4 band Baxandall tone control

[J0K3RX]

Not a baxandall but it has your bass, lo mid, high mid and treble controls and it's easy to implement...
http://milas.spb.ru/~kmg/files/schematics/Engl/530/1/530_full.gif

[Rob Strand]

bass, lo mid, high mid and treble controls and it's easy to implement.

Good find.

It's a bit like call HI a low-pass filter.

Maybe better to morph it into a Fender stack (like the F-2B) for bass?

[PRR]

> "Baxandall" circuit (though Baxandall really refers to active version of the circuit) is very lossy in passive form.

Baxandall's paper is for an *active* plan-- that was the whole point.

The bass/treb boost/cut passive tone control comes together in a paper by James, and has been called "James tone control", though it was not original with him.

The James (nearly all "passive" stacks) MUST have center-knob loss equal to the maximum "boost" you get at knob extreme. Passive can only cut, not boost. To get "boost effect" it must cut-down everything, then un-cut to give "boost". Also the action is limited by available pots. An "audio" taper naturally gives 20dB "boost", really up-to 20dB loss. A linear taper can be bodged to about 5dB "boost" and only 5dB loss, but that is not much boost.

That GA185B plan looks "poor" to me. It is all unity-gain through buffer, B/T Bax, and a couple filters. The first gain stage has 150K input resistor. The hiss level will be much higher (2X to 3X) than really necessary.

However if you are not annoyed by the hiss, add some more unity gain tone controls in front. Personally I would try to find one of the old graphic EQ pedals and put it in front. Using mostly boost positions, you get more level into the GA185B and therefore a better signal/hiss ratio; meanwhile 5 or 8 sliders gives many tonal possibilities.

[rankot]

I posted original schematic just for curious, but I already wrote that I intend to use tube preamp instead, and one of the main reasons for this was that I didn't like original preamp because of it's hiss (or noise).

So I decided to try with tone stack from Alembic F-2B, and to add fourth pot instead of switch for "Deep", like this:


The rest is standard Alembic F-2B topology, followed by MOSFET booster stage at the end.

[PRR]

You have a 26V transistor amplifier. You want over 100V to run tubes well, and a high-current heater supply too. Do you have all that worked out?

[rankot]

I know that, but I have also 50V from main amp PS, so I will use that and adjust tube resistors for that scenario. Or I can try using another tubes, for lower B+. I will build this one and see what happens, then adjust. 

[Rob Strand]

So I decided to try with tone stack from Alembic F-2B, and to add fourth pot instead of switch for "Deep", like this:

I think you have done well coming up with that.  It fits the front panel labels and you haven't  lost any of the F-2B sound you like.

Baxandall's paper is for an *active* plan-- that was the whole point.

Very true. 

Baxandall = Active Bass and Treble.
James = Passive Bass and Treble.

Unfortunately the passive often gets called Baxandall.

I believe the band-pass version of the Baxandall (often used for mid controls), and the 3-band Baxandall, should be attributed to Bohn (of Rane).

[Rob Strand]

So I decided to try with tone stack from Alembic F-2B, and to add fourth pot instead of switch for "Deep", like this:

R2 doesn't do anything because of the short from R3 to C16.
Is the schematic correct?

[rankot]

So I decided to try with tone stack from Alembic F-2B, and to add fourth pot instead of switch for "Deep", like this:

R2 doesn't do anything because of the short from R3 to C16.
Is the schematic correct?

You're completely right, this was a mistake when redrawing schematic. I have uploaded correct one right now. 

[PRR]

> should be attributed to Bohn

I dunno, I wasn't there (or can't remember). It has been around a long time, in Nat Semi notes and maybe in Jung. BiAmp mixers had a very low-cost 4-band EQ, but my notes are packed away.

[Rob Strand]

dunno, I wasn't there (or can't remember). It has been around a long time, in Nat Semi notes and maybe in Jung. BiAmp mixers had a very low-cost 4-band EQ, but my notes are packed away.

I believe it started here, the nat-semi audio handbook,
http://www.worldcat.org/title/audioradio-handbook/oclc/8249960

[rankot]

Look what have I found this morning: http://music-electronics-forum.com/attachments/33067d1425320675-all-tube-bass-preamp.jpg

At least one good thing arrived from waking up at 4 am

I will try this schematic, too.

[Rob Strand]

At least one good thing arrived from waking up at 4 am

The weird thing is I had that come in the last two days as well.
These things have very low Q's.  The 3-band barely works so I wouldn't get my expectations up 
I also found a Mesa Dual rectifier with a Presence which was part of the tone control.

What you have is probably more useable.   If you want you could play around with the cap values to fine to it to how you like it.

The only think that might be worth considering is a single band active band-pass EQ placed around a free tube ie. somewhere where it won't load the guitar or the tone control.

[rankot]

FMV tone stack with additional band pass EQ after the last tube sound as a good idea. I'll try that too.

[rankot]

OK, this is what I ended up with, I will try with this tube (I have few of them), and combine NE5534/5532 for Low Mid EQ (I have centred that at 250Hz) and output amplification. Amplification levels are balanced, so my new Low control's volume range is close to the old Mid (now called High, since it is somewhere around 900Hz) tone stack's pot. Now I need to build this and see what happens

[alfafalfa]

Look what have I found this morning: http://music-electronics-forum.com/attachments/33067d1425320675-all-tube-bass-preamp.jpg

That's very interesting but do you know what the frequencies are ?

Alf

[alfafalfa]

Here is the url where  it came from :
The second post mentions a lot of mistakes in the schematic !

http://music-electronics-forum.com/t38956/

[rankot]

I saw that there are errors in that schematic, but I thought that I could use it's 4-band tone stack. However, I decided to go without it, just use FMV 3-band tone stack with additional band pass filter with op amps at the end, as Rob proposed.

[PRR]

> the nat-semi audio handbook,

This is interesting.

It is in Jung Audio 1975 -- here's a scan from the 1978.

(Apology for ugly image; I do not want to flatten my copy on scanner.)

The '78 has references (general, not specific to each idea) which mentions Nat Semi Audio 1977 and editor "D. Bonn"{sic}. I do not have NatSemi 1977. I have a reprint of the 1980 issue, which lists Giles as editor and "Dennis Bohn" as mere contributor. (May be some company politics there.) I can not find the bump tone control in NS 1980 (cite?).

[Rob Strand]

The '78 has references (general, not specific to each idea) which mentions Nat Semi Audio 1977 and editor "D. Bonn"{sic}. I do not have NatSemi 1977. I have a reprint of the 1980 issue, which lists Giles as editor and "Dennis Bohn" as mere contributor. (May be some company politics there.) I can not find the bump tone control in NS 1980 (cite?).

Extremely cool find.  Thanks for looking it up by the way.

I don't have the 1977 NS Audio Handbook only the 1980.  However I did copy those sections from a friend's book when I was a teenager.  I still have the photocopies.  I do not know what edition he had.   For what I remember and what I was doing at the time it would have been 1979 or 1980  but I also remember he had that book before I borrowed it.  So I would put my money down that it wasn't the 1980 copy.  In fact I'm now sure of it ...

For  the photocopies.  The 3-band appears as fig 2.14.18 on page 2-46.  Whereas the 1980 copy has the 3-band as fig 2.14.18 on page 2-49.    The band-pass equalizer appears in the section about the 10-band graphic equalizer. On my photocopy it is fig 2.17.12 and 2.17.13 on page 2-55.    That section in the 1980 copy has gyrators and one opamp band-pass filters.   So it's obvious my photocopies don't come from the 1980 edition.

The 10-band equalizer using the band-pass "baxandall style" equalizer wasn't very good because it used a parallel structure which produced some weird responses.  Perhaps they decided to dump it, despite the fact the single equalizer section was quite useful on its own.


So I guess we can't know what book had it first until we can find an old Jung.

[Edit]
Hey cool, I found a 1976 (matches my photocopy)

https://archive.org/details/bitsavers_nationaldaAudioHandbook_17103876