Quote from: Littlewyan on November 15, 2013, 07:28:26 PM
Right we scoped the amp and there is no oscillation. Altho we did get it to oscillate a few times with no input and the volume turned up but that disappeared as soon as we plugged something into the input.

That leaves us with two possibilities. Either something in there is on the edge of instability - or you forgot to wire your input jacks as shown in the schematic, so that the inputs are grounded if nothing is plugged in.

Quote from: Littlewyan on November 15, 2013, 07:28:26 PM
We found The signal didnt distort until the PI output and then again a bit more on the Power Amp output.

That doesn't come as a surprise - the PI is just the second stage in this design, you'd need a really beefy booster to make your input stage distort...

I personally think you just have a minor leaddress issue - but check your input jacks first.

Toby

Not only do the picos have an inbuilt signalgenerator, they also have this really cool sweep feature, looks like it saves a lot of setup time...
I don't have any personal experience with these devices - I use Hitachi scopes in the shop and a Tektronix TDS 210 to carry around - but my buddy owns a 2206A and so far seems to love it.

Toby

Now that sounds like a good option - grandpa with a scope.
Does he have a signalgenerator, too? If not, just download a sinewave soundfile and use your iPod or burn a CD.
I did not scope your clip, I just opened it in Cool Edit and zoomed in on the waveform view, I guess I'm not fast enough to photograph the scope at the right moment...

Toby

Hello Ryan,
now that I've listened to your clips over decent speakers I think that fizz sounds like intermodulation.
I have attached a zoom into the waveform(the decaying chord in your first clip where the fizz is pretty audible) that makes the suspicion even stronger.
Something in your amp might be( on the edge of) oscillating(or picking up EMI).
Do you have a scope or can you borrow one?
I don't think the problem lies in the OT(it had to be a real POS if that were the case...) and therefore don't believe in putting a filter there. That would be like buying earplugs because your muffler's shot...

Toby

Quote from: Littlewyan on November 12, 2013, 02:20:20 PM
Although Phil it was my understanding that Grid Stoppers dont tend to reduce gain due to the miller capacitance. They might reduce treble slightly but not normally gain.

Not really, rather Ultrasonic/RF: Let's assume your first 12AX7 stage's gainfactor to be about 60(12AX7 with bypassed cathode resistor), its Miller capacitance equates to Cm=Cgk + (Cga * gainfactor). The datasheet says Cgk=Cga=1.6pF, so we get Cm= 1.6 + (1.6*60) = 97.6pF(~100pF).
With a 56k Gridstopper fc of the resulting lowpass calculates to fc= 1/(2 * PI * R * C)= ~28kHz.

Quote from: Littlewyan on November 12, 2013, 02:20:20 PM
Changed the Cathode Bypass cap btw to 1uF and now the tone is great! Its just the fizz thats the issue now -_-

There's two 47u cathode bypass caps(first stage and powertubes) - which one are you talking about?
Don't worry about using small values for C2 - even .001uF might be necessary here for a tight bass response.
C5 is obsolete btw. - looks like somebody did a sloppy job simplifying the 1974 schematic.
To get rid of the fizz I'd try a cap(100pF - 500pF) between the PI anodes first.

Regards,
Toby

It's been a while since I came across a Sidekick, but as far as I remember they all had clipping diodes somewhere in the signalchain.
I don't know if the attached schematic matches your particular amp, but if it did, I would remove diodes D3 to D6 and maybe change the value of R20 to compensate for the higher signal level.

regards,
Toby