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skarkowtsky

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I don't know where to begin
« on: Time Format »

I honestly don't know where to begin, and I just need to vent. I already know that the solution to whatever my problem is will be expensive, but maybe getting it all out here and reading your responses will help. I'm at my wits end, so grab the popcorn.

Firstly, I'm not a tube-savvy guy. I barely understand what's really happening with the technology. So, I put my trust in information from others, forums, reviews, repair guys, and do the best I can to filter it and determine what might help me achieve the sound I want.

Now that that is out of the way. I was a Mesa Mk IV combo guy for a while. As my tastes and playing evolved, I was drawn to the MP-1. For the first year and a half that I owned it (purchased on eBay April 2020), I used the power section (6l6) of the Mk IV, even bypassed the legendary 5-band EQ, but got the tone I wanted. Seeing that the Mk IV was being wasted, I sold it last October and purchased a Carvin Tube 100. I chose this power amp after reading about it's transparency. I also made the switch from 6l6 to EL34.

Now, I get conflicting information on the following. Everything I read on the internet, from reviews to forums tells me that power tubes do affect tone, not to the degree of pre-amp tubes, but they do influence your sound. However, my amp repair man, and another I recently went to tell me power tubes have no effect on tone, unless I'm playing at very high volumes, and the break up characteristics really shine through, but even then, it's not an affect on tone. However, the internet always seems to tell me differently, and since I have limited knowledge of tubes in general, I don't know what to believe. However, I trust my ears, and lately they're telling me something is way off in my rack.

I recently had the Carvin serviced (by the second repair man) as the entire thing went silent while playing a few weeks ago. I suspected bad power tubes, but as I bought it second hand, I thought it would be a good idea to have the entire unit looked over to establish a baseline as the current owner. It was the power tubes, and I also had the (2) 12ax7s replaced.

The amp was previously tubed with Svetlana, I received it back with re-issue Mullard's and EHX 12ax7s. From what I've read, both are well-defined tubes and pretty neutral. However, my tone is now very honky, with a mid-range boost and flubby bass. I've tried every EQ combination imaginable on the MP-1, boosted bass, scooped mids, spiked treble and presence. It goes from flat to shrill and ice-picky. I've tried EQing with my Rane MPE-28 to no avail. I even tried cranking the power amp, which did bring out some amazing crunch, but the tone was still awful.

I also adjusted both gain stages on the MP-1, achieved a nice tight gain structure, did hear a slight difference in tone when I drove them hard, but couldn't remedy the tone issues. The MP-1 has had 7025 tubes (from Doug's Tubes) for the past year, which I noticed clip when I push the Master Gain past 8. I rolled the JJ's that came with the unit from eBay and it actually sounded better, and the clipping disappeared, but the tone still sucks.

In October, I also had to buy a speaker and cabinet to make up for the Mk IV, which had the Electro-Voice Black Shadow in an open back cabinet. I have a mono rack, so I decided on a Celestion Redback 150w (to accommodate the 100w Carvin) and a MojoTone birch ply 1x12 closed-back cabinet with about 12" of depth. Maybe the Redback is a mid-range speaker? Maybe the cabinet sucks?

Maybe the repair guy cold biased the Carvin? But I don't even know if that affects tone. Maybe the EHX 12ax7s in the Carvin are wrong for the tone I want?

Or, maybe the MP-1 needs service? I've been in extensive talks with MarshallJMP about shipping it from NY to his country.

WILDCARD: I swapped the EMG 81/85 in my Jackson Soloist for a Seymour Duncan Jazz/JB in December. Maybe that's the culprit (but I doubt it).

As you can see, there are way too many variables and the expenses are piling up. Is it the MP-1, the Carvin, the Celestion, the cabinet? I don't have a second speaker, power amp or cabinet to cross check any of this. I'm ready to get rid of it all and just buy a Marshall head and reverb and call it a day.

Thanks for reading through this. Please talk me off the ledge.
« Last Edit: Time Format by skarkowtsky »
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rnolan

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Re: I don't know where to begin
« Reply #1 on: Time Format »

Hey skarkowtsky, well this is the right place to vent  :thumb-up: . I'm not sure your solution will have to be expensive  :dunno: .
As you say, there are now many variables so lets try to break them down into more manageable bits.  Firstly, lots of stuff with tubes is very subjective.  The main tone is made by the MP-1.  It uses the 2 12AX7s to create the initial gain.  12AX7s are twin triode tubes, each tube has 2 gain stages (triodes) which run in sequence (series). OD1 sets the V1 input and OD2 the level of V1 into V2. The master vol sets how much is passed to the eq section (bass, mid, high, pres) the eq is active as in you can boost or cut each band (this adds or takes away gain BTW). Now you changed these tubes for JJs and liked the result.  Not surprising as JJs work well in MP-1s.  It's a shame you don't still have the MarkIV so you can compare and rule out the MP-1 as the problem.
Carvin tube power amps are quite transparent.  Power tubes do make a difference but it is usually very subtle.  E.g. When I compare my Carvin TS100 (6L6s') to my ADA B200s the TS 100 is a "little" warmer but doesn't change my tone and it's not meant to.  However, there is a difference between 6L6s' and EL34s'.  Again it's subtle but if there was no difference, why do people go for one or the other?  EL34s' are supposed to be the English sound used in early Marshalls etc. and 6L6s' the US sound. Maybe you could describe it that 6L6s' are crisp and EL34s' a little rounder? But that shouldn't be your problem.  You'd need to try the MP-1 through a different power amp/speaker set up to rule the amp in or out of your issues.  I assume your Carvin is a stereo amp and you are running in bridge mode.  The 12AX7s in it are phase splitters/inverters, they don't add gain just split the signal into the +ve and -ve part of the wave (think sine wave +ve/-ve) which is sent to each power tube (push pull) one tube does +ve the other -ve and the bias is mostly about the cross over between the 2 power tubes (as it's where both tubes are acting at the same time (cross over distortion)).  Running in bridge/mono mode you only use one phase splitter (EHX 12AX7) but all 4 power tubes.  Not sure if one channel (2 power tubes) does +ve and the other channel 2 tubes -ve but that would make sense. Each channel has an output transformer (there are 3 transformers in you Carvin, 1 for power, and 1 output tranny for each channel).  The output tranny matches the high voltage tube output to what speaker wants and the speakers impedance. 16 ohm speakers tend to have tighter bass and are more sensitive, 4 ohm a bit floppier and not so sensitive (less copper windings in the speaker voice coil, harder to pull up/stop vibrating) This is a very high level explanation BTW it's actually allot more complicated.  I'm not a fan of EH tubes (they are rebadged whatevers) but that shouldn't matter as they are just phase splitting/inverting.  Now for a phase splitter, you want matched triodes as the each (of twin triode tube) do on half of the wave.  Output tubes you want matched output so +ve and -ve sides of the wave is the same.  Try just using 1 channel (50watts) in stereo mode, and then compare to the other channel. (Trying to rule out any bridged mode issue).  I assume you have the speaker impedance matched properly to the amp, bridge mode is quite specific as it's combining the 4 output tubes into one speaker.  If this is not set correctly, it won't be helping and can led to damage.  So my TS100 (it's a later model with 4 12AX7s , 2 buffer and 2 phase splitter/inverters) says in bridge mode, use channel 1, select bridge mode switch, for 8 ohm speaker select 4 ohms on ch1 and 4 ohms ch2, use channel 1 outs.  For 16 ohm speaker set 8 ohms ch1 and 8 ohms ch2.  (manual for my TS100 attached, I also attached the schematic for your older TS100).
Next is speaker (again very subjective, they all sound quite different).  Changing from open back to closed makes a difference and different speakers work better with each.  Generally open back needs stiffer cone (or can get floppy) as there is no back pressure that you get in a sealed box and also sound comes out the back and bounces off the wall etc. and mixes back into the sound. The boogie EV black shadow will sound very different to the Celestion Redback.  Both are supposed to be great speakers, but EV and Celestion speakers are quite different sounding.  Also the Redback resonant freq is 75 Hz and the EV 55 Hz (so much lower).  The resonant freq is where the speaker will vibrate (resonate) much louder.  In a sealed box you generally use a tuning port on the front tuned to the speaker resonant freq to counter act it's natural resonant freq.  So I suspect the Celestion will lack some low end distinction (guitar bottom E is 82.41Hz, dropped D is 73.4Hz - smack on (well very close) the resonance (75Hz) of Celestion) compared to the EV 55Hz.  Also Celestions tend to be quite mid-rangy and EV more smooth and even. (very honky, with a mid-range boost and flubby bass) sounding familiar?
Next PUs, again very subjective.  EMGs are active, quite flat freq response (bass, mid, treb balanced) high output (active) and very articulate (hear each note clearly), good for very high gain (as you don't get mush), also good for clean (a great match for the EV speaker).  SDs are more mid rangey, less articulate and your choices (jazz/JB) lower output so MP-1 input not being driven as hard and I suspect wouldn't help with "honky" aspect.  I tried a JB in my SG, it didn't last long, hey some love them, I changed it for a Gibson 57 re-issue, much better (for me).  But I prefer Ultrasonic PU (Bill Lawrence made them for a while).  They are called reference series PUs because they are quite flat freq response, similar to EMG in that way but they are passive 2 coil PUs.
Where to from here?  All the patches you ran up in the MP-1 for the EMG/MkIV/EV will be all wrong for now SD/Carvin/Redback so you will need to start from scratch.  If you put the MPE-28 between the MP-1 and Carvin and try -3db @ 75Hz (resonance issue), push up around 800Hz till you find the honk and pull it down a bit. Then try to adjust the mid issue in the MP-1 patch, maybe add a bit of presence in the patch to get some sparkle out of the SDs (does your Carvin have a presence knob? if so this may also help  :dunno: , my Carvin's presence is at 6kHz the MP-1 presence is set at 3kHz so they will sound different.  You may find you prefer the Carvin 6kHz (sparkle) rather than the MP-1 3kHz (more ice picky I spose) as the Redback has a hump around 2kHz (like all Celestion guitar speakers), the EV not so much.  Try just one channel of the Carvin in stereo mode (make sure the speaker impedance switches are set correctly), using just one channel wont hurt it.  I assume your speaker is 8 ohm? So set for 8 ohm on rear panel OR in bridge mode, you need to set each ch to 4 ohms (see manual).  Hopefully this will get you closer to what you want.  It will never sound like before (EMG/MkIV/EV) as everything is different. And if you get it sounding right(ish), put the MPE-28 in the MP-1 loop, get another cab and run it stereo with MP-1 chorus in, depth=100 rate=0 and it should melt you :headbanger:
Anyway hope my rave helps at least bring you back from the edge  :wave:
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skarkowtsky

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Re: I don't know where to begin
« Reply #2 on: Time Format »

Hey, it’s John.

Thank you for the breakdowns and explanations of what tubes are actually doing. You made it much easier to follow the basic principles of my gear. My amp is set to bridged mode with each channel set to 4ohms going to an 8ohm Redback. (I read the manual three times before ever powering up the amp to avoid any catastrophes in bridged mode  :facepalm:).

Unfortunately, the only test I can (maybe) try would be to connect the MP-1 to the front of a friends small solid state combo, and test his guitars too. I’m flying solo out here, not many musicians where I live with gear I can test on. Any other tests would require me to purchase more equipment, something I’m not fit to do at the moment.

In terms of setting the amp to stereo and 8 ohms on one of the two channels to go out to the Redback—there’s definitely no way the unused channel (in stereo) will cause fly back voltages and destroy its output transformer, right? I just dropped $300 having this amp serviced, I’m bleeding my wallet dry lately.

PS I love the Depth 100, Rate 0 trick. It oozes John Sykes!
« Last Edit: Time Format by skarkowtsky »
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Harley Hexxe

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Re: I don't know where to begin
« Reply #3 on: Time Format »

Hey John,

     It's not easy getting a specific tone you're looking for sometimes, and it may take a lot of research before buying any gear, so that you can be certain to get pretty close to what you are after the first time. Advertisements, are misleading in the fact that they are geared towards encouraging impulse buyers to pull the trigger. With that being said, let me suggest a few ways to go about finding what you're looking for, and maybe a little trouble shooting along the way to determine where your issues might be.

    The first thing I would do in your situation, is start where it matters the most. That would be with the guitar and the MP-1. In your case I would recommend plugging your guitar into the MP-1 and put on a set of decent headphones and dial in a tone or two that you like. Getting that part of the equation settled will eliminate any questions about if it's your guitar PU's or the MP-1.

     If you are getting the kind of tone you want from that step, then it's time to move on to the power amp and speaker(s). As far as the Carvin power amps go, I don't have any experience with them, and I'm not familiar with the Celestion Redback series of speakers. (I will do some research after posting this about them and see what they are all about). Just to put things as simply as possible about power tubes, I will say that the most obvious difference between 6L6's and EL34's would be they way they respond to your attack. EL34's have softer compression so they have more sag when driven harder, where 6L6's have tighter compression and they respond more quickly so they sound more punchy when driven harder. This could be what you were hearing in your Mesa combo,(but that also takes into account the speaker that was matched with the power amp section. In an integrated guitar amp such as you are building, it a bit different. The bulk of your tone is coming from the MP-1 and the power amp is there only to amplify it. It can add some color to the tone if the amp is modded slightly to react that way, but generally, they aren't meant to. They are designed to amplify cleanly and evenly.

    Richard brings up several important points about this in his reply, especially about the tubes needing to be matched, they do. If one tube isn't performing up to specs, it can make any good amp sound like three truck loads of shit. I'm not sure the EHX tubes will make much difference as they are only being used as phase splitters, but if you have a pair of lower gain, or weaker 12AX7's laying around, try swapping those out and see what it does. It shouldn't put your amp at risk trying this. Hopefully, your amp tech knew what he was doing with the amp when he went through it. Most of the amp techs around here won't touch Carvin equipment, because they aren't certain they can do a good job, and they tell everyone here to contact Carvin for repairs. Assuming that he did a good job on your amp and biased the tubes correctly, you should be able to get a good reproduction of your MP-1 tone at a lower volume, and it should hold together as you increase that volume. If it isn't, then it may be something was overlooked in the power amp.

     As I stated earlier, I'm going to have to do a bit of research on the Celestion and get back to you on that.

I hope you find this helpful

Harley 8)
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skarkowtsky

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Re: I don't know where to begin
« Reply #4 on: Time Format »

Without going back to the amp tech, how would I ever be able to tell if he set it up properly or not? Do you think I could find my way around one of those Eurotubes Multimeter probes?

The tech is definitely known in my region, NYC/NJ, as a qualified repair man,, but you do get the sense that he is arrogant and rigid. I don’t think asking him exactly what he did or to look it over again is going to yield good results.
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Harley Hexxe

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Re: I don't know where to begin
« Reply #5 on: Time Format »

Hey John,

     No sir, I do not mean to imply that he is arrogant or anything else for that matter. I simply meant he may view that amp as a piece of electronic equipment in general terms, and may possibly not see some silly little quirk that many amp builders incorporate into their designs for one reason or another. Many amp builders do things like that and techs who do spot weird things like that and up scratching their heads wondering what the designer was thinking.

     But before you go to the tech, you should really try to narrow down the possibilities at home. try to determine for certain where the actual issue is. It isn't that hard to do.

     Something else you said in your post that just turned on a light in my mind, was that you mentioned the amp sounded "flubby" and if that's the case try this: remove the back panel off your Mojotone cab and see what that sounds like.

Harley 8)
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Harley Hexxe

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Re: I don't know where to begin
« Reply #6 on: Time Format »

Hey John,

    Okay after doing some quick research on this speaker, it seems to have more bass response than what you'd expect from Celestion. Compared to the Cream back speaker this should have a more balanced tone and not so much midrange or presence as the cream back. It should work well in a closed back cab, and you might need to dial out some of the bass frequencies to get it to tighten up the bottom end. So try trimming out some of the bass in the MP-1 and see what that gives you.

Harley 8)
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skarkowtsky

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Re: I don't know where to begin
« Reply #7 on: Time Format »

Harley,

I should clarify that I got the sense of the techs arrogance, not that you were implying that. He’s definitely an arrogant guy.

So, I actually removed the back of the cabinet earlier, but didn’t hear an improvement. I also created a few different tones from the ground up, but everything still sounds flat and or mid-rangey. I also noticed that unless my face is squared in front of the speaker, the tone sounds even worse from left or right of the cabinet. As if the sound is traveling in a very narrow, straight column into the room I’m playing in.

I don’t know what else to do since I don’t have other gear to check against. Part of me wants to ditch the carvin and tubes in general and replace it with a solid state power amp I can color the hell out of with effects.

I’m really disgusted.
« Last Edit: Time Format by skarkowtsky »
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MarshallJMP

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Re: I don't know where to begin
« Reply #8 on: Time Format »

Well I'm a EMG user and I also have a Michael Shenker V with the same SD combo as yours. For me there is quite a difference in sound, EMG's tend to sound tighter because they have more midrange with less bass. So better for midium to high gains, but for cleans the SD wins.

Preamp tubes are less different between brands IMO, but there are differences. For me Russian tubes sound dull in a MP-1, JJ's sound more mid rangy and Chinese are a combo of the 2. There is also a difference between the EL34 and the 6L6, EL34 a bit more midrangy while 6L6 is opposite. For me EL34 are better for distorted sounds, 6L6 sound better for cleans. Me I'm a EL34 guy.

Speakers do also make up a big chunk of the sound, don't know the celestion you use but I use 4 marshall cabs with 4 different speakers in it to get "my" sound. Each one has it's good and bad thing. Using them all togheter makes it sound good for me.

As for biasing power tubes, yeah it makes a difference but I guess the guy knows how to bias them? Also tubes sounds better after while, they need to get hot, the hotter they get the better they sound. My rig sounds perfect after 2 hours of playing.

Harley makes a good point when he saying if one part of the tube is bad the whole sound is bad. And yes it can happen that you buy a bad new tube. I always test my tubes for gain, current and gm.
« Last Edit: Time Format by MarshallJMP »
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skarkowtsky

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Re: I don't know where to begin
« Reply #9 on: Time Format »

Anyone have experience with the Marshall 8008? I'm seriously considering ditching a tube power amp. If it worked for Dimebag, it can work for me in a home setting. I'll also ditch the Redback, go with a Creamback and just keep the volume down so I don't destroy the speaker.

In all seriousness, the first amp tech, the guy I know and trust, has his MP-1 hooked up to a solid state power amp in his shop and it sounds killer with just a little EQing. He's also the guy that turned me onto the MP-1, is an original owner since 1987, and knows the MP-1 inside and out from working on his for 35 years.

If you're wondering why I didn't bring the Carvin to him recently, it's because he's moving out of state April 1, hence why I had to find this other guy.
« Last Edit: Time Format by skarkowtsky »
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rnolan

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Re: I don't know where to begin
« Reply #10 on: Time Format »

Hey John, not sure I'd go the 8008 route (https://forum.fractalaudio.com/threads/marshall-8008-thoughts.18096/), no output protection is not a good look as you can fry speakers  :facepalm: .  The Carvin should be a good amp if it's working properly.  Try the one channel test, it wont hurt the other channel to have nothing plugged into it.  So try each channel on its own, they should sound the same.  This is to check if the bridge mode is making any difference.
Harley's suggestion to do the headphone test on the MP-1 is a good one.  The MP-1 headphone out has a couple of capacitors to take off some top end a bit like a very basic cab simulation.  If you can't get good tones from that then at least some of the issue is MP-1 and you'd need to sort that first.  Also worth swapping the MP-1 tubes back to the originals while doing the headphone tests and even try combining the 2 e.g. 7025 in V1 and JJ in V2 and vis versa - JJ in V1 and 7025 in V2.  The biggest difference re tubes in your setup is in the MP-1 and there are many post here about what works (and doesn't) for various members.   
Transistor power amps work fine with MP-1 but some are more suited to guitar.  So I have both and can compare.  As I said the main difference between my ADA B200s (transistor and designed for MP-1) and my TS100 (tube) is a little more warmth from the tubes.  It's very subtle.  I have the later model TS100 where they have added a buffer 12AX7 to the input to balance input gain better.  I'm not sure what else they changed.  With yours (no buffer tubes), you need to turn the MP-1 output up to ensure plenty of signal into the TS100 and control the overall volume on the amp.  If you ditch the Redback, I'd be more inclined to go with a EV speaker as you know you liked that in the MKIV.  All the various Celestion speakers sound different and that becomes another rabbit hole to work out.  The EV Black Shadow has a bigger voice coil, 200w and 55Hz resonance.  Nice speaker. 
Unfortunately, some techs are arrogant.  To say there is no difference in power tubes in wrong, they may be electrically equivalent but they all sound a bit different but again, it's subtle.  There are definite differences from EL34s' and 6L6s' (see MJMPs comments) but there are also differences between brands.  The Mullard re-issues should be fine although the original Svetlanas are really suited to guitar amp output stages.  I went to a tube rolling night where the guy changed various tube brands in a bunch of amps, Fender Marshall etc and the Svetlana 12AX7s worked much better in those circuits that other brands.
Can you test your MP-1 at your first techs before he moves? I'm now wondering if your new arrogant tech got the change over right (6L6 to EL34).  While the TS100 can run either, there are changes required in the amp to make that work.  6L6 and EL34s are quite different tubes and "NOT" electrically equivalent.  So my TS100 has some internal switches to select which tube type (I assume yours is the same) see power tube biasing in the manual. This is an easy check to do just to make sure though I suspect if he didn't get it right it wouldn't work at all.

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skarkowtsky

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Re: I don't know where to begin
« Reply #11 on: Time Format »

Hi RNolan,

I can try some of these tests and will. However, I have a Carvin Tube 100, not the TS100. The Tube 100 only accepts EL34s, so I can’t fault the tech in that regard.

Ok, I'm done bitching and moaning. I've come up with the following action plan.

• Testing the MP-1 with headphones today
• Install EMGs back in Soloist (not today)
• Approximate the Boogie cabinet specifications by cutting the back panel of the MojoTone cabinet into thirds, but only installing the top 1/3 (which has the speaker cable jack). This will simulate the top third of the Boogie combo which is the amp chassis, with the lower 2/3 open.
• Replacing Redback with either EV Black Shadow or Celestion Creamback H

To summarize, I'm hitting reset on the guitar, rolling it back to the last great tone I had. Replicating the Boogie cabinet and possibly the Black Shadow, also the last great tone I had. If sound quality issues persist, this might be an easier starting point for me to trouble shoot.

I definitely bit off more than I could chew with all the abrupt gear changes. Lesson learned.
« Last Edit: Time Format by skarkowtsky »
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skarkowtsky

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Re: I don't know where to begin
« Reply #12 on: Time Format »

FIRST UPDATE

Testing the MP-1 with headphones today
All the tone I could want came through the headphones. They are over-ear, oversized SONY, but not studio monitors. They do have a slight bass boost, but I could still hear the tonal improvement over the Redback.

I then switched back to the Redback and tried the same patches with the back of the cabinet mounted and removed. It sounded like a clock radio regardless of the configuration. I [want to] believe the amp was properly serviced and biased, because as I increased the Carvin's volume to insane levels, more pronounced and articulate crunch flowed from the power tubes. The power amp actually sounded great, but the guitar tone was still terrible. I'm starting to believe the Redback and or the cabinet are the culprits.

I guess a practical next step would be to purchase a different speaker and try it with the rear of the cabinet mounted and removed. If it improves with both configurations, it's the Redback, if it doesn't improve with the rear mounted, then a closed-back cabinet was also wrong for me.

SIDE NOTE

I noticed that on almost every factory preset that OD1 slightly clips. When I rolled the volume on my guitar back a hair, the clipping ceased. I'm a single volume, no tone guy. I like hot p'ups. However, I never had this issue with my EMG 81/85 wired the same way. Any thoughts?

I appreciate the help!
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rnolan

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Re: I don't know where to begin
« Reply #13 on: Time Format »

Hey John, well good news is you seem to have stepped back from the ledge LoL. 
Great news that the MP-1 sounds good through the headphones  :thumb-up: .  I'm keen to hear what happens with the 1 channel tests.  Then when you turn the amp up to decent levels (for it) it won't be as loud.  "Clock radio" has me worried,  to me this implies channels out of phase so lots of phase cancellation going on, particularly bottom end where phase issues are more prominent (longer wave lengths cancelling out).  Though how that would happen just from a retube  :dunno: .  The other thought for clock radio is lead or connector issues, signals not getting through properly.  So I assume you are using a proper speaker lead from amp to cab, not a guitar lead??  Just checking, as speaker leads need to be much thicker wire to carry the current (I use 20amp power cable to make my speaker leads).  Also is the lead from the MP-1 to the amp good?  A bad cable causes all sorts of "not good".  And we know the cable from the guitar to MP-1 is ok as the headphones sounded good and you have slight clip on OD1 led.
Slight clipping of the clip leds is not a problem, it means there is plenty of signal at that point of the circuit.  Clip leds are designed to flash (light up) just before clip, they always have a little headroom above where they flash and for distortion sounds even going on full isn't necessarily an issue. 

Speaker and cab combinations is a big rabbit hole.  They need to work well together. As MJMP said, he uses 4 different speakers in a Marshall quad box to get the sound he wants.  What you do know is that the EV in open back MkIV sounded good, not surprising as Boogie match speakers and cabs meticulously.  The dimensions of the MkIV and the rear opening will be matched to the speaker they chose.
Another possibility I just thought of is dud tube(s)  Unless the tech tested them individually (like MJMP does) or they were tested by the supplier (e.g. Doug tubes test all the tubes they supply) it is possible there is a problem with one (or more) of them.  A tube may still work but not properly.  A problem with the EHX tube of channel 1 (as that's the one used for bridge mode) could cause clock radio??  Again, do the channel tests.  The 2 channels should sound the same individually and it will help rule out tube issues in the amp.  As also a not great power tube will cause issues.
While in the end the Redback may not be the one for you and the Mojo cab, it shouldn't sound clock radio.  It may not sound as good as another combination, but it shouldn't be horrible.
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Harley Hexxe

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Re: I don't know where to begin
« Reply #14 on: Time Format »

FIRST UPDATE

Testing the MP-1 with headphones today
All the tone I could want came through the headphones. They are over-ear, oversized SONY, but not studio monitors. They do have a slight bass boost, but I could still hear the tonal improvement over the Redback.

I then switched back to the Redback and tried the same patches with the back of the cabinet mounted and removed. It sounded like a clock radio regardless of the configuration. I [want to] believe the amp was properly serviced and biased, because as I increased the Carvin's volume to insane levels, more pronounced and articulate crunch flowed from the power tubes. The power amp actually sounded great, but the guitar tone was still terrible. I'm starting to believe the Redback and or the cabinet are the culprits.

I guess a practical next step would be to purchase a different speaker and try it with the rear of the cabinet mounted and removed. If it improves with both configurations, it's the Redback, if it doesn't improve with the rear mounted, then a closed-back cabinet was also wrong for me.

SIDE NOTE

I noticed that on almost every factory preset that OD1 slightly clips. When I rolled the volume on my guitar back a hair, the clipping ceased. I'm a single volume, no tone guy. I like hot p'ups. However, I never had this issue with my EMG 81/85 wired the same way. Any thoughts?

I appreciate the help!

Hey John,

      Good deal! At least now you're beginning to narrow down the issue. I wouldn't think the next step is to buy any speakers just yet. I think the next thing to do is to resolve the issue with the speaker you have. I'm in agreement with Richard about the "clock radio" sound you're getting, it sound like something isn't connected right, or something is flipped out of phase somewhere in the signal path. What I would try first is to switch the connections to the speaker. Maybe the polarity is reversed somewhere along the line. Before you do that however, double check you're connection from the power amp, and be sure the leads are correctly matched if you are in bridged mode running to the speaker. I don't believe it would be a good thing to have the polarities flipped at the connections.

    The reason I'm suggesting this is because when I compared the sound of the Redback to the Creamback, I found the Redback has a bit less high end, and more enhanced bass frequencies, the Mids and Presence were tamed down also. In the Creamback, I found the Mids and Presence were boosted with a crisp high end, and very little bass to them. The cabinet itself won't matter with one 12" speaker, it does what it was built to do, and it should do it very well.

    As for the side note, I know hot PU's will drive the front end of the preamp, it's what they do. I can't say about the EMG's I've never used the active PU's. I would guess that they are tuned to a specific output level and the frequencies are tamed to match at any level. That would be my guess. As for the LED's at the input, I don't pay much attention to them most of the time. My simple theory is, if it sounds good, it's right.

Harley 8)
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