Re: 6SN7 Mu Follower Distortion Paper

flipper wrote:
On Tue, 27 Jan 2009 10:05:58 +0000, Ian Bell <ruffrecords@xxxxxxxxx>
wrote:

flipper wrote:
On Mon, 26 Jan 2009 18:28:38 +0000, Ian Bell <ruffrecords@xxxxxxxxx>
wrote:

Iain Churches wrote:
"Ian Bell" <ruffrecords@xxxxxxxxx> wrote in message
news:gktetl$dka$1@xxxxxxxxxxxxxxxxxxxxxxxx
I have written up the work I did on investigating distortion in a 6SN7 mu
follower and posted it at my website. You can read it here:

http://www.ianbell.ukfsn.org/data/mufollowerdistortion.pdf

Ian. Excellent paper.

You mentioned that you had, or were in the process
of acquiring, a HP spectrum analyser to examine the
differences between the distortion profile of the
different valves/tubes that you had tested.

Have you done this analysis yet? Some pics would be of
interest.

Not yet - I am at present struggling to get a twin T notch filter working properly so I can measure the individual harmonics. However, I can say from some initial tests without the twin T that at 20V rms the 2H level is close to -50dB, the 3H seems to be around -75dB and the third is below what my instrument will measure. So the contention that it is 'mainly second harmonic' would seem to be true.

As for pictures, the device I have bought is an HP 3581A Wave Meter - it is in effect a spectrum analyser but not with a PC interface for capturing nice pictures. You can connect it to a scope but as its scan rate is of the order of seconds you wont see much on a scope unless it is a storage type and mine isn't - it will interface directly to a pen plotter though!!!! I have seen a suggestion of using it with a USB data capture device but one of these costs more than I paid for the HP ;-) so for the present it will just have to be done by hand.


OTOH a cheap PC interface type scope might do the trick.
Very well might and there are a couple of free ones so all it would
take is some patch cables to see.

I have tried a couple of those that use your PC soundcard on my laptop. Could not get either one of them to work properly - probably something to do with the sound chip but it is a new laptop.

What did it not do? Or, what was the problem?


I made a loop back lead so output was connected to input. Then I ran the calibrate utility and it said there was insufficient gain and asked me to alter the input gain. Unfortunately Windows Bloody Vista has no such function. If you cannot get past this stage the program refuses to do anything.


Maybe they require sound blaster comparability. I don't recall, off
hand, because I've got them on an old notebook running win98 and never
really used them past seeing they 'worked' because I have a 'real'
dual trace scope anyway.

No I was thinking more of those that plug into a usb port and have some external = decent electronics.

Sure. I was just trying to be 'cheap' ;) Especially since, if I
gathered the setup correctly, all you need it for is display.


Pretty much and capture too of course.

Cheers

ian
Cheers

Ian
.

Relevant Pages

  • Re: 6SN7 Mu Follower Distortion Paper
    ... Ian. ... a HP spectrum analyser to examine the ... You can connect it to a scope but as its scan ... So basically any audio stuff I have tried on my laptop have been ...
    (rec.audio.tubes)
  • Re: 6SN7 Mu Follower Distortion Paper
    ... the device I have bought is an HP 3581A Wave Meter - it is in effect a spectrum analyser but not with a PC interface for capturing nice pictures. ... You can connect it to a scope but as its scan rate is of the order of seconds you wont see much on a scope unless it is a storage type and mine isn't - it will interface directly to a pen plotter though!!!! ... Could not get either one of them to work properly - probably something to do with the sound chip but it is a new laptop. ...
    (rec.audio.tubes)
  • Re: 6SN7 Mu Follower Distortion Paper
    ... the device I have bought is an HP 3581A Wave Meter - it is in effect a spectrum analyser but not with a PC interface for capturing nice pictures. ... You can connect it to a scope but as its scan rate is of the order of seconds you wont see much on a scope unless it is a storage type and mine isn't - it will interface directly to a pen plotter though!!!! ... It is a start and the spectral shape of the harmonics is the second step. ...
    (rec.audio.tubes)
  • Re: 6SN7 Mu Follower Distortion Paper
    ... a HP spectrum analyser to examine the ... You can connect it to a scope but as its scan ... I have tried a couple of those that use your PC soundcard on my laptop. ... So basically any audio stuff I have tried on my laptop have been ...
    (rec.audio.tubes)
  • Re: 6SN7 Mu Follower Distortion Paper
    ... Ian. ... You can connect it to a scope but as its scan rate is of the order of seconds you wont see much on a scope unless it is a storage type and mine isn't - it will interface directly to a pen plotter though!!!! ... Could not get either one of them to work properly - probably something to do with the sound chip but it is a new laptop. ... Then I ran the calibrate utility and it said there was insufficient gain and asked me to alter the input gain. ...
    (rec.audio.tubes)