Mid Control

[rzenc]

Hello guys,


I was fooling around the BENCH-type EQ on Duncan ToneStack Calculator and have some questions:


1) I would like to know whether it's possible to use only the mid control branch?
2) Do you guys have experience with this type of eq?


At least on 'paper' it seemed to be very flexible.


Thanks in Advance for your suggestions/thoughts/insights.


Best Regards


R.

[AZJimC]

It is my understanding that the mid control is the last in a chain of interactive controls, first Treble, then bass then mid. That being the case, it would seem like you could build fixed versions of the Treb-Bass sections, and have the only control be a pot on the mid section. Remember that the treb-bass react to somewhat change the mid frequency. If they were fixed, the mid would not change its freq, and would only effect a preset bandwidth.

[jjasilli]

Passive tonestacks work by bleeding signal to ground.  Steve Bench's mid control, all by itself, has no ground connection.  So you're left with a bizarre band-pass filter, along the lines of AZJimC's comment.  In the Bench circuit the mid control circuit is dependent, and interactive with, the bass & treble pots to establish a ground connection.


What do you wish to accomplish?

[PRR]

> possible to use only the mid control branch?

Yes.

First some misses:

> mid control is the last in a chain

There are four parallel paths. Any of them can be removed with little effect (except R4 R5; this controls "everything" so is somewhat important).

> has no ground connection.

The software's drawing is incomplete. Ground is at the bottom, but not shown. Compare the better-known Marshall or James- they need grounds which are not shown.

> only the mid control branch?

To model it in Duncan's tool, make the un-used branches so far-out that they will have no effect.

R2 R3 should be super-high. The software accepts "100M". (Note that 100m is very different!)

C2 should be super-high impedance for all audio frequencies. 0.1 pFd "never does anything" in audio circuits. (Even MHz circuits don't fool with such values.)

To make L2 super-high impedance, make it 1,000 times bigger. 20,000 Henries is impossible to actually wind, but the sofware does not complain. This is 6 Megs at the bottom of the audio band and even more at higher frequencies.

So we are hitting R5 5k with "leaks" like 6++ Megs. "No effect".

Check your mangles by sliding the Bass and Treble pot-sliders. With 20,000H I get a one-pixel twitch as I slide from 0 to 10; treble does not vary at all.

The mid-network remains.

> seemed to be very flexible.

There is a lot of loss, enough to need an additional tube stage.

The Zsrc (source impedance) is quite low for a tube stage.

A 6 Henry choke is a substantial lump of iron.

We could scale all the impedances higher to more tube-like values, but then the choke might be 20H, a very substantial lump.

Several/many Henry chokes are available as power supply chokes. But their rated Henries is usually for some large DC current. At lesser current the Henries will be higher. How much higher? We do not know.

If large signals are applied to an iron-core choke (we can't make these values in air-core) the varying flux will vary the Henries, causing distortion.

If small signals are run through a large iron-core choke, it tends to pick-up all the hum and buzz in the air and add it to the small signal.

The boost/cut is asymmetric. If the boost is useful, the cut is very narrow. If you have "too much midrange", this cuts such a narrow slice that you'd hardly hear the difference.

If you are not savvy on Tuned Circuits, ALL the component interactions are non-obvious.

Four opamps and a few small/cheap C and R can give similar curves in much more useful form, both electronically and musically.

[DummyLoad]

drive it with a CF.  trim R5 somewhat for less loss.


--pete

[eleventeen]

When I first read the thread title I misread it as "mind control" and since this is a tube forum, I was thinking, where would the typical person carry batteries for their "receiver" circuitry? Would some people be heterodynes? Some homodynes? Some regeneratives? Some degeneratives?


Amp humor.

[HotBluePlates]

I was fooling around the BENCH-type EQ on Duncan ToneStack Calculator and have some questions:


1) I would like to know whether it's possible to use only the mid control branch?
2) Do you guys have experience with this type of eq?


At least on 'paper' it seemed to be very flexible.

Empress ParaEQ. It can do everything you're contemplating here, and then some. It is an expensive pedal, though, and you'll need to buy a power supply separately (I think Empress assumes if you're buying their stuff, you already have a big pedalboard with a multi-output power supply). However, you can use it with any amp/instrument.

I have one and can vouch that it's at least as good/flexible as a 4-band parametric EQ on a good recording console.

[rzenc]

Sorry for the delay, busy weekend...Many thanks for your input guys!!!! I really appreciate it!

What do you wish to accomplish?

I asked whether it was possible to use only the mid branch of the mentioned filter because I want to use it twice, low mids and high mids. It's a eq. devoted to mid section only.

> possible to use only the mid control branch?

Yes.

The mid-network remains.

> seemed to be very flexible.

There is a lot of loss, enough to need an additional tube stage.

The Zsrc (source impedance) is quite low for a tube stage.

Thanks PRR.

The Zsrc is a cathode follower using ECC88. I computed it's output impedance on pentode press calculators and got the magical Zout: 77 ohms. I also plan to use an additional gain stage after the mid network.

I believe I will need a custom build choke with shields to avoid picking up hum and noises.

The boost/cut is asymmetric. If the boost is useful, the cut is very narrow. If you have "too much midrange", this cuts such a narrow slice that you'd hardly hear the difference.

This is my main concern with such filter. Changing the Q of it would also be interesting, however, I have no clue how to achieve it yet.

drive it with a CF.  trim R5 somewhat for less loss.

--pete

It's the idea, use an ECC88 as a CF. I did not draw a schem but that's it.

I have one and can vouch that it's at least as good/flexible as a 4-band parametric EQ on a good recording console.

I want to build a parametric MID eq. Two branches, low mids (120Hz - 500Hz) and high mids (1.2KHz - 4KHz). Cut and boost and if possible variable Q. 

When I first read the thread title I misread it as "mind control" and since this is a tube forum, I was thinking, where would the typical person carry batteries for their "receiver" circuitry? Would some people be heterodynes? Some homodynes? Some regeneratives? Some degeneratives?


Amp humor.

That's about it...I mis-titled the topic but You read in between the lines! We have a winner!!






I will try to draw a schem of it and bring back to further discussions.


Many thanks for your help so far.


Best Regards.


R.