Egnater Tweaker 15 Pre-amp modification (here it is!).

[Timo V]

There is a Egnater factory mod to make the FX-loop instrument level, so I will not touch that. That said, here we go.

This mod will give the pre-amp more headroom for clean tones, and it also will make distorted tones more defined. For some reason, the higher frequencies were in my opinion needlessly cut, that too will be remedied.

1. C12. Replace with a 470p cap. Consider this optional, there is no 'correct' value. Bigger values will give more aggressive tone.
2. C3, C18. Remove. These are low-pass filters to cut higher frequencies. Removing these will give the tone more 'air'.
3. C15. Replace with a 470p cap. This is a treble peaking circuit. Bigger value will give more 'British'-like tone. To my surprise, clean tones were not
negatively affected.
4. R23. Replace with a 820R resistor, or piggy-bag with another 1K5. This will make the gain stage clip more asymmetrically with grid saturation.
It will give the tone more 'width' or 'bloom'.
5. C21. Remove. See item# 7.
6. C7, C8. Replace both with a 2u2, 400V (min) caps. We lowered the low-frequency gain (item# 7.), and now we bring it back to give distorted tones
more girth with a bigger 'bright cap' (C12) value.
7. 'A' and 'B'. Solder a 0.68u cap between the points marked with red ovals, you can use the solder pads left empty when we removed C21
and C18. This will activate the new 0.68u V1B cathode cap when 'Clean/Hot'-switch is in 'Hot'-position. The 'Clean' setting has now more
headroom.

There you have it. let me know if there's typos or stupid mistakes!

Timo

 

[PelliX]

There you have it. let me know if there's typos or stupid mistakes!

I came here expecting voltage quadruplers, Zener... eh, Jose* diodes, variacs and such.

No, jokes aside, it makes sense. Hard to judge the invidividual choices without the amp itself, of course.

Curious, what are the JFET and IRF MOSFET on the left hand side doing?

 

[Timo V]

Curious, what are the JFET and IRF MOSFET on the left hand side doing?

It's a cascode-'totem pole' input stage, works bloody well too!

I like to keep things simple and minimalistic. If someone was comparing my modded amp side by side with an un-modded, he would probably comment: "I guess that one has better tubes", because the amp's character has barely changed, it just sounds more... refined?

Timo

 

[Timo V]

And please, no Pat-talk!

 

[PelliX]

It's a cascode-'totem pole' input stage, works bloody well too!

That's exactly what I was thinking, I know it from radio circuits, not something you generally see in a guitar amp. Very interesting!

And please, no Pat-talk!

I still think Andy and Pat should get together to design an amp. Voltage hexupler and Zener diodes all the way. Four master volume controls.