Framus mid control?

[ChopSauce]

As per https://robrobinette.com/5e3_Modificati ... id_Control

Framus_Mid_Control.png

Any thoughts/comments/criticims?
(as I could that it does take an inductor to cut mids)

[jabguit]

capacitor to cut mids; inductor to boost.


cheers,

[ChopSauce]

Thanks. That's noted.

[FUCHSAUDIO]

You can get a better notching effect when using an inductor (Howard Roberts Gibson models and Varitone circuits are a good example). The circuit pictured does affect midrange, just not as drastic as you might get with an actual choke coil.

[Vintagelove]

The Duncan tone stack calculator is online now and has that control. By playing with the values, you can get a lot of interesting curves. Also, at 10 there is almost no insertion loss. Perfect for a tweed amp to add versatility.

https://www.guitarscience.net/tsc/framu ... pot=Linear

[ChopSauce]

Thanks a lot! I'm not looking for a great mid control. I'm looking for a simple one. Ideally one I can build with the parts I have already have. The Framus one just looked like the one I need. Still does, even more then.

Note: the early propotype amp was using a big muff scaled tone control with presence (à la AMZ) which was working fine but missed some character - IMHO.

[ChopSauce]

The Duncan tone stack calculator is online now and has that control. By playing with the values, you can get a lot of interesting curves. Also, at 10 there is almost no insertion loss. Perfect for a tweed amp to add versatility.

https://www.guitarscience.net/tsc/framu ... pot=Linear

Talking about tweed amps, the link shows a schematic/curve for an input impedance of about 1k...

I'll try it and report here, anyway.

[Colossal]

The Duncan tone stack calculator is online now and has that control. By playing with the values, you can get a lot of interesting curves. Also, at 10 there is almost no insertion loss. Perfect for a tweed amp to add versatility.

https://www.guitarscience.net/tsc/framu ... pot=Linear

Talking about tweed amps, the link shows a schematic/curve for an input impedance of about 1k...

One more thing : the simulator linked above uses a lin pot, while I could read about a log pot elsewhere - so I'm a bit lost.

I'll try that and report here, anyway.

The Framus would be best driven by a cathode follower, hence the low output impedance shown in the model. You'll get some high end roll off, if plate-loaded, but that might be useful for some, depending on where it's placed. It's a pretty cool control because you can have your Tweed (no mid cut) or dial in some Blackface mid scoop when the mood strikes...(or whatever frequency you choose for the mid scoop).

[ChopSauce]

Sorry guys, but with due respect (& I do mean it!) I insist that the name of this mid control should be no more associated with the word "tweed" in the same sentence, but to mention that it would cut treble very badly - when placed after a tweed-style tone controle - according to the online simulator above.!?

Dave wrote that it is better be placed after some cathode (or MOSFET-)follower, but the truth seems to be that it MUST be, while the Robrob website shows a schematic showing this control in series with the original tweed ones.

To Robrob credit, I can hardly imagine the difficulty to maintain a most extensive catalogue of mods but I never asked for that, just for working solutions.

Right now I am pretty disapointed I seemingly dismantled a working tone stack for what seems to be a chimera, and the polite suggestion by Andy - to using an inductor, maybe - should be emphasized, as well as the lack of truely positive report over the whole internet - as far as my usual search engine knows ...

NB this is a debate that was launched in the research world as well: shouldn't non working solutions be published to be what they are really, as well as the working ones?
- so less efforts are being lost -

[pdf64]

It’s worth noting that anyone is allowed to publish / publicise twaddle on the internet, to their own website at least. If there’s libel or ‘breach of copyright’ implications, problems may arise, but the police won’t come knocking if your circuit doesn’t work as claimed.

[mikeywoll]

Sorry guys, but with due respect (& I do mean it!) I insist that the name of this mid control should be no more associated with the word "tweed" in the same sentence, but to mention that it would cut treble very badly - when placed after a tweed-style tone controle - according to the online simulator above.!?

Dave wrote that it is better be placed after some cathode (or MOSFET-)follower, but the truth seems to be that it MUST be, while the Robrob website shows a schematic showing this control in series with the original tweed ones.

To Robrob credit, I can hardly imagine the difficulty to maintain a most extensive catalogue of mods but I never asked for that, just for working solutions.

Right now I am pretty disapointed I seemingly dismantled a working tone stack for what seems to be a chimera, and the polite suggestion by Andy - to using an inductor, maybe - should be emphasized, as well as the lack of truely positive report over the whole internet - as far as my usual search engine knows ...

NB this is a debate that was launched in the research world as well: shouldn't non working solutions be published to be what they are really, as well as the working ones?
- so less efforts are being lost -

I'm not totally clear, did you try it and didn't like it or are you worried about the simulator? It's a pretty popular mod for 5e3 circuits on the shock brothers forum: https://www.tdpri.com/forums/shock-brot ... y-amps.49/. There's a fair bit of experience with it there. I seem to remember coming across a thread where someone suggested some adjustments for better impedance matching as well as a bypass switch. The bypass switch was interesting, since the potential treble issues are most prominent when this knob is turned up past about half way.

I've never used it on a tweed amp, but recently used the framus mid control as a "set and forget" trimpot after a paralleled 12ax7 and it worked amazing there. Very little loading and no appreciable treble loss with a few db of mids knocked off. The input impedance doesn't necessarily need to be 1K for it to sound good. The graph looks pretty ok to me with input impedance up to 30k or 40k. Isn't that about the typical impedance of a 12ax7 with a 100K load resistor?

Mike

[ChopSauce]

Yes I am very much worried about the simulator, not to mention Robrob's direction to put if right after the tweed controls, which should make it for an input impedance of order the mega Ohm. That is thousand times what you tried, which already is thousand times what the control seems to expect in order to work right...

By the way, you also can't say that it works ok in a tweed amp, which is my precise concern!

I tried to scale that but the simulation never behaved as expected with usual component values. Maybe it is OK with a teraOhms pot...
(just kidding!)

In addition, what remains from my late reading of the link you mentionned above is: the sole poster I could read a report from suggested that the control be switchable, so it can be de-activated, and I must admit that I do not consider that is a testimony of perfect satisfaction, beyond the usual "I"m proud I dit it myself!", which always ponder my readings about the achievements of people I don't know much about...

So, if I summarize well what I could take of suggestion from your post: the control should work almost as expected if I put it elsewhere, so would it be ok - you think - to put it just before the tweed controls?

That way I could use V1b as a cathode follower, right after V1a and before "the Framus ctrl", and the tweed controls, after that, should provide the expected output impedance...

In summary, might:

V1a(classic gain stage) --> V1b(cathode follower) --> FramusCtrl --> tweedCtrls

be all right?

[mikeywoll]

Yes I am very much worried about the simulator, not to mention Robrob's direction to put if right after the tweed controls, which should make it for an input impedance of order the mega Ohm. That is thousand times what you tried, which already is thousand times what the control seems to expect in order to work right...

By the way, you also can't say that it works ok in a tweed amp, which is my precise concern!

I tried to scale that but the simulation never behaved as expected with usual component values. Maybe it is OK with a teraOhms pot...
(just kidding!)

In addition, what remains from my late reading of the link you mentionned above is: the sole poster I could read a report from suggested that the control be switchable, so it can be de-activated, and I must admit that I do not consider that is a testimony of perfect satisfaction, beyond the usual "I"m proud I dit it myself!", which always ponder my readings about the achievements of people I don't know much about...

So, if I summarize well what I could take of suggestion from your post: the control should work almost as expected if I put it elsewhere, so would it be ok - you think - to put it just before the tweed controls?

That way I could use V1b as a cathode follower, right after V1a and before "the Framus ctrl", and the tweed controls, after that, should provide the expected output impedance...

In summary, might:

V1a(classic gain stage) --> V1b(cathode follower) --> FramusCtrl --> tweedCtrls

be all right?

I definitely understand what you are saying. It's hard to rectify the simulation results vs people saying it sounds good. I was hoping you had resolved that

I'm sure it would work well after a cathode follower. I think the "tweed" sound may change if you move the tone controls after a cathode follower though.

This person used it to good effect after a regular gain stage before the PI. Again not a tweed amp, but sounds pretty killer (inspired my use).
https://chasingtone.com/odds-and-ends/the-detour/

I might try it after V1a before the tone/volume stack, without messing with a cathode follower. Honestly, placing it between V2a and V2b looks most promising to me. It wouldn't effect the existing tone/volume stack. You could switch it out and essentially have an unmolested 5e3 circuit. Switch it in and get less drive and less mids hitting the PI. In fact, I think that's what this guy did, maybe?
https://youtu.be/Bv9bayNw5gY

But as you said, I've never messed with this in a tweed deluxe. It could turn out horrible. On the net, you get advice worth what you pay for it

Good luck, I'm interested in hearing about your results.

Mike

[echuta13]

I have a 5f2a chassis on the bench that I placed the mid control in. It's isn't finished, and probably won't be for a spell, but I placed it right after the first stage coupling cap and with the traditional tone & volume control following it.

I cannot confirm yay or nay on it yet, but I will as soon as I get it done (don't hold your breath!) With that being said... it's only a few parts. Seems like it would be an easy one to tack in temporarily to see if it's usable or not.

[ChopSauce]

Thousand thanks guys! I do appreciate your feedback passing over my grumpy comments - out of frustration...

I won't bother you with the prototype details, yet I wouldn't mind to share any details with the community in a dedicated post, but I need the controls to be after V1a or - at most - after V1b if (& only if) V1b is a cathode follower for its output will feed an EF86 (for one channel) and I don't want too much signal at that point.

The fact is I will try whatever appears as the best solution but I don't know what the most reliable source of information is - AND - to add to the confusion, Merlin Blencowe suggests (Fig. 14.6: Practial high-gain preamp circuit; p.258 of his "preamp book") that (almost) this tone control be placed in a similar configuration as suggested by Rob Robinette and advocates that the filter should not be loaded (by the following stage?) - as far as I understand things - which sound as the exact opposite of what the simulator suggests.

To summarize things: full of doubt, I am tempted to trust somewhat more the simulation - and Colossal - and put the tone stack right after V1b as cathode follower - because I have enough tubes to "sacrifice" one gain stage and because loosing highs so early is one of the last things I want for the amp - but it seems that Merlin himself tried the circuit he described in his book, so is putting the Framus after the tweed controls shouldn't be that bad, either...