Mark VII - dang double gang - messed up FX levels

[rarebitusa]

The coffee shop guy with his acoustic guitar makes it look so easy!

man don't you just hate that... sigh

 

[phreeman123]

So a cool way around this is to run the CabClone out into the looper then run the looper into some powered monitors or speakers. I do this because of the volume issues. Some loopers like my RC-5 have a built in drum machine which sounds way better with full range speaker than through a guitar speakers anyway.

 

[mace]

Just one more oddity I noticed when playing out last weekend. I had the FX LOOP on pretty much the whole time with a subtle delay. Well, when switching channels from 2 to 3 there was a very loud burst of sound. It ends up that the delay level in Ch 2 was fine but when switching to Ch 3 the delay echo would get overly amplified and be really loud for an echo or two.

Just another artifact of the drastic FX LOOP level differences between the channels.

 

[bandit2013]

Just one more oddity I noticed when playing out last weekend. I had the FX LOOP on pretty much the whole time with a subtle delay. Well, when switching channels from 2 to 3 there was a very loud burst of sound. It ends up that the delay level in Ch 2 was fine but when switching to Ch 3 the delay echo would get overly amplified and be really loud for an echo or two.

Just another artifact of the drastic FX LOOP level differences between the channels.

Too early of a release on the strobe mute circuit? They slow the response on the reverb circuit to get rid of the transient noise from altering the circuit path with the relays. Think they need something similar on the FX loop?

 

[ultra high gain]

what about the addition of an outboard fx unit that has volume control per preset?

 

[DECEMBER]

I have a Mark V 90W and the power amp changes volume with just about every setting. On ch3, extreme is much louder than mk4 and mk2, I have to engage the solo boost to get them as loud as extreme was without changing the channel volume.
Switching from EQ sliders to preset EQ makes a huge volume increase.
I'm also running stereo with another 4x6L6 power amp set to 50W. If I'm on channel 3, 45W, and have the two stereo channels' volume equal, if I switch to ch2, 45W, the stereo volume becomes unbalanced, one side is louder than the other.
If I run a preamp distortion pedal (i.e. Fortin Natas) straight into the FX return of Mark V, with ch2+3 both on 45W, one is louder than the other (even though the preamp channels aren't making it to the power amp). Also, the power amp volume still gets louder on extreme vs mk4 or mk2, even when bypassing the preamp with a pedal straight into the FX return.

 

[gtrnstuff]

I have a Mark V 90W and the power amp changes volume with just about every setting. On ch3, extreme is much louder than mk4 and mk2, I have to engage the solo boost to get them as loud as extreme was without changing the channel volume.
Switching from EQ sliders to preset EQ makes a huge volume increase.
I'm also running stereo with another 4x6L6 power amp set to 50W. If I'm on channel 3, 45W, and have the two stereo channels' volume equal, if I switch to ch2, 45W, the stereo volume becomes unbalanced, one side is louder than the other.
If I run a preamp distortion pedal (i.e. Fortin Natas) straight into the FX return of Mark V, with ch2+3 both on 45W, one is louder than the other (even though the preamp channels aren't making it to the power amp). Also, the power amp volume still gets louder on extreme vs mk4 or mk2, even when bypassing the preamp with a pedal straight into the FX return.

That isn't abnormal for that amp. The extreme mode reduces negative feedback to the power amp so it will cause a volume jump compared to other modes.
When I had my MK V, I selected the mode for each channel, the EQ (preset or slider) if any, the power amp wattage, then set the channel master volumes where I wanted them. With all the different circuits involved, the volumes aren't likely to be consistent as you switch features in and out.

I also just ran mine mono, so your stereo set up with a different model of amp may just not work like you hoped it would.
If you use the MK V preamp out to send to your other power amp in, and don't use extreme mode or different power amp wattage settings, you may be able to get a more consistent stereo image.

 

[DECEMBER]

That isn't abnormal for that amp. The extreme mode reduces negative feedback to the power amp so it will cause a volume jump compared to other modes.
When I had my MK V, I selected the mode for each channel, the EQ (preset or slider) if any, the power amp wattage, then set the channel master volumes where I wanted them. With all the different circuits involved, the volumes aren't likely to be consistent as you switch features in and out.

I also just ran mine mono, so your stereo set up with a different model of amp may just not work like you hoped it would.
If you use the MK V preamp out to send to your other power amp in, and don't use extreme mode or different power amp wattage settings, you may be able to get a more consistent stereo image.

It works and I can get it balanced, it just takes adjusting with every setting change. Good thing I'm not trying to use this live.
The point (for the OP) is that different channels have different power amp volumes, so running a looper in the FX loop will indeed change volume when channels are changed, unrelated to the channel volumes.

 

[mace]

It works and I can get it balanced, it just takes adjusting with every setting change. Good thing I'm not trying to use this live.
The point (for the OP) is that different channels have different power amp volumes, so running a looper in the FX loop will indeed change volume when channels are changed, unrelated to the channel volumes.

Appreciate the feedback and input (no puns intended!). It seems this issue is difficult to explain and I need to make some sound samples or video.

Maybe my VII has a defect and other folks aren’t experiencing this issue. Best I can tell is that the Mark V:25 FX LOOP volume level behaves very differently than the VII. Neither have a global OUTPUT so they are the same in that regard. But as far as LOOP volume when switching CHANNELs they are very different.

I’ll do some more comparing when I’m back next week.

 

[DECEMBER]

Appreciate the feedback and input (no puns intended!). It seems this issue is difficult to explain and I need to make some sound samples or video.

Maybe my VII has a defect and other folks aren’t experiencing this issue. Best I can tell is that the Mark V:25 FX LOOP volume level behaves very differently than the VII. Neither have a global OUTPUT so they are the same in that regard. But as far as LOOP volume when switching CHANNELs they are very different.

I’ll do some more comparing when I’m back next week.

The Mark V 90W does have a master volume, but even with that, if I had all 3 channels set to 45W and had a looper track playing into the FX return, the volume would be different on each channel. And on channel 3, switching the voicing from Extreme to Mark 4 or Mark 2 would cause a large volume drop to a looper running into the FX return.

 

[bandit2013]

There is reason why this volume difference occurs. For one, say the Mark V90, Ch1 is specifically all clean (with a bit of crunch on tweed). CH2 is a bit more Mark I voiced with a brighter approach using the crunch mode and the CH3 is all out distortion.

Mark VII on the other hand is not channel specific but mode specific since crunch is shared on CH1 and CH2.

So what is the point here exactly? The clean channel has the highest gain of all since there is no clipping to the signal through the shorter cascade of gain stages, the amplitude will be much greater than that of the distorted signal due to clipping or cut-off. So it will have a louder voice through the FX loop and will be compensated depending on the voice or mode chosen. Now with crunch, that uses a portion of the overdrive circuit common with the Mark IV or IIC modes. It gets cut-off almost like a you would get with a cold clipper circuit but not as dramatic. This adds in harmonic content, but the amplitude of that cut-off section will not be as great the clean channel. The other positive portion of the waveform may or may not get clipped, so you end up with this asymmetrical distorted waveform. To have the same sound level through the FX loop, there is some altering of the fx send circuit along with the recovery stage since that is tied to the channel. Hopefully this makes sense. It is difficult to say without a schematic what else gets modified from a clean mode to a distorted mode in relation to the negative feedback circuit with the Mark VII. When it comes to the extreme voice on CH3 and the Mark I mode on CH2, the feedback presence circuit is altered or shifted to the 4 ohm tap on the OT vs the 8 ohm tap on the OT. Extreme adds in another capacitor to reduce the effect of the NFB on CH3. There will be some volume shifting through the FX loop to maintain some sort of level but one would not expect it to be so dramatic of a change as it is with the Mark VII. Perhaps not writing this would be the better option. Just ignore me.

 

[DECEMBER]

There is reason why this volume difference occurs. For one, say the Mark V90, Ch1 is specifically all clean (with a bit of crunch on tweed). CH2 is a bit more Mark I voiced with a brighter approach using the crunch mode and the CH3 is all out distortion.

Mark VII on the other hand is not channel specific but mode specific since crunch is shared on CH1 and CH2.

So what is the point here exactly? The clean channel has the highest gain of all since there is no clipping to the signal through the shorter cascade of gain stages, the amplitude will be much greater than that of the distorted signal due to clipping or cut-off. So it will have a louder voice through the FX loop and will be compensated depending on the voice or mode chosen. Now with crunch, that uses a portion of the overdrive circuit common with the Mark IV or IIC modes. It gets cut-off almost like a you would get with a cold clipper circuit but not as dramatic. This adds in harmonic content, but the amplitude of that cut-off section will not be as great the clean channel. The other positive portion of the waveform may or may not get clipped, so you end up with this asymmetrical distorted waveform. To have the same sound level through the FX loop, there is some altering of the fx send circuit along with the recovery stage since that is tied to the channel. Hopefully this makes sense. It is difficult to say without a schematic what else gets modified from a clean mode to a distorted mode in relation to the negative feedback circuit with the Mark VII. When it comes to the extreme voice on CH3 and the Mark I mode on CH2, the feedback presence circuit is altered or shifted to the 4 ohm tap on the OT vs the 8 ohm tap on the OT. Extreme adds in another capacitor to reduce the effect of the NFB on CH3. There will be some volume shifting through the FX loop to maintain some sort of level but one would not expect it to be so dramatic of a change as it is with the Mark VII. Perhaps not writing this would be the better option. Just ignore me.

The clean channel actually has the lowest gain of all the channels of an amp, but has the highest headroom. High gain channels basically have no headroom because the gain doesn't change the volume at all past 3, just the amount of distortion/saturation.
If a clean channel and high gain channel are dialed to an equal perceived volume, the clean sound is actually louder because it's not being compressed by a wall of limited headroom. This becomes apparent when recording... mic up a high gain sound and set the mic preamp gain as high as possible without clipping. The level will be very consistent whether you're playing chords or single notes, high or low notes, because it's so compressed. Now switch to the clean channel that's dialed in to sound the same volume as the gain channel and it will be clipping the heck out of the mic preamp.
But the volume differences I'm talking about have nothing to do with the channel volumes or the preamp. Bypassing the preamp channels altogether and plugging guitar->pedal->FX return, so all we're hearing is the pedal thru the power amp, but still there are big volume differences between different modes on ch3, and between ch3 and ch2. If ch2 and ch1 are both on 45W and both on tube rectifier, there's no difference, those are using the same power amp configs. And it makes no difference if the channel volumes are at 0 or max, because we're not using the preamp. But between ch2 and ch3, there are different power amp configs being used, always solid-state diodes on all wattage settings of ch3, with the pentode/triode option. While ch2 has the option for tube or solid-state rectifier. So there are 4 selectable power amp configs. But there's something else going on, too, that makes the power amp volume change significantly between Extreme and Mark 4 or 2 on the same channel with the same settings.

 

[bandit2013]

You are using the word gain incorrectly as most people do. Many think that distortion means high gain, it does not. Gain is an increase in something. Your guitar signal for instance, typically at around 640mV peak to peak that gest increased between each gain stage. If it did not, there would be too weak of a signal to drive the phase inverter and power tubes. I never measured the voltage amplitude on the circuit level on each gain stage. but did at the FX loop output.

Gain is to increase. Does not mean it gets distorted. Unfortunately, the FX send level drops the signal down to near instrument levels so they will be in the same range. The first image the signal increased from 640mV peak to peak to 1200 mV peak to peak. That is an increase. All gain stages increase the signal level, if not cut-off or clipped the amplitude will be higher thus have more gain (do not confuse the proper use of the word with distortion, so many people use the word gain improperly, confuse the "high gain" with distortion. Not to stir the pot here. I miss-use the term myself so it is common to say high gain, but in reality it is high distortion that then gets amplified or increased on level (also called gain but that usually takes place in the power section more so than the preamp). I knew that using the literal meaning of gain was going to piss off a few. Just use an open mind, nothing more.

Believe it or not, the circuits that create the distortion generally have the lowest gain factor, they are meant to be overdriven by the previous stage to force it into clipping or cut-off. It will be followed by another gain stage to boost the signal levels. Those are the facts. Once you clip or cut off the signal it will have a lower amplitude than the clean signal that is not distorted. Hence there is more gain on clean, just without the distortion many confuse as being high gain. This was measured from the JP2C clean channel. The green line is the output waveform from the FX send. Yellow curve is the input signal measured on the input. The scale on the input and output channels used on the scope were the same. All channel controls were set at noon. Sorry, this was from a larger image and also had the status field showing details that are hard to make out with this image. This had an input amplitude of 649mV peak to peak. The FX output level was 1200mV peak to peak. The gain here is 184% increase.



This is the same applied signal with no changes, Only changed to CH2. The input and output amplitudes are about the same, input still at 649mV peak to peak, distorted signal is only 770mV peak to peak. That is only 118% increase or gain from the original signal but highly distorted due to the overdrive circuit. The waveforms do contain some complex harmonics and will have a more compressed sound compared to the clean channel.

OK, sure there are two additional gain stages in the circuit on CH2 of the JP2C, that is the overdrive and booster stage. the overdrive distortions only half of the waveform, the booster stage cuts the other half. The top and bottom of the distorted waveform are not identical, they are different.

Sure, there may also be differences in the gain stages from one channel to the next. I am not going to dispute that. I am only taking a look from an engineering perspective. The JP2C is similar in design to the Mark VII but with obvious differences as it has a dual pot on the channel volumes. One is after the FX loop and the other is more or less in front of the FX loop. Different modes, regardless of channel will address the signal level in front of the V2A triode that is used to create the send level and different configurations on the recovery stage V2B. Some of that will address the OP's issue relating to use of a looper in the FX loop with captured content from the clean channel and played back using the other channels in a more distorted configuration (yes, I mean high gain channel as I have also adopted the incorrect use of the term).

As for the Mark V90, There will be differences in the output of the amp based on voice and channel selected. That holds true to other amps as well like the Dual Rectifier. It is all based on changes in the presence circuit, if the NFB is connected or bypassed. This all ties into the phase inverter circuit on the control grid side. The power section does not change as it is at a fixed bias. OK, if you change the power mode from 90W to 10W or whatever.

Another point, considering the Mark VII amp, say on CH3, The IIB mode bypasses the overdrive gain stage and sends the tone stack signal directly to the high gain stage I referenced as a booster stage. Well, IIB has less distortion than say IIC or IV modes that use the overdrive gain stage (has the lower gain factor but used to force the signal into the cut-off region). I do plan on scoping the different modes using the same method I did when looking at the dB levels of the FX loop of the JP2C, Mark V90 and TC50. Note that the TC clean had the highest output level at +8dBu compared to the CH2 (vintage lo) or CH3 (vintage high). The "high gain" channels did not exceed 3dBu if I remember correctly. Less gain but more distortion. This is all due to clipping and cut-off of the signal. Also the TC50 uses op-amps following the tube circuits so on paper that amp has the highest gain ever, does not mean much if the signal level does not increase as much as the circuit gain would indicate. If it did, it would sound like crap. I am not fond of hearing square wave signals as that is more of an ice pick in the making.

 

[DECEMBER]

You are using the word gain incorrectly as most people do. Many think that distortion means high gain, it does not. Gain is an increase in something

Believe it or not, the circuits that create the distortion generally have the lowest gain factor, they are meant to be overdriven by the previous stage to force it into clipping or cut-off. It will be followed by another gain stage to boost the signal levels. Those are the facts

not cut-off or clipped the amplitude will be higher thus have more gain

Output level (amplitude) is not gain. Output level is volume. Input level is gain. The clean channel has the lowest gain but the highest headroom. Ch3 has the highest gain with low headroom. The clean channel output level is higher because it isn't limited by headroom, isn't conpressed.
Gain ≠ (does not equal) distortion unless/until the limit of available headroom is exceeded. Gain is the level of the input signal. Distortion is indeed the result of higher gain levels forced into a circuit with low headroom. The compression causes the output level to be lower than a clean signal, but that doesn't mean it's lower gain, that's the output volume. Gain and volume perform the same essential function (amplify/attenuate a signal), but because of their placement at opposite ends of the preamp circuit, they produce very different results.
Clean channels have low gain with high headroom. Distortion channels have high gain with low headroom. Heavy distortion is indeed the result of very high gain levels, but it's compressed (because that's the nature of distortion) because of the limited headroom. If the amount of gain used for heavy distortion was fed into a clean channel with higher headroom, it would still surpass the available headroom and cause more distortion than the max gain of the clean channel does, but less distortion than it causes on the distortion channel, because the clean channel has higher headroom.

 

[JAZZGEAR]

This is normal. The JP2C does the same thing. I tried it with recording a 12-sting acoustic guitar and found the change would occur on the sound of the recording, its character changed considerably and also gain some power tube distortion. Thought I could create something interesting since the looper had a recorded 12 string (it has a pickup I sent to a fishman preamp). So when I tried to make use of it and switched to CH2 or CH3 it just was not sounding all that good.

As for the Mark VII, the channel volume controls use a doble pot so volume is altered in two locations, the obvious is after the FX loop. Mark VII does not use a single global FX recovery master volume control like the Mark V, Roadster, MWDR, and TC series so I would expect it to be different. I would not doubt that some modes will alter the effect of the volume as well. Not sure if there are three different negative feedback circuits that may change circuits based on operating mode. Mark V90 in extreme or Mark I mode will shift the presence control as well.

The only way to make use of a looper, would be to run the clean channel only and then add in distortion with a pedal on the front end for any other guitar parts. Same thing done with the Roadster and that was utter failure, Modern mode changes the negative feed back circuit to a different circuit. There is no such thing as disconnecting the negative feedback, it may change component values but it is still in the circuit. If it was actually disconnected, the amp would sound like .

I gave up on loopers some time ago. Cool thing but pointless if you want to have something of different characteristics. I found them pointless in the FX loop. My opinion, so others may have different comments or opinions. Perhaps there is a way to get what you want.

Didn’t we both own the same Mark VII with the extreme volume differences? Is this issue similar to that?

 

[bandit2013]

Didn’t we both own the same Mark VII with the extreme volume differences? Is this issue similar to that?

That was not me. I never shipped any Mark VII's back as both are keepers. I do recall someone having the volume issue and they returned it to SW only to have someone else buy it as a demo unit at a reduced cost who is also a member here. .

 

[mace]

Didn’t we both own the same Mark VII with the extreme volume differences? Is this issue similar to that?

Yeah, that was mine. That issue (CRUNCH on channel 1 and 2 were radically different volumes when the dials were set the same) isn’t the same as this current topic. This current topic has to do with the FX LOOP and seems to be a design feature.