Mesa .50 Caliber+ Effects Loop and Boss GT-8 Issue

[gwertman]

Hi everyone,

I'm a new Mesa user who bought a 50cal+ recently. It's in great condition, serial number places it at the end of the run (27,000-ish) and next to my JSX I finally understand why so many players love Mesa's tone.

That being said I've run into a dilema and I'm not sure where to turn for help. Maybe one of you can help me?

I've used a Boss GT-8 with my Peavey JSX via the 4 cable method for a year now. Signal chain is:
Guitar to Boss GT-8 input
Boss loop send to 50cal+ input
50cal+ send to Boss loop return
Boss output to 50cal+ return

What that means (for those who are unfamiliar) is that you are dividing the preamp from the power amp on your tube amp simlilar to having a rackmount preamp/poweramp setup. This setup works great on my JSX but not on the 50cal+.

I get a shwishy, highpicthed noise-in-a-small-metal-pipe sound when using this setup. If I unplug the jacks from the Mesa's loop (but leave the signal going from guitar to boss to mesa input alone) everything is fine. So I'm not overdriving the input.

Is this a Mesa loop problem? The symptoms are worse when levels within the Boss are set to anything close to unity. Also when I use the GEQ on the 50cal+ things get nuts if I boost 2200 or 6600 hz. To top it off when I switch from lead to rhythm on the 50cal+ I get full blown highpitched oscillation!!!

50cal+ settings are:
Gain - 7
Master - 1.5
Lead Master - 1.7
Treble - 8
Bass - 3.5
Mids - 6
Reverb - 0 (tube has been pulled for more gain)
Presence - 5
GEQ: a sorta V with the 250hz pulled a little lower for tightness

Help!

Thanks for listening!

Regards,
Gary

 

[user 7737]

i can't help you... i never used the effect loop but i thought that the chain was like that :

guitar -> input amp

send loop -> input effect // output effect -> return loop...

3 cables... not 4 !! confused !!

:|

 

[gwertman]

It would be normally that way, yes. The way I'm doing it allows me to put wah, flanger, etc in front of the amp (like using pedals) and keep the time based effects post overdrive on the 50cal+.

Even with a normal "guitar to amp, processor in the loop" setup I have swishing noises though. The screaming oscillation is from overdriving the effects return - so that much I've figured out. But the swish is strange. I guess it's time to have the effects loop looked at by a tech.

Thanks!

 

[user 7737]

i don't think i deserve a "thanks" :wink:

in fact i know nothing about effect loop, i never used them... but i will at the next rehearsal... i have to put an EQ in the loop...

do you know why a disto can't be put in the loop ? this is a mystery to me !! why a turbo rat (for example :lol: ) can't be put after the preamp ?

 

[gwertman]

Well, you'd be distorting an already distored signal. You can do it, but it won't sound very good!

Just my .02$

 

[user 7737]

but the signal is distorted only on the lead channel... what if i use the disto with the rythm channel ?

[edit]

i think i have my answer... disto effect works by increase the signal which is not supposed to happend between the preamp and the power amp... it will hurt the power tubes... am i wrong ?

so what about a fuzz ?

 

[gwertman]

I don't see why you can't try it out. I have the same amp as you so I know that the rhythm channel can stay pretty clean depending on your gain position...

-g

 

[user 7737]

i think i will try... 'caus i don't want to have miles of cable (rat before preamp 4 cables, after 3 cables...) hope it won't hurt the power section :?

yeah it can stay very clean... i usually run the vol/gain at 3 or 4... very clean so... the lead channel is so huge even at gain 3

 

[gwertman]

...so, my local amp tech said that the mesa's loop is probably just too powerful for sensitive gear like the GT-8. He said I should try gear made for +4db signal instead of -10db consumer grade.

So I bought a new Digitech GSP1101 - will be here today. I'll post my results. The 4 cable method is actually described in the GSP's manual if you can believe it. I can't believe that something a bunch of crazy effects junkies came up with is now a standard configuration for current effects gear...

If this new effects box doesn't work I'll just have to get the fx loop on the .50 cal+ modded...

later for now,
-g

 

[user 7737]

i think i've got this mod on mine... there's a pot on my effect loop... never use yet...

maybe i will when i'll try my graphic EQ...

 

[gwertman]

Can you take a pic of the back of your amp for me? I'm not sure if the knob you're referring to is the direct out knob... maybe you have an effects send knob? Or maybe it's a mix knob and your loops is parallel instead of series.

-g

 

[user 7737]

i can't tell you guy ! sorry... but it seems to be a vol pot for the loop...

i'll take a pic as soon as i can, but you'll have to be patient, i won't see my amp before next week and i'm not sure if i'll have a cam :? (the cam of my cell phone sucks)

but believe me i'll do it as soon as i can...

 

[gwertman]

Thanks meursault - whenever you have time is fine with me!

 

[gwertman]

Hi all,

Just wanted to post my findings here for any other Mesa 50 Caliber + users who intend to use fx in the loop.

I bought a Digitech DSP1101 because the 4 cable method was in the manual and also because the loop receive in the DSP1101 was selectable between +4 and -10. Well, it didn't work Even at +4 the mesa overloaded it's loop input.

I also read that many 50cal+ users and old Mark amp users were able to put an Alesis MidiVerb2 in their loop safely. I bought a used one this weekend for 60 bucks to try it out and it worked fine. The massive cut control on the input knob was key and the boost on the output also helped. The verbs and delays were pretty clean, execpt for long trails - those distorted a bit - apparently because by lowering the input gain I was raising the noise floor a lot.

So I called my amp tech, sent him the 50cal+ schematics I found and we talked a bit. He told me that the effects loop in this amp isn't buffered at all but is merely a patch point between the preamp and poweramp. The 'loop' is coming off of the 3rd preamp tube and is very high impedance and getting full voltage from the plate. It's putting out like 12 volts, +22db there. 0db is more like 1.55 volts. (Don't quote me on all this - I didn't write down what he was saying and it went pretty far over my head!!) Only good for studio rack effects. Not for multifx, pedals, midgrade fx rack stuff, etc..

So he's building me a little 18 volt active opamp based loop buffer. It should be done Monday at the latest. When I test it out I'll post my results. The buffer will be small enough to velcro into the cabinet and the best part is that I'm not modding my amp!

Bye for now!

-Gary

 

[user 7737]

so what the hell can we put in this effect loop ? :?

 

[gwertman]

The TC Electronic Nova System, G-Major and G-Force oughta work because they're made for 24db line level signals. I was actually thinking of buying a Nova System - they look really cool.

So just read the specs in the manual for something before you buy it. You can't use anything that a guitar is supposed to plug into. Like say, a Boss DS-1. Not without padding down the signal - which is what my amp tech's little gizmo will do. If you want one I can have him build you one too. He said it'll be about $150. For me to keep using the Boss GT-8 it's worth it. I'm not ready to spend 400 bucks on a new FX unit and another 150 or so on a floor controller.

-g

 

[user 7737]

well... i hope my EQ will fit the effect loop 'caus i really want it to shape my lead channel... and i think it will be more effective in the loop than in front...

 

[phyrexia]

I've used a Boss GT-8 with my Peavey JSX via the 4 cable method for a year now. Signal chain is:
Guitar to Boss GT-8 input
Boss loop send to 50cal+ input
50cal+ send to Boss loop return
Boss output to 50cal+ return

Isn't this wrong? Did you make a typo, gwertman?

guitar -> GT8 input
GT8 output -> amp
amp fx send -> gt8 loop in
gt8 loop out -> amp fx return

 

[gwertman]

No typo. That's actually the way it's supposed to work.

The only way to separate an amp's preamp from it's power amp is to capture it's input (input jack on the amp) and it's preamp output (effects send). When you place that part of the real amp in the gt8's loop you can put effects before the amp's preamp and after it, as well as turn the amp's preamp off or change how much signal it's getting. You can also adjust your gt8 send levels (to boost or cut gain) and adjust the return levels (to make the amp louder or softer). This is cool way of gaining a 3rd or 4th channel on an amp like the 50cal+. You need more distortion but don't want it perceivably louder? Boost the gt8 loop send (drive the amp's input stage harder) and lower the gt8s loop return (give the power amp less to amplify overall). You need a pristine clean? Turn off the gt8's loop (which turns off the amp's preamp and tonestack), activate a 'booster pedal' and an EQ on the gt8. This would inject nothing but clean eq-ed tone into the power amp stage of the amp. Excellent for cleans! Or for using a 'preamp sim' if you want to play around with them. Provided you disable the fake cab sim on the gt8 output.

If you were to plug the gt8s final output into the amps front input all your time domain effects would also get distorted. Atleast that's my understanding of 4CM. And that's mainly from the bossgtcentral forum. That's also the way the new 4CM compatible fx processors say to do it.



Quite a lot of info there - and while this setup is a bit noisier and prone to tonal differences it's worth it for it's flexibility. If you need flexibility that is. I do. I also like running straight in with nothing more than a wah pedal and no fx in the loop. It's all good. The biggest difference you're apt to see with the 4CM setup is due to a different input impedance. See, the 50cal+ is a 470 k ohm input impedance. This places a different (higher than what is standard now) electrical load on your picukps which causes you to lose treble and shift the resonant frequency around - similar to using long high capacitance cable runs. Plugging into the gt8 puts a 1 Meg ohm impedance on my guitar which allows all the signal to come through and consequently brightens the tone. Then since the fx send of the gt8 is low impedance (and low feeds high for tone preservation) the 50cal+ gets a better signal which results in better tone and gain. The JSX is the same way actually - 470k ohm. That's an odd value for amps now a'days. Old Marshalls were like 68k I think - which really darkens the sound a lot. A lot of amp mods center on the input impedance to set the overall tone of the amp. And higher output pickups are more impacted by this (like my Bill Lawrence L500s). Old school low output pickups aren't as effected (due to lower dc resistance I think) so they'll sound "better" with low impedance inputs. If you put a newer pedal between you and your low impedance input amp it buffers the signal making it sound brighter. The 50cal+ sounds a lot different (to me) when I plug into a buffered pedal fist. That's why Radial has that Dragster thingy - it allows you to load down your pickups to alter the tone since some people like that sound.

Whew! Long post! Hope I didn't bore you! There's just SO MUCH technical stuff that can help you in the quest for tone. Unless you understand why something sounds the way it does you have no hope of changing it.

-g

 

[nomad100hd]

some of you guys are clueless. The reason not to put a distortion box in the loop is it sound like crap that's the only reason. It wont hurt the tubes or do any damage to the amp.

I agree with your tech, it could be as simple as a voltage divider. My only concern is if you want power tube distortion you might need a recovery stage to get your signal high enough again.