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Topic: Making the Fender Super Twin Reverb an even better steel amp |
Jan Jonsson
From:
Gothenburg, Sweden
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Posted 17 Apr 2008 4:14 pm |
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After reading several positive posts regarding the Fender Super Twin Reverb as a pedal steel amp, I became very curious to try one myself. So, last fall I got hold of a very nice one for a reasonable sum of money. It was completely original, except for the modifications done by SEMCO (the Swedish organization which controls and regulates 220 volt electrical systems.): fusing, power switch, grounding and new faceplate. As soon as I tried out the amp at the seller's house, I knew that this amp had a great potential to be a good amp for my steels. When I got home and had more time to try it out, I realized that there were some things that could definitely be improved in the original design. So, here is my list of changes that I have just finished implementing and my reasons for those changes.
1. Installation of a 15" Eminence Commonwealth speaker on a new baffle
The original 12" speakers sounded pretty good for my Nocaster guitar, but for my pedal steel I preferred to have less mids and more bass. After connecting the 15" speaker in my Steel King amp to the Super Twin Reverb, I realized that this was a very suitable speaker. So, I ordered a 15" Eminence Commonwealth, which supposedly is almost identical to the Steel King speaker. Then, I had to make a new baffle for the amp, which initially seemed a little tricky because of the permanently installed ("dado-ed") baffle board. But, with the aid of a nice saw and some precision cuts, I managed to remove the old baffle and instead install a 0.5" birch plywood baffle using the assembly technique used in blackface Fenders.
2. Moving the input signal for the reverb driver
As others have pointed out with the Super Twin Reverb, the reverb itself does not sound very good for many settings on the five-band equalizer. The reason for this is that the input signal to the reverb circuit is taken directly after the tone stack preamp, but before the input stage of the equalizer. The reverb return signal is then mixed with the eq:ed dry signal which gives rise to some nasty frequency clashes in many cases. To remedy this problem, I took the reverb input signal from the equalizer output (the rail from the tube anode that connects all equalizer potentiometers). And suddenly I had something that sounded very much like a nice blackface type of reverb ...
3. Moving the connector jacks for the reverb tank to get rid of noise and oscillation problems
However, the reverb was still not as clear and bright sounding as a real blackface/silverface one, which turned out to be due to a 0.022uF shunting capacitor on the return jack from the reverb tank. Once I removed that capacitor, the brilliance was back. And so was an unwanted oscillation that manifested itself when the reverb control was turned upwards 4-5. After some debugging, I realized that the oscillation was caused by too long wires from the reverb circuit tubes and the connector jacks for the reverb tank. So, my remedy was to drill new holes for these jacks as close to the tubes as possible. Now, the reverb sounded as great as I wanted it to!
4. Removing the distortion circuit and adding a negative feedback control
As almost everyone seems to agree upon, the distortion circuit in this amp is not too exciting. I therefore decided to remove it completely to get rid of unnecessary wires and also to free a half triode that could be used for something else in the future. In addition, I now had an unused potentiometer that I tried to find some use for. That was when I discovered that the boost function in the remote foot switch did nothing more than insert a 39 Ohm resistor parallel to the 100 Ohm resistor in the negative feedback loop in the power amp, that is, reducing the amount of negative feedback and thereby achieving an even more powerful amp (albeit at the cost of more noise). So what I did was to use the distortion potentiometer as a continuous NFB control by putting it in series with the aforementioned 39 Ohm resistor.
5. Installation of a "safe" ground-lift switch
When I took a closer look on the electronics in the chassis, I noticed that several jacks had isolation washers on them, and that the grounding scheme was more elaborate than on older types of Fender amps. Unfortunately, not all jacks were isolated and there were some strange choices of chassis grounding, so I ventured to try out something I have been wanting to do for a long time: implementing a true ground lift that is not hazardous for the player's health. In order to do this, I had to isolate all input and output jacks and disconnect all signal ground wires from the chassis (but keeping the power cord ground wire attached). All ground wires were then organized in a galaxy grounding scheme and terminated at the ground lift switch (which, when engaged, put a 47 Ohm resistor and a 10nF capacitor in series between the signal ground and chassis ground).
6. Installation of individual bias adjustment controls and cooling fan for the power tubes
Another thing that I just had to fix was the bias adjustment circuit. With six power tubes I was not too happy with a single bias balance potentiometer, since would like to have the possibility to, not only be able to use unmatched tubes of the same type, but also to mix tubes of different types (6L6, 6V6, EL34, 5881, 7581, etc). I therefore removed the existing bias circuit and installed a circuit with a separate adjustment potentiometer for each power tube, making the potentiometer shafts accessible from the underside of the chassis and adding measurement points at the back of the chassis (using a six-position switch to select the tube to measure). In order to allow for separate bias adjustment potentiometers, I had to install a piggy-back board with additional bias bleeder resistors and capacitors. Since I was already working on issues regarding the well-being of the power tubes, I installed a 12 V DC fan powered by a rectified heater voltage (around 6.9 VDC). Despite the resulting low speed of the fan, it still managed to blow away enough warm air to achieve a significant drop in the chassis temperature.
Have fun!
-- Jan
_________________
CDs: Waltz for Elma (2015), Steel Reflections (2009)
Gear: 10-string Desert Rose "Delta Blues", Fender Deluxe 8, Fender CS Nocaster
Transcriptions of Lloyd Green's music: www.lloydgreentribute.com (Tablature menu) |
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Curt Langston
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Posted 17 Apr 2008 4:36 pm
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| Schweet! Looks very nice! Good work! |
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John Groover McDuffie
From:
LA California, USA
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Posted 17 Apr 2008 4:36 pm
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It is my understanding that when Fender went to the dado-in-place baffle board they also stopped joining the top, bottom and sides with finger joints and instead used rabbet joint at the corners, which is a less robust means of construction. They counted on the dadoed baffle board to help maintain the structural integrity of the cabinet. For this reason I have refrained from modifying my '70s Fender cabinets to use changeable baffle boards.
Even un-modified, my well-used Sliver Face Deluxe Reverb is showing signs of the joints of the top to the sides starting to come loose.
Let us know how your cabinet holds up under the rigors of "the road". This being one of the heaviest Twins it should be a good test. |
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David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
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Posted 18 Apr 2008 7:11 am
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| Interesting, Jan. Thanks for the ideas. To deal with the weight issue, and to give more flexibility for using different speakers, I opted to put my Super Twin Reverb in a head cabinet. On the old cabinet I closed up the face plate slot and use it as a separate 2x12 cab. My other choices are two 8 ohm 15" JBLs in Marrs cabs, or a single 4 ohm 15" Eminence in an old Vibrasonic cab I converted into a closed-back bass reflex cab. I use an outboard reverb unit (POD XT), but it would be nice to mod the reverb as you have, to make it usable. Also, cleaning up the boost circuit seems really worthwhile. |
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Michael Johnstone
From:
Sylmar,Ca. USA
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Posted 18 Apr 2008 7:34 am
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| Now all you need is a semi-parametric mid EQ control and you'll have it all.You could do it with a stacked pot where the existing mid control is located. |
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Jan Jonsson
From:
Gothenburg, Sweden
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Posted 18 Apr 2008 12:14 pm
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Thanks for the comments!
John: Yes, I'm aware of the sloppier cabinet joints of the later Fender models, and will keep an extra eye on the Super Twins cabinet as I start hauling it around. I've done some repairs on JBL-equipped Twin Reverb cabinets of the later era where the top had begun disattaching from the sides. The remedy for that was to open the tolex at the top edges, remove the giant staples that fastened the sides to the top and then drill a couple of holes from the sides into the top and insert wood plugs to stabilize to construction.
David: If you have the option to modify the reverb circuit, please give it a try. The 6CX8 pentode driver works surprisingly well in this circuit. Regarding separate top and cabinet, I have thought about it, and will surely consider such a solution (I love the looks of Ricky Davis' green Twin Reverb + dual cabinets).
Michael: Funny you should mention it, but I have actually thought about installing some type of parametric mid-cut circuit to make the amp even more flexible. The current EQ fits my Fulawka D10 perfectly, as the 1250 Hz control is right on the spot. But for other steels, it would be nice to have an frequency-adjustment facility. After my modifications, I have one half of a triod to spare, so maybe I can implement some type of Wien bridge circuit around that tube.
-- Jan |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 22 Apr 2008 4:41 pm
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| Michael Johnstone wrote: |
| Now all you need is a semi-parametric mid EQ control and you'll have it all.You could do it with a stacked pot where the existing mid control is located. |
I beg to differ. The graphic EQ circuit that's already in the Super Twin Reverb is far superior to a simple parametric tone control, the kind you might find in some popular steel amps. This amp will give you tones that no mass-produced steel amp will even come close to. |
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Michael Johnstone
From:
Sylmar,Ca. USA
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Posted 22 Apr 2008 8:04 pm
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| I don't see a graphic on there and I don't remember there being one on there the one time I used a rented Super Twin on the road back around 1990. I've seen graphics on Mesa Boogie amps though. |
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Jan Jonsson
From:
Gothenburg, Sweden
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Posted 23 Apr 2008 12:34 am
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Well, there is a five-band equalizer on the Super Twin that is very powerful. Maybe it is not "graphic" in the traditional sense, since you cannot visualize the frequency boosts and attenuations as clearly as you can with e.g. a Boogie amp and its EQ controls.
-- Jan |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 23 Apr 2008 1:06 am
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I believe the Super Twin's 5-band EQ is, in any functional way, equivalent to a 5-band graphic EQ. The only difference is rotary vs. sliding pots. I personally prefer rotary pots from a functional and relability point of view.
Very nice job on that Super Twin, Jan - lots of good ideas. I guess I'm gonna have to dig one of these up - just what I need, another amp. You'd have to see my stable to know what I'm talking about.  |
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David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
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Posted 23 Apr 2008 12:15 pm
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In addition to a Super Twin and Super Twin Reverb, I have a rare Fender 140 head from the same Rivera era. It is basically a 135 watt ultralinear transformer Twin Reverb with the same 5-band EQ as the STs, but in the graphic format with sliders.
All these amps really have two EQ systems, that can interact or not, with a footswitch. They have the usual passive tone controls: bass, mid, treble, presence, and pull-bright. The 5-band active EQ can be switched off. When the active EQ is switched on, the passive EQ controls are still working. So basically the active EQ system reshapes the passive system. And that reshaping can be switched in or out, effectively giving you two different switchable tones. They really put a lot into these amps, which makes it strange that they got the reverb so wrong.  |
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Jan Jonsson
From:
Gothenburg, Sweden
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Posted 26 Apr 2008 2:35 am
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Again, thanks for the nice comments! In case anyone needs more pictures and/or descriptions regarding my modifications, don't hesitate to contact me.
-- Jan
_________________
CDs: Waltz for Elma (2015), Steel Reflections (2009)
Gear: 10-string Desert Rose "Delta Blues", Fender Deluxe 8, Fender CS Nocaster
Transcriptions of Lloyd Green's music: www.lloydgreentribute.com (Tablature menu) |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 21 Jan 2009 8:03 am
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What a cool amp you have there, Jan. Just awesome!!  |
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Jon Zimmerman
From:
California, USA
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Posted 30 Jan 2009 1:55 pm Bias Controls for each tube---
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Jan: Your amp mod's are very innovative. I am curious how you got onto the Individual Bias Adjust controls for EACH tube in the set. Who helped develop or how did the learning curve evolve into this method...can you reveal how it came about? Did you do this to other amps prior to this one with success? 
Thanks for all the photos in your thread. Simply amazing stuff! JON Z out in the West |
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Jan Jonsson
From:
Gothenburg, Sweden
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Posted 31 Jan 2009 4:07 am Re: Bias Controls for each tube---
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| Jon Zimmerman wrote: |
| I am curious how you got onto the Individual Bias Adjust controls for EACH tube in the set. Who helped develop or how did the learning curve evolve into this method...can you reveal how it came about? |
Hi Jon,
Thanks for the positive comments regarding my Super Twin Reverb, nowadays known as the "Steel Tzar" ...
As for individual bias adjustment for each tube, it is according to the Gospel of amp guru Kevin O'Connor at London Power (author of the amp mod book series The Ultimate Tone - TUT). With this modification you can use your tubes much longer even as they age in different paces. And, as mentioned above, you can also mix different types of tubes and experiment with some interesting combinations. I've installed individual bias adjustments on a couple of amps before, including ones using power amp bias modulation. I've always been pleased with the results of those mods.
Additional pictures of my modifications are available here:
http://gallery.me.com/janjomusic#100023
http://gallery.me.com/janjomusic#100030
-- Jan |
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Jon Zimmerman
From:
California, USA
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Posted 31 Jan 2009 8:56 am Kevin O'Connor
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Oh My! Thanks for the info about the Ultimate Tone guru--I will explore further. Your PTP wiring is a marvel to see, Jan.
My Best, JON Z |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 10 Aug 2010 4:34 pm
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Jan, How are you liking your Super Twin Reverb now that you have got some time on it?
_________________
"Good judgement comes from experience, and a lot of that comes from bad judgement"~old cowboy proverb.
shobud@windstream.net |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 12 Aug 2010 5:26 am
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Anyone else using the Supertwin Reverb?
_________________
"Good judgement comes from experience, and a lot of that comes from bad judgement"~old cowboy proverb.
shobud@windstream.net |
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Ken Fox
From:
Nashville GA USA
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Posted 12 Aug 2010 1:03 pm
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| I went thru a really nice one and re-capped it for Tommy Butler. It is a head only version. Nice amp, but Tommy prefers #0001 steel amp that I built. He tells me he will be selling it and any amps he has left to buy another one of my steel amps, probably a 212 model, so he has both a 115 and a 212 Fox amp. |
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Jan Jonsson
From:
Gothenburg, Sweden
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Posted 13 Aug 2010 2:22 pm
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Hi James,
Sorry for the late reply ... been on vacation and off the 'net. As for my Super Twin Reverb, it has not been used as much as I had anticipated. I just can't find the need for the volume/power of that amp right now with the relatively quiet and dynamic bands I play with. My Fender Princeton Reverb suffices in most cases, and if I need a little more volume I also use my Vibroverb w/ 15" speaker.
Maybe I need to join a band with a couple of Marshall-stack quipped guitar players with a hearing loss to find a real need for the Super Twin ...
Best regards,
-- Jan
_________________
CDs: Waltz for Elma (2015), Steel Reflections (2009)
Gear: 10-string Desert Rose "Delta Blues", Fender Deluxe 8, Fender CS Nocaster
Transcriptions of Lloyd Green's music: www.lloydgreentribute.com (Tablature menu) |
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chas smith R.I.P.
From:
Encino, CA, USA
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Posted 14 Aug 2010 9:52 am
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This is a Twin 135, that was "voiced" for steel guitar before I got it. I had a blackface head (the engine turned copper faceplate, because 20 years ago, it didn't matter) and I swapped out the heads into the tweed cabinet and the original cab with the K120 speakers, that make forklifts groan. The Standel cab has a EVM 15L speaker.
I now use a VHT head that has been voiced for steel guitar. |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 8 Jan 2013 5:34 pm
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I've always been facinated with the Super Twin Reverb. Gonna have to get me another one some time.
_________________
"Good judgement comes from experience, and a lot of that comes from bad judgement"~old cowboy proverb.
shobud@windstream.net |
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Ken Byng
From:
Southampton, England
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Posted 10 Jan 2013 5:17 am
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I had a Fender Super Twin around 35 years ago. It was a heavy beast with the 2 x 12"'s in it, and I swapped out the 2 speakers and put a 15" Electrovoice in there. It sounded good to my ears, but not a huge difference over my silverface Twin that I had at the time with 12" JBLs in it. I didn't keep the Super Twin too long as I PX'd it for a Session 500. BIG MISTAKE!! The Fender had 100 times more character and definition than the Peavey, but as everyone was buying the Session 500 at the time I jumped on the bandwagon. Peavey UK swapped the 500 for a Nashville 400 at no cost to me because of the unreliability of the Session 500. Just wish I'd kept the Super Twin. 
_________________
Show Pro D10 - amber (8+6), MSA D10 Legend XL Signature - redburst (9+6), Sho-Bud Pro 111 Custom (8+6), Emmons black Push-Pull D10 (8+5), Zum D10 (8x8), Hudson pedal resonator. Telonics TCA-500, Webb 614-E, |
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Michael Lee Allen
From:
Portage Park / Irving Park, Chicago, Illinois
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Posted 10 Jan 2013 9:45 am
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[deleted
Last edited by Michael Lee Allen on 21 May 2018 1:55 pm; edited 1 time in total |
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John Billings
From:
Ohio, USA
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Posted 10 Jan 2013 3:03 pm
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MLA!
I just knew you'd have the "paper" on this amp!
JB |
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