Fender Twin EQ mod

Brad Sarno · Post by **Brad Sarno** » 29 Mar 2002 12:32 pm

I just made a really cool modification on my '69 Fender Twin. And really this mod goes for any Fender tube amp of the '62-'78 vintage that has the 3-band eq.

The stock Fender eq has the midrange cut set at around 500Hz. What I see on 8 out of 10 steel rigs and Profex settings, is that people love to cut around 800Hz. That's the honk/bark that many steels love to make. So what I did was changed a 100kOhm resistor to a 56kOhm resistor and it shifts the midrange cut frequency from about 500Hz to about 800Hz. Now my twin will do the same cut that I always made on my Nashville. This resistor is the one that feeds the .1uF and .047uF caps from the input to the 250pF treble cap. Email me for more details.

Also, just a comment on the Fender tone circuit. A simple replacement of the stock values of the capacitors with higher quality modern film/foil types brings a huge improvement to the tone, especially for steel. My Twin has all film/foil Orange drop cap's in it and the sound is way way cleaner and tighter. Better sparkle, better dynamics, better pitch definition in the bass, everything. There are more expensive caps out there that also sound great. The Orange drops are a cheap way to do it. Also, there is a very very critical cap in there that in my opinion brings more sweetness to the amp than anything. It's the 250pF treble capacitor. The way the Fender tone circuit works is called a tone stack. The signal actually passes thru the capacitors always. Unlike the tone control on a guitar where the cap merely dumps highs to ground. What this means is that the quality of the cap directly effects the tone, no matter where the tone is set. Fender puts a really crappy 250pF ceramic disk cap in the treble path. These are awful souding for audio, grainy and harsh. We're all used to this sound because all the Fenders came that way. If you put in a Silver mica 250pF it helps. I did this and it was OK. I finally found a source for polystyrene film/foil caps for this role and man oh man, I've never heard such a clean sweet high end from any amp ever. For steel especially with all those complex upper harmonics and overtones, they just shimmer and sing now. Email me for a source for these caps if you want to do this mod.

Angela Instruments at www.angela.com sells many very cool cap's for tube amps. If you can solder and know how not to get electrocuted, the process is pretty simple.

Brad Sarno
St. Louis
Mullen U-12/Fender Twin/15"BW

Patrick Smith · Post by **Patrick Smith** » 29 Mar 2002 1:43 pm

the 100K to 56K sounds like the slope resistor in the tone stack.

I've beat this to death here, but if you really want a kick in the butt, redo the preamp to 50's tweed specs, do this to the normal channel after wiring it through the reverb circuit and giving it reverb/tremelo....change the .1 and .047 tone caps each to .022uF, replace the 250pF ceramic disc treble cap to a 250pF mica cap, the slope resistor to 56K as you mentioned, and change the bass and mid pots to 1MA and 25KA, respectively, undo your 100pF cap from the bright cap and replace according to taste....for steel I'd drop a 390pF mica cap on the volume pot.

You will now smoke any amp within a 200 mile radius!....ha!....no kidding!

PMS[This message was edited by Patrick Smith on 02 September 2003 at 08:34 AM.]

Brad Sarno · Post by **Brad Sarno** » 29 Mar 2002 4:05 pm

Cool. Can you describe the sonic results of the "tweed" mod?

Brad Sarno

Jon Light · Post by **Jon Light** » 29 Mar 2002 4:54 pm

Just for the record, both of you guys, I'm most interested. Patrick--I certainly made note of your previous postings and saved you prior description of the tweed mod. Sadly, I'm too ignorant and scared to start messing inside my amp but I hope to find a way to learn some basic safety stuff and try some of these things.
Just wanted you to know you weren't just talking to the walls.

JB Arnold · Post by **JB Arnold** » 30 Mar 2002 8:33 am

I fully intend to do tis as well

john

------------------
Fulawka D-10 9&5
Mullen Royal Precision D-10 8 & 5
"All in all, looking back, I'd have to say the best advice anyone ever gave me was 'Hands Up, Don't Move!"
www.johnbarnold.com/pedalsteel
www.buddycage.net

Patrick Smith · Post by **Patrick Smith** » 31 Mar 2002 9:59 am

Well, the best I can describe it is, for one, you'll have a real live sweet midrange instead of the typical scooped mid twin tone....now bear in mind that when we started we hooked the normal channel through the reverb circuit and modded it, so your regular twin reverb channel is unchanged....we only messed with the channel that no one in the history of guitar amplification has ever played!...ha!

The coolest part of all of it for me was, I liked twins, but they just didn't have the volume that I sometimes needed on stage....folks say "they just don't have the power"....well, I quickly found out that ain't right at all!.....in doing these changes, particularly the bass and mid pot changes, you increase the loudness of this channel by at least 2-fold!.....no kidding!....you get soooooo much gain back by doing this!.....on mine I ended up doing the mod on both channels (I have another blackface twin if I need a straight twin) and put a 500pF tone cap in the tone stack and another 500pF cap on the vol pot and use that channel as a bright channel....I cross channel and play through both channels....on the loudest gigs I've played, and some were loud!, I have yet to take either channel vol knob above 3!....no kidding!...this amp smokes!

I would reccomend just modding the normal channel to start out with and see what you think....again, it's not affecting the reverb channel at all so you have nothing to lose!

hope any of this helps

PS-FWIW I have a 200 watt Evans, which I dearly love!...it now sits in my music room

Steve Feldman · Post by **Steve Feldman** » 31 Mar 2002 1:36 pm

PMS - I've heard the word 'scooped' used with both positive and negative connotations. For example, regarding a certain unnamed amp (flame suit at cleaners right now....), someone described the tone they liked as having a "'scooped' sound .... like "the mids got scooped out and bottom was added." Someone else talked about a certain mod "scooping the mud out and separating the notes".

So, how do you define a scooped sound (cut the mids and boost the bass?), or alternatively, could you elaborate on your comment that your Tweed mod gives the Fender a 'sweet midrange instead of the typical scooped midrange twin tone'?

Thanks.[This message was edited by Steve Feldman on 31 March 2002 at 01:46 PM.]

Patrick Smith · Post by **Patrick Smith** » 1 Apr 2002 9:01 am

Sure Steve, I can try, but tone is so subjective and a little difficult to describe but I'll do what I can.

The techies can talk frequency numbers, I don't know them, wish I did but I don't....I'll compare two of my personal amps for example....I inherited a Peavey Artist (the only way I would own a Peavey BTW, just not my cup of tea)....this thing sounds great with the mid knob OFF....it has the worst honkiest mids I've ever heard!...just absolutely horrible!....now let's take my 1973 50 watt Marshall model 1987, this thing has the sweetest midrange I've ever heard in an amp!...while the techies can probably lay out which mid freq are the nasty one's and which are the sweet ones, I can't, I just have my ears.

Now the scooped tone which is used to describe twins, usually refers to a nice bottom end, a top end, but not much of a midrange to em'....all of course IMHO....twins aren't very midrangy amps by nature.....a lot of that is governed by the values of the caps in the tone stack and the slope resistor....the mods I mentioned just put these values back to the original tweed specs, which happen to be EXACTLY the same values that Jim Marshall used in the early plexi amps.

Ok, now for the fun part!.....This is another thing that I absolutely LOVE about rigging a twin this way and the cool midrange that you have as a result, not to mention that the thing is now loud enough to play on a LOUD stage, I've found, as have probably the majority of you guys, that an amp will sound BEAUTIFUL in your practice room, but when you get on stage with symbals, strings, horns, and the rest of the frequency-cancellation-circus going on, it's hard to get your tone to cut through...it just gets lost....the sweet midrange that I've described does just that!...cuts through that is!....I've never had an amp cut through so much crap so well as this one does! I played a couple of jobs with a guy who used a sequencer with strings, steel drums, horns, banjos, all kinds of crap and this twin cut right through it all....it's the only amp I've got for steel that will do that, that well!

I know I'm talking in abstract and probably little of this makes any sense but hope any or some of this helps

PMS

PS-last year we were to "send more hookers".....seeing your new post, did they all leave?.....

Steve Feldman · Post by **Steve Feldman** » 1 Apr 2002 3:51 pm

Nah, I just moved out of Nevada last year. Used to be I could get all my errands done in just one trip to town. Bank, post office, grocery store - everything you need - right there on the same block.

Jerry Hedge · Post by **Jerry Hedge** » 1 Apr 2002 7:14 pm

The "Tweed Mod" leaves out the key to the Fender tweed sound-the tone stack driven by a cathode follower. The output impedance of a cathode follower is lower,and you get better bass response. In my own Twin I've used a 47pF bright cap,a 2.2k cathode resistor (on the first preamp stage and a 100mF cathode bypass cap along with beefing the filter caps (for a good solid bottom end).

Patrick Smith · Post by **Patrick Smith** » 2 Apr 2002 8:01 am

"....along with beefing the filter caps "

Jerry, just out of curiosity, what did you up the filter caps to?....and did it get boomy on you or just add a little more thump?

I also started with 47pF bright caps, one on the pot, one on the switch, but with the other changes it was still too dark for steel guitar....just not enough high end, so I upped them[This message was edited by Patrick Smith on 02 April 2002 at 09:05 AM.]

Jerry Hedge · Post by **Jerry Hedge** » 2 Apr 2002 8:25 pm

Patrick,I changed the 70uFs to 100uFs and the 22uFs to 47uFs. I also lowered the dropping resistors between the filter stages so I would get higher plate voltages on the preamp stages for more headroom. One day I would like to replace the transformers with larger Hammond units to set the amp up for 6550's. 4 6550's @ 540 volts should get around 150 to 200 watts of beautiful,warm tube POWER!!! Headroom is where it's at!!![This message was edited by Jerry Hedge on 02 April 2002 at 08:26 PM.]

Patrick Smith · Post by **Patrick Smith** » 3 Apr 2002 12:29 am

Jerry, funny you should mention it, but two days ago I ordered some 100uF caps from Doug Hoffman for just that purpose.....lol.....Over the last year, I did the complete repro of a JTM45 RI amp back to original specs....and dug it!...but have slowly worked my way back to turning the thing into a plexi 1987, hey I like what I like!...ha!....I put a SS rectifier in, and put the filter caps back to 50uF....from the "what's supposed to be"...and what I'd changed to 32uF and 16uF....now I know it's a balancing act with filtering and power sections, but man!...the SS recty with the 50uF caps blew my skirt waaaaaay up!....bottom end that'll thump yo azz off!..I like that!..not woofy!...thumpy!......this will be my first go at fiddling with the filter caps in a Fender though, and I appreciate the feedback.

Another thing that I've been planning to do in the next day or so, is to try the 820/250uF combo at V1....what's there now is the standard 1500/25uF....may be cool, may not, but that's half the fun of it!....ha!

The funny thing is, and I've got my asbestos underpants on so they can flame away, but man!...you fiddle around with a circuit of a tube amp and get it juuuuuuuuuust right.....ain't nothing like it!

"One day I would like to replace the transformers with larger Hammond units to set the amp up for 6550's"

One question, who you gonna get to carry that thing around?....ha!.....want a kick in the headroom pants?....plug into and crank up a HIWATT DR103!....wow!...I mean wow!

PMS

Jerry Hedge · Post by **Jerry Hedge** » 3 Apr 2002 2:02 am

Patrick, I know what you mean about the Hiwatt. I own it's grandfather,a Sound City 120R w/6 EL34's in the output. If you want to try an amp that you'll go nuts over check out a Traynor YBA 1-A or even better a Traynor Custom Deluxe. They bombed in the marketplace because they were too clean and too powerful for the 60's Rock players they were aimed at.High plate voltages,HUGE Hammond transformers and headroom out the wazoo.They were a steel player's tube amp dream

Michael Brebes · Post by **Michael Brebes** » 4 Apr 2002 8:56 am

Even doing something as simple as changing the 10K Mid pot to a 25K will make an incredible tone difference. (The Bass control 500K to 1M is a very very small tone difference, and is questionable on whether it is worth the expense.) The thing that needs to be remembered about the Fender style tone circuits is that the Mid and Bass controls interact a lot. The position of the Mid control actually changes both the Mid and Bass control frequencies, while the Treble control is a balance control between the highs and the Mid/Bass circuitry. Theoretically, the way it works is pretty strange, but sounds very good. I have installed the 25K pot on all my Fender amps, even the ones that have a fixed 6.8K resistor (Deluxe Reverb, Bassman, etc.).

Patrick Smith · Post by **Patrick Smith** » 4 Apr 2002 12:31 pm

"(The Bass control 500K to 1M is a very very small tone difference, and is questionable on whether it is worth the expense.) "

Actually, the bass pot is 250K, not 500K, at least in the BF and SF twin reverbs.....I didn't do a step-by-step test, but I can say that changing both reeeeeeeeeeally did a job on mine....as did changing the tone stack, sloper, and bypass cap.....so, yeah, I'd change it to a 1M, but that's just me, plus, it's only about $2.50 from Hoffman

I guess the thing that amazed me, more so than the tone change, was the change in volume!.....3 on the vol pot is VERY LOUD!....Man, you just gotta love those Fender amps!

PMS[This message was edited by Patrick Smith on 04 April 2002 at 01:02 PM.]

Keith DeLong · Post by **Keith DeLong** » 10 Apr 2002 9:04 am

I changed the 250 pf capacitors in the treble circuit on a '64 Super Reverb, it seems to have really cleaned up the high end. I don't use the amp for steel so I'll hold off on the other mods. Haven't taken it out on a gig yet, but I'm looking forward to doing that this weekend.

Brad Sarno · Post by **Brad Sarno** » 10 Apr 2002 5:38 pm

So what does the change in value on the midrange pot do exactly? If I were to make that mod only, what would I hear?

Thanks,
Brad Sarno

Michael Brebes · Post by **Michael Brebes** » 11 Apr 2002 8:03 am

Making the Mid pot change only would actually increase bass and mid ranges. The way the circuit is, the bass and mid controls interact. To me, something magical happens when you hit 6 and above, with a 25K pot. To me, it adds more presence and depth to the sound. When just changing the pot, remember that previous 10K settings can be had by setting it at slightly under half of the old value (6 on 10k is now 2.5 on 25k, etc.). Hope that helps.