Fender 65 DRRI

[moff]

I like my DRRI. Great tone, but in order to get it to break up nicely, it has to be turned up a bit (which equals "pretty loud"), and it's a little harsh at "friendlier" stage volumes, especially when using a pedal trying to get some overdrive. I'd like to get a little more gain from it at lower levels, without using a pedal, and try to get closer to that "British" sound.

I'm going to try a few of the known preliminary things like clipping the Vib channel high-pass cap (I may install a switch to engage\disengage it), as well as changing\rearranging the tubes and speaker.

From what I've read, I understand that removing the Normal channel pre tube altogether, and changing the Power Tube Driver to a 12AX7 will each add some gain\drive, which may do the trick. However, I was wondering if it's possible to swap out the stock 6V6 power tubes for EL34s, and if it was a lot of work to do so. Can anybody offer some advice?

[MWJB]

Swapping the 6V6s to EL34s will require either a new power transformer (PT), or an auxiliary 6.3VAC transformer to supply additional heater current. Either of these coures of action are quite involved. Simply fitting EL34s will burn out your PT.

Try the preamp tube swaps & try different brands of 12AX7, the Sovtek 12AX7WA that are usually fitted to modern Fenders are quite low gain.

[moff]

Thanks for the information. Going to EL34's is more involved that I thought it would be, so I guess that's out.

I disassebled the amp and removed one leg of the Vib channel treble bypass cap (C10), and the tone at lower volumes is much better. I then shuffled the tubes around (removed the Norm channel 12AX7, and used it in place of the 12AT7 power tube driver), which also added a little more drive. I tried a Celestion V30 I had in a spare cabinet, and although it was more inclined to break up at a lower volume, it was a bit harsh in the high-mids, so swapped back to the stock Jensen C12K.

I used it on a gig the next night, and it was much better, but could still use a tad more gain at my disposal at lower volumes.

My amp needs have always been schitzophrenic, because I play a bunch of different styles, from jazz to blues to Motown to classic rock to new rock. Over the years, my music room has had a revolving door for amps, with many Marshalls, Fenders, and Mesa\Boogies passing through, some being replaced after only a few months.

Not long after they came out, I started using a Line 6 Flextone, which I later upgraded to Flextone II. It's not perfect, but very versatile, and went a long way to solving my amp GAS. I've used it for a number of years, and despite being very good amps, I found that they just don't have that real tube "mojo". So this year, I decided it was time to go back to the real thing.

I will take your advice and try some higher output pre tubes (JJ's?), and maybe some 5881 power tubes. Or, I may just go out and buy something like a Tiny Terror and A/B the amps as needed. Oh no - I feel my GAS coming back again!!!!

Again, thanks.

[stokes]

You might try checking the bias.It may be a bit cold,if so drawing a few more ma's might just do the trick.

[chipaudette]

Hey Moff,

You got the classic guitarist's dilemma...you want a Fender clean and a Marshall crunch. There's no way you can do that without two amps. The Orange Tiny Terror might be the right call.

But, if you're still interested in modding the Fender DRRI, there are lots of things you can do. I have really beat on my DRRI and gotten some ridiculous high-gain sounds out of it. You probably don't want to go that far.

For adding just a bit of grit to your tone, I'd put all the stock tube types back in. They don't have to be the original tubes (upgrading tubes is often a good thing) but I like having the designed-for tube types in each socket. It keeps the stock clean sound, which is, after all, why you bought in the first place.

Next, I would open up the amp and slide the amp's chassis forward an inch or two. Slide it just enough so that you can see the front PCB, which holds all the pots like the volume knob and tone controls. Being a DRRI, that front PCB is installed bottom-side-up. So, you'll actually be looking at the underside of that PCB and you won't actually see the bodies of the pots. You'll just the traces and solder joints of the PCB.

What I would do (and have done) is find the three solder joints corresponding to the vibroto "Intensity" plot. It's the very last pot on the right, so it's three solder bumps should be easy to find. Then, solder in a very short piece of wire (1" long or less) between the left solder bump of the pot and the center solder bump of the pot. I'd then add some electrical tape to keep anything from touching your new solder joints.

By adding this wire, you're turning the pot into a variable resistor. Fine. Its effect within the circuit is to turn the "Intensity" knob into a "Master Volume" for your amp. And, it's the easiest Master Volume mod out there. By doing it this way, you don't have to cut into your circuit, you don't have to drilling or cut any holes, you don't even have to buy another pot. Oh, and it's completely and easily reversible by simply removing the one wire you added. Nice. Now put the amp back together.

OK, here's the fun part, turn on the amp, plug into the Vibrato channel, turn the "Intensity" up to 10 (but keep the vibrato "off") and start playing. With the "Intensity" (now called "Master Volume") turned all the way up, your amp is completely stock. The sound is completely unaffected by your mod. Sweet.

Next, turn the "Master Volume" down to "2" or so and start playing. Your total volume should be way reduced. You can now turn up the amp's original volume knob to start getting some grit while at a reasonable volume. You can continue turn the amp's volume all the way up to 7 or so and then turn the Master Volume down to 1.1 or so. If you've got humbuckers, this'll give you some fairly broken up grit. I actually like setting it on 4-5 and letting the gritty chords fly without getting too much of the "splatty" sound you get when on 7.

So, there's your grit that you need. Sure, it's pre-amp distortion and not power-amp distortion. But, unless you're going to buy a power attenuator (I bought a THD hot plate and it works really well) you're stuck with pre-amp distortion. With this master volume mod, I actually think it sounds not-too-bad. I've tried several other Master Volume configurations within this amp. Of them all, this is the easiest and actually sounds the best.

You'll also find that as you turn up the amp's original volume knob, the bright cap has less effect (its design guarantees it to be that way). Therefore, you may find that you don't need to put it on a switch. I like having mine on a switch, but not everyone likes installing one in their amp.

Have fun with the master volume. Let me know if you want even more gain and we can talk about stupid-fun mods to your DRRI.

Chip

[moff]

Thanks for the advice. I was thinking of having it rebiased anyway, as I've heard these amps are known for being on the cold side out of the box...

chipaudette: The "Intensity\Master" sounds like it might be a cool mod, and might be a way to get what I'm looking for. I'll give it a shot.

BTW, I Googled around looking for gain and master volume mods for the DRRI, but didn't find much in terms of DIY stuff, just a couple of amp tech shops that do mods. Do you know a good Master Volume mod other than the Intensity mod - specifically one that doesn't call for the reuse of an existing pot? I don't mind installing an extra one, maybe in place of one of the Normal channel inputs, or on the back panel.

[chipaudette]

Well, I recommend the "Intensity/Master" mod because it is super quick to do and super quick to undo. As a result, you can try the mod to see if you like it. If not, probably no master volume mod is really going to suit your taste.

If you do like it, but don't want to keep using the pot on the front (the vibrato still works, by the way, just give it a try) you can indeed add a master volume pot in other places, but tapping into the circuit is harder.

You'll need to start with a 1Meg Audio-Taper Pot. I recommend putting it in the back, in place of the jack currently used for the extension speaker. Just unscrew the 1/4" jack, unsolder the wires attached to the inside of the jack, and remove. Now you've got a hole ready to receive your pot. Once you've fit your pot, you need to find which is the "high" side of the pot and which the "low" side. I'm sure it's standardized, but I always forget which is which. When the pot is on "10", the you should read 0 ohms between the high side and the wiper. When the pot is on "0", you should read 0 ohms between the low side and the wiper. Have you found which side is which?

I'd start with wiring in the "low" side. You'll need to get a piece of wire and you'll need to connect it to ground somewhere in your circuit. I assume that you have the schematic that came with the amp. If not, you can get a copy from Fender at (http://www.fender.com/support/amplifier_schematics.php)

For your ground connection, I'm thinking about maybe using the grounded side of C16 or C11 or R24 or R30. It doesn't matter which as long as you use your ohmeter/multimeter to find which side of the cap or resistor is the one connected to ground. Then, tack-solder your wire to the exposed lead wire on the grounded side of the cap or resistor. Finally, properly solder the other end of your new ground wire to the low side of the pot.

OK, now you've got to move on to attach the high side of the pot. This is the side of the pot that you have to insert into the signal path. The trick is in deciding where to tap into the actual circuit to intercept the signal. Because this is a circuit board, there are no great spots. The least annoying part of the circuit to tap into would be to find R35 (the 200k resistor for the Vibrato channel). Use your ohmmeter or multimeter to find the side of R35 that connects back towards the C18. I call this the "upstream" side. Have you found it? Now comes the only tricky part...

You're going to have to carefully snip the lead on the upstream side of the R35 in such a way that you've got some of the resistor's lead still attached to the resistor and some of the lead left attached to the circuit board. Don't cut it tight -- cut it in the middle! The resistor doesn't have a very long lead, so it's tough to leave enough in both places. You'll need this lead wire in both places so that you can solder a wire to the bit still attached to the resistor AND so that you can solder a different wire to the bit still sticking out of the circuit board. If this were not a circuit board, tapping into the circuit for your volume pot would be trivial. But, since it is a circuit board, this snip-and-solder method is the only reasonably-easy way to tap into it. Sorry.

OK, assuming you've snipped the resistor and have enough leg on each side, gently bend the resistor upward so that it is standing vertically on the board. Solder one new piece of wire to the stubby piece of metal remaining on the resistor. Then, solder another new piece of wire to the stubby piece of metal remaining on the circuit board. Whew, the hard part is done.

Next, solder the wire attached to the circuit board to the high side of the pot. Then, solder the other wire (the one attached to resistor) to the wiper of the pot (the wiper is the middle tab on the pot). Add some electrical tape to the resistor to prevent inadvertent shorting. Tuck your wires down nice and neat (hopefully you didn't leave too much excess wire...that would be annoying). Finally, put the amp back together and play.

With your new Master Volume on 10 (assuming you wired it right), there should be no perceptible impact on the sound of the amp. It should be basically stock. When you turn your Master Volume down, though, the amp's volume should go down. Sweet.

The only problem with this particular mod is that the master volume only works on the Vibrato channel. It has no impact on the normal channel. If you want a master volume that works on both, you can do exactly the same mod except instead of tapping into the upstream side of R35, you'll have to tap into the upstream side of C25.

I think you'll find it impossible to use C25. My experience with this amp is that the snip-and-solder trick works for the resistors, but does not work for the caps (like C25). The caps tend not to have a long enough metal lead for snip-and-solder. Check it out for yourself. Usually there just isn't enough there. Don't try to use C25 unless you're sure that you can finish it.

Since I only use the vibrato channel, I'm fine with using R35. It's your call. There are other methods, but this is the one Mesa Boogie used back in the early days when they turned Fender amps into the Boogie Mk I. Hopefully, it works for you, too.

Good Luck.

Chip

[moff]

Thanks Chip. I tried the "Intensity" mod, and it works well for what it is, but the pre distortion doesn't quite cut it for me. It must be power amp distortion I'm looking for.

For general gigging, the amp's sound and gain is just about perfect (for my purposes) when the volume's at about 6 or higher. It's got that classic rock thing going. If I want more drive, I have the MXR\CAE overdrive (and\or a Tech 21 Double Drive 3X); and if I want to clean up a bit, I just roll the guitar volume back. Only problem is it's just too loud. Next step is to try an attenuator. I suspect that's the only way I'll get close to the sound I want without making my ears bleed.

Thanks anyway, I appreciate the help.

[Steve A.]

Post-PI MV in DRRI

I added the Ken Fischer Type 2 MV (which replaces the two 220k bias splitters with a 100-250k dual ganged pot) on my friend's DRRI and he loves it. I had first put in the Type 3 MV (this is the 1M cross-line pot) and it just did not work as well, especially at low volumes.

I usually use the Type 1 MV with the two extra coupling caps, but there isn't a lot of room on these PCB amps...

BTW I also added a "beer belly boost" to the Normal channel of this DRRI- something like a 1M pot on the "tail" of the tone stack (I forget the exact value I used) which helps him get nice dirty tones from his amp. One my own DRRI I added this mid-boost to one of the channels and the "Texas Tea" style mid-boost to the other channel (that is a 2-3M pot in series with a .01-.022uF cap which bypasses the whole tone stack- from the plate to the Volume control).

HTH

Steve A.

P.S. I put the Trainwreck Pages on my Blue Guitar site:

http://www.blueguitar.org/new/schem/...reck_pages.pdf

[moff]

Hi Steve - I'm a guitarist that can solder, and not really an electronics guy. If I know what to add or change, as it relates to physical parts or the markings on the curcuit board, I'm OK. Lifting one leg of capacitor C10 is easy - but "bias splitter" means nothing to me. Can you supply a step-by step "idiot's guide" to doing the Type 2 MV?

[Steve A.]

Hi Steve - I'm a guitarist that can solder, and not really an electronics guy. If I know what to add or change, as it relates to physical parts or the markings on the curcuit board, I'm OK. Lifting one leg of capacitor C10 is easy - but "bias splitter" means nothing to me. Can you supply a step-by step "idiot's guide" to doing the Type 2 MV?

I was going to write it up with pictures next time I take that amp apart. But it might be awhile before I get around to doing that...

Steve Ahola

P.S. The 220k bias splitters are R56 and R57. You can run into problems following instructions based on component designations if the manufacturer decides to change the board (like on the Fender Blues Deluxe/Deville Reissues).

[moff]

Thanks, Steve. No worries, I've got nothing but time...

[Unadan]

So moff - what mods (if any) did you decide on? Lots of time has passed since your last post.

[Enzo]

Hi Una, welcome to the forum.

I suspect moff has left the building. He has 6 posts and all are in this thread.