[Stone]

Hi Nigel

No differences to the first recording, except that I connect the Sennheiser mic to mic input of my laptop and so I can lower the level; I am using a TTpro power soak And the PI is driven hard (removed the power scaling potentiometer).

There is still some hiss on top of the sound, which is unfortunately added by the laptop or whatever

Regards, Stone

[dukeamps]

Hi stone, have you made any changes to the amp?

Cheers

Nigel

[Stone]

Hi Nigel

Hi stone, have you made any changes to the amp?

Cheers

Nigel

No, not to the circuit - I removed the power scaling pot, that 's all.

Regards, Stone

[dukeamps]

Hi, stone, could you please tell me a bit about your power soak, can you use it also with 100w amps?

cheers

Nigel

[Stone]

Hi Nigel

It is one of Dirks attenuators - most of the information including schems can be found here: http://www.tube-town.net/diy/tt-pos/tt-posx-de.html - I have got the 200 watts version (TT PoS200 Pro). I built it a few months ago for a friend of mine, but he changed the amp and gave it back to me.

At least I find the treble "correction" pretty useful while attenuating signals to a very low level. The overall performance is pretty good, at least in relation to the price of DIY kits of them. Refering to calculations I have done on their resistance they do not react exactly like a speaker, but resistance increases with input frequency which is close to the behaviour of a speaker.

I think Aiken has a more complex model, but which is a power soak / load box and which behaves like a guitar speaker - I tried to build it years ago but was not able to get most of the parts, so I left it.

Overall I would recommend Dirks attenuators before spending around 300 to 400 euros for a THD or Scholz.

Regards, Stone

[dukeamps]

Hi stone, thanks for answering. I was looking at that model, but the only thing is its 8ohm, what do you do with your 16ohm box?

Cheers

Nigel   

[Stone]

Hi Nigel

According to Dirks documentation it is designed for 8 and 16 ohm loads (speakers) - the input impedance is around 8 ohms (for the amp); I measured 7,2 ohms at input.

Regards, Stone

[dukeamps]

Hi stone, thanks for the info.

Cheers

Nigel

[dukeamps]

Hi Guys, found this mod on the net. http://img263.imageshack.us/img263/9439/36mod.jpg

What do you think?

Cheers

Nigel

[Stone]

Hi Nigel

I am not sure if this is a #36 layout, it seems to be a mod / variation of the #36 modification - but it is interesting. The first thing I had in mind while seeing this was the layout of the London 4-stage preamp as described in one of the TUT books.

Having a closer look it is basically a "reversed" 220x layout (10k triode at first followed by 2k7 triode): the first triode acts as a tube booster and the cathode follower is rewired to a anode follower with tone stack.

What I am missing is a coupling cap between anode of V2b and 33k slope resistor - on the one hand side it is not really needed because of the voltages of the tone caps usually, on the other hand side it adds a little extra safety.

Regards, Stone

[dukeamps]

Hi stone, thanks for answering. On another forum someone said it was from the Kevin O’Connor’s 4 gain stage Marshall Mod, from the TUT books, & also very similar to the Roccafortes HG100.

I think I will give it a try & see what comes out.

Cheers 

Nigel

[Stone]

Hi Nigel

Yes, Kevin O'Connor is the man of London (Power Amps). It is right, basically - with a few changes - it is the Kevin O'Connor 4-stage preamp option mentioned within TUT volume 2 (I think) ...

It should sound a little bit harder than a stock #36 mod, because of the 1k5 resistor at the last cathode - the 10k system in front of the whole preamp acts like a tube booster which will give you more drive / saturation to the tone.

I have tried something similar with my #39 mod and it is pretty good for soloing and rythmn tones - latter ones if you are backing your guitar volume.

Regards, Stone

[dukeamps]

Hi stone, Just tried that mod, its really highgain. Sounds ok just a bit too bassy, I will tweak it a bit & see what happens.

cheers

Nigel 

[dukeamps]

Hi stone, got the bass sorted out, it was a B1M pot that i had use because i didn't any A1M pots, changed that & the amp sounds ok.

Cheers

Nigel

[Stone]

Hi Nigel

Try a second 1M or 500k potentiometer instead of 68k / 680k voltage divider ;-) This will come close to what I have done many times and you are able to adjust the "shape" of distortion and not only the tone.

Regards, Stone