Seeking a different tone.

[Boy Howdy]

I was wrong about that Garnet thing. That amp is pretty different. I used a 660p/420K mixer. Those numbers are correct, and not just because that's what I had on hand. I always audition several (at least) values for pretty much every part I put in an amp. That's what I liked the sound of for that channel.

For the treble cap, I put in a 3-way switch that had 270p, 390p, and 500p caps. There's very little noticeable difference between them. But oddly, playing the amp this morning and comparing it side by side with the Acoustic, the 270p was the one that sounded closest and best. So now I'm thinking it may be more of a low mids issue. I played three amps this morning, the Garnet, a tweaked MOD kit amp, and the Acoustic. The two tube amps sounded very midrangey. These are not amps I particularly like, mind you. I have a Traynor YBA-1 and a Sunn Sceptre (both highly tweaked) that are much better sounding amps. I'll compare them possibly tomorrow.

This Acoustic is the head-only version of the amp that Pat Metheny used for twenty years. I read an article from around 1980 where he said he loved that amp. It does have something special. It's very snappy, the notes don't have to be coaxed out of the amp, they are all too willing to show up and do their thing. I've got to find a way to get this sound out of a tube amp.

I don't know if you can hear it clearly without some direct comparison but here's a pretty good sample. The tone gets better as the song goes along and the playing more active. Start in the middle if you're impatient.

Three Wishes - YouTube

[Helmholtz]

I think the conception that passive controls can only cut is at least misleading.
Truth is that passive filters have an insertion loss, meaning an overall gain smaller than 1 (corresponding to negative dB values).

To compensate for the insertion loss, all passive tone stacks need/have a gain stage either before or after the TMB.
So when viewed together with the gain stage, a passive stack allows for cut as well as boost.

Don't forget that a frequency response is always relative, i.e. referring to some reference (gain) level.

[gui_tarzan]

Any thoughts on the fact that a Gallien Krueger stereo chorus amp I used to own had two midrange controls?
vorne.jpg (1600×450) (amazona.de)

Just that I used to have one and traded it to Daddy's Junky Music for a '68 Bandmaster head that my brother has now. I wish I still had the GK, I loved the chorus it has.

[Boy Howdy]

Yeah, I had a couple at various times. I was playing in a variety band at the time, so my Marshall with no channel switching wasn't cutting it. I needed something that could do clean and dirty, and it didn't hurt that it weighed in the negative ounces. And, of course, I was a sucker for that chorus too. That amp was just what the doctor ordered for that time in my musical life.

[Chuck H]

Boy Howdy,

Regarding your preference for a boosted upper midrange and your desire for dual frequency mid control, have you ever experimented with the old school Fender "pull boost" circuit? Mesa used it a lot on their amps too. It's just a switch that increases the value of the treble cap in the tone stack. This effectively boosts frequencies below the amps normal treble range and lowers the frequency of the mid scoop. I have one on my personal amp and I use it a lot. For more control I think a circuit with a pot could be worked out to give some adjustability. This wouldn't be for your new Acoustic amp, of course. But you could experiment with one of your tube amps if you think it might be useful.

[Boy Howdy]

Thanks for the suggestion, Chuck. This is all, more or less, theoretical at this point. I honestly don't know what I'm after. I'm not quite sure what it is that I'm hearing that I like about that Acoustic. Now I'm thinking that what I might be after is more about shifting the midrange to a lower frequency, and cutting rather than boosting (at least in that frequency range). The Garnet amp with its three-position switch for three different treble caps is telling me that a bigger treble cap isn't necessarily what I'm wanting to do.

Take a look at this. I was looking through Gar Gillies' book last night and came upon this tone circuit. Notice the midrange control. He used it with the Baxandall as well as the conventional Fender type tone controls.

Any thoughts?

*Furman (schematicheaven.net)

[Chuck H]

Ah yes. The "T filter" as I've seen it called. I like them. I haven't used them much but I have a dozen ideas sketched out that use this circuit and most prove out well in CAD simulations. Gibson used it in their encapsulated tone module to get their signature tone.

Being a passive filter it has relatively high losses so my own experience indicates it's best designed into a circuit. Adding to an existing amp would almost certainly require other circuit changes if overall preamp gain is to be preserved.

[Boy Howdy]

Any possibility of shifting the frequency at which it cuts?

[bbsailor]

I recently acquired an old (early Seventies) Acoustic 150 head. I'd been curious about them for decades because one of my jazz heros used one, so when I found one for cheap I grabbed it.


I've been playing it for a month or so now. And my observations: It of course has that hard, clinical, transistory treble, which I don't love (though I must say I do enjoy the extended high treble frequencies that you don't get with tube amps). But I've found when comparing it to my tube amps that it has a much better TONE for instrumental playing. I'm talking exclusively about clean playing here, no distortion at all. It lacks the mid dip of the usual Fender/Marshall tone stack. Acoustic got something way right here. The upper mid/low treble region is just perfect. The notes practically jump off the guitar.

I'm starting to wonder how that might be duplicated in a tube amp - to lose that ugly hard, clinical treble, but keep those beautiful upper mid freqs. (There does seem to be less low mids muddying things up.)

So, a couple of questions. I know nothing about solid state tech. Can anything be learned from looking at the schematic that could be applied to a tube tone stack? And what are some possible approaches to getting that tone with a conventional or alternative tone stack, such as say the James (which I've never built and have only limited experience with)?

fetch (1041×762) (music-electronics-forum.com)

There is a way to change the tone by using a Tillman buffer circuit in the guitar end of the cable jack. The Tillman buffer is a 5 to 10 meg load on the guitar that goes out of the buffer at a low impedance to minimize the effect of the cable capacitance.

Just look up Tillman buffer and build your own buffer cable. I made one with the power supply on the amp end of the guitar cable.

The effect is a brighter sound, if that is what you are looking for.

If you try it, let us know.

Joseph J. Rogowski

[Chuck H]

Any possibility of shifting the frequency at which it cuts?

Yes. Of course. But it will require some idea of where you want to go and how much mid dip is desired. This can be easily (relatively) worked out with CAD programs and I'm happy to do it because that sort of thing is fun and helps me procrastinate the thing I SHOULD be doing . Keeping the mid dip the same and shifting it's frequency will probably mean using something like a rotary switch rather than a pot. So the effect would be consistent but making it variable in depth would be more problematic. Simply applying a variable resistor to the shunt of the T filter changes the target frequency with adjustment which is undesirable. It get's tricky. Best if you post what you think might get you closer to what you want.

[loudthud]

This Marshall Bass amp has passive James type Treble and Bass controls and a Baxandall active Midrange with a 6 position switch to set the frequency. You can boost or cut the mids.

Link: https://el34world.com/charts/Schemat..._2001_375w.pdf

[Mick Bailey]

A tone stack that I like is the Sound City MkIV active setup. It uses a triode for each band and though a little noisy as a result has a wide range of sounds within the context of its own amp design. There was a long period where there was no interest in these amps, but I really rate them - especially the 50W models.

[Boy Howdy]

Yes. Of course. But it will require some idea of where you want to go and how much mid dip is desired. This can be easily (relatively) worked out with CAD programs and I'm happy to do it because that sort of thing is fun and helps me procrastinate the thing I SHOULD be doing . Keeping the mid dip the same and shifting it's frequency will probably mean using something like a rotary switch rather than a pot. So the effect would be consistent but making it variable in depth would be more problematic. Simply applying a variable resistor to the shunt of the T filter changes the target frequency with adjustment which is undesirable. It get's tricky. Best if you post what you think might get you closer to what you want.

I figured the 680p would determine the frequency, and the pot would determine the amount of cut. Not so?

I remembered that I have a 6-band graphic eq pedal. I'll hook that up to one of my tube amps and compare side by side with the Acoustic to see what I can learn.

[Boy Howdy]

This Marshall Bass amp has passive James type Treble and Bass controls and a Baxandall active Midrange with a 6 position switch to set the frequency. You can boost or cut the mids.

Link: https://el34world.com/charts/Schemat..._2001_375w.pdf

Hold the phone! Are you telling me that the James and the Baxandall are two different things?

That's a very interesting schematic. I never would have expected such from Marshall. That definitely bears further study.

[Boy Howdy]

A tone stack that I like is the Sound City MkIV active setup. It uses a triode for each band and though a little noisy as a result has a wide range of sounds within the context of its own amp design. There was a long period where there was no interest in these amps, but I really rate them - especially the 50W models.

I had one once. A 120 watt. I never got to spend any time with it before my brother stole it and took it on the road to play bass through . . . and completely trashed.

I'll grab the schematic for further study.