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Old 8th January 2013, 08:39 PM   #11
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The color codes are on the schematic, but some of them are pretty hard to read. The Studio Bass schematic that I have is much clearer and we should be able to glean the actual values from the color codes. Looks like I have five of the six, including the one you need. I'm guessing I may have left the Presence one in circuit, but it's been a really long time since I worked on that amp, probably at least twenty years.

PS: If you want to change this to the Studio Bass EQ circuit you'll still need another one of the 011945 inductors, or something equivalent, as the SB uses two of those.
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Old 8th January 2013, 09:01 PM   #12
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Did you get my PM and email?
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Old 8th January 2013, 09:20 PM   #13
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Originally Posted by cyclecamper View Post
Did you get my PM and email?
Yep, emailed you back last night. I'll ship tomorrow.
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Old 8th January 2013, 09:48 PM   #14
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Quote:
Originally Posted by Passinwind View Post
PS: If you want to change this to the Studio Bass EQ circuit you'll still need another one of the 011945 inductors, or something equivalent, as the SB uses two of those.
I don't think it really does, I'd always assumed that was a typo on the schematic, unless you know that to be true from looking at one. Perhaps they wanted the lowest bass contols to have more gradual overlapping low-pass???

I would be more interested in how to vary the =/- range.
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Old 8th January 2013, 09:54 PM   #15
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Quote:
Originally Posted by cyclecamper View Post
I don't think it really does, I'd always assumed that was a typo on the schematic, unless you know that to be true from looking at one. Perhaps they wanted the lowest bass contols to have more gradual overlapping low-pass???

I would be more interested in how to vary the =/- range.
I'll do a quickie model in LTspice and see what I can figure out. I really don't want to mess with my friend's Studio Bass anymore if I can help it.
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Old 8th January 2013, 10:57 PM   #16
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Quote:
Originally Posted by cyclecamper View Post
I don't think it really does, I'd always assumed that was a typo on the schematic, unless you know that to be true from looking at one.
Don't think it's a typo after running some quick online calcs to solve for simple LC resonance frequencies. Here are the actual inductor values, as best as I can figure:

011941: 50mH
011942: 100mH
011943: 200mH
011944: 500mH
011945: 1H
011946: 2.5H

A few of the frequencies are as much as 20% or so off the schematic/front plate labeled values -- close enough for rock 'n roll.
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Old 9th January 2013, 03:53 AM   #17
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I got your email, I just wasn't on that system until just now...thanks!
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Old 9th January 2013, 01:53 PM   #18
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You're right, it does show the color codes on the schematic; I guess I'd assumed that was a wire color with stripe color or something long ago, and has been "invisible" to my selective brain since!

Also, as I investigate possible power supply upgrades I discover the Studio Bass has a lower 395 V B++ compared to the Super Twin 400 V B++ (B+ is shte same 500 V on both).
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Old 4th February 2013, 09:22 PM   #19
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I want to make sure I thanked you publicly for really coming thru on this one! If I get the right test setup I'll try to measure these, so they are reproducible. If nothing else, it is an interesting tube graphic EQ.

I added epoxy to the ends of each, where the leads exit the cylinder body. Then I added some GOOP glue to anchor them to the turret-board. Several leads were loose, making it just a matter of time before fatigue failure from the vibration of setting a head atop a cabinet.
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Old 5th February 2013, 04:46 AM   #20
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Cyclecamper,
The REAL values for your edification

Frequncy Band (centre) is set by the LC resonant frequency which you can calculate from
f = 1/ 2pi (LC)^-2

or 1 over 2 pi root L C (in words.)

OR cheat:
Resonant Frequency Calculator

2300 Hz and 0.047 uF => 101.88mH, call it 0.1 H
1250 Hz and 0.082 uF => 197.7 mH, call it 0.2 H
485 Hz and 0.22 uF => 489.48 mH, call it 0.5 H
235 Hz and 0.47 uF => 975.9 mH, call it 1 H
100 Hz and 1 uF => 2.5 H

You can match those values up with the Fender Part Numbers above.

Next go to Mouser or similar and search for those values. Should be cheaper than a Fender spare part.

Edit: responded from page 1, just noted Passinwind's response above - well this is his design review, he passes (if you'll forgive the pun).

Cheers,
Ian

Last edited by gingertube; 5th February 2013 at 04:51 AM. Reason: Noted Passinwind's post above
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