A base, so not for everyone and probably a reason why stocks aren't moving very fast, besides which it's a relatively obscure tube.
I can't choose between them in my system - EL33 is the choice for voices, warm and euphonic. EL12n is the choice for orchestral music - clean, focussed and very detailed. I'd like a combination of both! One or two more types in the post to try out, but this is the solution I have in mind. Mu of around 20, low bias voltage so can be used as a driver without a cathode bypass capacitor given a plate choke with a high inductance, which I have (180H). I still need a gain stage in front but with a mu of 20 it goes down to maybe x2 or x3 gain. Well within the scope of a transformer - plenty of options for 1:2 step-up. Or indeed my op-amp solution.
I can't choose between them in my system - EL33 is the choice for voices, warm and euphonic. EL12n is the choice for orchestral music - clean, focussed and very detailed. I'd like a combination of both! One or two more types in the post to try out, but this is the solution I have in mind. Mu of around 20, low bias voltage so can be used as a driver without a cathode bypass capacitor given a plate choke with a high inductance, which I have (180H). I still need a gain stage in front but with a mu of 20 it goes down to maybe x2 or x3 gain. Well within the scope of a transformer - plenty of options for 1:2 step-up. Or indeed my op-amp solution.
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A little time has passed and I've been relatively happy with driving the 300b with an indirectly heated tube with mu = around 20. Tried out stuff like KT61, EL41, EL33, EL12n. I've needed some extra gain which I've got from my NE5534 op-amp stage at the front of the amp. Haven't tried a 1:2 step-up transformer on the input yet.
I've avoided higher mu drivers up to now - I didn't much like the smaller 9-pin tube options I tried and preferred the sound of the lower mu larger pentodes/tetrodes in triode. I haven't tried well-respected tubes like C3G yet, though, and I know it's a favoured solution.
So with the problem of getting enough gain in the system still in my head I asked myself what would happen if I used an output tube with higher gain instead of the 300b. A mu of anything from 8-10 up would be enough for my system, given a driver with a mu of 20 which I now have. That opens up the door for PSE 4P1L which I've used for many years, or various indirectly heated tubes. I could move the KT61, EK41 etc into the output in PSE for instance.
So with an output tube with a mu of 20 I could then go back to a DHT driver tube - 10Y, 46, 26 etc. Maybe that way round would give me some nice sounds. I started by using the EL12n in the output, since it's higher power. Results were interesting. Eliminating the op-amp stage made the sound more dynamic. The effect of the op-amp stage wasn't so much on tone and detail, which was well preserved, but on flattening out the dynamics a little and taking a little of the life out of the sound. The EL12n is good for detail and clarity but it's a touch grainy in my implementation of it. It lacks the smooth sound of the 300b. So it's close but no cigar. I liked eliminating the op-amp stage, though, so I'm back to the drawing board.
In conclusion there are 2 ways I can go for the next step:
- output tube or tubes with a gain of at least 8-10 plus a driver with a mu of around 20. This points to 4P1L in PSE as a first step
- output tube or tubes with a gain of around 20 plus a driver with a mu of 8-10 up. This would include DHTs.
All this is very time consuming, even if my constructions are modular and easier to link together in various permutations. Hopefully there's a magic solution somewhere in there. So that's it for now - my updated status report.
I've avoided higher mu drivers up to now - I didn't much like the smaller 9-pin tube options I tried and preferred the sound of the lower mu larger pentodes/tetrodes in triode. I haven't tried well-respected tubes like C3G yet, though, and I know it's a favoured solution.
So with the problem of getting enough gain in the system still in my head I asked myself what would happen if I used an output tube with higher gain instead of the 300b. A mu of anything from 8-10 up would be enough for my system, given a driver with a mu of 20 which I now have. That opens up the door for PSE 4P1L which I've used for many years, or various indirectly heated tubes. I could move the KT61, EK41 etc into the output in PSE for instance.
So with an output tube with a mu of 20 I could then go back to a DHT driver tube - 10Y, 46, 26 etc. Maybe that way round would give me some nice sounds. I started by using the EL12n in the output, since it's higher power. Results were interesting. Eliminating the op-amp stage made the sound more dynamic. The effect of the op-amp stage wasn't so much on tone and detail, which was well preserved, but on flattening out the dynamics a little and taking a little of the life out of the sound. The EL12n is good for detail and clarity but it's a touch grainy in my implementation of it. It lacks the smooth sound of the 300b. So it's close but no cigar. I liked eliminating the op-amp stage, though, so I'm back to the drawing board.
In conclusion there are 2 ways I can go for the next step:
- output tube or tubes with a gain of at least 8-10 plus a driver with a mu of around 20. This points to 4P1L in PSE as a first step
- output tube or tubes with a gain of around 20 plus a driver with a mu of 8-10 up. This would include DHTs.
All this is very time consuming, even if my constructions are modular and easier to link together in various permutations. Hopefully there's a magic solution somewhere in there. So that's it for now - my updated status report.
But merlin - there isn't an all-DHT option unless you use expensive boutique DHT drivers with a mu of 20 or more. Or put a gain stage in front of the amp. Or use a DHT driver in pentode, which isn't in my present plans. The common DHTs don't have a mu of more then 10-11 (4P1L). OK, there are output tubes with higher mu like the 211 but they're high voltage tubes, and again not in my plans.
There's not exactly "no way out" - there are several ingenious options already listed earlier in the thread, especially pentodes. But there isn't a commonly available DHT all-triode solution that doesn't involve boutique tubes and that offers enough gain in 2 stages. Hence the need to be more creative and do some lateral thinking. The easy option is a higher mu indirectly heated driver for a 300b or 2a3, but there are already plenty of threads on that.