I had enough spare parts to build a 5F1 for a friend of mine. Actually, it was a Amp Maker WF-55, which is basically a 5F1 with solid state rectification.
Anyway, it's working and sounds very good using the neck pickup of my les paul, but there's too much mids when I switch to the bridge pickup. I did a bit of search and found the Framus mid control (https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Framus_Mid_Control), which seems to be a good solution to my mids issue.
Now, the dumb question: where should I add it? Before volume pot, after volume pot, or it doesn't make any difference at all?
Schematic of the WF-55 (https://www.ampmaker.com/wp-content/uploads/2020/07/wf55guide.pdf) on page 7 for reference
The 5F2A tweed Princeton has the tone control "around" the volume control. It serves as a treble bleed or treble bypass in reciprocal fashion. Whent tone is up full, it operates exactly like a bright switch on a silverface amp. That is, the treble bypass has more effect when the volume is turned down, and is basically "invisible" when the volume is up full. The treble cut aspect, however, remains the same at any volume level.
That Framus mid control is intriguing. It's sort of like adding (or subtracting, you could say) the scoop of a BF tone stack, without the other controls.
If you note that the TSC web page uses a 1M load at the end for its simulation, that's a pretty logical place to have the 1M volume control, so all you would need is a coupling cap up front: https://www.guitarscience.net/tsc/framus.htm
I do like the 5F2A Princeton control a lot if you only need to tweak the brightness, too.
Mark, I took a look at the 5F2A, and it's easy enough to add that tone control to the one I built. But it works on treble, correct? I think treble on my build is fine, actually it's exactly how I like my treble settings. What's bothering me a bit is the mids. That's why I didn't considered the 5F2A tone at first.
Scott, another dumb question, but where exactly do you think I should put a coupling cap? Seems to me the Framus mid control should go between the 22nF cap and the volume pot, so should I add another cap between the Framus mid control and the volume pot?
If you can't be happy with a Champ's no tone control, then just put in a full BlackFace tone network. The AA764 has it but with a fixed Mid resistor, use 25k like the 5F6a.
https://el34world.com/charts/Schematics/files/Fender/Fender_champ_aa764_schem.pdf
https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_5f6a.pdf
Quote from: Marcos - Munky on December 10, 2020, 01:26:31 PM
Mark, I took a look at the 5F2A, and it's easy enough to add that tone control to the one I built. But it works on treble, correct? I think treble on my build is fine, actually it's exactly how I like my treble settings. What's bothering me a bit is the mids. That's why I didn't considered the 5F2A tone at first.
Scott, another dumb question, but where exactly do you think I should put a coupling cap? Seems to me the Framus mid control should go between the 22nF cap and the volume pot, so should I add another cap between the Framus mid control and the volume pot?
The control provides treble cut and at lower volumes, treble boost. If your ultimate goal is to have more mids, then I suppose there are two things you might consider if implementing such a control:
1) simply raise the value of the treble bypass cap from 500pf to 1000 or even 1500pf, such that an advantage is provided to mids as well as highs; or
2) figure out some inductor/capacitor combination that provides an advantage to a specific band, rather than just anything above frequency X.
Have you tried changing the speaker (if that's an option) or making adjustments to the cab?
The Framus does a variable depth mid-cut. It's basically a bridge-T circuit except the pot allows the depth to be controlled.
You will get some loading but with the values shown it's probably not bad.
Put the network between R3 and C1, or, C1 and VR1.
Some Gibson amps had a built-in mid-dip using a bridge-T,
https://davidguilbault.typepad.com/GibsonScout/Gibson%20Scout%20GA17RVT%20Schematic.jpg
The difference here is it's not variable. Gibson use the version of the Bridge-T network which has the caps and resistor positions swapped.
If you want you could use a fixed version of either type of network.
Quote from: Marcos - Munky on December 10, 2020, 01:26:31 PMScott, another dumb question, but where exactly do you think I should put a coupling cap? Seems to me the Framus mid control should go between the 22nF cap and the volume pot, so should I add another cap between the Framus mid control and the volume pot?
You've got it figured out -- keep the 22nF coupling cap and stick the mid-scooper after it. :)
So it seems making the variable could end-up with more insertion loss. It's better to set-up the bridge-T to get the desired amount fo cut.
Another effect is you get a "tilt" in that the bass or treble is raised. To avoid the tilt you have to:
- select the resistor ratio to get the amount of mid-cut
- scale the resistor values to remove the tilt
- scale the caps to put the mid cut at the right frequency.
Here's a few examples,
VFR1 and VFR2 are the basic circuit. You can see the tilt affect.
VFRMOD1 is when the mid cut is set to -6dB and the notch frequency set to 600Hz.
VFRMOD2 is using the Gibson form of the bridge-T. If you aim at the same specs of -6dB and 600Hz with no tilt, you can see the performance of both types of Bridge-T networks pretty much produce the same result.
With the -6dB VFR mods you can see there is about 4dB loss of signal.
(https://i.postimg.cc/qgDNBh3F/Bridge-T-Mid-Cut-Tweak-2020-12-11-13-45-54.png) (https://postimg.cc/qgDNBh3F)
Note the 60k, 22n and 1M are not added they are part of the original circuit. (60k for tube impedance + 100k which I haven't checked BTW maybe it's 38k)
You can see that small tweaks are required for 38k source impedance,
(https://i.postimg.cc/XrCyXfSJ/Bridge-T-Mid-Cut-Tweak-38k-source-2020-12-11.png) (https://postimg.cc/XrCyXfSJ)
Quote from: PRR on December 10, 2020, 02:53:29 PM
If you can't be happy with a Champ's no tone control, then just put in a full BlackFace tone network.
Paul, that's one option I'm considering. While I was intended to keep it as simple as possible, a full tonestack will surely make it more versatile and I have everything as spare parts to add it.
[/quote]
Quote from: Mark Hammer on December 10, 2020, 03:50:07 PM
If your ultimate goal is to have more mids
Mark, actually I want a mid cut. The tone is almost amazing, but for a bit of excess of mids. Just a bit.
Quote from: andy-h-h on December 10, 2020, 04:07:15 PM
Have you tried changing the speaker (if that's an option) or making adjustments to the cab?
Andy, I tried it with a 1x12 cab with a Jensen speaker and a 4x12 cab (don't know the speakers). The 1x12 cab seems to have more mids than the 4x12. The 4x12 cab have almost my mids prefference, but it won't be a nice idea to carry a 4x12 cab to use with a 5W amp :icon_lol:.
Quote from: Rob Strand on December 10, 2020, 09:00:04 PM
Put the network between R3 and C1, or, C1 and VR1.
Quote from: ThermionicScott on December 10, 2020, 09:20:22 PM
You've got it figured out -- keep the 22nF coupling cap and stick the mid-scooper after it. :)
Rob and Scott, I'll give it a try on this weekend.
Quote from: Rob Strand on December 10, 2020, 09:57:25 PM
So it seems making the variable could end-up with more insertion loss ...
Another effect is you get a "tilt" in that the bass or treble is raised.
Rob, losses aren't an issue since I don't really like the cranked sound of the 5F1 (yeah, maybe this one should go to the "confessions" topic :icon_lol:). So I set the volume pot to less than half. Even with losses, I'll still have room on the pot to set it to sound as I like. And yeah, I didn't thought on the tilt and it is pretty noticeable. So, to be sure, if I want to keep it as variable, should I wire the pot as a variable resistor and take the output from R12+C9 instead of wiring the pot as Robinette's schematic with the output at the wiper?
have you considered changing the feedback network?
if you take out bass and treble and boost mids in the feedback loop, it will boost bass and treble and scoop some mids in the signal.
maybe this would work, i'm like 75% sure that it would:
(https://i.postimg.cc/QHZsycjD/mid-feedback-loop.png) (https://postimg.cc/QHZsycjD)
i have done a modification similar to this to an amp a friend of mine build to his own design, its basically a 5F1 pre-amp with a solid state class A power amp that's quite close to the 5F1 power amp in design (inductor loaded capacitively coupled, instead of transformer loaded)
it will change the fundamental nature of the amp tho, since the feedback is varied by the pot.
on the one extreme, there is a noticeable mid scoop and its clean and on the other side of the pot's travel, its mid-range heavy and distorted
i don't know it it will work on your version with a true tube power stage and output transformer.
cheers, Iain
QuoteSo, to be sure, if I want to keep it as variable, should I wire the pot as a variable resistor and take the output from R12+C9 instead of wiring the pot as Robinette's schematic with the output at the wiper?
Here's an example where you get a variable mid control like the Framus. With the values shown there is minimal tilt around the settings I expect you will use. You can move the notch frequency down by increasing the cap or up by reducing the caps; values from 1nF to 2.2nF would suite most cases. At full cut the circuit will give about 10dB max cut. Just to be clear the pot is a 470k pot and I've drawn it as two resistors for the purpose of the simulator.
(https://i.postimg.cc/QF3YfvKD/Variable-Bridge-T-mid-cut-2020-12-12-08-29-46.png) (https://postimg.cc/QF3YfvKD)
Quote from: Rob Strand on December 10, 2020, 09:57:25 PM
So it seems making the variable could end-up with more insertion loss. It's better to set-up the bridge-T to get the desired amount fo cut.
Another effect is you get a "tilt" in that the bass or treble is raised. To avoid the tilt you have to:
- select the resistor ratio to get the amount of mid-cut
- scale the resistor values to remove the tilt
- scale the caps to put the mid cut at the right frequency.
Here's a few examples,
VFR1 and VFR2 are the basic circuit. You can see the tilt affect.
VFRMOD1 is when the mid cut is set to -6dB and the notch frequency set to 600Hz.
VFRMOD2 is using the Gibson form of the bridge-T. If you aim at the same specs of -6dB and 600Hz with no tilt, you can see the performance of both types of Bridge-T networks pretty much produce the same result.
With the -6dB VFR mods you can see there is about 4dB loss of signal.
(https://i.postimg.cc/qgDNBh3F/Bridge-T-Mid-Cut-Tweak-2020-12-11-13-45-54.png) (https://postimg.cc/qgDNBh3F)
Note the 60k, 22n and 1M are not added they are part of the original circuit. (60k for tube impedance + 100k which I haven't checked BTW maybe it's 38k)
You can see that small tweaks are required for 38k source impedance,
(https://i.postimg.cc/XrCyXfSJ/Bridge-T-Mid-Cut-Tweak-38k-source-2020-12-11.png) (https://postimg.cc/XrCyXfSJ)
Quote from: Rob Strand on December 11, 2020, 04:36:24 PM
QuoteSo, to be sure, if I want to keep it as variable, should I wire the pot as a variable resistor and take the output from R12+C9 instead of wiring the pot as Robinette's schematic with the output at the wiper?
Here's an example where you get a variable mid control like the Framus. With the values shown there is minimal tilt around the settings I expect you will use. You can move the notch frequency down by increasing the cap or up by reducing the caps; values from 1nF to 2.2nF would suite most cases. At full cut the circuit will give about 10dB max cut. Just to be clear the pot is a 470k pot and I've drawn it as two resistors for the purpose of the simulator.
(https://i.postimg.cc/QF3YfvKD/Variable-Bridge-T-mid-cut-2020-12-12-08-29-46.png) (https://postimg.cc/QF3YfvKD)
Hi Rob, By quoting your posts i can see you've included links but in the posts neither the link addresses nor the images are visible and i haven't been able to make the links work working with them directly.
dave
QuoteHi Rob, By quoting your posts i can see you've included links but in the posts neither the link addresses nor the images are visible and i haven't been able to make the links work working with them directly.
That's weird, I'm only using the default "Add image to post" link generated by the forum.
From thumbnail, if you click on the thumbnail, or right click on the thumbnail and open in a new window, you should get the image server's page. The image is displayed by might not be full size.,
https://postlmg.cc/qgDNBh3F
After that, if you click on the image it opens the image as full size
After that, you can open in a new page and get only the original image in the browser window.
Alternatively, from the image server page, you can click "download original image".
I often open the images as full size because the quality looks bad, or for very large images, the default resized image is too small to see the details.
Quote from: Rob Strand on December 11, 2020, 06:31:36 PM
QuoteHi Rob, By quoting your posts i can see you've included links but in the posts neither the link addresses nor the images are visible and i haven't been able to make the links work working with them directly.
That's weird, I'm only using the default "Add image to post" link generated by the forum.
From thumbnail, if you click on the thumbnail, or right click on the thumbnail and open in a new window, you should get the image server's page. The image is displayed by might not be full size.,
https://postlmg.cc/qgDNBh3F
After that, if you click on the image it opens the image as full size
After that, you can open in a new page and get only the original image in the browser window.
Alternatively, from the image server page, you can click "download original image".
I often open the images as full size because the quality looks bad, or for very large images, the default resized image is too small to see the details.
It's getting weirder, i now the see thumbnails in your original posts and in my quotes of your posts, as well the address you just posted and see that @iainpunk has a thumbnail in his post.
dave
My last post does have the "https://postlmg.cc/qgDNBh3F" shown literally.
Literal link to image server,
https://postlmg.cc/qgDNBh3F
Same but linked as Image, [doesn't display anything]
(https://postlmg.cc/qgDNBh3F)
Linked as image to original image,
(https://i.postimg.cc/0xJn9CTK/Bridge-T-Mid-Cut-Tweak-2020-12-11-13-45-54.png)
Quote from: Rob Strand on December 11, 2020, 07:01:15 PM
My last post does have the "https://postlmg.cc/qgDNBh3F" shown literally.
Literal link to image server,
https://postlmg.cc/qgDNBh3F
Same but linked as Image, [doesn't display anything]
(https://postlmg.cc/qgDNBh3F)
Linked as image to original image,
(https://i.postimg.cc/0xJn9CTK/Bridge-T-Mid-Cut-Tweak-2020-12-11-13-45-54.png)
Perfect, all of that appears as i would expect.
So what's screwed up on my end...
On another forum, youtube links only show for me in posts if, i have just freshly signed onto the forum, there, others are having the same issue with seeing youtube links. So it goes.
dave
Blame the CME.
QuoteOn another forum, youtube links only show for me in posts if, i have just freshly signed onto the forum, there, others are having the same issue with seeing youtube links. So it goes.
There are browser settings that stops images being loaded but if it was that then *every* image on every website would be affected.
Maybe you should do a web search for the issue no doubt others have the same issue. Whether there's one or ten causes with the same symptoms is another matter ;D
Quote from: iainpunk on December 11, 2020, 08:58:51 AM
have you considered changing the feedback network?
if you take out bass and treble and boost mids in the feedback loop, it will boost bass and treble and scoop some mids in the signal.
Iain, didn't considered that. Seems to be an interesting mod to do.
Quote from: Rob Strand on December 11, 2020, 04:36:24 PM
Here's an example where you get a variable mid control like the Framus.
I tried it, and with the suggested values I got exactly what I was looking for and even more settings. The amp sounded so good a friend took it to his house, so I wasn't able to test it for too long :( :icon_lol:. Thanks again!
QuoteI tried it, and with the suggested values I got exactly what I was looking for and even more settings. The amp sounded so good a friend took it to his house, so I wasn't able to test it for too long :( :icon_lol:. Thanks again!
Hey that's pretty cool.