Pete Cornish Tube Buffer

MWichni · Post by **MWichni** » 12 Jun 2009, 08:42

Hi guys, I found a picture of Pete's tube buffer. Maybe picture show enough to trace it down. So here it is:

https://img8.imageshack.us/i/tubes3n.jpg/

salvoinz · Post by **salvoinz** » 14 Sep 2009, 09:07

Hi MWichni, and hi you all

Have you found the schematic (and the part list) of this tube-buffer?

Cheers

lolbou · Post by **lolbou** » 14 Sep 2009, 10:56

What about this? http://www.freewebs.com/valvewizard/accf.html

MWichni · Post by **MWichni** » 14 Sep 2009, 18:33

lolbou wrote:What about this? http://www.freewebs.com/valvewizard/accf.html

Who knows?

MWichni · Post by **MWichni** » 19 Oct 2009, 15:38

Here is what my dad traced from the picture above. Anyone bet any values?

lolbou · Post by **lolbou** » 19 Oct 2009, 15:54

MWichni wrote:Here is what my dad traced from the picture above

Dad?!

Mine would have say "démerde-toi"...

Well, sort of a classic tube cathode follower... Since Pete's claiming 1Mohms input impedance and 20pF input cap, with the link I provided above, some values should be easy to determine...

Anyway, it would be perfect to have some clue about what patr of the pic is what part of the drawing (to check for any doubt)?

MWichni · Post by **MWichni** » 19 Oct 2009, 16:00

lolbou wrote:
MWichni wrote:Here is what my dad traced from the picture above
Dad?! Mine would have say "démerde-toi"...

Well, sort of a classic tube cathode follower... Since Pete's claiming 1Mohms input impedance and 20pF input cap, with the link I provided above, some values should be easy to determine...

Anyway, it would be perfect to have some clue about what patr of the pic is what part of the drawing (to check for any doubt)?

I'll try to do that, but don't have much time nowdays.

Ben N · Post by **Ben N** » 19 Oct 2009, 21:54

Seems odd--why would a CF have a bypass cap, or take its signal below the cathode resistor, and what is with the R from the plate to the cathode?

salvoinz · Post by **salvoinz** » 06 Nov 2009, 12:44

Hi guys,

Well, about the value of the parts used for the tube buffer on Gilmour pedalboard, they should be just like the Hiwatt pre-amp, infact Mr. Cornish says that : "We decided to eliminate the loading influence of a large chain of effects by incorporating unity gain tube pre-amps, with identical characteristics to his amp input stage, as the guitar input stage and also as isolators between effects."

You can find this on the following link:

http://www.tonefromheaven.com/

on the "All Tube Effects Board" section.

hope this help.....

guiddruid · Post by **guiddruid** » 06 Nov 2009, 16:14

and for schems of every conceivable Hiwatt input stage; http://mhuss.com/Hiwatt/tech2.html

salvoinz · Post by **salvoinz** » 06 Nov 2009, 16:50

guiddruid wrote:and for schems of every conceivable Hiwatt input stage; http://mhuss.com/Hiwatt/tech2.html

Yes, guiddruid

and in particular the following links could help better:

http://mhuss.com/Hiwatt/Schematics/DR_P ... put_v2.gif
this should be just the schematic of the Hiwatt amp used right by Gilmour infact it has the linked input.

http://mhuss.com/Hiwatt/Schematics/STAInputPre.gif
and this link could help better to find the values of parts, i guess (because it is just the slave preamp without the tonestack), but I'm not able to do this.

So please help......

flood · Post by **flood** » 09 Nov 2009, 07:28

lolbou wrote:
MWichni wrote: Well, sort of a classic tube cathode follower... Since Pete's claiming 1Mohms input impedance and 20pF input cap, with the link I provided above, some values should be easy to determine...

Anyway, it would be perfect to have some clue about what patr of the pic is what part of the drawing (to check for any doubt)?

isn't 20pF a bit too small? wouldn't it cut too much low end?

guiddruid · Post by **guiddruid** » 09 Nov 2009, 08:18

1M/20pF is the sort of thing you would find marked on an ancient oscilloscope input or probe (both impedances are to gnd - thee 20pF is a parasitic capacitance, not a physical component). Perhaps _that's_ the type of app note the circuit was copied from?

JiM · Post by **JiM** » 09 Nov 2009, 21:54

Using the above schematic, i tried a quick&dirty Spice simulation, using almost random values.
Hmm, not random, but re-using components from an existing amp schematic.

It has probably nothing to do with the actual Cornish Tube Buffer, but here it is anyway, as a starting point for discussion.
The frequency response is linear over the guitar frequencies, within -0.25dB.
The waveform shows very little distortion, and an FFT analysis confirms the absence of even harmonics, the 3rd harmonic is at -40dB.

Let's tweak that !

regnad · Post by **regnad** » 10 Nov 2009, 03:52

i am sooo glad i found this forum. eager to see this final schematic!

flood · Post by **flood** » 10 Nov 2009, 05:38

it reminds me of a hi-fi tube buffer i built some time ago called the yaqin tube buffer. this uses the 6ak5 pentode strapped as a triode. the values are a bit different, but the basic topology is essentially the same.

regnad · Post by **regnad** » 11 Nov 2009, 02:27

come on guys, dont stop now! has anyone come up with the schematic for the buffer?

regnad · Post by **regnad** » 12 Nov 2009, 03:24

so is this topic dead? i have been looking to build some of these tube buffers. can anyone work out the schematic from the pic or compare the highwatt input schem to the pic to see if its the same?

Bernardduur · Post by **Bernardduur** » 12 Nov 2009, 15:53

I would use something like the other suggested Cathode follower

Check the schematics of the Vox FX loop, the Valvulator or the Dumbleator.

I used something like this, with a tad more gain, on my newest amp build to overcome the (impedance) problem of 8 powertubes

AllegedRetroFreek · Post by **AllegedRetroFreek** » 18 Aug 2013, 02:48

Bernardduur wrote:I would use something like the other suggested Cathode follower

Check the schematics of the Vox FX loop, the Valvulator or the Dumbleator.

I used something like this, with a tad more gain, on my newest amp build to overcome the (impedance) problem of 8 powertubes

I'm bringing this post back from the dead. Gilmour uses a modded Alembic F2B Preamp which is then sent to the power amp sections of the hiwatts. The Hiwatt preamps are bypassed completely. I've read that Pete Cornish modified the Alembic to better suit guitar (it's a bass preamp) but the values are pretty well unknown. It could be that the Cornish tube buffer is the input stage of the F2B. I can't add the schematic as I'm on my ipad but it's widely distributed. Any thoughts on what the buffer schem would look like?