Circuit designers - cathode follower, or plate fed tone stack?

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cstenger5
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Circuit designers - cathode follower, or plate fed tone stack?

Post by cstenger5 »

For those of you that build the circuits here for download, what do you base your decision on for what drives your tone stack, between plate or cathode? I get that you get a less pronounced impact on gain through the tone stack with a cathode follower, so why ever drive it with the plate? EDIT - I got off my ass and did a little further research, and got some things my brain isn't ready for, but did read some things that resonated with me for plate driven. One described cathode follower driven as characteristically "mid-gutted", which is not what I'm ever after. I don't have the experience to know that that's true or not, but the one18 watt that I built is a plate driven tone stack, and that amp leaves me wanting for nothing at all.
Last edited by cstenger5 on Fri 09/24/21 7:29 am, edited 1 time in total.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by cstenger5 »

Yet again, I try and edit a post and I instead quote myself. I've been in IT 24 years now, but there's no stopping the getting old factor.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by colossal »

I can't see how the frequency response of a DC couple cathode follower-driven tone stack is "mid gutted" :lol: Oh, internet, you never cease to be entertaining.

Check out Merlin Blencowe's quick piece of the CF, which quickly summarizes some of the properties:

http://www.valvewizard.co.uk/dccf.html

Plate-driven tone stacks are frequently used in multi-stage, high gain amps.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by cstenger5 »

Thanks!!! I'll get reading.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by zaphod_phil »

cstenger5 wrote:
Fri 09/24/21 8:41 am
Thanks!!! I'll get reading.
I like the clarity of Merlin's explanations and here IIRC he's focusing on how a DC-coupled cathode follower overdrives asymmetrically , rather than how it interacts with a tone stack. That nice asymmetry is a key part of the warm sound of overdriven Bassman/JTM45/Plexi amps

If you want to understand how the driving impedance affects the behaviour of a tone stack, try modelling a Fender/Marshall tone stack in Duncan's tone stack calculator - https://www.duncanamps.com/tsc/
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by zaphod_phil »

colossal wrote:
Fri 09/24/21 8:20 am
I can't see how the frequency response of a DC couple cathode follower-driven tone stack is "mid gutted" :lol: Oh, internet, you never cease to be entertaining.
cathode follower-driven tone stacks just tend to have a better high-end sweep than anode-driven ones."Mid gutted" suggests to me that the tone stacks in question have a "slope resistor" value that's too high. Some F*nd*r amps use a100k value for their classic mid scoop, while Marshalls typically use a 39k value to get their stronger mids.
colossal wrote:
Fri 09/24/21 8:20 am
Check out Merlin Blencowe's quick piece on the CF, which quickly summarizes some of the properties:

http://www.valvewizard.co.uk/dccf.html

Plate-driven tone stacks are frequently used in multi-stage, high gain amps.
Yes,they use the triode to get more voltage gain (relative to a CF), which more than offsets the insertion loss of the TMB tone stack.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by zaphod_phil »

cstenger5 wrote:
Thu 09/23/21 7:23 pm
the one18 watt that I built has a plate-driven tone stack, and that amp leaves me wanting for nothing at all.
Is that an 18W Superlite TMB amp? If so, I tweaked its tone stack component values using Duncan's TSC to get the best overall frequency range with anode-drive :) I also warm-biased the second preamp stage with a 600ish ohm cathode resistor, to get some Plexi-like asymmetric overdrive. :)


Also note, there have been a number of variations of the Superlite, some of which aren't so good. The authentic Superlite TMB has this tweaked tonestack, which I call the "Jalepeno" stack, shown below:
Just one thing to be aware of, you might find the preamp is hitting the PI too hard now. If so, you might like to split the 2nd preamp stage's 100k anode load resistor (shown as R18 below) with a 33k/68k combination, the 68k going to the +ve rail and the 33k to the anode (pin 6). This is similar to the SuperLite IIb's arrangement, but with the 33k and 68k positions swapped. Or to make it simpler, just use a pair of 56k resistors in series, as the load, with the output signal to the tone stack taken from where they join.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by colossal »

zaphod_phil wrote:
Fri 09/24/21 11:43 am
If you want to understand how the driving impedance affects the behaviour of a tone stack, try modelling a Fender/Marshall tone stack in Duncan's tone stack calculator - https://www.duncanamps.com/tsc/
As noted, the follower increases gain of the prior stage, can add compression, and the very low impedance (about 600Ω or so) provides a current source to drive the tone stack. But the follower itself does nothing to cause a cut in midrange. More internet amp hokum. It will give more apparent high-end because of reduced insertion loss.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

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zaphod_phil wrote:
Fri 09/24/21 12:02 pm
Is that an 18W Superlite TMB amp? If so, I tweaked its tone stack component values using Duncan's TSC to get the best overall frequency range with anode-drive :) I also warm-biased the second preamp stage with a 600ish ohm cathode resistor, to get some Plexi-like asymmetric overdrive. :)
Nah - it's a Mojotone kit. I'll be building one of Josh's soon, and a superlite would be such an awesome build - particularly for my needs (which are particular, but simple).
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by zaphod_phil »

cstenger5 wrote:
Fri 09/24/21 1:17 pm
zaphod_phil wrote:
Fri 09/24/21 12:02 pm
Is that an 18W Superlite TMB amp? If so, I tweaked its tone stack component values using Duncan's TSC to get the best overall frequency range and minimized insertion loss with anode-drive :) I also warm-biased the second preamp stage with a 600ish ohm cathode resistor, to get some Plexi-like asymmetric overdrive. :)
Nah - it's a Mojotone kit. I'll be building one of Josh's soon
Cool! I never knew Mojotone's TMB had an anode-driven tone stack. Most TMB 18Ws use a cathode follower. So I was under the mistaken impression that the Superlite TMB was the only 18W with an anode-driven stack. :?
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by ewizard »

I messed around with MANY circuits that would fit into the 18 Watts available tube sockets. After much ado, I came to a breakthrough; I don't like cathode followers. In my case, going between a plate-driven and CF-driven tone stack, as well as bypassing the tone stack altogether to just hear what a CF would sound like on its own, The CF does have a sound. I would not call it mid gutted, but more hi mid-focused perhaps. For me, it created this stiff, high mid-focused sound that was not easy to tame out. My experience has also been that CF-driven tone stacks are not as responsive to conventional FMV tone stack topologies as compared to plate-driven. In short, I tend to enjoy amps that don't have cathode followers in them more. Marshall has its thing going for them, the only Marshall style amp I own is the 18-Watt and it never actually had a CF in them. The older I get the fewer tubes and other components I like between my guitar and the speaker.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by Bieworm »

"The older I get the fewer tubes and other components I like between my guitar and the speaker."
Hahaha.. on your way to solid state amps? Maybe start looking out for a running valvestate!!!👍😉
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by cstenger5 »

Bieworm wrote:
Wed 12/01/21 11:20 pm
"The older I get the fewer tubes and other components I like between my guitar and the speaker."
Hahaha.. on your way to solid state amps? Maybe start looking out for a running valvestate!!!👍😉
I hear Kemper has a great Tweed Champ model.

:lol:
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Re: Circuit designers - cathode follower, or plate fed tone stack?

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ewizard wrote:
Wed 12/01/21 10:29 pm
I messed around with MANY circuits that would fit into the 18 Watts available tube sockets. After much ado, I came to a breakthrough; I don't like cathode followers.
Thanks so much for that thoughtful response. I have a bit of FOMO over the cathode follower thing in terms of what I've built (I've never built one), and your post helps diminish that.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by Bieworm »

I disagree. Tweed bassmen, plexis, 2204... all great sounding amps with very good and responsive tone controls IMHO
All have a CF
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Re: Circuit designers - cathode follower, or plate fed tone stack?

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Bieworm wrote:
Thu 12/02/21 11:02 am
I disagree. Tweed bassmen, plexis, 2204... all great sounding amps with very good and responsive tone controls IMHO
All have a CF
No argument there whatsoever. I just feel a bit less like I'm missing out, considering my current build is plate driven.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by ewizard »

Keep in mind I did not say unresponsive, just less responsive as compared to anode driven tone stacks. The cathode follower is good at reducing insert loss from tone stacks, which do suck a lot of volume and load down the previous stage a bit. Because they can reduce insertion loss so well, it changes how the tone stack interacts with the rest of the circuit. In my experience, it is less responsive. The bass control has a wide sweep for little change, the mid pot doesn’t suck the mids out quite as much, and the highs stand strong even with generous amounts of cut. This is of course relative to an anode driven tone stack of pretty much identical topology.
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by Bieworm »

ewizard wrote:
Sun 12/05/21 11:49 pm
Keep in mind I did not say unresponsive, just less responsive as compared to anode driven tone stacks. The cathode follower is good at reducing insert loss from tone stacks, which do suck a lot of volume and load down the previous stage a bit. Because they can reduce insertion loss so well, it changes how the tone stack interacts with the rest of the circuit. In my experience, it is less responsive. The bass control has a wide sweep for little change, the mid pot doesn’t suck the mids out quite as much, and the highs stand strong even with generous amounts of cut. This is of course relative to an anode driven tone stack of pretty much identical topology.
Agreed on the brightness that's pretty present, even on low treble settings.. but some like that in an amp (like me)
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Re: Circuit designers - cathode follower, or plate fed tone stack?

Post by ewizard »

I thought I would circle back around this topic, it has been quite some time now, and while the topic went dead, I thought I would take another stab at it.

Having designed a few more amp circuits since my last post, one thing still stands for me, I am not a fan of CF's. I have also learned I like having my mids too, so I don't use conventional tone stacks. But contrary to all that, my newest build has guess what? A cathode follower...

Now, let me clear some things up. No " tone stack " after it, only a Hi-cut filter ( adjustable treble bleed to ground ). My bass controls are pre CF. And I am using a local negative feedback loop around the CF into its driver stage. Similar to a Fender Tweed Super-Amp. I like my mids, so no mid-control is in the works as of yet. So why a CF, and what does this amp do? Well, it sort of does the Dumble thing, but without having 4 gain stages. It is creamy, rich, and it does the clean to breakup thing that is spongy, mid-forward, and smooth. I am on the fence about going with cathode biased, or staying with fixed bias for this amp, I may just do both? I feel that cathode biased would give it some more harmonic character, but may be too raunchy when pushed. I have not tested it yet, but in fixed bias mode, it brings the spank.

What I am getting at is that you just never know where you will get to unless you keep an open mind. While I don't like CF's, there are ways to make them not do the things you don't like, and get a different flavor. In this case, for me, it was a necessary evil and there is a chance this design will be my flagship design ( there is only one at the moment )? I had a client tonight who is a 50-year veteran guitar player, and using my 18-watt design, he said he has never had a better sound!! I find that shocking and flattering, considering my 18-watt design is about as simplified as you can get an 18-watt to be. It is similar in some ways to the Lite iib, except I have a bass control, a cut control and a post phase MV. Ok, so not as simple, but all the major tone controls are not sucking out gain at least. I have seen his amp collection, and he has Marshall Plexis, JCM-2000's and 800's as well as A Diezel Lil Fokker and some other vintage amps. For him to be as stoked about an 18-watt derived design of mine as he is, shocks me. So again, you just never know what will bring the win, if it sounds good it is good. So try it, even if you don't like it normally, you may just find it does what you need...
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