Yeah, eddie25, that is definitely a dual pot MV on the front panel of that amp. This is no doubt a change from what I saw. Good catch on the pic, BTW.
As to what is on the back? Hm, hard to say. Anybody?
Oh. As to the LarMar working best in a non-NFB Rocket type circuit? And in particular the non-NFB being a plus due to it's lack of interaction with the MV function? No, I strongly disagree. I will say it again, having installed the LarMar MV in Rockets and Express's, it definitely performs better in the Express. And I say this because, beyond the good sonics with the Express and the Rocket, you are able to drop the volume more gradually and over a longer sweep of the MV pot with the Express than you can with the Rocket. I appreciate the longer sweep, call me crazy.
BTW, Aikens talked about this issue with this type MV on his website. I get that the science is there, sure. But the thing is, in practice, whatever the MV is doing to remove any particular benefit of the NFB, you would not hear it.
Paulster, have you tried this MV in an Express? Now that's a report I would like to read, Brother.
PPIMV in Rocket?
Moderators: pompeiisneaks, Colossal
Re: PPIMV in Rocket?
Last edited by rooster on Sat Mar 19, 2011 2:22 am, edited 1 time in total.
Most people stall out when fixing a mistake that they've made. Why?
Re: PPIMV in Rocket?
http://spinoo.free.fr/projetG5/Images%2 ... 0-%202.jpg
I was thinking more of this one, which is a different amp and looks like it could be a Type 2 on the back. Judging from the differences, I'm sure he's made ones without a master at all, which would explain what you guys have seen.
I was thinking more of this one, which is a different amp and looks like it could be a Type 2 on the back. Judging from the differences, I'm sure he's made ones without a master at all, which would explain what you guys have seen.
Re: PPIMV in Rocket?
Yeah, eddie25, there it is, too, as you say. Not the LarMar, but a dual pot. I agree, his site is interesting, offering custom options. I suppose a LarMar version is just one request away, as you also suggest.
Gads, I really hate to see those blue metal films in an amp, however...
Gads, I really hate to see those blue metal films in an amp, however...
Most people stall out when fixing a mistake that they've made. Why?
Re: PPIMV in Rocket?
Rooster, I have not put a type 2 master in an Express, but have put them in a number of plexi clones. I am not familiar with the Aiken article on it, but it was obvious to me the first time I put one in that when the master was turned up that output became smoother, or less distorted. The reason is because less NFB is injected into the PI at lower master settings. It also affects the effectiveness of the presence control.rooster wrote:
BTW, Aikens talked about this issue with this type MV on his website. I get that the science is there, sure. But the thing is, in practice, whatever the MV is doing to remove any particular benefit of the NFB, you would not hear it.
As far as the LarMar or type 2 goes, I always thought that these controls were designed for fixed bias amps. The LarMar improvement on the type 2, as far as I understand it, is that the resistors added are meant to protect the bias from shooting to the moon in the event of a wiper failure in the pot. So, what I am getting at is that I don't understand why anyone would use the LarMar in a cathode biased amp. it seems more logical to me to just use a standard volume control setup by replacing the power tube grid load resistors with the outer lugs of a pot and to have the signal come in off of the PI blocking caps into the wiper. Since the incoming signal and power tube grid connections are reversed on the Type 2 compared to the other way I suggested, the grid load resistance is reduced as the type 2 is turned down in a cathode biased amp and I would like to know if there is any reason why this is better or worse than having a fixed grid load. Since the type 2/larmar works fine with cathode biased amps I expect that there is no issue and is a matter of taste, but maybe an engineer type can explain the importance or lack thereof of the value of grid load resistors on power tubes.
Below are illustrations of the 2 types of controls in case anybody doesn't understand what i am talking about with this overly wordy post :
You do not have the required permissions to view the files attached to this post.
Re: PPIMV in Rocket?
The 2M2s are to stop a wiper failure causing the bias to skyrocket but also to bring the value of the 250K pots down to the 220K of the bias splitter resistors that they are replacing, so their purpose is twofold.
A Rocket (or AC30) also has the 220K resistors but they are used as grid references to ground instead, since negative bias isn't being injected here. A wiper failure here would also cause the bias to skyrocket since the lack of a grid reference would allow the grid to float.
The design of the PI to power tubes is identical between a fixed bias Marshall and cathode biased Vox with the sole exception that the bias voltage is set at the cathode rather than the grid in the case of the Vox.
This design will therefore work perfectly in the AC30, and as I said before, is actually better suited to this application because there isn't a global negative feedback loop which will collapse at low output levels.
Hope that makes sense.
A Rocket (or AC30) also has the 220K resistors but they are used as grid references to ground instead, since negative bias isn't being injected here. A wiper failure here would also cause the bias to skyrocket since the lack of a grid reference would allow the grid to float.
The design of the PI to power tubes is identical between a fixed bias Marshall and cathode biased Vox with the sole exception that the bias voltage is set at the cathode rather than the grid in the case of the Vox.
This design will therefore work perfectly in the AC30, and as I said before, is actually better suited to this application because there isn't a global negative feedback loop which will collapse at low output levels.
Hope that makes sense.
Re: PPIMV in Rocket?
Ryan - I could post the whole Randall Aiken section here that pertains to this discussion but I think Randall might not like me for doing that.
So go here: http://www.aikenamps.com/ , and then click on 'Tech Info'. Here go down about 3/4s of the page. Look for: Q: Does negative feedback reduce harmonics and distortion?
This section preceeds the section on MVs, but you will find both of these interesting I think. In fact, the whole Tech Info section is really interesting to read, and very informative.
OK, and not to dis in any way what Randall has offered here, because it is good information and well written, I still think that ultimately there's reading about something, and then there's trying something in the flesh and seeing what you think. There are so many parameters to consider here, afterall, and not all of it mappable science.
Going to your point that the Marshalls you installed the PPIMV in sounded more distorted when you turned the MV down? Did this happen when you left the preamp controls alone? If so, I don't hear this happening on my amps. I would also add, to Randall, when he says that the PPIMV makes the tone controls behave poorly? No, I don't hear this on my Express's or the Marshalls with the PPIMV installed, either. Hm, so I don't know how to respond at this point.
I think it could be that empirically what Randall says is true, but in the real world of playing into the amps I am refering to, it doesn't come into play. That even though the tone controls are changed, they are not changed enough to override the use and purpose of the PPIMV perhaps? What do you think?
As to your thoughts and experiences with the PPIMV on a Marshall, well I just don't hear what you hear. And yes, I have installed them in 3 metal panels, one of them a 100 watter. My experience with the LarMar on the Marshalls and my Express's is that - if anything is happening - it's that the sound stays pretty similar with the speaker sounding less overdriven. Almost opposite of what you are experiencing, Ryan.
I can also offer to this discussion that I have used the Pre PI MV that Randall talks about, in a few 50 watt Marshalls (metal panel type), and it was really lame. And of course, it doesn't have near the gain that an Express has so this may be why (not to say that I have tried this in an Express, I haven't - it might work well here for all I know). Also, in this case, if having the option of the tone controls - as Randall reports - made any difference, it wouldn't be for me to say. So much power and feel went away with this style (Pre PI) MV circuit in this amp that they didn't sound too good below 3/4 'on'. Well, the JCM800 series, where the PrePIMV came from, had more gain so maybe it's better suited there? Eh, still not the gain of an Express however.
Whew, and you thought your post was long! Later.
So go here: http://www.aikenamps.com/ , and then click on 'Tech Info'. Here go down about 3/4s of the page. Look for: Q: Does negative feedback reduce harmonics and distortion?
This section preceeds the section on MVs, but you will find both of these interesting I think. In fact, the whole Tech Info section is really interesting to read, and very informative.
OK, and not to dis in any way what Randall has offered here, because it is good information and well written, I still think that ultimately there's reading about something, and then there's trying something in the flesh and seeing what you think. There are so many parameters to consider here, afterall, and not all of it mappable science.
Going to your point that the Marshalls you installed the PPIMV in sounded more distorted when you turned the MV down? Did this happen when you left the preamp controls alone? If so, I don't hear this happening on my amps. I would also add, to Randall, when he says that the PPIMV makes the tone controls behave poorly? No, I don't hear this on my Express's or the Marshalls with the PPIMV installed, either. Hm, so I don't know how to respond at this point.
I think it could be that empirically what Randall says is true, but in the real world of playing into the amps I am refering to, it doesn't come into play. That even though the tone controls are changed, they are not changed enough to override the use and purpose of the PPIMV perhaps? What do you think?
As to your thoughts and experiences with the PPIMV on a Marshall, well I just don't hear what you hear. And yes, I have installed them in 3 metal panels, one of them a 100 watter. My experience with the LarMar on the Marshalls and my Express's is that - if anything is happening - it's that the sound stays pretty similar with the speaker sounding less overdriven. Almost opposite of what you are experiencing, Ryan.
I can also offer to this discussion that I have used the Pre PI MV that Randall talks about, in a few 50 watt Marshalls (metal panel type), and it was really lame. And of course, it doesn't have near the gain that an Express has so this may be why (not to say that I have tried this in an Express, I haven't - it might work well here for all I know). Also, in this case, if having the option of the tone controls - as Randall reports - made any difference, it wouldn't be for me to say. So much power and feel went away with this style (Pre PI) MV circuit in this amp that they didn't sound too good below 3/4 'on'. Well, the JCM800 series, where the PrePIMV came from, had more gain so maybe it's better suited there? Eh, still not the gain of an Express however.
Whew, and you thought your post was long! Later.
Most people stall out when fixing a mistake that they've made. Why?
Re: PPIMV in Rocket?
I'm a newb to all this but I often wonder why guitar amps even use NFB around the PI and output stage. According to Randall the idea is to reduce distortion, flatten frequency response and reduce output impedance. I don't understand why the first 2 reasons would be an advantage. Randall says NFB only works up until the PI/output stage starts clipping, after that, what does it do then, nothing?
I built some experimental circuits into a small 8W PP amp, some benefitted from NFB, in others it was not required. The benefit I noticed is that some circuits would not transition smoothly into breakup, they would fart a bit before delivering the goods so to speak. With NFB, they would pass through this transition without farting. Which makes sense, because as soon as the PI or an output tube starts square-waving, the NFB is going to try to crank more signal into the PI to fix "the problem", leading to even more distortion.
A preamp is often described as having 2 or 3 gain stages, and the PI is not generally counted as a gain stage, but with a PPIMV or a non-MV amp I would consider it to be an extra gain stage, because it is. Maybe that has something to do with the improved sound from a PPIMV or a non-MV circuit?
I find this stuff very interesting...
I built some experimental circuits into a small 8W PP amp, some benefitted from NFB, in others it was not required. The benefit I noticed is that some circuits would not transition smoothly into breakup, they would fart a bit before delivering the goods so to speak. With NFB, they would pass through this transition without farting. Which makes sense, because as soon as the PI or an output tube starts square-waving, the NFB is going to try to crank more signal into the PI to fix "the problem", leading to even more distortion.
A preamp is often described as having 2 or 3 gain stages, and the PI is not generally counted as a gain stage, but with a PPIMV or a non-MV amp I would consider it to be an extra gain stage, because it is. Maybe that has something to do with the improved sound from a PPIMV or a non-MV circuit?
I find this stuff very interesting...
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solderstain
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Re: PPIMV in Rocket?
Late to this thread, but nothing new there... 
I've put the LarMar PPIMV in several amps, and have found that it works quite well in cathode-biased EL84 amps. I've even gone so far as to put one in my '63 AC30/TB, which is, of course, what a Rocket is based on. I hard-wired the Cut control internally using a fixed resistor at the value I normally set the (former) Cut pot to, and put the dual-ganged pot in that hole in the chassis.
I've also put it in a few EL84-based personal builds that aren't of the AC30 type circuit, including a Marshall 18w-style amp.
Whether the LarMar circuit works well in a fixed-bias amp depends on the amp topography. I tried it in a couple of BF Fenders (both of them Bassmans), and briefly in my old metal-panel Marshall SL, and I wasn't as happy with the MV in those amps. The MV is now out of all three of those amps. However, I have played through a friend's early JCM800 combo that has that MV installed and it works VERY well in that amp (the owner just keeps the original MV on '10'). Go figure.
I'm going to be building a 'pool soon, and it's getting the LarMar MV. If I end up not liking it there, I'll just leave it dimed and keep rockin'. But I suspect it will be just as good there as any other cathode-biased amp I've put it into.
I've put the LarMar PPIMV in several amps, and have found that it works quite well in cathode-biased EL84 amps. I've even gone so far as to put one in my '63 AC30/TB, which is, of course, what a Rocket is based on. I hard-wired the Cut control internally using a fixed resistor at the value I normally set the (former) Cut pot to, and put the dual-ganged pot in that hole in the chassis.
I've also put it in a few EL84-based personal builds that aren't of the AC30 type circuit, including a Marshall 18w-style amp.
Whether the LarMar circuit works well in a fixed-bias amp depends on the amp topography. I tried it in a couple of BF Fenders (both of them Bassmans), and briefly in my old metal-panel Marshall SL, and I wasn't as happy with the MV in those amps. The MV is now out of all three of those amps. However, I have played through a friend's early JCM800 combo that has that MV installed and it works VERY well in that amp (the owner just keeps the original MV on '10'). Go figure.
I'm going to be building a 'pool soon, and it's getting the LarMar MV. If I end up not liking it there, I'll just leave it dimed and keep rockin'. But I suspect it will be just as good there as any other cathode-biased amp I've put it into.
Re: PPIMV in Rocket?
Are you sure you prefer it in cathode-biased to fixed-bias amps rather than those without global negative feedback to those with global negative feedback?
The effect of the PPIMV is three-fold:
You won't get power tube saturation which you may (or may not) get without the PPIMV
You won't get the same level of power supply compression (but how much compression there is will vary hugely with each design)
You will lose the negative feedback
but with a non-NFB amp (like the AC30) you won't get the 3rd effect at all.
It'll be interesting to see how well this works with a Liverpool because it relies quite heavily on power supply compression to keep the clean-to-scream volume level fairly constant, and uses a fair amount of global negative feedback.
The effect of the PPIMV is three-fold:
You won't get power tube saturation which you may (or may not) get without the PPIMV
You won't get the same level of power supply compression (but how much compression there is will vary hugely with each design)
You will lose the negative feedback
but with a non-NFB amp (like the AC30) you won't get the 3rd effect at all.
It'll be interesting to see how well this works with a Liverpool because it relies quite heavily on power supply compression to keep the clean-to-scream volume level fairly constant, and uses a fair amount of global negative feedback.
Re: PPIMV in Rocket?
Well, I am confused when folks go on about the LarMar type MV in a Rocket type build - and then seem to dis it in an Express. I read what you say and I know you are sincere but I suspect you are really just basically 'Rocket' (broad term implied - cathode biased/ClassA becoming ClassA/B, etc.) 'kind of people' at heart, and you try it there and think, 'Oh yeah, this is it!', without having first hand knowledge of it in an Express. (..Er, so yes, on a side note, the Liverpool experiment will be interesting, what with the NFB.)
Is this the case? (And sorry to say, but a BF AB165 Bassman with it's three triode signal path does not qualify as an Express. These are two very different amps.) I don't think I am being rude and I am not trying to put anybody on the spot.
Honestly, the fact that Randall's tech notes reinforce the idea that the LarMar type MV performs better in a Rocket type amp than it does in an Express... well, let's just say it confuses me, too. Because, having tried it, I very strongly disagree with what his tech notes suggest on the subject. So sign in, if you can, tell me that you tried it in an Express and it sounded 'wrong' or not right' or whatever the words you will choose might be. I would like to hear this.
Is this the case? (And sorry to say, but a BF AB165 Bassman with it's three triode signal path does not qualify as an Express. These are two very different amps.) I don't think I am being rude and I am not trying to put anybody on the spot.
Honestly, the fact that Randall's tech notes reinforce the idea that the LarMar type MV performs better in a Rocket type amp than it does in an Express... well, let's just say it confuses me, too. Because, having tried it, I very strongly disagree with what his tech notes suggest on the subject. So sign in, if you can, tell me that you tried it in an Express and it sounded 'wrong' or not right' or whatever the words you will choose might be. I would like to hear this.
Most people stall out when fixing a mistake that they've made. Why?
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guitarsnguns04
- Posts: 286
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Re: PPIMV in Rocket?
ive put it in a few express builds.I prefer it over any attenuator Ive ever tried. I enjoyed being able to use my express at some medium and small gigs where stock to get the killer tone it was way too loud. The downside I feel that the clean to mean effect with the guitar pots is obviously compromised in a gig enviroment it was still a good trade off for live performance. It made the amp more usuable to me. I dont know if this helps at all or not ...just my 2 cents 
Re: PPIMV in Rocket?
I haven't tried anything other then fast/gradual switching in an Express and watts control on the PI used as a volume device.
But........ I thought people preferred the VVR to PPIMV or Lar-Mar in an Express?
Mark
But........ I thought people preferred the VVR to PPIMV or Lar-Mar in an Express?
Mark
Re: PPIMV in Rocket?
That MV configuration grounds out (loads down) the outputs of the PI when the control is down. Using the wiper for the output instead of the input keeps the load on the PI consistent as with no MV. The small "safety" wiper resistors used to ensure bias during wiper failure (in fixed outputs) are still a good idea in cathode bias. This because a break in the grid leaks' path ground lets the grid voltage float up positive and the tube over conducts.KT66 wrote: [img:463:459]https://tubeamparchive.com/files/cathod ... mv_135.gif[/img]
If it says "Vintage" on it, -it isn't.
Re: PPIMV in Rocket?
I haven't tried any kind of master in an Express because the nature of the design is that you want to push the power tubes as well as getting power supply compression to get the full Express experience. So I use mine with a Faustine Phantom attenuator instead to get the best of all worlds, save for tube wear!
Same with my Liverpool, and my AC30 Top Boost (so basically Rocket) build.
That's not to say that a master won't work or even work well with the Express, but even Larry will tell you that the downside of the LarMar PPIMV is the fact that the negative feedback loses effectiveness as the level is turned down which means your presence control stops working and it'll loosen up compared to when it's running flat out, whereas on a Rocket with no global NFB you won't run into this scenario at all. So that's an unquestionable advantage of using this type of master in an amp with no global NFB over one that uses it. The biasing methodology isn't relevant.
So I stand by my statement that this master should function better in a Rocket than in an Express or a Liverpool, but that doesn't mean it'll be bad by any stretch of the imagination in any of the amps.
Same with my Liverpool, and my AC30 Top Boost (so basically Rocket) build.
That's not to say that a master won't work or even work well with the Express, but even Larry will tell you that the downside of the LarMar PPIMV is the fact that the negative feedback loses effectiveness as the level is turned down which means your presence control stops working and it'll loosen up compared to when it's running flat out, whereas on a Rocket with no global NFB you won't run into this scenario at all. So that's an unquestionable advantage of using this type of master in an amp with no global NFB over one that uses it. The biasing methodology isn't relevant.
So I stand by my statement that this master should function better in a Rocket than in an Express or a Liverpool, but that doesn't mean it'll be bad by any stretch of the imagination in any of the amps.
Re: PPIMV in Rocket?
paulster - Woah, $950, that's not chump change. And, since Randall 'rips' on attenuaters equally if not more than MVs, I suddenly feel a closer bond, Brother. 
Too, reading the development story of the Phantom, I was actually surprised to see that Randall Aikens was actually going to make an attenuator at one time? I never heard this before and it makes me wonder why he didn't. Here, like the creator of the Phantom felt at one time, and having read what Randall has to say about attenuators - man, I would really love to see/hear what he came up with to overcome all his own objections!
Well, if the Phantom has a backorder like it does, and a price tag of $950, maybe Randall is gearing up? For that matter, maybe he would respond to this news (to me) of his plans to design and build an attenuator? I know he drops in on occasion. Too, I wonder if he has tried the Phantom and what he thinks of it? Mr. Aikens?
In the meantime, paulster, I wouldn't mind hearing your review of it.
Too, reading the development story of the Phantom, I was actually surprised to see that Randall Aikens was actually going to make an attenuator at one time? I never heard this before and it makes me wonder why he didn't. Here, like the creator of the Phantom felt at one time, and having read what Randall has to say about attenuators - man, I would really love to see/hear what he came up with to overcome all his own objections!
Well, if the Phantom has a backorder like it does, and a price tag of $950, maybe Randall is gearing up? For that matter, maybe he would respond to this news (to me) of his plans to design and build an attenuator? I know he drops in on occasion. Too, I wonder if he has tried the Phantom and what he thinks of it? Mr. Aikens?
In the meantime, paulster, I wouldn't mind hearing your review of it.
Most people stall out when fixing a mistake that they've made. Why?