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Post subject: Re: 1967 BF vibro champ
Posted: Fri May 20, 2016 8:40 pm
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I switched out the 2 prong for a 3 prong
Image
Put in the 40/20/20/20uF 525VD, but hooked up the 3x 20uF for now
Image
Sounds pretty sweet, louder than one would think. I at some point thought it was my imagination, but I heard a difference in input 1 and input 2, with input 2 being lower in volume, did some internet searching and found this
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Inputs 1 & 2 use a simple resistive mixer to combine the two channels and to provide a gain cut for Input 2. Each resistor has a value of 68K.

The gain cut is -6dB, and as others have said, means only that the amp will have to be turned up higher to achieve the same levels of gain as in Input 1 alone.

There is one other effect here; when plugged into Input 1, the amp presents an impedance of 1Meg to the instrument. When plugged into Input 2, the instrument sees an impedance of 2 x 68K = 136K. This is a relatively low value, and will affect the response of passive pickups by reducing the resonant peak in the treble range - hence the guitar will sound "smoother" and less aggressive.

If one is using any active preamps, such as effects pedals or active pickups, then this effect will not occur.

Image

Here you can see what happens. Plugged into Input 1, the signal is paralleled with Input 2 due to the switch inside the #2 jack. The signal passes through the 2 68K resistors in parallel (equivalent to a 34K resistor, insignificant) and then to the grid of V1 with a 1Meg resistor to ground - hence the nominal 1Meg impedance.

When plugged into Input 2, the switch in the jack is opened and the bottom 68K resistor is connected to ground due to the jack switch shorting in #1 input, resulting in an input load of 136K. The signal is tapped at the point between the 2 resistors, resulting in 6dB of cut.

Looking at it made sense to me
mud


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Post subject: Re: 1967 BF vibro champ
Posted: Fri May 20, 2016 9:55 pm
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I'm not sure that the 12AX7 grid "sees" 136k-ohm with input #2. If you look carefully, both inputs have one 68k-ohm tied to them. The 1-meg ohm is grid-to-ground (not an impedance load). This resistor helps set the idle bias on the 12AX7, but not directly effect loading impedance.

All that said, my guess why Input 2 is louder on your amp, is the 68k-ohm resistor one that leg has drifted. Or the one on Input 1.


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Post subject: Re: 1967 BF vibro champ
Posted: Fri May 20, 2016 11:58 pm
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BMW2002Ti wrote:
All that said, my guess why Input 2 is louder on your amp, is the 68k-ohm resistor one that leg has drifted. Or the one on Input 1.


You've misread his post:

"I at some point thought it was my imagination, but I heard a difference in input 1 and input 2, with input 2 being lower in volume"

Input two on vintage Fender amps was always lower in gain because it was intended for high-output instruments such as an accordion or electric piano, with Leo reasoning (correctly so) that attenuating the input signal would prevent first-stage saturation and intermodulation distortion.

Arjay

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Post subject: Re: 1967 BF vibro champ
Posted: Sat May 21, 2016 1:28 am
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Arjay,

Ok, got it.


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Post subject: Re: 1967 BF vibro champ
Posted: Sat May 21, 2016 6:49 am
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Arjay thanks for the explanation, as this amp is so new to me, and working on my tone trying to find my settings, I noticed a difference between the inputs. I am kinda liking input 2 with my SG and input 1 with my Strat, with the gain structure as explained, this makes sense as the humbuckers have a lot more output and seem harsh in input 1, and my Strat seem lacking something in input 2. Of course I will be experimenting with both channels until I get the tone that suits my playing, hey I'm a sound guy, my nature is to make minor/major adjustments

mud


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Post subject: Re: 1967 BF vibro champ
Posted: Sat May 21, 2016 6:45 pm
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mud wrote:
hey I'm a sound guy, my nature is to make minor/major adjustments


Most of us here enjoy tweaking and diddling -- it's how we learn (and sometimes make useful discoveries).

8)

Arjay

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Post subject: Re: 1967 BF vibro champ
Posted: Wed May 25, 2016 9:23 am
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Now that I can play it I have bonded with it, seems the filter cap breathed some life back in to it. I missed the reverb though, went digging pulled out the Roland Space Echo 201 to use it's reverb, plugged it all in and had that ocean sound along with reverb, turned it off plugged my guitar directly into the amp, all was quiet, put the Roland back where it was. Than pulled the Digitech Studio 400 multi fx, it is quieter but the reverb is better for PA mix, nothing so far that is real springy, still better than nothing and it will do until I find a reverb pedal I like. I feel I spend more time tweaking the digitech than playing, I will settle at some point. Miss that SR sound, but I must say the Vibro in the Champ does not have that clicking that the SR has ( different circuit all together), and it is a lot louder than I thought it would be. Around volume 7 it sounds as loud as the SFSR on a nudge below 2, except it has more of something, maybe it would be called presence, I always felt the SFSR never left 1st gear, where as the VC at 7-9 sounds like it went into overdrive.
While digging I was looking to spot the speaker I saw in BMW2002Ti's post in "Pro Amp 61" of the picture of his speaker in his combo. I thought I had 1 or 2 and I found 120F-6 Metered 6.6 Ohms, first thought was keep looking for the other one or more, they are back there, and put 2 in a cabinet for the VC, but I think in reality the VC could not move to much air though these,
Image Image
than I found this Utah it Metered 2.9 to 3.1 Ohms, alright a 4 ohm 12" speaker to try, and it looks like it does not need the power needed for the 2x 120F-6.
Image Image
Thing is I know nothing about this speaker and the net does not have much.. Arjay would you happen to know anything about theses
mud


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Post subject: Re: 1967 BF vibro champ
Posted: Wed May 25, 2016 12:34 pm
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That Utah likely came from a large console hi-fi system (Zenith, Philco, Admiral, etc). I'd say it's good for at least fifteen watts so it would be safe for use with your Vibro Champ.

You should give that pair of JBL D120F's a try as well -- I've played a Vibro Champ through a Dual Showman enclosure (2 x 15" JBL D130F's) and it sounded downright ballsy.

Arjay

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Post subject: Re: 1967 BF vibro champ
Posted: Thu May 26, 2016 10:21 am
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Retroverbial wrote:
That Utah likely came from a large console hi-fi system (Zenith, Philco, Admiral, etc). I'd say it's good for at least fifteen watts so it would be safe for use with your Vibro Champ.

You should give that pair of JBL D120F's a try as well -- I've played a Vibro Champ through a Dual Showman enclosure (2 x 15" JBL D130F's) and it sounded downright ballsy.

Arjay


The Utah came in a wall mount box I think some sort of School PA in the day. Maybe the Stromberg Carlson amp I have powered it at 70v, just a guess because I was not there,
Image
and I am thinking about turning it over and maybe put in a bottom and top baffle on the back
Image
and add new grill cloth
Image
As far as putting together a box for 2 x 120F-6 That will be another day, but it sound like it could be fun.
mud


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Post subject: Re: 1967 BF vibro champ
Posted: Thu May 26, 2016 1:57 pm
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mud wrote:
Retroverbial wrote:
The Utah came in a wall mount box I think some sort of School PA in the day.


If that be the case I wouldn't expect a very broad or very linear frequency response. Most of those vintage PA speakers were optimized for spoken voice, ie: bingo games, the pledge of allegiance, classroom announcements of duck-and-cover drills and the like.

Arjay

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Post subject: Re: 1967 BF vibro champ
Posted: Thu May 26, 2016 6:28 pm
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Retroverbial wrote:
mud wrote:
Retroverbial wrote:
The Utah came in a wall mount box I think some sort of School PA in the day.


classroom announcements of duck-and-cover drills and the like.

Arjay


Oh yes How I remember those drills :lol:
Before I make any baffles I will just have to hear it with the VC. I have used it with a Wollensak T1500 using the PA mode with my guitar in it, and it sounded better than the Wollensak's speaker, had that overdrive sound. The Wollensak I might use as a tube distortion but I will need to put in new filter caps first
mud


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Post subject: Re: 1967 BF vibro champ
Posted: Thu May 26, 2016 10:17 pm
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mud wrote:
Before I make any baffles I will just have to hear it with the VC.


Wire it up and let 'er rip. Let us know how it sounds.

Arjay

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Post subject: Re: 1967 BF vibro champ
Posted: Fri May 27, 2016 2:29 pm
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[/quote] Most of us here enjoy tweaking and diddling -- it's how we learn (and sometimes make useful discoveries).

8)

Arjay[/quote]

Tweaking and diddling? Useful discoveries?...boy I'll say...oh wait you meant on the amps! Gotcha!

:wink:

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Post subject: Re: 1967 BF vibro champ
Posted: Tue May 31, 2016 12:43 pm
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First of all I have not been a fan of the 12", and I do like the 10" in amps that I have tried. I hooked up the Utah 12" and it did work, though it did sound rather flat and hollow, sought of had a sound of a 1938 recording, I don't mean like a scratched record, kind of lacking fidelity. The original 8 sounds way better, although the Utah could have an interesting effect, if that was what I was looking for. Trying to make one of Leo's perfect design's better, or modified to my liking more than likely will prove futile. More than likely I will end up with one of the Webers as I only hear good thing about them.
mud


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Post subject: Re: 1967 BF vibro champ
Posted: Tue May 31, 2016 1:07 pm
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mud wrote:
I hooked up the Utah 12" and it did work, though it did sound rather flat and hollow, sought of had a sound of a 1938 recording, I don't mean like a scratched record, kind of lacking fidelity.


Recall my previous comments re this speaker.

Arjay

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