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Post subject: New TBV Mod for Blues Jr
Posted: Wed Jun 13, 2018 10:42 am
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Professional Musician
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Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
This is my TBV mod for Blues jr It has been the most difficult of the three amps I created the Tone Before Volume for. It reroutes the preamp signal chain so the preamp drives the tone stack at full volume, then sends it to the volume control. It results in a brighter tone at low volume and better definition at all volumes.
One of the difficulties was making it stable on the early green fiberglass boards. I never could, so for those early amps I make a little piggyback board that I build the new front end and tone stack on.
http://imgur.com/gallery/hjKrDWH
http://imgur.com/gallery/HNAxvGg

Like the other mods, these aren't for beginners. If you can't do it safely refer it to a tech.

Cream board http://imgur.com/gallery/yZV5Cah
http://imgur.com/gallery/yVHpvjN
http://imgur.com/gallery/cNmIpAo
This last pic is what i had to do to prevent on board oscillations. I now recommend it for all installs.

1. Remove R2, R7, R15.
2. Install 33k resistor from R1/R2 to R7/ribbon cable.
3. Install 10k from R7 to R15/ribbon cable.
4. Cut trace at Treble control wiper to R15.
5. Ground cut trace at R15 pad.
6. Install 10k at R2/ribbon cable.
7. Install shielded wire from that 10k to treble wiper
8. Ground shield one end only near R2
9. Install 100k from V2 pin7 to ground.
This amp has a tendency to hum or go into oscillation when the shield cover is off. Cut down the length of PW1 and separate the 2nd & 5th wires out. Push the other wires forward and dress 2 & 5 outward so they will lay against the shield cover when its installed. Pull the other ribbon cables out so they rub the back too. Keep the OT wires away from the ribbons. You won't really hear the oscillation because the speaker won't reproduce the ultrasonic frequency. But the music gets thin and squealy. High master and treble settings should be free of oscillation with the cover on and tight.
Now the jr is voiced much like a Marshall. That is, mostly treble, a departure from most Fender voices that are much warmer with bass. The Fromel mod adds a .1 cap in the tone stack to warm up the bottom end. This is a good start, but I have found the bass doesn't really open up until you change out the .0022 coupling caps for something bigger. I use .02 in C8 & C12 to open up the tone.
The intent of the TBV mod is to brighten the tone at low volumes. This means you don't need as much treble bypass in the volume control. So I change out C3 100pf to a 47pf.
I change the tone stack caps to standard Fender values, 250pf, .1, .047. The Fromel mod uses a .015 mid and grounds the wiper of the mid pot. This effectively removes mids and leaves the treble and bass alone. With a stock unit, this makes sense because the mids sound bad. With TBV and coupling cap improvements, the mids sound good. I leave the mid circuit as designed to pump as much mid through as possible. Mids are where the bulk of the music is, so I try not to kill them.
The reverb should get an upgraded ic, tle2072 or similar. If you have a pair of tin snips, you can get a long type 4 tank and cut the metal ends off by 1/4". It can fit in snugly and improves reverb delays.
The sparkle cap at C9 adjusts overall treble. I use 680 to 820 pf for my mods, but it’s a matter of taste.
This amp makes a great platform for modding. Like its bigger cousins, getting to the backside of the board is a snap compared to most amps. You don't even have to pull the chassis. You can also run them with the board pulled back, saving time and making changes easier. You can make an incredible difference in the quality of the music coming out of the amp.


Last edited by TimsAudio on Mon Mar 04, 2019 1:08 pm, edited 1 time in total.

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Post subject: Re: New TBV Mod for Blues Jr
Posted: Sun Jun 17, 2018 7:40 pm
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Aspiring Musician
Aspiring Musician

Joined: Thu Dec 12, 2013 2:54 pm
Posts: 618
Hey Tim,
Didn't want you think no one is paying attention, thanks for sharing your Tone Before Volume Mods. Don't think your wisdom and carefully thought out mods go un-appreciated here.

Saw your post somewhere about a Yamaha RD400, I remember when TZ 350s took 1, 2, and 3 at Daytona against the 750s. What a great bike.

Cheers,

_________________
"Where confusion abounds, there's money to be made."


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Post subject: Re: New TBV Mod for Blues Jr
Posted: Mon Jun 18, 2018 7:21 am
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Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
I didn't figure on many replies until folks try out the mods. Its something I gotta get out there before I forget how to do them. I think all deluxes should get these mods, but I can't do them all. I don't want these notes to be lost in my "filing system"
I watched Kenny Roberts on a TZ at Ontario Ca. He took 4th behind DuHamel and 2 other Kawasakis.
I tell people you can't buy hi performance off the showroom floor. The Yamaha TZ was the exception. You could buy this hot GP racer off the showroom floor.


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Post subject: Re: New TBV Mod for Blues Jr
Posted: Sun Mar 03, 2019 7:56 am
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Hobbyist
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Joined: Fri Sep 12, 2008 12:40 pm
Posts: 75
TimsAudio wrote:
This is my TBV mod for Blues jr It has been the most difficult of the three amps I created the Tone Before Volume for. It reroutes the preamp signal chain so the preamp drives the tone stack at full volume, then sends it to the volume control. It results in a brighter tone at low volume and better definition at all volumes.
One of the difficulties was making it stable on the early green fiberglass boards. I never could, so for those early amps I make a little piggyback board that I build the new front end and tone stack on. Don't try this mod on a green fiberglass board.
Like the other mods, these aren't for beginners. If you can't do it safely refer it to a tech.

1. Remove R2, R7, R15.
2. Install 33k resistor from R1/R2 to R7/ribbon cable.
3. Install 10k from R7 to R15/ribbon cable.
4. Cut trace at Treble control wiper to R15.
5. Ground cut trace at R15 pad.
6. Install 10k at R2/ribbon cable.
7. Install shielded wire from that 10k to treble wiper
8. Ground shield one end only near R2
9. Install 100k from V2 pin7 to ground.
This amp has a tendency to hum or go into oscillation when the shield cover is off. Cut down the length of PW1 and separate the 2nd & 5th wires out. Push the other wires forward and dress 2 & 5 outward so they will lay against the shield cover when its installed. Pull the other ribbon cables out so they rub the back too. Keep the OT wires away from the ribbons. You won't really hear the oscillation because the speaker won't reproduce the ultrasonic frequency. But the music gets thin and squealy. High master and treble settings should be free of oscillation with the cover on and tight.
Now the jr is voiced much like a Marshall. That is, mostly treble, a departure from most Fender voices that are much warmer with bass. The Fromel mod adds a .1 cap in the tone stack to warm up the bottom end. This is a good start, but I have found the bass doesn't really open up until you change out the .0022 coupling caps for something bigger. I use .02 in C8 & C12 to open up the tone.
The intent of the TBV mod is to brighten the tone at low volumes. This means you don't need as much treble bypass in the volume control. So I change out C3 100pf to a 47pf.
I change the tone stack caps to standard Fender values, 250pf, .1, .047. The Fromel mod uses a .015 mid and grounds the wiper of the mid pot. This effectively removes mids and leaves the treble and bass alone. With a stock unit, this makes sense because the mids sound bad. With TBV and coupling cap improvements, the mids sound good. I leave the mid circuit as designed to pump as much mid through as possible. Mids are where the bulk of the music is, so I try not to kill them.
The reverb should get an upgraded ic, tle2072 or similar. If you have a pair of tin snips, you can get a long type 4 tank and cut the metal ends off by 1/4". It can fit in snugly and improves reverb delays.
The sparkle cap at C9 adjusts overall treble. I use 680 to 820 pf for my mods, but it’s a matter of taste.
This amp makes a great platform for modding. Like its bigger cousins, getting to the backside of the board is a snap compared to most amps. You don't even have to pull the chassis. You can also run them with the board pulled back, saving time and making changes easier. You can make an incredible difference in the quality of the music coming out of the amp.



Hello Tim

Found the TBV mod you told me about in the Fromel Kit post. I saw in the forum the TBV for Blues Deluxe and Blues Jr, but can't find it for the Hot Rod Deville or Hot Rod Deluxe. Super very interesting this info. Thank you very much for disclosure it for all of us.


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