Hi!
I'm looking to build a tube preamplifier kit for an LM3886 based amplifier. Does anyone know of a good (and not too expensive) kit? The cheaper the better. 🙂
Can I connect it to the same PSU as the LM3886 based amplifier? In the same case?
Best regards
j
I'm looking to build a tube preamplifier kit for an LM3886 based amplifier. Does anyone know of a good (and not too expensive) kit? The cheaper the better. 🙂
Can I connect it to the same PSU as the LM3886 based amplifier? In the same case?
Best regards
j
I agree that there is apparently no need for a preamp for the LM3886 unless you want to play low level signals like that coming from a RIAA preamp etc. (about 250 mV I guess)
However I have done something similar with a TDA7294 power amp just for the sake of seeing what happens to the sound. I did not use a typical tube preamp with gain but used a Cathode follower with slightly less gain than unity ! So it's just a buffer with very high input impedance !
I used a 6992 tube and apart from the heater supply ( 6.3V ac) I used the same supply from the power amp ( +/- 36V ) to power the tube circuit.
For sure the measured performance will now be poorer than the chip power amp itself. I don't find any significant change in the sound. However for a reason I can't explain , I get more LF ( as in extended bass rather than 'boosted' bass !) from some sources ! I haven't done much comparison work but I have just taken it out of circuit and I seem to have lost 'something' ...not just extended bass ! Maybe the 'distortion...harmonics ?' If that is the case I should say ......'harmonics is good !' 😀
Note: The LF extension could not be due to the higher impedance ( 100K in my case ) of the tube stage as compared to the power amp itself ( 22K ). The LF -3dB point with the 22k itself is below 3 Hz.
However I have done something similar with a TDA7294 power amp just for the sake of seeing what happens to the sound. I did not use a typical tube preamp with gain but used a Cathode follower with slightly less gain than unity ! So it's just a buffer with very high input impedance !
I used a 6992 tube and apart from the heater supply ( 6.3V ac) I used the same supply from the power amp ( +/- 36V ) to power the tube circuit.
For sure the measured performance will now be poorer than the chip power amp itself. I don't find any significant change in the sound. However for a reason I can't explain , I get more LF ( as in extended bass rather than 'boosted' bass !) from some sources ! I haven't done much comparison work but I have just taken it out of circuit and I seem to have lost 'something' ...not just extended bass ! Maybe the 'distortion...harmonics ?' If that is the case I should say ......'harmonics is good !' 😀
Note: The LF extension could not be due to the higher impedance ( 100K in my case ) of the tube stage as compared to the power amp itself ( 22K ). The LF -3dB point with the 22k itself is below 3 Hz.
Hi,
Some audiophile think that a preamp is not necessary, I add a buffer tube preamp in front of my power amp, and the music opens up. Tube preamp makes it more necessary if your DAC does not have a tube output.
If you are interested I can direct you to a tube buffer from Ebay.com, it's cheap yet sounds very good.
Some audiophile think that a preamp is not necessary, I add a buffer tube preamp in front of my power amp, and the music opens up. Tube preamp makes it more necessary if your DAC does not have a tube output.
If you are interested I can direct you to a tube buffer from Ebay.com, it's cheap yet sounds very good.
set your chipamp gain to ~ 28times (+28dB)
If the maximum output is 50W (28Vpk, 20Vac). then the input required to give maximum output is 1Vpk or 700mVac.
Most Sources can give this and some a lot more. CDP is around 3Vpk (2Vac)
A few sources may not be able to drive the amp to maximum power, maybe only to a quarter of that level. i.e. 12.5W (10Vac) if they are only 350mVac maximum output.
So what?
Most of us listen to less than a watt of amplifier power and some a lot less than 1watt. I quite often measure just 1Vac average (125mW into 8ohms) at my speaker's terminals, when playing music from radio or TV.
If the maximum output is 50W (28Vpk, 20Vac). then the input required to give maximum output is 1Vpk or 700mVac.
Most Sources can give this and some a lot more. CDP is around 3Vpk (2Vac)
A few sources may not be able to drive the amp to maximum power, maybe only to a quarter of that level. i.e. 12.5W (10Vac) if they are only 350mVac maximum output.
So what?
Most of us listen to less than a watt of amplifier power and some a lot less than 1watt. I quite often measure just 1Vac average (125mW into 8ohms) at my speaker's terminals, when playing music from radio or TV.
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A well-designed preamp should add little to the signal apart from a little noise and a little distortion - in both cases probably too small to notice - and (unless you use a cathode follower) far too much gain. A poorly designed preamp can add much more!
Jsthlm-
Seems you're getting more answers to questions you didn't ask than answers to the question you did 🙂
I second the suggestion of a buffer instead of a pre-amp if you're set on building something. If you're interested in tubes, look up cathode follower schematics. Doesn't get more simple than that. I've always thought I'd go with a John Broskie design or kit if I ever get around to trying a Gainclone-type amp.
Build it and then listen to your system with and without the buffer. Measurements notwithstanding, only you can decide which is better.
Seems you're getting more answers to questions you didn't ask than answers to the question you did 🙂
I second the suggestion of a buffer instead of a pre-amp if you're set on building something. If you're interested in tubes, look up cathode follower schematics. Doesn't get more simple than that. I've always thought I'd go with a John Broskie design or kit if I ever get around to trying a Gainclone-type amp.
Build it and then listen to your system with and without the buffer. Measurements notwithstanding, only you can decide which is better.
A simple cathode follower will work fine. If you add RC filters for the supply on both rails the PSRR will improve dramatically. I haven't compared the circuit with or without RC supply filtering. But I think it might be better with filtering.
If you add a capacitance multiplier on the +ve rail and CCS on the cathode, the PSRR improves even more. But is it required ? I am not sure.
Start with the simplest circuit first !
If you use a circuit with gain then you might have to use a voltage divider at the input of the power amp . You will also have a circuit with gain going wide open into the power amp and increasing the potential of becoming noisy even with the volume turned down at the input of the tube stage.
If you add a capacitance multiplier on the +ve rail and CCS on the cathode, the PSRR improves even more. But is it required ? I am not sure.
Start with the simplest circuit first !
If you use a circuit with gain then you might have to use a voltage divider at the input of the power amp . You will also have a circuit with gain going wide open into the power amp and increasing the potential of becoming noisy even with the volume turned down at the input of the tube stage.
I want tubes to "open up" my music. I want the warmth that tubes are said to produce. I do not however want the high voltage stuff related to "real" tube amps. Is this an impossibility?
Which of these cathode followers should I get? GlassWare Line Stage & Headphone Amplifiers Kits and PCBs
Thanks 🙂
Which of these cathode followers should I get? GlassWare Line Stage & Headphone Amplifiers Kits and PCBs
Thanks 🙂
"Real" tube amps don't add warmth, they just amplify.
Low voltage 'tube buffers' add warmth by adding distortion, so what you desire is quite possible.
Low voltage 'tube buffers' add warmth by adding distortion, so what you desire is quite possible.
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