65 Deluxe Reverb RI mod to Mesa Mk I

[chipaudette]

Hey All,

I'm new around here. It looks like there's a lot of knowledge floating around here. I'm currently in my first serious amp-mod project and was looking for some thoughts on how to fix some of my issues...

So, a month or so ago I bought a new Fender '65 Deluxe Reverb Reissue. It's pretty sweet. I like it. My previous amps were a Roland JC77 (like the JC120, only smaller) for my light-weight amp and a Mesa-Boogie rack system for my heavy-weight amp. I got the Fender DRRI because I was doing more Rolling Stones kinda stuff and I needed a better clean-broken up kind of sound.

Upon getting the DRRI home, I saw that it came with the schematic (I'd never bought a new amp before). The schematic totally lit me up.

Since I never use the "normal" channel (it has no reverb...why would I use it?), there sat both halves of a 12AX7 that were just begging to be used. Begging!

It didn't take long for the idea of using those gain stages to give me an overdrive lead tone. All I'd have to do is patch over one of those gain stages into the input of the "vibrato" channel. Simple cascade. Nothing shocking. I mean, the Boogie Mk I pre-amp was just a fender pre-amp with one more gain stage added at the beginning. That's exactly what I'm talking about here. If they could do it, why not me?!? If successful, I'd be able to get my clean thing going and then I could switch in some gain to get some Santana action as well. That would be awesome. OK, I got out the soldering iron...

So, from the "normal" side of the amp, my plan was to let the signal go through one half of the 12AX7, go through the tone stack, through the volume pot, and then lift the wire before it heads back to the other half of the 12AX7. I could then patch this wire (via a switch discussed below) and patch that into the "vibrato" channel. Yes.

Of course, the boogie MK 1 doesn't have a tone stack between the first and second gain stage as would happen with the above description. So, I lifted the tone stack's ground resistor. This defeated the tone stack allowing it to maintain full signal strength through to the volume pot. Since the MK 1 does have a volume pot after its first gain stage, I left this volume pot (the volume for the "normal" channel) in the path. Sweet.

Then, I added a DPDT switch to the "vibrato" channel just prior to its first 12AX7 gain stage. The switch swaps from (a) the traditional input from the instrument jack (after the 68K resistors and after 1M to ground) and swaps to (b) the gained-up signal from just after the volume pot on the "normal" channel described above. So far so good.

Now, the final major topological feature still missing in my amp versus the MK 1 is a master volume. My amp has a volume 1 and volume 2 like the MK 1 (volume 1 is the volume knob from the "normal" channel and volume 2 is the volume knob from the "vibrato" channel) but no master volume. In the Mk 1, Volume 2 really likes to sit around 6-7 to get a good saturated lead tone. Without a master volume, I can't turn up my volume 2 knob up this high without also getting really loud and overdriving my power tubes. While that's cool in its own way, it doesn't sound at all like the MK1. I need a master volume to allow me to control the second level of pre-amp distoration (Volume 2) from the amount of power tube distortion (master volume).

So, to give me a master volume, I tied in a high-value log pot to ground on the line heading out of the pre-amp section toward the phase inverter. The pot is switchable into or out of the circuit. Nice.

With all of these switches, I can easily swtich everything back so that the "vibrato" channel is stock. After all, I bought the amp because the stock "vibrato" channel sounded so good. Any gained-up sounds I add to the amp should not be at the expense of my cool clean channel.

Okay, I've gotten pretty long here. Sorry. It's just so much fun! While the mods went pretty well, my problems are thus:

(1) I played a MK1 re-issue in the store last weekend and it has a lot more saturated gain than I get out of mine. I want that saturated Santana lead sound.

(2) my lack of saturated gain might be due to the fact that I can't turn up Volume 1 past 7 without getting a high-pitched squealing sound and I can't turn up Volume 2 past 5.5 without getting a similar high-pitched squealing. Ouch!

Here are the questions for all of you out there...I was wondering if anyone has tried this type of mod with their old-style Fender? How did it go? Did you get the squealing problem? What can be done to squash it?

Finally, if the squeal can be squashed, I've got the other half of the "normal" channel 12AX7 doing nothing...what can I do with it?...mod the amp some more to put that in the signal path like the boogie Mk II/III/IV??? Mmm...more fun!

Thanks for you thoughts...

Chip

[HTH]

squeeling has gotta be lead dress issues right? - how about shielding the grid wire connections.

you could also put some small caps between the plate & cathode to get that squeel under control - try anything from 50pF to 250pF. this is something that Marshall did as standard on the later 2203 amps (my own JMP-era 2203 did this squeeling and the cap fixed it).

[chipaudette]

A cap between the plate and cathode? For high frequencies, that shorts the whole tube, right? I'd heard of a cap across the plate resistor (the 100K guy) as a snubber, but not across the whole tube. I'll have to check out the marshall schematics. Interesting.

Presumably, that cap would have to be a high voltage cap, right?

Thanks for the suggestion.

Chip

[HTH]

here's a link to the Marshall 2203 schematic with the 100pF cap between the plate and cathode of V1a...

http://www.schematicheaven.com/marsh..._100w_2203.pdf

[chipaudette]

Sweet!

I don't suppose that you know the plate voltage on the first two gain stages, do you? The voltage at "X" isn't labeled, so I'm having trouble figuring it out myself.

Thanks for the pointer!

Chip

[fluddman]

How did it go?

Hi Chip,

How did the mod go? I am in the same boat - looking to get a good overdrive sound out of the spare channel.

I thought I'd just have to be happy with the great clean sound and use another amp for the dirty tones. I have trouble getting a good dirty tone even with a pedal.

Is anybody else getting a great overdriven sound out of a deluxe reverb?

Cheers

[chipaudette]

Man o man...it's been a long time (and many modifcations) since that post on "starting" to mod my DRRI. Here's a couple relevant things that I've learned...

1) Distortion/overdrive pedals in front of a DRRI stink. Actually they only stink if you use them with the "vibrato" channel. The cause of this? The vibrato channel has a "bright" switch that you can't see. Actually, it's inside the amp and is wired permanently "on". That's why you get that nice sparkling clean sound. But, when you put a distortion pedal in front, it sounds way to fizzy. If you're going to use a pedal, try it on the normal channel. If you can make it sound decent over there, then it can be made to sound good on the "vibrato" channel but opening the amp, cutting one side of the capacitor jumping the volume pot, and putting that cut end onto a switch. That's what I did. It's my best mod on the amp (lots of other people have discovered this, too).

2) If you want a good overdrive, you have to get a power attenuator. None of my overdrive experiments sound decent except when used in conjunction with a power attenuator. Maybe you'll have more achieving saturated pre-amp distorion with this amp then I did, but all my high-gain sounds need some power amp overdrive to smooth things out. Since power amp overdrive means that the amp will be frickin' loud, I think a power attenuator is necessary. I bought a THD Hot Plate and I like it. But, that's serious extra cash (~$300?).

I've learned of other stuff to...but I'm not sure what you're looking for. If you're thinking about modding your amp, post again. If you're just looking for advice on pedals, try out your pedals on the normal channel. If you like what you hear, let me know, and I can point you along the path of lifting that "bright" cap in the "vibrato" channel of your amp.

Chip

[fluddman]

Thanks Chip,

That's good advice. I love the clean sound on the Tremelo Channel so I am reluctant to remove the bright cap. My understanding is that this cap is bypassed when you crank the volume up anyway - so the attenuator sound like a good plan.

The downside to an attenuator is obviously that it makes it hard to quickly switch from a dirty to a clean sound. I guess this is also the downside to a deluxe reverb - but still worth it for glorious clean sounds.

Thanks

[chipaudette]

So the bright cap is only relevant if you want to use a distortion pedal. If you're never going to use a pedal, there's little need to bypass the cap. If you do want to use a pedal, though, I don't think that you'll ever get one to sound good with the cap in the circuit.

If you ever want to bypass the cap, it's very easy to put it on a switch. "Bypass" isn't really the right word...the switch really just lifts one leg of the cap into or out of the circuit thereby allowing it to make its effect or not. I've got mine on a switch and it's really helpful to have control over it. With my Les Paul, I usually have it enabled. With my Strat, I usually switch it out...even when clean. I have no idea why Fender hardwired it when many other of their amps have it on a switch. I like having control over it.

A slight correction to your language...when you turn up the volume on your amp, the cap is not actually "bypassed". The better way to think about it is that, as the volume pot is turned higher, the cap ssimply has less effect.

The bright cap is wired to allow the highest frequencies to "go around" the amp's volume pot. So, when the volume pot is set low, the mids and lows are quiet but the highs are going around the volume pot and being amplified at full volume. Therefore, they stand out nice and bright compared to the quiet mids and lows. As the volume is turned up, though, the mids and lows are getting louder and louder thereby making the highs stand out less. See what I'm talking about? It's not really that important...but I figured you might want to know.

Finally, you should know that any power attentuator like the THD Hotplot is NOT going to give you heavy-metal-saturated kind of distortion. As you turn up the amp, it's gets a cool classic rock sound...but it's not heavy metal...it just doesn't have enough gain to overdrive that hard...even with the amp on "10",

Oh, and I think the amp sounds bad when set to 10. I never go about "7". On "7", my Les Paul gets good and distorted. But, it's not a heavy metal sound...it's also not a Marshall sound...it's a overdriven Fender sound. Big chords are BIG and single not stuff has some richness and sustain...but it's no Boogie. And with a Strat, you're going to get much less overdrive. You'll get a great great blues sound with dynamic break-up that's highly responsive to your pick attack and to your guitar's volume pot...but you're not going to turn your strat into a Santana-sounding sustain machine.

Chip