Some Discussion on Amp EQs

[Bassmec]

Originally Posted by dunwichamps

I buy them from Wilco Inductors. you can get some up to almost 1H in small sizes

Used some in a mid boost pedal, FET based design

Thanks so much I will look strait into that then, as Sowter are great on quality transformers but I think £152 is a lot for a few small coils of wire.

[dunwichamps]

yea man wicked money. Maybe ask Heyboer Transformers if they will wind u stuff. I get custom amp transformers from them

[DethByDoom]

What about a Peavey VB2's eq? How do the resonance and presence controls work? Some kind of hpf/lpf that affect the treble and bass?

[dunwichamps]

Pres and Res are most likely the same old NFB eq controls which decouple the NFB loop at low or high frequencies. When you decouple the NFB loop at a frequency that increases the gain of those frequencies in the power amp. i dont have a scheme for its preamp EQ

[Bassmec]

Originally Posted by dunwichamps

yea man wicked money. Maybe ask Heyboer Transformers if they will wind u stuff. I get custom amp transformers from them

Well bit late as we already have invested in the Lundahl transformers as they have a reputation like god.

[dunwichamps]

Originally Posted by Bassmec

Well bit late as we already have invested in the Lundahl transformers as they have a reputation like god.

I usually go with Heyboer or Merc or Mag Comp.

heyboer has been doing most of my DR103, DR201 and DR400 iron. Very nice stuff

[Passinwind]

Originally Posted by esa372

Great thread!

This caught my attention:
According to the Duncan Calculator, the Alembic F-1X (which is a modded FMV) can be set to have an almost ruler-flat EQ:

The settings have to be pretty extreme to get it, however:
Bass - 0.3
Middle - 5.5
Treble - 0.0

It does appear impossible to get a mid-boost from it, but that's why we have the SF-2.

The TSC is a great visualization tool, but actual measurements are a bit more useful when they're available.

I modified the second channel of my F2B to do mid boost in such a way that you could sum both channels and have controllable mid boost and cut. The guy I sold it to preferred just using the second channel though.

There are some graphs in my DIY tube preamp thread showing various mid boosts achieved with no inductors, starting here. Personally, I like some aspects of the interactivity of the Fender stack, so I tried to do my own riff on that with active bass and mids, and a quasi-passive treble circuit. And being the contrarian that I am, I made the whole thing optimized for active basses only.

[esa372]

Originally Posted by Passinwind

The TSC is a great visualization tool, but actual measurements are a bit more useful when they're available.

Very true!

I don't suppose you have an F-1X on hand to see the actual results of those settings...? (I'm not set up for such things, or I'd do it myself.)

[DethByDoom]

This is all I could find. Controls are bass, middle, four way mid toggle switch, treble. And of course presence and resonance.

http://assets.peavey.com/literature/manuals/03595970_4.pdf

[Passinwind]

Originally Posted by esa372

Very true!

I don't suppose you have an F-1X on hand to see the actual results of those settings...? (I'm not set up for such things, or I'd do it myself.)

Nope. There was one around here for a while which I worked on and played through, but it's long gone, as is the F2B.

[dunwichamps]

Originally Posted by DethByDoom

Attachment 313188

thats just a rough block diagram but I was correct about pres and resonance. Thats like the same stuff you might see on a SLO100

[DethByDoom]

Originally Posted by dunwichamps

Pres and Res are most likely the same old NFB eq controls which decouple the NFB loop at low or high frequencies. When you decouple the NFB loop at a frequency that increases the gain of those frequencies in the power amp. i dont have a scheme for its preamp EQ

NFB?

Never understood how the pres/res controls worked.

Originally Posted by dunwichamps

thats just a rough block diagram but I was correct about pres and resonance. Thats like the same stuff you might see on a SLO100

It functions alot like an ampeg tone set up but the mid selector just sounds/reacts pretty different.

[dunwichamps]

negative feedback. Its refers to a portion of the output signal that is injected back into the circuit, usually at the phase inverter. It forms a loop which encompasses the phase inverter, power tubes, and OT. Its called negative feedback because it is out of phase with the signal at the inverter. Negative feedback decreases the gain inside the loop but if we select portions of frequency band where we decrease the amount of negative feedback that will increase the gain of that frequency band. Thats what the presence and resonance do

[DethByDoom]

Ah ok gotcha. Thank you sir

[dunwichamps]

I can simulations with approximated NFB curves for those kinds of controls

[Sartori]

Is the 60's Sunn EQ just your basic FMV?

[dunwichamps]

in the 200s and the Model T yes. 200s is a Fender style, Model T is Marshall style

[Sartori]

Ah right, just without an actual mid control for the 200S/2000S.

[dunwichamps]

yup

[DethByDoom]

Originally Posted by dunwichamps

I can simulations with approximated NFB curves for those kinds of controls

That be interesting to see. Never gonna say no to free knowledge.