Ok here is what I propose to do. I'm going to take out the tone control completely and in it's place on the chassis I shall install a SPDT that has three positions. The switch will basically change the JFET Source Capacitor to give me three different 'Channels' if you will. I've attached a picture showing what I plan to do. Not sure about the clean channel at the moment though, wondering whether its best to have that part of the switch not connected to anything to clean up the sound as I imagine the 220uF will make the amp VERY bassy. Also I may need a resistor in series with the input as when I switch to the 0.68uF Cap I imagine it will pop as the capacitor charges up.

No i mean i simulated the tone control LtSpice and didnt get as much drop, obviously at the moment i don't really get any signal drop as its doing sod all at the moment. I might remove the Tone Control and put a switch in it's place to switch between different capacitors on the JFET Source. Need to do a few tests first to see if it'll do what i want it to though.

Well the good thing about my old Tone Control was that I didn't lose much signal at all, not compared to this one anyway. When you said Tone Cut Roly did you mean the Tone Control I'm currently using or a different one?

O thats not right, I've lost it 

Actually I just checked using LTSpice and whereas the Tone Control did lower the output it would only go from 5v +/- down to 3v +/- which obviously isn't a massive drop compared to the Big Muff Tone Control. Back to the drawing board me thinks.....

I'm wondering if perhaps I should just lose the Tone Control and maybe add a different option in. Perhaps a switch to go from Clean to Distortion? Could switch between Source Bypass capacitors, from 0.68uF for distorted to 0.1uF for clean perhaps?

Used the Big Muff Tone Control in LTSpice on my amp and the output went from 5V +/- to 900mV +/-. I'm guessing I'd need another gain stage for this tone control?

I've got an 18K resistor so I'll install that, that should drop the current down by at least 3ma. Although going by LTSpice this won't make much difference to the tone control, however that Big Muff tone control looks very interesting so I may give that a go

Thanks for that Roly. I've attached a screenshot of what I've put together in LTSpice, these are the changes I will try I have made tonight based on your recommendations. Only thing I didn't do was connect the BJT to the JFET's Source as this seemed a bit bizarre as I won't have any voltage gain at all if I do that? Or am I misinterpreted?

Anyway the amp sounds much better now and cleans up perfectly when rolling back the guitar volume. Only issue now is the tone control doesn't work, as I should have suspected really as its in parallel with the BJT's Emitter Resistor. Going to look into how to get around this another night.

Just had a thought, I could change the Tone Pot configuration to be the same as the volume control, so the middle wiper goes to the output, one side connects to the input and the other then to the capacitor that goes to ground. Would that not work as a tone control?

The JFET is currently at 19volts and the BJT is at 13 volts. If I change the BJT Collector Resistor from 10K to 6K8 then the collector voltage goes up to 15.7volts which is about right. So I'll just try that first, if it still doesn't sound right then I'll change the JFET resistor from 22K to 27K which will put it at 17 volts. Does this sound ok Roly? If I need a higher value resistor on the JFET then I can get hold of one.

The other thing is it doesnt really clean up with the guitar volume knob, i'm guessing this is because of the high gain?

I've now changed the Source Resistor to a 6K2 value from 5K6, however I haven't been able to test the amp at high volume (parents and neighbours get annoyed!). I'm hoping to get the amp to a point where I have a clean sound at low volume and distorted at high volume. This should be possible by increasing the Source Resistor shouldn't it? I'm sure I can do that on the 1 watt amp I built earlier this year.

The pre amp valve seperate from the others? This is the phase splitter valve so this should affect all channels really. The lead channel uses pre amp valves 2 to 5, whereas the crunch channel uses valves 2 and 6. The valve you say you touched is number 7 so thats very odd.

I've got one of these amps myself and I've never had an issue with the Lead channel like that, HOWEVER I do have it every now and then where the crunch channel doesn't make any sound. I usually fix it by going back and forth between channels or if I leave it a second sound will eventually come through. Probably same issue as yours, valve contacts are loose.

Ah ok thanks guys I think I understand it a bit more now

With regards to the amp I have changed all coupling capacitors to 1uF which has improved the sound greatly, I'm sure I can hear a bit more clarity in the distortion now (weird saying I know). I also changed the input capacitor from 100n to 4700pF as JM advised but I may change it back as the sound is a bit trebly for my liking now. However I have also changed the JFET Source Resistor to 5.6K from 4.7K which has lowered the distortion a bit but it is still a tad high, so I'm going to try swapping it for a 6K or even a 6.6K as I get distortion even at low volume! So I'm thinking once I've lowered the distortion the amp may not have as much treble, but we shall see, one step at a time.

As always I've attached an updated schematic, I noticed an error in the schematic where I included an extra capacitor that isn't present in the circuit, apologies.

Haha Roly

Ok i've done some reading and am i right in saying the Phase Shift is basically a change in the audio signal? Like a delay perhaps? And that its for mixing two signals together? Which for a guitar would be the original note that was picked and then the harmonics that come after?

On LTSpice when I run a simulation using the AC Analysis, I get these two lines. The solid line I believe shows how the volume increases with the frequency, however I cannot work out what the dotted line is?

You did JM but I was too naive to use them. I'm still learning 

Also I'm not using 0.68uF because Marshall uses them, I went to 0.68uF as 1uF was still too much and as I have about 20 of these capacitors now I may as well use some as coupling capacitors.

Apologies JM I thought I remembered you used 0.1uF as the coupling capacitors in your modded version of my pre amp. I shall use 1uF capacitors instead of 0.68uF. What I shall do is first change the coupling capacitors and then move onto the others you've specified. I like to hear the tonal differences as I change these things

Again also I agree there is no magic in electronics.

I shall make changes to the circuit tomorrow night and will post the results. Once I'm happy with the circuit I'll see if I can create some audio clips and take some photos.

Good point Kaz, I didn't realise they affected the tone that much, I thought as the Source and Emitter capacitors were 0.68uF it shouldn't matter. I'll change these tomorrow night for 0.68uF capacitors as I have plenty of them. Unless you think 1uF would be better?