That’s a sweet looking and sounding amp, congrats.
I see you used 100/82K resistors on the CF. Did you try even lower on the cathode resistor?
Did the CF render a different tone, would you say?
Thanks!
If you look closely, I used node D for the 100k plate resistor. I used node C for the 82k cathode follower resistor. Compare the listed voltages on each of those (plate vs. cathode) to one another.
I did not try a lower value cathode resistor. I have on occasion, found a CF to seem to add some compression and smoothness on an amp. I don't know if that is always the case?
I put a CF on this single ended amp to function like the "send" of an active FX loop. V2a is the CF (FX loop "send") and the V2b is the return of the FX loop in my thinking. It seems to work that way for me on several amps I have tried it on. I was happy with how the amp turned out. The owner is a much better guitarist than I am and he reports liking it alot. The sound clip was my mediocre playing. The owner plays in more of a Nashville country style.
So my goal was a SE amp with an active FX. So that was the motivation behind the schematic design.
10thTx wrote: ↑Sun Aug 14, 2022 9:13 pm
If you look closely, I used node D for the 100k plate resistor. I used node C for the 82k cathode follower resistor. Compare the listed voltages on each of those (plate vs. cathode) to one another.
I did not try a lower value cathode resistor. I have on occasion, found a CF to seem to add some compression and smoothness on an amp. I don't know if that is always the case?
I put a CF on this single ended amp to function like the "send" of an active FX loop. V2a is the CF (FX loop "send") and the V2b is the return of the FX loop in my thinking. It seems to work that way for me on several amps I have tried it on. I was happy with how the amp turned out. The owner is a much better guitarist than I am and he reports liking it alot. The sound clip was my mediocre playing. The owner plays in more of a Nashville country style.
So my goal was a SE amp with an active FX. So that was the motivation behind the schematic design.
With respect, 10thtx
Yes, the CF will supposedly add compression – the lower the Rk the more compression (if on the same node, that is!)
That’s the reason I’d like to try it.
ViperDoc wrote: ↑Mon Aug 15, 2022 2:11 am
Regarding your schematic, do I read correctly that your CF involves one half of the 12AY7 and one half of the 12AX7 tube?
sluckey wrote: ↑Mon Aug 15, 2022 2:29 am
No. V2A, and only V2A, is the CF.
Thanks for clarifying that, Steve. Aah, when light bulbs and face palms unite! In reading Blencoe's CF info, his drawings always include the gain stage that the CF is following (hence the name, of course), so I always wondered why they were 'collectively' called the follower, which in fact THEY are not, just the CF triode itself. Huh.
ViperDoc wrote: ↑Mon Aug 15, 2022 5:28 am
In reading Blencoe's CF info, his drawings always include the gain stage that the CF is following (hence the name, of course), so I always wondered why they were 'collectively' called the follower, which in fact THEY are not, just the CF triode itself. Huh.
The wizard shows the previous gain stage in the direct coupled cathode follower mainly because it's important to see where the CF gets the positive voltage for the grid bias. But he doesn't show any previous stage in his AC coupled cathode follower because the accf gets it's grid bias by bootstrapping to the cathode (or from a fixed bias voltage divider).
Here's a cathode follower that has no previous gain stage. It's ac coupled directly to the input jack and uses a fixed bias voltage divider for grid bias. It's used as a buffer between the input and output jacks...
If I’m not mistaken the name comes from the output following the input in phase and (nearly) in amplitude. Similar cases are emitter and source followers in BJTs and FETs.
direct coupled CF can be like in SLO amps , 220k anode-100k cathode, and there are 2 stages like this!
SLO is brilliant sounding amp and has a lot of compression. similar effect can be 100k anode -68k cathode or so (82k), easy to mount something on fly (100k anode, 100k cathode, and put something in parallel to cathode resistor)
Tobyk wrote: ↑Sun Aug 14, 2022 8:27 pmGreat, finally a schematic – thanks!
This is exactly one way of doing it.
Please note that by doing it you are triodizing the curves of the output tube (but keeping the g1=0 curve tight to the very left), so for a guitar amp do not exceed with the lnfb.
I use a similar concept for my hi-fi amps (a combination of a-g1 and a-g2 feedback).
I do a pretty cool mod to the Jet City Custom 5, which looks like it tries to be a JCM800 in SE form. The main issues as I saw it were overcoming the lack of a Phase Inverter, but also the fact that there is no Negative Feedback. I wound up stealing the NFB idea from the Fender Champ. Check out how it turned out (Quick pajama pants cell phone clip with my Tokai LoveRock straight in. Speakers I think were a 2x12 cab loaded with Eminence CV-75's). I can scrape up a schematic if anyone cares.
Gainzilla wrote: ↑Mon Aug 15, 2022 11:34 pm
I do a pretty cool mod to the Jet City Custom 5, which looks like it tries to be a JCM800 in SE form. The main issues as I saw it were overcoming the lack of a Phase Inverter, but also the fact that there is no Negative Feedback. I wound up stealing the NFB idea from the Fender Champ. Check out how it turned out (Quick pajama pants cell phone clip with my Tokai LoveRock straight in. Speakers I think were a 2x12 cab loaded with Eminence CV-75's). I can scrape up a schematic if anyone cares.
That really does sound like a jcm800. Please do scrape up!
Here is one way to have some NFB when you don't have a common cathode gain stage in front of the power tube. The polarity on the OT needs to be reversed as compared to the typical injection into a previous gain stage.
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In reading Blencoe's CF info, his drawings always include the gain stage that the CF is following (hence the name, of course), so I always wondered why they were 'collectively' called the follower, which in fact THEY are not, just the CF triode itself. Huh. 
