Question about MESA BOOGIE STUDIO PREAMP

Ben Godard · Post by **Ben Godard** » 2 Jun 2008 2:14 pm

My pickups (the BL710's) are too hot for the studio preamp. Its distorts no matter what. I've seen on this forum that there are 2 or 3 ways to fix this.

1. One way is two remove the 1 Meg reisitor on the input and use 2 68k resistors to make it like the lower gain input of a Fender amp.( note: you can also add a toggle switch with this so you can switch back and forth in case you using a less hot pickup.)

2. Another way is to remove the first stage tube which is a 12ax7 and replace it with a 12at7 which is about 30% less gain

3. Or just simply use a buffer in front of the preamp such as a pedal of some kind that would lower the gain.

I went and bought a 12at7 tube but I also have the 68k reistors to go the other route as well. My question is to which way is the best way to go. What are the pro's and cons of each method.

Ben Godard · Post by **Ben Godard** » 2 Jun 2008 2:15 pm

Darn. I put this in the wrong place. Please move to Electronics.

Thanks

Ben

Ben Godard · Post by **Ben Godard** » 2 Jun 2008 6:41 pm

anybody??

Tony Dingus · Post by **Tony Dingus** » 2 Jun 2008 7:00 pm

Ben, I remember reading were Paul Frankin said his studio pre was stock and he uses 710 and 705 and he aparently doesn't have any trouble. I use the studio pre too and I put the new 705 in my guitar and it distorted so I put the E66 back in the guitar and everything is fine. You and I must be doing something wrong but, I don't know what. I hope Paul sees this tells us what he does.

Tony

Jonathan Cullifer · Post by **Jonathan Cullifer** » 2 Jun 2008 7:48 pm

Where on the amp are you plugging the preamp? If you're going from the pre outs to the normal inputs on the Fender amp, that's probably overdriving the amp. Is there any place past the first gain stage on the amp that you can plug the pre into?

Jack Stoner · Post by **Jack Stoner** » 3 Jun 2008 2:26 am

The 710's can distort on any amp if they are set too close to the strings. The older 705 can be set using a quarter as the gauge for the distance from the strings (where they were set on my Franklin when I got it new). However, the 710's need 3/16" from the strings - the 710's on my Franklin are set a "loose" 3/16 and Mr Franklin told me I have mine at the correct distance. Some guitars barely make the 3/16" distance, I have a friend with an Emmons Legrande II and the adjustments on the Emmons barely get them far enough away from the strings.

I've never had any input overload (distortion) on any amp I've owned, with the Franklin, either tube or solid state.

Ben Godard · Post by **Ben Godard** » 3 Jun 2008 3:03 am

If I pick it moderately, it's on the verge of distorting, if I pick it hard, it distorts pretty bad. The spacing is set at 3/16"

This is my set-up.

Guitar goes straight to input of MB studio pre, the effects loop goes through a lexicon MPX1, the output of the MB studio pre then goes to Mosvalve 500 power amp. It is not clipping on the Lex MPX1 because I can see the level meter. Only 75% (Normally I put the stero volume pedal just before the power amp, but to get this thing set where it won't distort, I took out the volume pedal for now so I can get full volume.

Brad Sarno · Post by **Brad Sarno** » 3 Jun 2008 8:17 am

It's pretty easy for a steel pickup to overdrive that preamp input if you don't use a volume pedal between the pickup and preamp. No matter where you set the preamp's first gain control, you're still slamming that first tube stage full on. With a volume pedal before the input of the preamp, you're taming the signal WAY down, far enough to have clean headroom.

That's your problem right there, I bet.

Brad

Olli Haavisto · Post by **Olli Haavisto** » 3 Jun 2008 8:58 am

Listen to Brad!

Ken Fox · Post by **Ken Fox** » 3 Jun 2008 10:25 am

I have one on the bench now. The schematic shows a 1 megohm to ground on the input. That is the same as an Fender amp. What is missing is the 68K in series to the grid of the tube. Just added that to this one on the bench and it really helped a lot!

Ben Godard · Post by **Ben Godard** » 3 Jun 2008 3:35 pm

I thought the best way for a volume pedal to be placed is just prior to power amp. That way you don't affect the tone or overdrive the preamp.

Having the volume pedal after the preamp and effects let you change the volume without any tone change or any overdrive. That way, the volume pedal is doing only what it is suppose to do. Raise and lower the volume of the overall sound.

Ken Thanks for responding. Something else I thought of is to install and wire a pot right on the studio preamp itself which would basically be the equivalent of a volume pedal. And of course I still have my actual volume just before the power amp.As matter of fact I have an original good quality clarostat 500K pot just for the job. What do you think about this.
Or should I just go with the resistors and let it be.

Ben Godard · Post by **Ben Godard** » 4 Jun 2008 2:15 am

Ben Godard · Post by **Ben Godard** » 4 Jun 2008 2:27 am

When I spoke of overdriving the preamp I mentioned above, I was refering to when you step on the volume pedal all the way down. Sorry to confuse anyone.

Optimally I guess it would be best with the input volume fixed (provided it not overdriving). And of course the volume pedal still just before the power amp.

Brad, I'd like to hear your thoughts as well. Would installing a pot right on the preamp itself be OK or would it be better to go with the resistors. Or does it even matter. I'm thinking about going with the pot, that would give me more control obviously.

Thanks for all the input everyone

Ken Fox · Post by **Ken Fox** » 4 Jun 2008 5:50 am

You could try it, Ben. Not my first choice for a placement of a volume pedal. I prefer it before the preamp.

I would recommend adding a series 68K right off the input jack, as I did yesterday with this one. You can also change the first tube, near the input jack to a 12AT7 (ECC81).

Also keep the final output level controls at near max or max for best signal to noise ratio, using the power amps volume control as the master volume.

The first volume control on this preamp is right after the first gain stage. You can still overdrive this tube with a pedal steel pickup. More input padding may still be required.

ajm · Post by **ajm** » 4 Jun 2008 5:38 pm

With all due respect to Ken Fox, I don't see how adding a 68K series resistor will help. When I do the math it only attenuates the input by 0.6db at best. If I remember right those resistors were added for RF suppression. It may get rid of a little transient distortion but something tells me that is not his problem.

Rigging up two 68K resistors to provide some input attenuation will lower the signal going to the tube. However, you are now modifying the MB. Also, you'd be lowering the input impedance to around 130K, which I would think would take away some of the sparkle from the pickup.

If you want to try still another tube get a 12AU7. It has a gain of about 20, where a 12AX7 is around 100.

My suggestion has already been stated: Put the volume pedal in between the guitar and amp like 99% of us do. It works. By the way, you didn't mention what kind of volume pedal you are using. If it's a passive pedal make sure your pot is at least 500K. If it's an active pedal it shouldn't make any difference.

Ben Godard · Post by **Ben Godard** » 5 Jun 2008 2:40 am

It's a simple passive Goodrich pedal. Except I modified it to make it stereo.

Maybe I will try to put the volume pedal before the preamp like everyone else does. I just thought that I remember a section on the forum that discussed this.stating that the volume pedal was placed after all of the effects just proir to power amp to have better control of volume without affecting the tone or causing it to clip when engaging the volume pedal allt the way down.

How does's Paul place his volume pedal? Does anybody know?

Brad Sarno · Post by **Brad Sarno** » 5 Jun 2008 6:37 am

I believe it's definitely wise to put a VP before a high gain input stage. It's about the only way to keep your preamp clean without mods. Steel pickups are HOT.

Series resistance to a grid is not a bad idea. Actually in the Fender input circuit if you look closely at the way the jack switches work, the high gain input jack gives you 34k series resistance to the grid because both 68k's get paralleled. The second jack actually creates a pad or voltage divider as one 68k is in series, and the other is to ground. This also, like Artie said, gives the pickup an impedance load of 134k which can rob you of some sparkle.

Alembic and Boogie apparently like to remove all series resistance to the grid. Although the added gain is negligible, a series resistor working with the capacitances of the tube does create a bit of a low pass filter, taming the crispy high end a bit, and that can be a good thing. So no resistor will yield a slightly crisper tone. Personally I've run into trouble on occasion when there's zero resistance to a grid. The problem I've run into is that with a normal guitar or volume pedal pot you can suddenly get some radio interference when the pot volume is at zero.

I guess that by turning a pot to zero, you are creating a zero-resistance path to ground, but the grid sees this path to ground all the way out thru the cord, thru the pot, and back to the amp. This path seems to act like an inductor or sort of like an antenna, I think. This may or may not happen with the Boogie, but I've run across this symptom on occasion when there's no resistor to the grid.

Brad

Ben Godard · Post by **Ben Godard** » 5 Jun 2008 1:40 pm

Brad I can see you really know your stuff. I've forgoten a lot of the stuff I use to know about electronics. Thanks for your help.

I just realized one main problem with the way I am hooking it up. I have the VP after the preamp output in which you pointed out to me. I don't know what I was thinking!!! I know that I wanted the VP after effects but when I did this once before with my old rig, I had the volume pedal just before my NV1000. Well, looking back, I was using the preamp of the NV1000. (In other words I had the VP before the preamp)

Any way, I will do as you say and put my VP right after the guitar. It seems that what most people are doing so it must work good.

Thanks to everybody who posted on this topic as well.

Ben Godard · Post by **Ben Godard** » 5 Jun 2008 1:40 pm

Brad I can see you really know your stuff. I've forgoten a lot of the stuff I use to know about electronics. Thanks for your help.

I just realized one main problem with the way I am hooking it up. I have the VP after the preamp output in which you pointed out to me. I don't know what I was thinking!!! I know that I wanted the VP after effects but when I did this once before with my old rig, I had the volume pedal just before my NV1000. Well, looking back, I was using the preamp of the NV1000. (In other words I had the VP before the preamp)

Any way, I will do as you say and put my VP right after the guitar. It seems that what most people are doing so it must work good.

Thanks to everybody who posted on this topic as well.

Bob Snelgrove · Post by **Bob Snelgrove** » 5 Jun 2008 7:40 pm

Why re-invent the wheel? I have 705's on my Franklin into a Mesa pre and it's the best tone I've ever had. Ansd that's w/ the mesa volume on 7! Standard Goodrich vol pedal, too.

If it's good enough for Paul, it's good enough for us

bob

Brad Sarno · Post by **Brad Sarno** » 6 Jun 2008 8:56 am

Indeed Bob!

Also, it's always good practice to have a VP before any reverb effect. That way you don't alter the natural decay envelope of the reverb with changes in the VP.

Brad

Olli Haavisto · Post by **Olli Haavisto** » 6 Jun 2008 9:14 am

If you want the tone to remain constant throughout the travel of the pedal, the Matchbox or similar buffer between the pup and vp will do that. Tone control is an added, IMO very useful bonus.