Ken Fisher type I/II and LarMar. PPIMV

[Willabe]

Any preference as to which sounds best? (Probably splitting hairs.)

Type I (B) is also what KOC prefers for maintaining -bias in the event of a wiper failure but with the 2 x 2M2R's across the pots in the LarMar why bother with another pair of coupling caps? Saves space on the eyelet/turret board.

Or another way, wire the MV dual pots backwards, wiper to PI coupling caps?

Any sound change doing that?


              Brad     

Edit; added (B) after type 1 for clarity. Type 2, LarMar is A.

[HotBluePlates]

I have not done much experimenting with master volume circuits. Those who have experimented often say which circuit sounds best depends on the amp in which it is installed.

The best approach seems to be to do your own experiments and draw your own conclusions.

[Willabe]

Those who have experimented often say which circuit sounds best depends on the amp in which it is installed.

Yeah, that's what I've noticed and I don't understand that. Why should they sound different in a different amp, -FB loop, PI?

I could see that using a 2nd pair of caps might cause a slight difference in sound but I don't see why using only 1 type or the other (A or B) in a different amp would sound that much different or really any at all. 

All it's doing is limiting signal to the output tubes.   

I don't recall anyone using the one in drawing C.


                 Brad     

[TIMBO]

Hey Willabe, I have a PPIMV in most of my amps and I don't think that you are going the hear much difference and "A" is what I use, because it's the bestest. I'n not sure "C" works.

[Fresh_Start]

Hey Willabe, I have a PPIMV in most of my amps and I don't think that you are going the hear much difference and "A" is what I use, because it's the bestest. I'n not sure "C" works.

C might work.  However, I don't see the first "leg" you need for a voltage divider. Also, the pots arranged that way create variable impedance for the preceding tube stage if I'm not mistaken

One thing that bugs me about most of these circuits is putting a relatively small cap before the MV pot. I think that creates a variable high-pass filter. Might explain why it sounds ok in some amps and not so good in others.

Cheers,
Chip

[kagliostro]

I agree with Fresh_Start

the reason may be there are two in-series capacitors

I would consider to use as value for the added capacitor an 1uF cap, this way if the value of the standard cap is 0.022 now you'll have 0.0215 varying the planned value only by a very small amount

I just remembered that this thing comes from Mr. KOC and you discussed with me this thing here in the forum 



one other approach is the Bruce Collins of Mission Amps approach

that uses an in series resistor between the wiper of the pot and the cap whose purpose is to avoid interactions between the cap and the rotation of the pot



Ciao

Franco

[Willabe]

C will work. It's wired just like the volume pots on a 5E3.

It just shunts the signal to ground.

Thanks K, I forgot about the Mission amps 1.

           Brad     

[kagliostro]

C will work. It's wired just like the volume pots on a 5E3.

Maybe I'm distracted, but are you sure ?

It just shunts the signal to ground

Ahem .... where ??

http://el34world.com/charts/Schematics/files/fender/Fender_DELUXE_5E3.pdf

Franco

[Willabe]

Maybe I'm distracted, but are you sure ?

Yes.

As you turn the pot towards the '0' end where will the signal go? It will go to ground through the -bias supplies filter caps.

Look at a 5E3 schemo.


              Brad   

[Willabe]

Also, the pots arranged that way create variable impedance for the preceding tube stage if I'm not mistaken.

Or it's because of this ^ or because of both?


                     Brad     

[kagliostro]

Via the bias PS caps ........... AH, OK!, right
and this give a good result ? If you try I would like to know
Ciao

Franco
p.s.: But in the 5E3 do you refer to the volume pots or to the Tone Control pot ?

[Willabe]

One thing that bugs me about most of these circuits is putting a relatively small cap before the MV pot. I think that creates a variable high-pass filter. Might explain why it sounds ok in some amps and not so good in others.

the reason may be there are two in-series capacitors

I would consider to use as value for the added capacitor an 1uF cap, this way if the value of the standard cap is 0.022 now you'll have 0.0215 varying the planned value only by a very small amount

I just remembered that this thing comes from Mr. KOC and you discussed with me this thing here in the forum 

If the PI coupling cap is, lets say 0.1uF, then you would use either a 1uF (C=10x) for the 2nd cap or you would double the uF value of both caps, 0.2uf to keep the bass response of the amp close to the same, 1st example ~90%, as before inserting the PPIMV.

I seem to remember now that when we talked about this before that HBP said it didn't matter which cap, stock and 10x or 10x and stock, came 1st.

That might be worth trying with respect to Fresh Starts concern?


                      Brad       

[Willabe]

p.s.: But in the 5E3 do you refer to the volume pots or to the Tone Control pot?

Volume pots.


            Brad     

[Willabe]

Via the bias PS caps ........... AH, OK!, right
and this give a good result ? If you try I would like to know

I don't see why not.

The reason to wire the MV pots backwards is for safety. Wiring them backwards if the wiper fails the amp still has -bias.


              Brad     

[Willabe]

Hey SG, with the boss hoss custom breadboard, are you reading this thread?     


                Brad     

[SILVERGUN]

Hey SG, with the boss hoss custom breadboard, are you reading this thread?     

Yes, I've been on and off...

I used the Mission Amps drawing on my T-wreck, and hated it below 4 on the dial....felt ok from 4-6,,,,and it finally got good around 7 and up

[Willabe]

I used the Mission Amps drawing on my T-wreck, and hated it below 4 on the dial....felt ok from 4-6,,,,and it finally got good around 7 and up

What tapper pot where you using, A or L? 

What value R's after the pot (in series) did you use?

I'm not sure that any MV sounds great all the way down to 4 and below?

Same thing with attenuators, you can only go so far with them.


                 Brad     

[SILVERGUN]

I used the Mission Amps drawing on my T-wreck, and hated it below 4 on the dial....felt ok from 4-6,,,,and it finally got good around 7 and up

1)What tapper pot where you using, A or L? 

2)What value R's after the pot (in series) did you use?

3)I'm not sure that any MV sounds great all the way down to 4 and below?

4)Same thing with attenuators, you can only go so far with them.

1) 250k Audio (the one Doug sells)
2)I used 56K because I took a guess and figured that was between the 33K and 100K....at one point I questioned the use, and wound up just eliminating it because I couldn't hear a difference (not to say there wasn't one)
3) Yup, that's the concensus,,,I tried messing with it, but like most early experiments, I'm just learning
4) Yup, I hate mine and I don't use it

There was one schematic that we were looking at recently out of a Marshall, that had some type of filter next to it.....I'll find it and post soon

[SILVERGUN]

Here's that Marshall one...
I was questioning the filter just before the PPIMV that consists of a 2M2 resistor in series with a 47p cap

 ....it looked like a possible attempt at a performance improvement 

The bias rides in on the wiper, so I'm not a big fan.

[HotBluePlates]

C will work. It's wired just like the volume pots on a 5E3.

Gretsch guitars (at least most of the old ones) also use an arrangement exactly like this for individual pickup volume controls. In that situation, if you have both pickups selected and turn the volume all the way off for one pickup, the other pickup's output is unaffected.

In a Gibson, which uses conventionally-wired volume pots for each pickup, if you turn off the volume of one pickup when both are selected, it kills all output from the guitar. That could be useful, or it could prevent you from adjusting the relative volumes the way you want.

So C will absolutely work.

Those who have experimented often say which circuit sounds best depends on the amp in which it is installed.

Yeah, that's what I've noticed and I don't understand that. Why should they sound different in a different amp, -FB loop, PI?

My limited understanding is that it has to do with the master volume being inside the feedback loop (in a post-phase-inverter master volume), and that master volume setting changes also change the amount of negative feedback and how the phase inverter might break over into distortion.

That may not be entirely accurate, and could very well be different for different amps. But any variable controls inside a feedback loop tend to behave in ways you don't expect when you are used to hearing them outside of a feedback loop (ask anyone with tone controls inside a feedback loop).

[Fresh_Start]

HBP - thanks for that insight about frequency filters inside the feedback loop.  I didn't understand how "C" worked at all before.

Cheers,

Chip

[kagliostro]

I remember that I've seen some schematics that used a tone control on the NFB circuit

may this be a solution on using a PPIMV in an amp that has NFB ?

K

[RobBozic]

I remember that I've seen some schematics that used a tone control on the NFB circuit

may this be a solution on using a PPIMV in an amp that has NFB ?

K

This is what Randall Aiken does when he uses the PPIMV. He disconnects the NFB and runs a 'cut' control. He posted this on the Metro Amp forum. From memory I think he uses a 1M pot and a 2.2n cap (see pic)

[RobBozic]

Correction it's a 470pf cap.

[HighFlyingV]

  just eyeing this !

[roseblood11]

I wonder why version C isn't used more often? It looks so easy, but isn't there any disadvantage? It obviously affects the gain of the phase inverter stage, but is that bad? I tried this version on my small Vox built (top boost channel into LTP phase inverter and push/pull power amp with a ecc99) and liked it better than the typical LarMar. I started with the LarMar (250k stereo pot and 1M8 safety resistors), and when I swapped the wires, I left the resistors in place, which go from input (wiper) to ground now (ground, not bias - it's a cathode biased amp!). Which means that the output tubes "see" 220k, when the MV is fully clockwise, rising to 250k when it's turned down.
The sound stays intact better at lower settings. If the MV is set to around 9 o'clock, the sound with the LarMar is quite muffled, there's definitely more high frequencies left with the pot wired backwards.
http://el34world.com/Forum/index.php?PHPSESSID=t0jqfglpbmbso0kq3b4hedmta2&action=dlattach;topic=17045.0;attach=43112;image

[Ed_Chambley]

Brad,
I have tested all of these and more.  Never found a Master other than the JCM 800 that I thought was very good just needed.  I do add a cut control as was mentioned when using the LARMAR Master.  To me master volumes are only good to drop the sweet spot a little, after that the amp sounds anemic.


If it is cathode bias, should try the Samamp design.  He connects to the ground side of the cathode resistor a lead wire to a 4 position switch, but you can use whatever you wish.


From the switch, position 1 he runs a string of 2, 4 watt bulbs.  Second position adds 2 more for a total of 4 and position 3 takes it way down and adds 2 more 7 watt bulbs.  I have done this on many amps now and is by far my favorite wattage reduction as the light bulbs have the feel of tubes and actually compress.


I used to drill the chassis, but now in combos I simply drill a small hole and put a rubber grommet.  The bulbs I string down the inside of the cabinet.  This gives me light inside the cab when I play.  Don't use red tho, looks too evil.  So easy to try.


Here is a link to the bulb string I use.
https://www.1000bulbs.com/product/86872/SOCK-801912.html?gclid=CPWw6f2P49QCFdgLgQodaM0AuA


I have tried VVR, master volumes, but this doesn't change any plate voltages, just limits the cathode.  If you play very lightly, the bulbs glow and if you hit it hard they get brighter.  I know you play a lot of slide and this beats the snot out of a Ross Style Effect Compressor.  I have a PP 6l6GC Pro Tweed Build, the older version with lower voltage and the 6K Primary/8 ohms I just installed a Warehouse Veteran (great speaker and what they say is true about the smother out mid hump).  Wide open it is just over 28 watts, first switch puts it at 18 watt, second about 11 and third 2 watts.


You will have to play with the amount of bulbs and bulb wattage to get exactly what you want, but IMO for cathode bias this is king.  I even installed a fixed, cathode bias switch on my 73 Super Reverb, the modded one so I could do this.  This still maintains a big bottle sound.


Just my 2¢


Finally, I will mention if you have room, I know you are handy with construction.  A dual wall, dual door room in the back corner of a garage.  I can be as small as 4 x 4 x 4.  You can mic your cab back to monitors, headphones or most of the time I just open the door a little and crank that baby.  I built mine with egg crates between the inner and outer sheetrock and put some sound absorption foam which is pricy, but I helped a friend build one and we hung movers quilts in his.


To me, this is the real solution simply because you get a true cranked amp tone because it is cranked.

[punkykatt]

Ed, do i have this right. One string will have 2 bulbs, the second string will have 4 bulbs and the third string will have 6 bulbs? Thanks

[Ed_Chambley]

Ed, do i have this right. One string will have 2 bulbs, the second string will have 4 bulbs and the third string will have 6 bulbs? Thanks

Sort of.  A string of 6 bulbs.  first position turns on 2, second position adds 2 more, for a total of 4 and third position adds 2 more.  The first 2 are the first wattage reduction position.  You wire the switch on-on-on.


Works on any power tube, but El84's are fiddly.

[punkykatt]

thanks, you would have to use a  four  position progressive switch correct?

[Ed_Chambley]

thanks, you would have to use a  four  position progressive switch correct?

Yes, this is correct. But it is much easier and a simple switch will do.  I should have attached this in the first place.  Keep in mind if you use this you must rearrange the wiring or remove it if you sell the amp.  Plus I have found 6 bulbs to work best all around and change wattage bulbs to get the exact volume I want at each position.


In smaller amps 3 positions usually work fine.

[punkykatt]

Thanks Ed, a picture is worth 1k words.

[kagliostro]

Thanks for the link ED

Something like in the VOX AC30CC2 (look at R11 & R12)

but the use of lamp is different from the use of swappable resistors because the lamp vary the resistence during the play



Franco

[Ed_Chambley]

Yea K, very similar approach. I have seem the VOX and tried this method. A few builds I have use a 5 watt, 5k pot. I like to use one to get the correct bias and if I have room, I will leave it for tube swaps.


The bulbs work great as it just varies resistance as you say, but different bulbs "feel' different. Incondescent bulbs some feel will not be available in the near future, but I think these smaller ones will be. Thing is folurescent works good too.


LCD, not so much even the dimming type. If having a bulb tied to the cathode concerns, you can actually use a tube with low Rp, but it takes a lot more work to get to reduce the wattage on the attack. Usually you will get a lot of sag, but also get a lot of compression.


This is not a good mod for a high gain amp, only an amp for Blues type stuff and clean too. It is definitely for a spongy feel.


Check out TXBA.com Anthony gives lessons on the site and uses one of the amps. He also does a demo for the amp.


It is one of those things you do have to fiddle with. I simply work out my first half watt first as this is what I want at position one. The next two switch positions work best using less bulbs of higer wattage. Keeping in mind the more the bulb lights, the more resistance so getting them to burn fairly bright at idle helps. Less sag this way, but you will burn them out, so it is something of trial and error.

[kagliostro]

Thanks for the info ED 

Franco

[dbishopbliss]

I wonder why version C isn't used more often? It looks so easy, but isn't there any disadvantage? It obviously affects the gain of the phase inverter stage, but is that bad? I tried this version on my small Vox built (top boost channel into LTP phase inverter and push/pull power amp with a ecc99) and liked it better than the typical LarMar. I started with the LarMar (250k stereo pot and 1M8 safety resistors), and when I swapped the wires, I left the resistors in place, which go from input (wiper) to ground now (ground, not bias - it's a cathode biased amp!). Which means that the output tubes "see" 220k, when the MV is fully clockwise, rising to 250k when it's turned down.
The sound stays intact better at lower settings. If the MV is set to around 9 o'clock, the sound with the LarMar is quite muffled, there's definitely more high frequencies left with the pot wired backwards.
http://el34world.com/Forum/index.php?PHPSESSID=t0jqfglpbmbso0kq3b4hedmta2&action=dlattach;topic=17045.0;attach=43112;image

I have been considering implementing a Version C recently as well but I'm not sure I understand... It looks to me like the 250K pot is replacing the grid leak resistors. Assuming I use the original circuit (not the one with the 220K resistors in place that roseblood11 describes), does this mean that the grid leak values will change as you adjust the volume?

Also, this seems to be the same MV that Rob Robinette describes as the Frondelli Master Volume. Correct?

[Ed_Chambley]

I wonder why version C isn't used more often? It looks so easy, but isn't there any disadvantage? It obviously affects the gain of the phase inverter stage, but is that bad? I tried this version on my small Vox built (top boost channel into LTP phase inverter and push/pull power amp with a ecc99) and liked it better than the typical LarMar. I started with the LarMar (250k stereo pot and 1M8 safety resistors), and when I swapped the wires, I left the resistors in place, which go from input (wiper) to ground now (ground, not bias - it's a cathode biased amp!). Which means that the output tubes "see" 220k, when the MV is fully clockwise, rising to 250k when it's turned down.
The sound stays intact better at lower settings. If the MV is set to around 9 o'clock, the sound with the LarMar is quite muffled, there's definitely more high frequencies left with the pot wired backwards.
http://el34world.com/Forum/index.php?PHPSESSID=t0jqfglpbmbso0kq3b4hedmta2&action=dlattach;topic=17045.0;attach=43112;image

I have been considering implementing a Version C recently as well but I'm not sure I understand... It looks to me like the 250K pot is replacing the grid leak resistors. Assuming I use the original circuit (not the one with the 220K resistors in place that roseblood11 describes), does this mean that the grid leak values will change as you adjust the volume?

Also, this seems to be the same MV that Rob Robinette describes as the Frondelli Master Volume. Correct?

Yes, the grid leak resistors become adjustable and this is the issue.  Amps usually will sound fine with this type of master volume when the pots read above 100K.  You have not cut a lot of volume at 100K, but it does help.


For instance, I still have a Marshall Super Lead, just like EVH's Vanhalen 1 amp.  Smaller OT and Syvania Power Tubes.  Great sounding amp with a wonderful tone no matter the volume, but with a pre master it thins out.  Using the LARMAR master, dual 250K pots and 2.2m resistors I can get this amp in its wheelhouse at the same volume as a 40 watt amp.


Still, a 40 watt amp is fairly loud.


I just finished a 4, 10" cab with Warehouse Speakers, the American 10 ceramics.  These are fairly cheap at $50 each and a total of 80 Watts.  The nice thing is they are 93db and when pushed have a lot of midrange like a Greenback.  With this and the 100 watt Marshall, I can actually use it again, but it is still fairly loud.


It is true that volume doubles every 3db I suppose, at least this a "rule of thumb" some say.  What I am suggesting is if a master volume is needed sometimes considering other things in conjunction with the Master will make a for the best overall results.  Least I think so.

[dbishopbliss]

Yes, the grid leak resistors become adjustable and this is the issue.  Amps usually will sound fine with this type of master volume when the pots read above 100K.  You have not cut a lot of volume at 100K, but it does help.

My amp, Traynor YBA-1, has 68K grid leak resistors.  If I put a 100K pot in there, does that mean that if I turned it all the way down that the grid leak values would be zero? Isn't that a bad thing?

[sluckey]

If I put a 100K pot in there, does that mean that if I turned it all the way down that the grid leak values would be zero? Isn't that a bad thing?

Talking about type C, right? The grid leaks will always be 100K.

[dbishopbliss]

I need to pull out a pot and my ohm meter and see how these things work. 


I raised the question in another thread about changing the grid leaks to the "Marshall" value of 220K and the consensus seemed to be don't bother. I assume changing from 68K to 100K will be no problem.

[Ed_Chambley]

Oops, sorry! Looking at the wrong thing. C version at the top. Just revised a 1987 Marshall LARMAR to version C. In this amp it reduces the highs, but there is a treble control.


Don't see much difference, but I could probably get it working just fine. Still the same problem. Seems when you cut signal after the PI you lose highs very similar to a long cable run. Variable high pass for sure.


I guess it simply depends on how much signal you are willing to dump. To me it seems the pre PI master does the job best if you want to cut a lot of volume, which is what I always use on practice amps.

[dbishopbliss]

The 100K dual pot I have is not very balanced. That is when I measure across the different wipers there is a difference. A couple of questions...

• Should I just try out Version C/Frondelli MV with the pot I have and not worry about it?
• Should I buy a few Alpha 100K dual gang pots ($3.50) and pick the one that tracks most closely?
• Should I buy a PEC pot ($33) and hope it tracks more closely?
• Should I build a switch based that would use resistors. Not as granular control, but I'm a set and forget type so once I find the level I like I don't change very often. Anyone know where I could get a dual rotary switch with 6 to 12 poles?

[pompeiisneaks]

I don't know how much that matters, unless you've got a circuit that specifically has a PI balance pot, all PI's are somewhat unbalanced and that's good for guitar amp drive/distortion, adding a slight amount more or less balance to the PI shouldn't change a whole lot. 

Or at least that's my understanding of it. 

I mean if the dual pot reads out of spec then just replace it for sure.  but a 94k and 102k for either sides shouldn't matter.

~Phil

[dude]

Any preference as to which sounds best? (Probably splitting hairs.)

Type I (B) is also what KOC prefers for maintaining -bias in the event of a wiper failure but with the 2 x 2M2R's across the pots in the LarMar why bother with another pair of coupling caps? Saves space on the eyelet/turret board.

Or another way, wire the MV dual pots backwards, wiper to PI coupling caps?

Any sound change doing that?


              Brad     

Edit; added (B) after type 1 for clarity. Type 2, LarMar is A.

What does the "x and o" on the three way M/V schematic that you posted mean? Sorry for my ignorance, I've never seen these marking on a schematic?


al

[TIMBO]

Hey dude, (I've always wanted to say that  )
The x & o are there to denoted wiring connections, the "grounded end" that being the "O"

[dude]

Hey, my kids call me dude after I dressed up for a Halloween Party as Lebowski. Ha, all I could think of at the time.


al   

[Ed_Chambley]

The 100K dual pot I have is not very balanced. That is when I measure across the different wipers there is a difference. A couple of questions...

• Should I just try out Version C/Frondelli MV with the pot I have and not worry about it?
• Should I buy a few Alpha 100K dual gang pots ($3.50) and picddk the one that tracks most closely?
• Should I buy a PEC pot ($33) and hope it tracks more closely?
• Should I build a switch based that would use resistors. Not as granular control, but I'm a set and forget type so once I find the level I like I don't change very often. Anyone know where I could get a dual rotary switch with 6 to 12 poles?

Usually people find an area on a master they use often and Tubenit for one will balance a dual pot with a resistor to work best in this area.


I have seen dual 1 meg alpha pots that are too far apart and you can hear the imbalance. Some imbalance in a guitar amp is not really a big deal, but you wouldn't install a 220k and a 180k would you?


I use PEC or check with Steve at apexjr.com as he often has old AB or clerostat pots. Also the old audio taper I prefer. Ramps up a little slower, 10 percent.


The 100k dual in a old better quality pot should be fairly easy to find. I have one amp with 2 single pots so I could actually hear the imbalance. I prefer balanced as you tend to start losing punch when you get too imbalanced.


Course everyone is different. Just sharing my experience. Truthfully I think they are a necessary evil. Even 15 watts is loud, but so is a Champ with a efficient 10.