# Hiss in the effects loop of a Mesa V:25



## bgreenhouse (Jan 4, 2014)

Hi Everyone

I got a new (to me) V:25 and am loving it. Only thing I am noticing is a hiss in the effects loop. More detail - I have a device I built myself that I call a router that allows me to switch the routing of my pedal board between all in front of the amp (No Loop), Wet/Dry, and running time-based effects in the loop (so I don't have to rewire the board depending on what amp I'm using).

If I switch the router to No Loop, putting all the effects in front of the amp the hiss disappears - it only seems to happen when I run pedals in the loop. My loop pedal chain has a secret preamp in the front, and turning it on and off reduces the hiss, so it seems to be coming from the amp. I haven't taken everything apart to see if the hiss is induced in my router, before I do that, I wanted to get a sense of whether there's something obvious based on it only happening when there are pedals in the effects loop.

Presume I can just roll some tubes and see if that solves it - any idea of which one I start with?


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## bgreenhouse (Jan 4, 2014)

I should mention that it is worse in the clean channel, but I do have the gain up higher in that channel. Actually, just checked, and it's about the same in each channel with the gain set the same...


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## TWRC (Apr 22, 2011)

I have a Mesa MKV:25 and just tested my loop after reading this, and there's no hiss in mine to report. Definitely try rolling some tubes. The manual states the V5 is associated to the FX Loop, so I'd start there.

Mesa Boogie MKV:25 Manual


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## bgreenhouse (Jan 4, 2014)

TWRC said:


> I have a Mesa MKV:25 and just tested my loop after reading this, and there's no hiss in mine to report. Definitely try rolling some tubes. The manual states the V5 is associated to the FX Loop, so I'd start there.
> 
> Mesa Boogie MKV:25 Manual


Thanks - will do.


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## bgreenhouse (Jan 4, 2014)

Hmm...rolled the V5 and no change.


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## gtrguy (Jul 6, 2006)

I would suggest isolating where the hiss is coming from. Try putting a cable in the loop and activating it (the loop). If the hiss is not there, it's not a tube problem or other issue with the amp and it's related to one of the pedals or your switching box. Hiss kind of sounds like an impedance mismatch to me but it could also just be a noisy pedal.


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## bgreenhouse (Jan 4, 2014)

Good idea. Tried it, and it's still there. The preamp in the pedal chain definitely boosts the hiss, but it's there at roughly the same level with the pedal chain (with the preamp off) and the cable just "shorting" the loop.


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## gtrguy (Jul 6, 2006)

bgreenhouse said:


> Good idea. Tried it, and it's still there. The preamp in the pedal chain definitely boosts the hiss, but it's there at roughly the same level with the pedal chain (with the preamp off) and the cable just "shorting" the loop.


Could just be a noisy loop implementation.


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## bgreenhouse (Jan 4, 2014)

gtrguy said:


> Could just be a noisy loop implementation.


What does that mean? This model of amp has a noisy loop, or this one in particular?


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## gtrguy (Jul 6, 2006)

bgreenhouse said:


> What does that mean? This model of amp has a noisy loop, or this one in particular?


It could be either situation. Any way to get your hands on another one to try?


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## Mike_Blaszk (Sep 16, 2021)

I currently have a Mark Five:35 that I've owned for a little over a year now. I can tell you that, with an ISP Decimator II G String, Southampton Pedals Utility Knife and TC Electronics Flashback Delay constantly in my FX loop (as well as others that I've cycled through), the Mark's Loop isn't noisey. However, what I have experienced is that the Mark can get very noisey depending on your EQ settings and exacerbate any existing noise in your setup (e.g. low quality/failing/faulty power supply or cables, etc). Essentially, most of this is detailed in the link below and was described to me by Rich Gowman at Amplifiers Plus (an authorized Mesa repair shop) as the result of both a very complicated internal design and a gain structure that dumps the entirety of the previous (high) gain stage into the subsequent one:









Help! Mesa Boogie Mark Five:35 High Gain/Volume Squealing


Hi all! I've been dealing with noise issues on my Mesa Mark Five:35 for the past few months and was wondering if anyone could help. Specifically, I purchased the amp brand new on December 28, 2020 and have noted that the amp is excessively noisy on Channel 2's Mark IV mode. In particular, I...




forum.grailtone.com





Additionally, its worth noting that my brand new Mark Five:35 came with a faulty power tube and one of the replacement power tubes that was provided to me in exchange also ended up being bad (worth checking). And lastly, somewhat unrelated, I'm currently experiencing a tone suck issue with a Boss GE-7 in the FX loop of my Mesa Dual Rectifier Multi-Watt that isn't present with any other pedal. So, it might be worth trying individual pedals one at a time in the loop to see if one is specifically causing the issue or if your router device is.


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## bgreenhouse (Jan 4, 2014)

Dumb question - how do you read the tube chart in a mesa manual? This is my first non-fender amp, and it's not as simple (of course). What is the "A" and "B" uses for the preamp tubes below?


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## gtrguy (Jul 6, 2006)

bgreenhouse said:


> Dumb question - how do you read the tube chart in a mesa manual? This is my first non-fender amp, and it's not as simple (of course). What is the "A" and "B" uses for the preamp tubes below?


Each of those preamp tubes has 2 functional “blocks” inside it. Each block can be used independently for different functions.


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## Paul Running (Apr 12, 2020)




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## bgreenhouse (Jan 4, 2014)

Thanks. Fascinating - so clean CH1 runs as follows: V1A (input stage) > V1B (2nd gain stage) > V3A (3rd gain stage) > V3B (4th gain stage) > V4B (Reverb Send) > V4A (Reverb Return) > V5A (FX Loop Return) > V6.

It bypasses V2A and B entirely in the clean channel, fascinating.


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## bgreenhouse (Jan 4, 2014)

Paul Running said:


> View attachment 400956


You learn something new every day...


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## bgreenhouse (Jan 4, 2014)

Okay, a few more tidbits. Running a guitar directly in I now get a hum/hiss in channel 1 regardless of something in or out of the effects loop. However, if I plug a jack into the return of the loop (but not the send), it is quiet. When I'm running through my "router", when I switch out the loop there is still a jack in the return loop, it just is effectively disconnected, so this is effectively the same thing.

Channel 2 is still silent. One more thing I noticed, there's a notable "pop" with reverb on the tail end as I switch with the footswitch from Ch. 1 to Ch.2, but the same thing doesn't happen when I switch from 2 to 1.


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## Mike_Blaszk (Sep 16, 2021)

bgreenhouse said:


> Dumb question - how do you read the tube chart in a mesa manual? This is my first non-fender amp, and it's not as simple (of course). What is the "A" and "B" uses for the preamp tubes below?
> 
> View attachment 400955


Unfortunately, Mesa's are notoriously complicated to deal with (some repair shops outright refuse to service them) and the Mark V is probably at the top of that list lol. As a starting point, I would reach out to Mesa directly as they don't have a problem troubleshooting with you over the phone (the easiest) or by e-mail. Beyond that, I also don't think it's a bad idea to post this issue over at the Mesa Boogie Board. Alot of those guys are lifelong Mesa guys and a couple of them are actually certified Mesa techs who are very knowledgeable. Then, if you're anything like me expertise-wise, its probably a good idea to get a certified Mesa tech to take a look at it if tube and basic pedal/cable/connection/power supply/grounding/EQ troubleshooting doesn't work. Personally, I can vouch for Rich Gowman at Amplifiers Plus as a solid Mesa tech, if that's anywhere close to you.


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## Mike_Blaszk (Sep 16, 2021)

Out of curiosity, does the Reverb work on your amp?


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## bgreenhouse (Jan 4, 2014)

Mike_Blaszk said:


> Out of curiosity, does the Reverb work on your amp?


it does, yes.


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## Mike_Blaszk (Sep 16, 2021)

bgreenhouse said:


> it does, yes.


Complete shot in the dark:


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## bgreenhouse (Jan 4, 2014)

Mike_Blaszk said:


> Complete shot in the dark:
> View attachment 400977


Interesting - thanks. I tried plugging it in backwards and it didn't seem to help. I don't have a squeal, just white noise. It is dead quiet when I plug something into the return jack of the effects loop (of course, nothing is coming out then because it's getting no signal into the return). Just to reiterate (as my understanding has been evolving), it is on both channels - I just had the gain on channel one set higher so thought it was more pronounced there - when gain is the same the sound is the same.

It also seems to be before the effects loop as it gets amplified by the "Secret preamp" I have in the effects loop, I guess that means it's in the amp's preamp section somewhere. I may try running my hx stomp into the return jack just to make sure that it's not in the power amp. Don't have time for that tonight.


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## Mike_Blaszk (Sep 16, 2021)

If you're experiencing the noise even without anything in the loop, you can send me a pic of your Channel 1 settings and I can pop them into my amp and record what I get when I have a chance.


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## bgreenhouse (Jan 4, 2014)

Thanks Mike. PMd


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## nonreverb (Sep 19, 2006)

V3 might be your problem as it's common to both channels


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## Mike_Blaszk (Sep 16, 2021)

bgreenhouse said:


> Thanks Mike. PMd


Sent.


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