Hey all,
some of this may have already been discussed, so apologies if this is the case and please just point me to the rejects discussion thread:
I’m in need for a decent tube preamp. Unfortunately my taste for music is very wide, ranging from classical to metal and anything in between, and I’m aware that some tube designs may lead them better for done music than for other music styles. Fortunately, if going the diy or Chinese modified stuff route, that should be cheaper than buying brand new well establish stuff.
My immediate thought goes to buying one of those 12ax7 12au7 units, also sometimes referred to as marantz 7 clones. They’re affordable and relatively easy to modify.
Other options include:
https://a.aliexpress.com/_mOTfK6M , which seems to be a triode based design, and could be a decware clone.
https://a.aliexpress.com/_mOTjWjO , which I’m completely unfamiliar with.
https://a.aliexpress.com/_msm2w3e , another one that has my interest.
I’m aware that some people consider these rather inferior, but as I’ve never build a tube amp before, and don’t have the skills to design one, I’m looking for some advice on what my options are.
Chinese stuff and play around with upgrades, or full diy?
thanks!
some of this may have already been discussed, so apologies if this is the case and please just point me to the rejects discussion thread:
I’m in need for a decent tube preamp. Unfortunately my taste for music is very wide, ranging from classical to metal and anything in between, and I’m aware that some tube designs may lead them better for done music than for other music styles. Fortunately, if going the diy or Chinese modified stuff route, that should be cheaper than buying brand new well establish stuff.
My immediate thought goes to buying one of those 12ax7 12au7 units, also sometimes referred to as marantz 7 clones. They’re affordable and relatively easy to modify.
Other options include:
https://a.aliexpress.com/_mOTfK6M , which seems to be a triode based design, and could be a decware clone.
https://a.aliexpress.com/_mOTjWjO , which I’m completely unfamiliar with.
https://a.aliexpress.com/_msm2w3e , another one that has my interest.
I’m aware that some people consider these rather inferior, but as I’ve never build a tube amp before, and don’t have the skills to design one, I’m looking for some advice on what my options are.
Chinese stuff and play around with upgrades, or full diy?
thanks!
I like to diy so I make my own audio stuff (but I did buy some preamps/compressors/effect units for recording music instruments).
I see many others doing all kinds of 'upgrades' on (mostly) Chinese products. I find that odd. Why buy something of which you already know that you want to 'upgrade' it? And if your diy skills are not good enough yet, there's a big chance on damaging what you bought while 'upgrading'. So I advise you to start to diy, using a proven schematic. If you don't start to diy, you will never learn it.
About your links:
The schematic in the first link shows a 6J8P in pentode mode. There is only some local feedback, caused by the cathode resistor not having a capacitor in parallel with it. The voltage gain of a 6J8P in pentode mode with only this local feedback will be way higher than the specified 5 x (I estimate a gain of close to 60 x). The 60 mA power supply also doesn't make sense. Two 6J8P in pentode mode will pass a couple of mA's only. So several specifications are wrong. I advise against buying this one.
I don't see clear mistakes in the schematic and specifications in the second link.
The third link doesn't show a schematic so I can't say anything about it.
I see many others doing all kinds of 'upgrades' on (mostly) Chinese products. I find that odd. Why buy something of which you already know that you want to 'upgrade' it? And if your diy skills are not good enough yet, there's a big chance on damaging what you bought while 'upgrading'. So I advise you to start to diy, using a proven schematic. If you don't start to diy, you will never learn it.
About your links:
The schematic in the first link shows a 6J8P in pentode mode. There is only some local feedback, caused by the cathode resistor not having a capacitor in parallel with it. The voltage gain of a 6J8P in pentode mode with only this local feedback will be way higher than the specified 5 x (I estimate a gain of close to 60 x). The 60 mA power supply also doesn't make sense. Two 6J8P in pentode mode will pass a couple of mA's only. So several specifications are wrong. I advise against buying this one.
I don't see clear mistakes in the schematic and specifications in the second link.
The third link doesn't show a schematic so I can't say anything about it.
I think it comes down to whether or not you want to build your own chassis. Metalworking is the biggest pain in the neck when building from scratch. IMHO a lot of the Chinese interpretations of "classic" circuits are compromised. My preferred route would be to use a modern circuit, something from Tubecad.com guy Broskie (see link), and to minimize metalworking fatigue buy a generic chassis from one of the Chinese eBay sellers and do a little hole drilling yourself.
With regards to "best" circuit depending on musical styles, would that mean a bright tizzy one for heavy metal or perhaps a slow "tube-y" one for classical? My preference would be for neither but an amp that does the least amount of editorializing on the signal passing through it.
Start with a good tube circuit - one of Broskie's perhaps - then season to taste with a bit of tube rolling. https://glass-ware.stores.yahoo.net/listheam.html
Just my 2 cents.
S.
With regards to "best" circuit depending on musical styles, would that mean a bright tizzy one for heavy metal or perhaps a slow "tube-y" one for classical? My preference would be for neither but an amp that does the least amount of editorializing on the signal passing through it.
Start with a good tube circuit - one of Broskie's perhaps - then season to taste with a bit of tube rolling. https://glass-ware.stores.yahoo.net/listheam.html
Just my 2 cents.
S.
Thanks for the response,
I kinda suspected that. Worth checking though.
since I plan to play around with power amps and biamping, do you know of a good design with multiple inputs and multiple pre-outs?
At the moment I have a need for 3 inputs: turntable, sacd, and a digital source.
I kinda suspected that. Worth checking though.
since I plan to play around with power amps and biamping, do you know of a good design with multiple inputs and multiple pre-outs?
At the moment I have a need for 3 inputs: turntable, sacd, and a digital source.
Just for giggles, I simulated the circuit in the second link, https://a.aliexpress.com/_mOTjWjO.
The audio circuit is basic, simple:
![H17e8edcdd79148f4b839a49ca7d98ec3i[1].jpg](https://www.diyaudio.com/community/attachments/h17e8edcdd79148f4b839a49ca7d98ec3i-1-jpg.1036153/ "H17e8edcdd79148f4b839a49ca7d98ec3i[1].jpg")
I will assume the power supplies are competent. I didn't check them.
LTspice predicts 13x gain (22dB). For a 1kHz sine wave input, 1V rms out into a 100k ohm load, THD is predicted to be 0.04%, which is OK/mediocre.
The first triode draws about 4mA plate current. The second triode draws about 5mA plate current.
The voltages and currents on the schematic agree with the voltages in the simulation, so the design looks OK.
This looks like it should be a good choice if all you want is a line level control preamp that adds a bit of tube sound.
The gain is quite high, so it will be best used with power amp or powered speakers that aren't already very sensitive. If you have powered speakers that can be set to 'pro' +4dB level (instead of 'consumer' -10dBV level) then this should work fine.
How would one improve it?
You could try Broskie's 'CCDA' idea and get the plate current of the two triode sections to match. That would require getting the voltage at the plate of the first triode to be about 125V (half the B+) and adjust values of R2, R3 and R4 so that both triodes draw the same plate current and the value of R2 equals that of R4. Whether this would be an actual improvement in use is debatable. It would reduce the gain a little.
PS - You can make it a CCDA by changing the value of R2 and R4 to 22k (2W or better), leaving R3 at 500 ohms. The voltage at the plate of the first triode (on the left) would be about 124V. Both triodes should then draw about 5.7mA each. Gain would be about 10x (20dB) and THD would be just a bit higher.
--
The audio circuit is basic, simple:
I will assume the power supplies are competent. I didn't check them.
LTspice predicts 13x gain (22dB). For a 1kHz sine wave input, 1V rms out into a 100k ohm load, THD is predicted to be 0.04%, which is OK/mediocre.
The first triode draws about 4mA plate current. The second triode draws about 5mA plate current.
The voltages and currents on the schematic agree with the voltages in the simulation, so the design looks OK.
This looks like it should be a good choice if all you want is a line level control preamp that adds a bit of tube sound.
The gain is quite high, so it will be best used with power amp or powered speakers that aren't already very sensitive. If you have powered speakers that can be set to 'pro' +4dB level (instead of 'consumer' -10dBV level) then this should work fine.
How would one improve it?
You could try Broskie's 'CCDA' idea and get the plate current of the two triode sections to match. That would require getting the voltage at the plate of the first triode to be about 125V (half the B+) and adjust values of R2, R3 and R4 so that both triodes draw the same plate current and the value of R2 equals that of R4. Whether this would be an actual improvement in use is debatable. It would reduce the gain a little.
PS - You can make it a CCDA by changing the value of R2 and R4 to 22k (2W or better), leaving R3 at 500 ohms. The voltage at the plate of the first triode (on the left) would be about 124V. Both triodes should then draw about 5.7mA each. Gain would be about 10x (20dB) and THD would be just a bit higher.
--
As said - this chi-fi preamps are worth it for the case and the mains transformer. After that you can play around with the circuit. Very tempting!
Ksporry;
Do you want a preamp that has both line level and phono sections or go the separates route?
S.
Do you want a preamp that has both line level and phono sections or go the separates route?
S.
I got a good phono preamp, I just need a line level preamp, ideally for 3 sources (the phono stage, sacd, and a digital source).
Thanks! That’s very useful stuff!
Out of curiosity, what do you use for simulation circuits?
This preamp, with some good tubes, actually was the winner in my china preamp shootout. Lots of gain, sounds sweet with the only downside having a bit of hum, which would only be a problem with super efficient speakers. I fixed most of the hum simply twisting the wires that go to the front mounted switch.
Edit: And just noticed Andy also linked this video lol
What is the gain of your phono preamp? If it's much more than 40dB at 1kHz, you may not need a line level preamp at all.
The manufacturer quotes 40dB (MM ) / 66 dB ( MC ,5 ohm)/ 57dB(MC ,40 ohm), but didn’t specify a frequency.
Since a phono preamp is an equalizer (different gain at different frequencies), the standard is to quote the gain at 1kHz. I expect that quote of 40dB MM / 66dB MC is for gain with a 1kHz input.
Doing a little math... Let's say you have a MM cartridge with nominal 5mV rms signal out at the nominal deflection (another standard measurement):
Many power amps can be driven to clipping (full power) with 500mV rms signal input. What is the input sensitivity of your power amp(s)?
Now let's say we add a line preamp with 22dB (13x) gain to the above:
Let's say your power amp requires 1V rms to be driven to full power. You'll be using the volume pot to burn off almost 15dB of gain for full blast output from the power amp. You'll burn off even more signal to get the volume down to normal listening levels.
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Now let's look at a digital source with a maximum 1V rms output (audio data at 0dBFS).
You'll use the volume control to burn off all 22dB of gain from the line preamp to reduce the system gain so that a 0dBFS peak just clips the power amp. In this case you don't need a line preamp with gain at all.
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What we want is a line preamp with no more than 12dB (4x) gain.
One cheap 'n easy way to do that is to apply a little negative feedback (( 😱 ))
R6 and R7 create negative feedback to reduce the gain of the circuit to about 3x, You could make R7 a bit larger in value (560k or 680k) to reduce the amount of gain reduction from negative feedback, to your taste.
--
R5 is added as good practice. It provides a load to the cathode follower even if it's powered up but not connected to anything.
Doing a little math... Let's say you have a MM cartridge with nominal 5mV rms signal out at the nominal deflection (another standard measurement):
- 5mV out from the cartridge
- The phono stage provides 40dB of gain, which is 100x gain, so now the 1kHz signal leaving the preamp is 0.5V rms.
Many power amps can be driven to clipping (full power) with 500mV rms signal input. What is the input sensitivity of your power amp(s)?
Now let's say we add a line preamp with 22dB (13x) gain to the above:
- 0.5V rms out from the phono preamp,
- 22dB (13x) gain from the preamp will make that 0.5V signal 6.5V rms (9.2V peak).
Let's say your power amp requires 1V rms to be driven to full power. You'll be using the volume pot to burn off almost 15dB of gain for full blast output from the power amp. You'll burn off even more signal to get the volume down to normal listening levels.
__________________________________________________
Now let's look at a digital source with a maximum 1V rms output (audio data at 0dBFS).
- 1V rms out from the source
- 22dB (13x) from the preamp means up to 13V rms output.
You'll use the volume control to burn off all 22dB of gain from the line preamp to reduce the system gain so that a 0dBFS peak just clips the power amp. In this case you don't need a line preamp with gain at all.
___________________________________________________
What we want is a line preamp with no more than 12dB (4x) gain.
One cheap 'n easy way to do that is to apply a little negative feedback (( 😱 ))
R6 and R7 create negative feedback to reduce the gain of the circuit to about 3x, You could make R7 a bit larger in value (560k or 680k) to reduce the amount of gain reduction from negative feedback, to your taste.
--
R5 is added as good practice. It provides a load to the cathode follower even if it's powered up but not connected to anything.
Nice!
i don’t actually know about the power stages. The ones I have are integrated amps where I can bypass the pre-stage via pre-inputs. I have a good tube amp (though I think it’s time to replace the tubes), and a solid state amp. In theory I wouldn’t need a tube pre for the tube amp, as it’s pre-state it’s also tube driven. (Is an opera consonance reference 5.5 mk2), but it’d be nice to experiment.
i also like to play with a tube pre on a solid State Power stage.
I’m contemplating getting an older marantz power amp on fleabay (sc500) for variety to play with.
It’s probably also mentioning that I’m putting together an OB speaker set based on the Leonidas OB design, but with twin woofers , kinda like a PAP unit. I was thinking of driving a 15“ woofer using the solid state power stage, and use the tube power stage for the full range driver (thus my desire to have a pre with two out)