Negative Feedback Question
- Thread starter Cap217
- Start date
So you mean just soldering it over the top and attaching the legs to the .0047 legs or do you mean disconnecting one leg and attach it to one leg of the new cap and then the other leg to the lug?
glpg80
Well-known member
Solder over the top of the other one so they both connect in the same manner.
FourT6and2
Well-known member
Just use a 50K linear pot in series with a 33K resistor for the NFB and see what sounds good to you. Then measure the pot and add 33K to get your final value. A lot easier than swapping out resistors. And you can play as you spin the dial.
RedPlated
Well-known member
Here’s how you can get .0047 and .0068. Only need a .0047 and .0022 cap. This is 1 Meg audio alpha switched pot. This is the front of the pot facing you.
Valvestorm has the pots. They are listed as Alpha 16mm switched.
You can use linear or audio taper. Linear comes on a lot faster. I like them both actually.
Valvestorm has the pots. They are listed as Alpha 16mm switched.
You can use linear or audio taper. Linear comes on a lot faster. I like them both actually.
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psychodave
Well-known member
I honestly think the OP is overly fixated on specific values. I feel they should try .001, .002, .003 as well as .004 and .006. Without hearing each value in real life, they are doing a disservice to themself.
Then there is adding the 39k resistor to focus in the mids like Cameron does. Of course trying several different values is always best here as well.
Then there is adding the 39k resistor to focus in the mids like Cameron does. Of course trying several different values is always best here as well.
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I ordered all of the stuff. I also bought a 50k pot and a 33k resistor to measure and see what I will like. Can you tell me how to hook this up and test?
It was hard to find a .0068 cap so I ordered a bunch of stuff. Ceramic, silver mica, mallory, synergy, and sozo. I guess I will end up testing them all.
It was hard to find a .0068 cap so I ordered a bunch of stuff. Ceramic, silver mica, mallory, synergy, and sozo. I guess I will end up testing them all.
FourT6and2
Well-known member
Your stock NFB resistor is 47K, right? If you want to experiment with a lower value, you'll need to remove it entirely. If you just want to know what higher values sound like, just lift one end of the stock resistor (the end that's connected to the hardwired depth circuit at the junction of the 220K/4700pF).
1. Lift that end of the stock NFB resistor and attach the pot between it and where the resistor was previously attached. Or...
2. Remove the stock NFB entirely and place the pot and new 33K in its place.
To wire up the pot as in #1: One wire to the pot's lug 1. Solder the pot's middle lug and lug 3 together. Then attach another wire to middle lug. Alligator clips on the other end of the wires. Attach one clip to the turret and the other clip to the free end of the 47K resistor. Now your NFB is variable from 47K to 97K.
For #2: Attach the 33K resistor to lug 1. Solder lug 2 and 3 together. Attach one wire to lug 2 and another wire to the free end of the resistor. Alligator clips on wires to attach to turret board where the stock resistor used to be. Now your NFB is variable from 33K to 83K.
You can also experiment with moving the NFB from the 8ohm to the 4ohm or 16ohm taps.
Attachments
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FourT6and2
Well-known member
And to test, find the pot setting that sounds good to you. Give it time. At least a few hours of playing so you know what you like. Then unclip pot from circuit and measure with a meter. Resistor + pot value = NFB resistor value. For example, if pot is 42K with 33K resistor = 75K total.
scottosan
Well-known member
Yes, measuring the pot out of circuit is a must.
psychodave
Well-known member
Agreed, but I would suggest he actually solder in the parts. Nothing against him, but he seems pretty green and I’d hate to see something bad happen to him or the amp.
FourT6and2
Well-known member
Whatever he's comfy with lol
glpg80
Well-known member
Racerxrated
Well-known member
I’m gonna jump in, and ask a question for all of you knowledgeable tech meisters…
What are your thoughts on getting rid of the NFB completely?
glpg80
Well-known member
That’s what the Mesa modern mode does - it cuts all NFB completely.
RedPlated
Well-known member
I bought a 75' JMP a few years back, which I still have, that has an Aldrich type mod on it. It had no NFB when I got it. I added a NFB circuit though. It sounds better with it. Very raw and loose without one.
If you want the option, use a 47k NFB resistor with a 250k pot inline. You'll be pretty close to having no NFB wit the pot all the way up.
If you want the option, use a 47k NFB resistor with a 250k pot inline. You'll be pretty close to having no NFB wit the pot all the way up.
harddriver
Well-known member
Although it seems like NFB would be a really subtle affect on overall tone when it's not there you really notice it and miss it.
I have a 5 watt single ended 2203 circuit amp that has no NFB and it is very noticeable to me when I play it. I don't have the same experience when I play that amp versus my 72 1987, 79 2203(which has alot less NFB than my 68 which is 47K on the 8ohm tap, I feel the dynamics and overall feel is more interactive with my amps that have NFB.
So I definitely agree that NFB sounds better to my ears, but you almost have to go without it to actually understand what it does.
Racerxrated
Well-known member
Reason I ask is, I had a local tech check out my 83 2205 and he did find some cold solder joints that needed refreshing; he also removed the NFB. So far I really dig it; sounds much better and with a boost it’s among the best 800s I’ve owned. Now, I haven’t turned it up very far yet but the clarity of the chords, single note stuff is much improved. He wanted me to try it and see…he can always put it right back in. Impressed so far.