The high impedance active load produced by a mu-follower allows the lower valve to produce its lowest distortion. Unfortunately, ECC82 will produce 13dB more distortion than 7N7 or 6SN7GT in this configuration because it's a horrible little valve designed for field scan in televisions (I have tested this). 7N7 is much cheaper than 6SN7GT, and you can get PTFE sockets. Don't use the high impedance output, it will increase distortion. Go for the circuit, just use a 7N7.
karma said:
It's one of the circuits in my mind for my next (and the first tube) project. I've read good reputations from other forum. If I go with this one, I would use well-filtered DC supply for heater (6.3V for parallel connections). Power supply section could be a little bit different from the circuit. I may go with tube rectifier and chokes.
Anyway, if you decide to go with this circuit, please let me know. We can go along together. This would be fun.
BTW, have you thought about using 7N7? Is it pin-to-pin compatible to 12au7?
Isn't 7N7 a locktal 6SN7?
I don't see what everyone's problem is with the 12AU7.. go for it. Maybe it's one of those minority type things... you know.. like... it's obviously a very popular tube for something since everyone has thousands of them, so naturally you just can't use them in DIY hi-fi since they're a commoner's tube...
Circuit looks fine but personally I'd just ignore the hi-imp. output. I mean, what's the point? The low impedance output gives just as much voltage and gain (well probably a little less) but having a lower Zo it has higher frequency response, especially when driving cables.
Tim
I don't see what everyone's problem is with the 12AU7.. go for it. Maybe it's one of those minority type things... you know.. like... it's obviously a very popular tube for something since everyone has thousands of them, so naturally you just can't use them in DIY hi-fi since they're a commoner's tube...
Circuit looks fine but personally I'd just ignore the hi-imp. output. I mean, what's the point? The low impedance output gives just as much voltage and gain (well probably a little less) but having a lower Zo it has higher frequency response, especially when driving cables.
Tim
I don't mind mu followers, but I wouldn't build that. In my opinion/experience the 12au7 is crap. Try a 6SN7, 6FQ7, 6H30 etc as the lower element and a pentode, or better yet a CCS like one of Gary Pimm's, as the upper one. The mu of the lower tube will set the gain for the amp.
Good article on the mu follower by Allen Kimmel can be found here.
http://laplaza.taos.nm.us/~fvuotto/mustage.html
I'm also not a big fan of doubler supplies. I bet there's a Hammond with the correct secondary (+ filaments) to do the job with a simple fullwave rectifier available cheaply.
Good article on the mu follower by Allen Kimmel can be found here.
http://laplaza.taos.nm.us/~fvuotto/mustage.html
I'm also not a big fan of doubler supplies. I bet there's a Hammond with the correct secondary (+ filaments) to do the job with a simple fullwave rectifier available cheaply.
This circuit looks like Bruce Rozenblit's first preamp, a lot of people have built it and like it. Even better is his Grounded Grid preamp from his book Audio Reality. This uses the same tube. A lot of people _really_ like this preamp, don't worry about the tube - the preamp sounds great.
Clive.
Clive.
karma said:i ended up buying 8 12au7 off e-bay i got em cheap. so when thay
get here ill make a few changes and share it with you as im building it
Are you going to use the power supply as drwan in the schematics? What transformer will you use? Hammond? I'll order one from Angela pretty soon.
12AU7
It's a nasty , shrill , 9 pin fart-bottle , a 'trainer' tube . I have seen how these measure compared to a 6SN7/6J5 and the measurements speak for themselves in the sound : a diffused 'tubey' one . Lots of that 'lovely' high order stuff . Use a loctal 7AF7 instead which are electrically identical but actually sound good
Otherwise a 6SN7 , 6J5 or 7N7 !
316a
It's a nasty , shrill , 9 pin fart-bottle , a 'trainer' tube . I have seen how these measure compared to a 6SN7/6J5 and the measurements speak for themselves in the sound : a diffused 'tubey' one . Lots of that 'lovely' high order stuff . Use a loctal 7AF7 instead which are electrically identical but actually sound good
Otherwise a 6SN7 , 6J5 or 7N7 ! 316a
Re: 12AU7
HOLY CRAP MAN. Lay off the crack pipe sometime!!??!??! Seriously!! Geez.
Here are the curves, height compensated for equal current and voltage scales. 12AU7 curves go in -2Vg steps.
Tim
316a said:It's a nasty , shrill , 9 pin fart-bottle , a 'trainer' tube . I have seen how these measure compared to a 6SN7/6J5 and the measurements speak for themselves in the sound : a diffused 'tubey' one . Lots of that 'lovely' high order stuff . Use a loctal 7AF7 instead which are electrically identical but actually sound good
316a
HOLY CRAP MAN. Lay off the crack pipe sometime!!??!??! Seriously!! Geez.
Here are the curves, height compensated for equal current and voltage scales. 12AU7 curves go in -2Vg steps.
Tim
Attachments
The curves don't tell the whole story
Crack pipe ? I prefer the ashes and beer-can approach but anyway , don't assume what's in the glass performs exactly to the curves . I wonder just how many new old stock valves test exactly on the money ? Have you tried a 6SN7 etc against a 12AU7 ? If you can honestly say that in the same application a 12AU7 sounds better , I'll eat my whole 12AU7 collection !
316a
Crack pipe ? I prefer the ashes and beer-can approach but anyway , don't assume what's in the glass performs exactly to the curves . I wonder just how many new old stock valves test exactly on the money ? Have you tried a 6SN7 etc against a 12AU7 ? If you can honestly say that in the same application a 12AU7 sounds better , I'll eat my whole 12AU7 collection !
316a
What is involved in switching my 12au7 preamp over to 6SN7s? ..if the've got the same curves, cant i just throw an Octal socket in there to replace the 9pin and rewire? I've got a foreplay with 2 12AU7s, but my 300b has 6SN7s in it.....might be cool to switch them just for the aesthetics
-Maz
-Maz
BON APPETIT...
Hi,
Done that...and there is no comparison.
While the the 6SN7 can really sing the 12AU7A and all its so called equivalents don't even come close.
I usually rely a lot on curves, I even go as far as putting each and every valve I intend to use on the plotter before I decide to use it or not.
The 12AU7A has often given me unexpected results in that it tends to distort like a really bad transistor.
The worst are the French 6189 which sport chromium plated anodes...very odd sounding valve.
Anyway, if you absolutely must use that stash than take Bretts' advise and may the valve gods be with you....
And may I add that I agree 100% with Brett that voltage doublers are a sows' ear sonically.
All SRPP based circuits benefit from a stiff, well regulated B+ supply for the simple reason that the name SRPP: shunt regulated PP is just one hell of a misnomer.
Cheers,
Hi,
Done that...and there is no comparison.
While the the 6SN7 can really sing the 12AU7A and all its so called equivalents don't even come close.
I usually rely a lot on curves, I even go as far as putting each and every valve I intend to use on the plotter before I decide to use it or not.
The 12AU7A has often given me unexpected results in that it tends to distort like a really bad transistor.
The worst are the French 6189 which sport chromium plated anodes...very odd sounding valve.
Anyway, if you absolutely must use that stash than take Bretts' advise and may the valve gods be with you....
And may I add that I agree 100% with Brett that voltage doublers are a sows' ear sonically.
All SRPP based circuits benefit from a stiff, well regulated B+ supply for the simple reason that the name SRPP: shunt regulated PP is just one hell of a misnomer.
Cheers,
And me
With my "moniker" you'll guess which side I am on.
And yes I willingly concede that ECC82/12AU7 has a nice set of curves.
Sadly the curves do not, repeat not, tell the whole story.
As EC8010, Fdegrove and 316A have stated it produces a large amount of odd-order distortion; I know I have tested it too.
7N7
With my "moniker" you'll guess which side I am on.
And yes I willingly concede that ECC82/12AU7 has a nice set of curves.
Sadly the curves do not, repeat not, tell the whole story.
As EC8010, Fdegrove and 316A have stated it produces a large amount of odd-order distortion; I know I have tested it too.
7N7
Re: The curves don't tell the whole story
The data sheets themselves state that operating points, curves, etc. are based on an average. A typical tube will be maybe 10 or 20% (I don't know the real figure) from that. Note the key word, average, meaning that a random 12AU7 is most likely to fit this curve, though likely with a small bit of deviation; conversely, those which fit tight to the standard as as uncommon as those on the fringes. Also read up on the 'bell curve'.
Can't say I've done that yet, but come to think of it I bet I could try it with Hept'AU7.. yeah, wire up an octal socket and hang a 12AU7 on wires. Think I'll go do that, in fact!
I'd try 6SN7 in my preamp but the reason I have 12AU7 in it in the first place is because it only has 600mA of heater available (the other half being used by the AU/AT/AX amp tube).
Tim
316a said:
The data sheets themselves state that operating points, curves, etc. are based on an average. A typical tube will be maybe 10 or 20% (I don't know the real figure) from that. Note the key word, average, meaning that a random 12AU7 is most likely to fit this curve, though likely with a small bit of deviation; conversely, those which fit tight to the standard as as uncommon as those on the fringes. Also read up on the 'bell curve'.
Can't say I've done that yet, but come to think of it I bet I could try it with Hept'AU7.. yeah, wire up an octal socket and hang a 12AU7 on wires. Think I'll go do that, in fact!
I'd try 6SN7 in my preamp but the reason I have 12AU7 in it in the first place is because it only has 600mA of heater available (the other half being used by the AU/AT/AX amp tube).
Tim
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