Hey guys, just built the sun audio 2a3 using all Hammond transformers. I like what I'm hearing (clear/transparency/detailed) but I'm looking for a more warmer/meatier sound. Any advice?
Also there's too much gain, my volume pot is super sensitive! Should I convert the DC 6sn7s to parallel?
Any help would be appreciated, Thanks!
Also there's too much gain, my volume pot is super sensitive! Should I convert the DC 6sn7s to parallel?
Any help would be appreciated, Thanks!
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For a meatier sound I'd suggest a driver valve with more current through it, like even 20mA or more. If you're going to do this in 2 stages, which would be good for clarity, that means a mu of more like 30 at least. Something like a 6J49P or 6N1P in parallel if necessary, but you could try singly. Or a C3g is a popular driver, D3a too, both in triode.
If it were my amp I'd use a plate choke on the driver tube and a Russian FT-3 teflon coupling cap.
If it were my amp I'd use a plate choke on the driver tube and a Russian FT-3 teflon coupling cap.
6SN7GT with 70V (62K) and 210V (27K) seems like it's being starved but that's also inline with the Andy's comment about current.
Perhaps someone can educate/correct me a little. It me the design has a bypass cap on the input 6SN7 for feedback then feeds back through the voltage pot.. so vary the volume it varies the feedback too (although a 100K pot is minimal at normal levels of music)?
Perhaps someone can educate/correct me a little. It me the design has a bypass cap on the input 6SN7 for feedback then feeds back through the voltage pot.. so vary the volume it varies the feedback too (although a 100K pot is minimal at normal levels of music)?
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I can’t think of any reason at all for making a link between driver standing current and a subjectively meatier sound. I know some people think everyone else is mad when they use low driver current, but for the 2A3 this is not substantiated by experience. There is an engineering argument that says high frequency fall off occurs below 20kHz due to Cmiller but it’s not been found to be a serious issue. And besides, how would extending the roll off higher help with the meatier sound; most adults can’t hear to 20kHz either.
Going out on a limb, I might assume meatier sounds means subjectively a bit more upper bass, or at least a bit more 2nd harmonic. Are you saying that there’s an operating point at higher current which achieves this ?
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There’s a lot of reading you can do to learn more about how your amp works, on line. But it might be worth giving yourself some time with the amp.
Your amp has no loop feedback, your volume control is not part of any feedback loop. Removing either, or both, of the 6SN7 cathode capacitors will cut the gain, especially the 2nd one.
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Just personal experience - I can't quote any science for you. It may be a question of slew rate, but again, I can only point to other posters who mention this. e.g. Miles Prower
"For VTs, the limiting factor for slew rate is input capacitance and how fast you can charge it so that the grid sees the true signal level in a timely fashion. Slew rate becomes a problem if you try to drive the grid(s) of the final with something like a 12AX7 drawing plate currents on the order of a milliamp. It isn't going to be able to source the required current. Yet you see that all too often."
Driving 211 with VT25 or EL34?
Also see Bartola Valves
Slew Rate in Preamps – Bartola(R) Valves
Maybe you could talk a little about how slew rate applies here?
Hi,
For those interested in a C3M driving a 2A3, this schema by Oguri-san was given to me years ago.. I haven’t tried it but seems not too complicated. You can use a zener string for the Esg 60V B+..
For those interested in a C3M driving a 2A3, this schema by Oguri-san was given to me years ago.. I haven’t tried it but seems not too complicated. You can use a zener string for the Esg 60V B+..
So I removed the bypass capacitor on the first input stage, this greatly helped with the gain problem, I'm liking what I'm hearing.. Is this more of the 2a3 doing the amplification?
The 6SN7 tube data lists operation at 90V plate, and 250V plate.
Two steps:
1. Remove the 2nd 6SN7 triode's cathode bypass cap, and if you have the amount of gain you want (versus the volume control), you will know if a single 6SN7 stage will work for you.
A single 6SN7 triode with the proper bias and plate resistors should be able to drive a 2A3, if there is enough B+, and if the current is not starved, and not near the max either.
2. With your B+, a single 6SN7 triode, a cathode resistor of 1.5k to 2k, the same bypass cap across the 1.5 to 2k cathode resistor, and a plate resistor of 27k might be a good place to start.
If the amp is wired point to point, that will be a lot easier to try than if it has a PCB.
What are your loudspeakers (model or model(s)? if 2 or more speaker types).
Before any modification of the amp, ask yourself, is it mostly the amplifier, or mostly the speakers, etc.
Part of how a speaker sounds is controlled by the output stage damping factor, and also by how the amplifier's output stage deals with the loudspeaker load (such as eliptical load at each frequency that has capacitive or inductive reactance).
Two steps:
1. Remove the 2nd 6SN7 triode's cathode bypass cap, and if you have the amount of gain you want (versus the volume control), you will know if a single 6SN7 stage will work for you.
A single 6SN7 triode with the proper bias and plate resistors should be able to drive a 2A3, if there is enough B+, and if the current is not starved, and not near the max either.
2. With your B+, a single 6SN7 triode, a cathode resistor of 1.5k to 2k, the same bypass cap across the 1.5 to 2k cathode resistor, and a plate resistor of 27k might be a good place to start.
If the amp is wired point to point, that will be a lot easier to try than if it has a PCB.
What are your loudspeakers (model or model(s)? if 2 or more speaker types).
Before any modification of the amp, ask yourself, is it mostly the amplifier, or mostly the speakers, etc.
Part of how a speaker sounds is controlled by the output stage damping factor, and also by how the amplifier's output stage deals with the loudspeaker load (such as eliptical load at each frequency that has capacitive or inductive reactance).
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A 6SN7 has a mu of 20. That might be rather borderline unless there's some gain in the preamp if one is used. When I use an EL33 to drive a 300b output, I could do with more amplification into 89db sensitive speakers coming from a DAC with the usual 2v stated output. EL33 is also mu of 20. That's why I'm thinking a driver with a mu of 30 or more.
I'm using Altec 604E speakers Sensitivity: 100dB.
Problem I had was with the stock SV-2a3 circuit was that barely turning the volume knob up would make the volume super loud, I couldn't listen at low listening levels.
Removing the bypass cap on the input helped a lot! Its actually enjoyable now. I'm still missing some of that warmth/tubey lush sound I miss with my old Scott 299D amplifier.
I will try the other suggestions recommended!
Problem I had was with the stock SV-2a3 circuit was that barely turning the volume knob up would make the volume super loud, I couldn't listen at low listening levels.
Removing the bypass cap on the input helped a lot! Its actually enjoyable now. I'm still missing some of that warmth/tubey lush sound I miss with my old Scott 299D amplifier.
I will try the other suggestions recommended!
This amp is in fact a power amp incl. a pre. So swap the first amp stage, that helps.
Mostly the tubes and iron make the sound. Get some good NOS 2A3 and the same NOS 6SN7/CV1988 (the best!) for this amp and you'll get rid of thin sounding chinese tubes.
Btw, every excellent tube amp shouldn't sound like a bad tube radio. Instead it should sound like a super transistor amp. And thats what they going to sound, if build with the best parts. That makes the difference. Your reference should not be a cheap consumer amps sound, but a very much refined transistor amp without all their inherent design flaws. Thats what a good tube amp can sound like.
Mostly the tubes and iron make the sound. Get some good NOS 2A3 and the same NOS 6SN7/CV1988 (the best!) for this amp and you'll get rid of thin sounding chinese tubes.
Btw, every excellent tube amp shouldn't sound like a bad tube radio. Instead it should sound like a super transistor amp. And thats what they going to sound, if build with the best parts. That makes the difference. Your reference should not be a cheap consumer amps sound, but a very much refined transistor amp without all their inherent design flaws. Thats what a good tube amp can sound like.
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Unless one is hard of hearing, or unless one is far from the speakers, or unless the listener likes near ear splitting volume, a speaker with 100dB sensitivity does not require much power, and an amplifier with too much gain is not necessary.
Is there enough sensitivity with the bypass cap removed?
The gain difference between tubes with a mu of 20 and a mu of 30, is only 3.5 dB.
Just for fun (and to hear the difference, you might like it), connect the 2A3 plate to the 3.5k tap, instead of the 2.5k tap).
Is there enough sensitivity with the bypass cap removed?
The gain difference between tubes with a mu of 20 and a mu of 30, is only 3.5 dB.
Just for fun (and to hear the difference, you might like it), connect the 2A3 plate to the 3.5k tap, instead of the 2.5k tap).
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Yes removing the first bypass cap helped a lot, The volume pot would only have to be moved a millimeter and it would be too loud for low listening.
I'm gonna remove the second bypass capacitor and see how it goes!
I'm gonna remove the second bypass capacitor and see how it goes!
This amp is super loud and high gain, thats part of the design. It was my first tube amp, but with 300B. In the wrong combination, that could make the problems described here.
Yes - 100db is more than the 89db of my units. Didn't realise the guy had such sensitive speakers.
Removing both the 6sn7 capacitors greatly helped with the gain problem! I can turn the volume knob to halfway and there's no sharp increase in gain, smooth.
Put the first bypass cap back in.
Take out the second bypass cap.
Do that just to see about the gain issue.
If the gain is correct now, the new problem might be less total output power before clipping, because the second stage will not have enough dynamic range.
And, with the floating 2nd cathode (un-bypassed), there may be hum.
But, if the gain is correct, then you can use a single 6SN7 triode gain stage. Just change the self bias resistor and plate load resistor to optimize the input stage, and use RC coupling to the 2A3 grid.
See Post # 9 for a description of a single triode circuit (1.5 to 2k, bypass cap, 27k plate load, and RC coupling from the plate to the 2A3).
That may do it for you.
After that, do not forget to try with the 2A3 plate connected to the 3.5k primary tap.
Take out the second bypass cap.
Do that just to see about the gain issue.
If the gain is correct now, the new problem might be less total output power before clipping, because the second stage will not have enough dynamic range.
And, with the floating 2nd cathode (un-bypassed), there may be hum.
But, if the gain is correct, then you can use a single 6SN7 triode gain stage. Just change the self bias resistor and plate load resistor to optimize the input stage, and use RC coupling to the 2A3 grid.
See Post # 9 for a description of a single triode circuit (1.5 to 2k, bypass cap, 27k plate load, and RC coupling from the plate to the 2A3).
That may do it for you.
After that, do not forget to try with the 2A3 plate connected to the 3.5k primary tap.
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I think I may try to wire this amp to use something like a 6j5, (one half a 6sn7). The gain is perfect, I don't really need anymore.
I chose this circuit because it was super simple to build, barely any passive parts, but didn't realize how much input sensitivity (150mv) would be.
I chose this circuit because it was super simple to build, barely any passive parts, but didn't realize how much input sensitivity (150mv) would be.
By swapping out second bypass cap, driver stage impedance is greatly enhanced. Something no one would want because it destroys ability to sound dynamic without neg. feedback.
This amp is something not to modify easily, because it all makes sense. And more sense than all mods I've seen from amateurs who think they can be smarter than the asian man who developed this amp. But most of them weren't smarter in the end.
Best is, if this amp is too loud, attenuate the input signal not modding the amp.
Especially when your a noob, swapping just this and that without understanding the concept behind this simple looking design.
This amp is something not to modify easily, because it all makes sense. And more sense than all mods I've seen from amateurs who think they can be smarter than the asian man who developed this amp. But most of them weren't smarter in the end.
Best is, if this amp is too loud, attenuate the input signal not modding the amp.
Especially when your a noob, swapping just this and that without understanding the concept behind this simple looking design.
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