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Post subject: How much difference in changing a 1976 twin to blackface
Posted: Sat Jan 09, 2016 3:08 pm
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Will changing a 1976 master volume twin to blackface specs make a huge difference in the sound? What is the difference?


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Post subject: Re: How much difference in changing a 1976 twin to blackface
Posted: Sat Jan 09, 2016 3:33 pm
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While I am no amp tech, this a pretty huge project and not easily done and if this is an ultra-linear MV twin, I am not even sure it is possible at all.

The tone may just not be worth the effort it would take to get you there, and it might be cheaper just to buy a BFTR. There are a couple more on here that can give you the technical side of it but I think they'll also lead you to the same conclusions I stated.

FWIW

T2

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Post subject: Re: How much difference in changing a 1976 twin to blackface
Posted: Sat Jan 09, 2016 3:55 pm
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A '76 Twin Reverb already sounds pretty much like a blackface model. That is to say, LOUD and CLEAN. The only way to elicit any sonic "dirt" from the amp is via some carefully-selected stompboxes. Ditching the OEM Oxford or Rola speakers will provide some audible improvement though your fundamental issue will remain.

Arjay

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Post subject: Re: How much difference in changing a 1976 twin to blackface
Posted: Sun Jan 10, 2016 10:52 am
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The specialty of the old Twins is their low gain structure.
The old Twin = <1volt, but the modern Twins = 3 -20volts.
This means your fingers can jump up n down on the strings and you still won't clip the amp. They are great for energetic surf rock players.
The gain structure of your SF is still pretty close to the BF, so I wouldn't mess with that
Tone wise, the biggest difference is that the SF has significantly more low end response than the BF.
The SF, with it's extra bass response sounds good for play without a bassist. The low harmonics are boosted for a warm effect.
For a band, it will conflict with the bass guitar and cause low frequency acoustic harmonics.
To make a SF more bandfriendly, you can cut the bass in two places.
The coupling cap to the phase inverter tube is usually .01uF. This can be dropped as low as .001uf. This chokes bass and midrange to a certain extent and makes the midrange dip more pronounced. There is an overall tightening of the tone. Adjust to taste with 600 volt Poly caps.
The other change, and this is my preference, is to change the V1 & V2 cathode capacitors. They are 25uF/25V electrolytics and I drop this value to 2.2uF.
Select a value for your ear. The bass starts to audibly taper at 10uF and you can go as low as .68uF. This limits only the low end cutoff. Only the bottom end is attenuated.
You can use low voltage caps here. 50 to 250 is fine. I ditch the electrolytics for the faster responding Poly caps.
.


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Post subject: Re: How much difference in changing a 1976 twin to blackface
Posted: Tue Jan 12, 2016 10:18 pm
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Or, simply turn the bass knob down. :wink:

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Post subject: Re: How much difference in changing a 1976 twin to blackface
Posted: Wed Jan 13, 2016 9:49 am
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Yes, for a picker, that's the drill.
For a tinkerer, we can do better.
Turning down the bass only lowers the subsonic bass of the SF; a 2.2uF cathode cap cuts it off. It sends the bass control a more usable band of low tones.
The tone stack is a passive network that drops signal level a lot.. Turning the down the Bass control loads down the stack and flushes a lot of perfectly good tone down the toilet to ground.
Maintaining the 6 Oclock rule {thanks Retro} is a sure way to pass more good tone through the stack. You can modify the response of the tone stack with capacitors or at the cathodes to keep the stack properly loaded for your range of play..
The interaction of the bass and treble caps create the midrange dip and the Fender shimmer. When the stack is loaded excessively; eg the bass turned down, these effects disappear.
You can't hear the subsonics, but the low frequencies take a tremendous amount of power compared to mids.
The mids can't be focused or well defined when they are surfing on a big bass wave.
Since guitar tone is mostly mids, eliminating this bass wave is a sure way to allow your amp to focus on mids.


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Post subject: Re: How much difference in changing a 1976 twin to blackface
Posted: Wed Jan 13, 2016 11:54 am
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TimsAudio wrote:
The mids can't be focused or well defined when they are surfing on a big bass wave.
Since guitar tone is mostly mids, eliminating this bass wave is a sure way to allow your amp to focus on mids.


You wanna put some muscle into a Twin Reverb's mids?

Install a pair of JBL D120F's......

Image

I guarantee you, the amp will rip your head off with robust mids and bright, shiny highs.

And it won't matter if the amp is a blackface, a silverface, or no face whatsoever.

Arjay

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Post subject: Re: How much difference in changing a 1976 twin to blackface
Posted: Wed Jan 13, 2016 1:57 pm
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Beautiful photo of those JBL 120's in that SF Twin, Arjay, almost makes me want to go out and buy a stronger truss! :lol:


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Post subject: Re: How much difference in changing a 1976 twin to blackface
Posted: Wed Jan 13, 2016 2:18 pm
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Better to merely hire a couple of roadies.

:mrgreen:

Arjay

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