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Post by Magic Dragon on May 1, 2023 18:49:10 GMT -7
I wonder if any of the technical minded folks out there have some insight into the newer PPI Master Volume that is being implemented in recent Dr. Z amps. The most common PPI master I see used, particularly in amps with no negative feedback, is the Trainwreck Type-2/Larmar.
My Monza was sent back to the the factory and had a textbook Larmar PPIMV installed with the grid-leaks removed and 2.2M safety resistors tagged on the pots in parallel.
In looking at photos of the layouts of the Maz18 MKII and Jetta, I'm noticing that the PPIMV appears to be a Type2/Larmar but with the stock grid leaks left in place and no parallel safety resistors.
Any thoughts on this approach vs the straight Larmar that was used previously by the factory?
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Post by Chilly Gibbons (Todd T.) on May 2, 2023 3:23:26 GMT -7
I’m going to say “Ancient Dr Z Secret…”. Now if that doesn’t show my age, I don’t what does. 🤟
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Post by scottyc13 on May 2, 2023 3:37:42 GMT -7
I’ve tried the Type 2/ Larmar with a couple of my amps and it didn’t sound very good. But those two amps had fixed bias. I recall Dr Z mentioning that his PPIMV worked much better with cathode biased power tube designs. Perhaps this is where the difference is.
I’ve just bought a Carmen Ghia and will most likely send it in to have the PPIMV installed.
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Post by Don A on May 2, 2023 7:07:03 GMT -7
I've had 4 Dr. Z amps, all with a PPIMV and it was implemented slightly differently in each amp- fine tuned to the circuit's needs.
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Post by pcns on May 2, 2023 7:15:10 GMT -7
I've had 4 Dr. Z amps, all with a PPIMV and it was implemented slightly differently in each amp- fine tuned to the circuit's needs. I think this is an important point. Dr Z designs each of his amps himself and does the engineering and design and prototyping. I am sure he tailors each circuit to optimize the tonal goals for the amp.
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Post by Magic Dragon on May 2, 2023 9:17:41 GMT -7
Interesting input guys. I own 4 Z amps myself but only two have master volumes: The aforementioned Monza and a 2015 Maz18 MKI. I don't own a lot of amps with PPI master volumes so it's a subject area I am less familiar with in my years of working on amps. I installed a cross line in my Super Reverb years ago but keep it switched out of the circuit unless I really need to wind it up and maintain a reasonable volume. From the photos I've found online, many of the newer Dr. Z amps that are cathode biased with no negative feedback have the master implementation described in my original post: a Type 2 with the paralleled grid-leaks left in place. Cocktail napkin math doesn't really give a quick indication as to why this choice was made so I was hoping someone here might have the easy-button answer. I have been considering sending my Maz 18 and Ghia in for MV updates but was trying to understand the technical aspects of the specific MVs being implemented. The Ghia has negative feedback and that can be problem with some of the PPIMV implementations. My Maz 18 was built with 470K grid leaks vs the 220K that the MKII has, so it will have to be modified beyond just adding the dual-gang pot and tweaking the snubber voicing. Dr. Z's update prices are a bargain so, while I can do the work myself, it doesn't make a lot of sense to do so. I'll keep researching the PPIMV technical rabbit hole to get comfortable with the specifics of the design.
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Post by scottyc13 on May 2, 2023 9:39:18 GMT -7
Interesting input guys. I own 4 Z amps myself but only two have master volumes: The aforementioned Monza and a 2015 Maz18 MKI. I don't own a lot of amps with PPI master volumes so it's a subject area I am less familiar with in my years of working on amps. I installed a cross line in my Super Reverb years ago but keep it switched out of the circuit unless I really need to wind it up and maintain a reasonable volume. From the photos I've found online, many of the newer Dr. Z amps that are cathode biased with no negative feedback have the master implementation described in my original post: a Type 2 with the paralleled grid-leaks left in place. Cocktail napkin math doesn't really give a quick indication as to why this choice was made so I was hoping someone here might have the easy-button answer. I have been considering sending my Maz 18 and Ghia in for MV updates but was trying to understand the technical aspects of the specific MVs being implemented. The Ghia has negative feedback and that can be problem with some of the PPIMV implementations. My Maz 18 was built with 470K grid leaks vs the 220K that the MKII has, so it will have to be modified beyond just adding the dual-gang pot and tweaking the snubber voicing. Dr. Z's update prices are a bargain so, while I can do the work myself, it doesn't make a lot of sense to do so. I'll keep researching the PPIMV technical rabbit hole to get comfortable with the specifics of the design. I think this is key. The Trainwreck MV designs were originally set up for Marshall amps per the Trainwreck pages. As you know Marshall’s had a lot of NFB and were fixed bias, solid state rectifier amps. I’ve only tried this design in fixed bias 6V6 designs with 5AR4 rectifiers with moderate NFB. I found it a bit harsh so I removed it. Each circuit probably requires a lot of tweaking and experimenting to dial it in.
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Post by hammonated on Dec 4, 2023 20:47:53 GMT -7
If I were you, and you wanted to try it yourself, and you don’t have a warranty to worry about, start with a crossline (#3). I find they work better in cathode biased amps in my experience. But use 250k rather than the 1meg pot the Trainwreck pages have. The crossline is extremely noninvasive. If you don’t like it,try a Lar Mar with 250k pot and 1.8 to 2.2 meg resistors. Won’t really affect tone. The resistors are for safety to maintain bias if the pot goes bad. You can twist the leads to and from the pot or use shielded cable. Both type of MV will be removed from the circuit when cranked. You may need try a different pot value or taper depending on your liking. I put a Lar Mar in my home built (ao35 Ghia)and it works well but gets a bit fizzy at low master volume settings when overdriven. Probably an el84 thing. Different pairs will cause the fizz to increase or decrease. But it’s always still there a bit at low master volumes with the regular volume overdriven. I’m going to try the crossline(#3) out of curiosity. I should’ve started with that one. It’s my usual starting point because it’s very easy to install and remove. I don’t hate the Lar Mar, tho. Really, I love the Ghia for its cleans and how well it works with pedals,so..Have fun! Edit: I tried the crossline in my Ghia and it’s WAY better than the Lar Mar! Glad I tried it. Much more high end is retained when the MV is turned down. Just a lot more like it’s true self. I used a 250kA pot. I’m always starting with the crossline in cathode biased amps from now on. They just seem happier with it than a #2 type.
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Post by Magic Dragon on Jan 22, 2024 9:49:33 GMT -7
If I were you, and you wanted to try it yourself, and you don’t have a warranty to worry about, start with a crossline (#3). I find they work better in cathode biased amps in my experience. But use 250k rather than the 1meg pot the Trainwreck pages have. The crossline is extremely noninvasive. If you don’t like it,try a Lar Mar with 250k pot and 1.8 to 2.2 meg resistors. Won’t really affect tone. The resistors are for safety to maintain bias if the pot goes bad. You can twist the leads to and from the pot or use shielded cable. Both type of MV will be removed from the circuit when cranked. You may need try a different pot value or taper depending on your liking. I put a Lar Mar in my home built (ao35 Ghia)and it works well but gets a bit fizzy at low master volume settings when overdriven. Probably an el84 thing. Different pairs will cause the fizz to increase or decrease. But it’s always still there a bit at low master volumes with the regular volume overdriven. I’m going to try the crossline(#3) out of curiosity. I should’ve started with that one. It’s my usual starting point because it’s very easy to install and remove. I don’t hate the Lar Mar, tho. Really, I love the Ghia for its cleans and how well it works with pedals,so..Have fun! Edit: I tried the crossline in my Ghia and it’s WAY better than the Lar Mar! Glad I tried it. Much more high end is retained when the MV is turned down. Just a lot more like it’s true self. I used a 250kA pot. I’m always starting with the crossline in cathode biased amps from now on. They just seem happier with it than a #2 type. I actually installed a crossline in my Z-28 some time ago and have been very happy with it. I don't care for the Larmar with fixed bias amps. I used a Fender "no-load" 250K detent pot so when the MV is maxed it is physically switched out of the circuit.
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