VMP2 mods

[luckybastard77]

I’ve been maximizing gear I already own and one of those is a Peavey VMP2. I’ve gone through the unit and have replaced all of the polyester coupling caps with polypropylene and replaced 180pf ceramic hf caps with polystyrene. These are all things that Jim Williams suggested. I’ve also swapped the output transformers with Edcor WSM’s.

This has led to a unit that sounds noticeably better in every way. I have owned a Hamptone HVTP2 before selling it to buy an engagement ring years ago and the unit as it stands now is every bit as good as that one- and I think the Hamptone takes a backseat to no tube pre in any price range.

Now the questions I have are concerning bits and pieces of mod suggestions I didn’t understand. Jim Williams has said the following

“ They do improve with the Jensen input transformer, one must be aware that the grid load resistor is set to 470k ohms, that needs to be changed to 150k ohms to match up to the Jensen.”

Does this also apply to the Reichenbach input tranny it comes with? I like the understated vintage vibe it gives and don’t want to change it out.

Also, I read something Jim said about taking out some high rolloff caps to flatten the response.

“ If you don't mind, do you know why the first tube stage rolls off the top end with a 100 pf cap from the plate to ground? The last tube stage/driver also has a HF lift using three 10 pf ceramic caps across a 2.2 meg resistor. Seems like an emphasis network to lower noise but the boost at the end would wash out any noise reduction gains.

FWIW, when I rework these I pull those caps out, seems fine and response is flat to 50k hz.”

Do I just remove these from the circuit without replacing them with anything?

 

[JohnRoberts]

Sorry I worked at Peavey for 15 years (last century) and did have some involvement with that specific SKU, so I may be a little biased.  :

I’ve been maximizing gear I already own and one of those is a Peavey VMP2. I’ve gone through the unit and have replaced all of the polyester coupling caps with polypropylene and replaced 180pf ceramic hf caps with polystyrene. These are all things that Jim Williams suggested. I’ve also swapped the output transformers with Edcor WSM’s.

I think Jim suggests that you send him money....  : You might be able to ask him personally over at geekslutz forum.

This has led to a unit that sounds noticeably better in every way.

cough....? If you have access to a decent test bench maybe you could publish some before and after data to quantify your "noticeable" circuit design/component selection improvements.

I have owned a Hamptone HVTP2 before selling it to buy an engagement ring years ago and the unit as it stands now is every bit as good as that one- and I think the Hamptone takes a backseat to no tube pre in any price range.

I hope you girlfriend appreciates your sacrifice.  8)

Now the questions I have are concerning bits and pieces of mod suggestions I didn’t understand. Jim Williams has said the following

“ They do improve with the Jensen input transformer, one must be aware that the grid load resistor is set to 470k ohms, that needs to be changed to 150k ohms to match up to the Jensen.”

The Jensen was more expensive ( we used a Jensen in the very first prototype). The Reichenbach transformer is a fraction of the cost and checked all the boxes (does not suck IMO).

Does this also apply to the Reichenbach input tranny it comes with? I like the understated vintage vibe it gives and don’t want to change it out.

Vintage from only decades ago? I have t-shirts older than that. 

Also, I read something Jim said about taking out some high rolloff caps to flatten the response.

“ If you don't mind, do you know why the first tube stage rolls off the top end with a 100 pf cap from the plate to ground? The last tube stage/driver also has a HF lift using three 10 pf ceramic caps across a 2.2 meg resistor. Seems like an emphasis network to lower noise but the boost at the end would wash out any noise reduction gains.

I do not know the minor circuit details. My involvement was mostly with big picture feature definition. It was my idea to have the gain knob go to 11.  8)

FWIW, when I rework these I pull those caps out, seems fine and response is flat to 50k hz.”

Some small caps in high Z circuits are used to provide RF rejection or support overall negative feedback stability. They rarely impact audio path linearity (speculation).

Do I just remove these from the circuit without replacing them with anything?

It's your unit... but you might void the warranty...   

That unit is just about old enough you might want to check it for tired electrolytic capacitors.

JR

 

[luckybastard77]

Thanks for your response, John.  I’m not exaggerating when I say that I’ve read pretty much everything you’ve said about this unit on here and Gearslutz. You guys were ahead of your time with the VMP2, imo. The circuit is fantastic. The only thing I’ve done to it so far is upgrade or swap parts out for more clarity. The polypropylene coupling caps are considered an upgrade, the polystyrene caps replaced less than ideal ceramic caps used in the eq circuit and it’s pretty common knowledge that the output transformers are unusable, so I switched them with well-regarded and modestly priced Edcors. These mods bring the Peavey into the heavyweight class, IMO- especially after I dropped the NOS Telefunken badged Siemens into the first two tube stages; GE NOS in the third along with the NOS Phillips 12AT7’s.

These things are so cheap and easy to work on that I want to buy another one and try to make a more vibey unit with PIO and tantalum caps with tubes that give it a thicker tone.

Also, thank you for the unbalanced outs. They make this unit even more versatile than it already is.

 

[pucho812]

you are going to have to define noticeably better. if you can hear it you can measure it.  If it measures right and sounds like shit, you measured the wrong thing. 

 

[luckybastard77]

you are going to have to define noticeably better. if you can hear it you can measure it.  If it measures right and sounds like sh*t, you measured the wrong thing.

I don’t have any bench testing equipment. I just have my ears that have been around good gear since the time I started recording almost 20 years ago.  I don’t think it’s controversial to think changing 20+year old polyester caps with new polypropylene and swapping out a known crappy output transformer for a decent one improves the sound before dropping in $500 worth of NOS tubes. Ymmv.

 

[JohnRoberts]

Thanks for your response, John.  I’m not exaggerating when I say that I’ve read pretty much everything you’ve said about this unit on here and Gearslutz. You guys were ahead of your time with the VMP2, imo. The circuit is fantastic.

The VMP was more of a throw back to a classic design, along with the VCL tube comp/limiter. Jack Sondermeyer (RIP) the senior analog design engineer knew his way around tubes (me not so much).

The only thing I’ve done to it so far is upgrade or swap parts out for more clarity. The polypropylene coupling caps are considered an upgrade, the polystyrene caps replaced less than ideal ceramic caps used in the eq circuit and it’s pretty common knowledge that the output transformers are unusable, so I switched them with well-regarded and modestly priced Edcors.

Polypropylene are marginally better than polyester but not significant IMO except for passive loudspeaker crossovers where DF can matter in higher current applications.  I used truckloads of polystyrene in my hand soldered kit business back in the 70s but at Peavey polystyrene caps do not survive the wave soldering and other high volume production processes.

OK you made me look at a schematic and the caps used in the EQ have "MY" in their part number designation suggesting polyester film (Mylar).  If it makes you feel better to upgrade those, enjoy.

For my daily dose of TMI it was also my idea to limit the EQ boost/cut to only around 6dB to make it harder to get bad sound from it.

These mods bring the Peavey into the heavyweight class, IMO- especially after I dropped the NOS Telefunken badged Siemens into the first two tube stages; GE NOS in the third along with the NOS Phillips 12AT7’s.

These things are so cheap and easy to work on that I want to buy another one and try to make a more vibey unit with PIO and tantalum caps with tubes that give it a thicker tone.

?

Also, thank you for the unbalanced outs. They make this unit even more versatile than it already is.

You are welcome, that was also my idea to provide an unbalanced direct output completely bypassing the output transformer (that shouldn't really be needed for a modern studio interface). It was impossible to bypass the input transformer. 

JR

PS: I also had to design an external pad for the service department to help all the Peavey customers who called because they tried to feed their hot VMP output into the very popular Mackie 8bus input console, overloading it.  :

 

[JohnRoberts]

I don’t have any bench testing equipment. I just have my ears that have been around good gear since the time I started recording almost 20 years ago.  I don’t think it’s controversial to think changing 20+year old polyester caps with new polypropylene and swapping out a known crappy output transformer for a decent one improves the sound before dropping in $500 worth of NOS tubes. Ymmv.

Film caps generally do not suffer age related deterioration.

After 20 years there may be some marginal electrolytic caps in PS etc.

JR

 

[ruffrecords]

I don’t have any bench testing equipment. I just have my ears that have been around good gear since the time I started recording almost 20 years ago.  I don’t think it’s controversial to think changing 20+year old polyester caps with new polypropylene and swapping out a known crappy output transformer for a decent one improves the sound before dropping in $500 worth of NOS tubes. Ymmv.

Strange, you think it necessary to change a 20 year old capacitor but then you pop in a tube that is over 50 years old.

Cheers

Ian

 

[Rob Flinn]

One would never change the Mullard mustard caps in a vintage Neve module or a vintage guitar amp.

 

[pucho812]

I don’t have any bench testing equipment. I just have my ears that have been around good gear since the time I started recording almost 20 years ago.  I don’t think it’s controversial to think changing 20+year old polyester caps with new polypropylene and swapping out a known crappy output transformer for a decent one improves the sound before dropping in $500 worth of NOS tubes. Ymmv.

I never said it was controversial. FWIW I owned a vmp2 I never felt the need to mod or upgrade anything in it.  Changing one part of the same value to another part of the same value is more an upgrade or downgrade then it is a mod.  the circuit will still behave the same.  A mod would have the circuit behave differently.  As for the NOS tubes, if that's your bag that's cool but note how every tube of the same type and even same production batches will have a variance in sound.  Some better, Some worse.  proceed with caution.  And lastly unless you just have the unit to look at and tinker with, I assume you have a daw and you can easily take test and measurements with the daw, I have subbed a daw on many occasions when my AP is at home and I am in the field.
But all good. the VMP2 stock and the compressor vcl2? are quite good value for the money.

 

[john12ax7]

The changes mentioned are reasonable imo.  Polypropylene is a better dielectric than polyester,  and polystyrene is generally better than ceramic (C0G is very good).  Most likely the changes brought the overall distortion level down.

Capacitor quality has also gotten better over the years,  where you could argue the opposite for tubes. So new caps  old tubes is reasonable too.  NOS  can be a mixed bag though,  as a lot of the good stuff has been picked through.

For the input transformer question,  generally there is an optimum load for top performance , best to start with manufacturer datasheet suggestion,  which is probably where the 150k came from.  No need to change the resistor if you don't change the transformer, as it is probably already optimized.

For the other caps I don't know the design to comment. Sometimes parts are added to assure performance in unknown environments.  So something like an RF filter is good practice, but may not always be necessary.

 

[Winston OBoogie]

... The Jensen was more expensive ( we used a Jensen in the very first prototype). The Reichenbach transformer is a fraction of the cost and checked all the boxes (does not suck IMO). 

Depending on which Reichenbach is in there, it may actually be *exactly* the same as the Jensen equivalent.

Reichenbach made the first transformers that were sold by Jensen and a lot of the early Jensen's were actually designed by Ed Reichenbach.
Until around 1998, you could buy these from Reichenbach Engineering  for a fraction of what the Jensen  cost until Jensen issued a cease and desist.  Reichenbach closed down shortly thereafter and the assets of R.E. were acquired by Tom Reichenbach (Ed's son) and became Cinemag. 

History lesson over

 

[luckybastard77]

Depending on which Reichenbach is in there, it may actually be *exactly* the same as the Jensen equivalent.

Reichenbach made the first transformers that were sold by Jensen and a lot of the early Jensen's were actually designed by Ed Reichenbach.
Until around 1998, you could buy these from Reichenbach Engineering  for a fraction of what the Jensen  cost until Jensen issued a cease and desist.  Reichenbach closed down shortly thereafter and the assets of R.E. were acquired by Tom Reichenbach (Ed's son) and became Cinemag. 

History lesson over

It’s the Reichenbach RE-115k-e which I think is the equivalent of the the Jensen JE-115k-e, the predecessor to the JT-115k-e. It sounds really good.

 

[luckybastard77]

For the input transformer question,  generally there is an optimum load for top performance , best to start with manufacturer datasheet suggestion,  which is probably where the 150k came from.  No need to change the resistor if you don't change the transformer, as it is probably already optimized.

For the other caps I don't know the design to comment. Sometimes parts are added to assure performance in unknown environments.  So something like an RF filter is good practice, but may not always be necessary.

Does this schematic of the circuit give a better idea?  Thanks so much for your help.

 

[JohnRoberts]

It’s the Reichenbach RE-115k-e which I think is the equivalent of the the Jensen JT-115k-e. It sounds really good.

Like I said the Reichenbach input transformer doesn't suck...

Maybe tomorrow I'll revisit the capacitor advice.... or not.

JR

 

[JohnRoberts]

I should let this go and try not to debate subjective impressions on the WWW, but I have a personal connection to this SKU and first wrote about capacitors in my "audio mythology" column back in the 80s.

The changes mentioned are reasonable imo.  Polypropylene is a better dielectric than polyester,

True, but a matter of degrees. Polyester is good, polypropylene slightly better.

I've shared this story before, back last century while working at Peavey I once signed an ECN (engineering change notice) for a different engineering group than I worked in. ECNs that involved a cost increase had to be signed (approved) by a director level engineering manager. An  engineer I knew working in the transducer (mics and speakers) group wanted to upgrade the capacitor used in a passive loudspeaker crossover to polypropylene. This was something like a $0.20 cost increase, but the transducer engineer's director refused to sign the ECN because he knew how tight our boss was, and didn't want to be called on the carpet for  increasing cost.

I didn't expect this upgrade to make a huge audible difference for the majority of Peavey customers  :, but the transducer engineer and I both knew it could make a difference in that application.  I was willing to piss away some of my scant political capital on this ECN. I signed it because I could, and was willing to defend it (BTW I was never asked to explain it ).

  and polystyrene is generally better than ceramic (C0G is very good).

IMO polystyrene is a better dielectric than both polyester and polypro. Polystyrene was both good and cheap, while cheap but good. The only problem and it was a real problem is that polystyrene is fragile... Not only did it have trouble with wave soldering temperatures, forget about SMD reflow. I even had one entire production run (before Peavey) trashed by a business partner who tried to wash off a PCB full of polystyrene caps with a high pressure air hose... he ended up forcing water inside the caps and trashed that entire production run of PCB. We had to replace all the polystyrene caps.
---
Ceramic is not one thing but a number of different dielectrics optimized for different things. Some are optimized for volumetric efficiency (a lot of C in a tiny package), some for benign breakdown characteristics from voltage overload for use across mains supplies, etc.

COG is another name for NPO and a very linear dielectric good for audio (or any) applications. In the old days they were used for things like stabilizing crystals and the like. Early this century I had difficulty finding SMD film capacitors for use in filter circuits that would survive contract manufacturing... I specified a nice new film SMD cap sold by Panasonic(?) that on paper would survive SMD reflow temperatures.... bzzzt, they didn't survive. The caps physically deformed (melted) and experienced parameter shift if not complete failure.  These days I could just pop in some NPO/COG ceramic SMD caps but they were not widely available a couple decades ago.

Most likely the changes brought the overall distortion level down.

While better is always better, I am not so sure about even measurable, let alone audible reductions in distortion from that swap. I repeat maybe check for any tired electrolytic caps.

Capacitor quality has also gotten better over the years,

Not as much as you might expect.... Instead of new dielectrics emerging I see some old one falling out of favor due to cost , or manufacturing robustness.

The one area where I have seen a lot of development is in aluminum electrolytic capacitors. There the improvement effort appears to be on two major fronts. #1 size/cost... Electrolytic caps have been shrinking for several decades, smaller also translates to cheaper for a win-win in business. #2 I have seen vast improvement in lower ESR for use in switching power supplies. These improvements are not without glitches...

I once had to black ball a new series aluminum electrolytic caps that were so noisy in a phantom voltage blocking application the factory line workers gonged them. Alternately I recall some of the early low ESR aluminum caps having the bad habit of failing short circuit (I didn't expect to see that again after quitting tantalums  ).

where you could argue the opposite for tubes.

I am not a tube guy, but they have been in commercial decline for a very long time. I recall the difficulty Peavey had trying to source decent tubes in production quantities for specialty guitar amps (the customer is always right).

So new caps  old tubes is reasonable too.

About the only thing possible.

  NOS  can be a mixed bag though,  as a lot of the good stuff has been picked through.

In this day of hucksterism I would be suspicious of any significant caches of NOS  tubes.

For the input transformer question,  generally there is an optimum load for top performance , best to start with manufacturer datasheet suggestion,  which is probably where the 150k came from.  No need to change the resistor if you don't change the transformer, as it is probably already optimized.

I am very confident that the VMP design was competently executed. 

For the other caps I don't know the design to comment. Sometimes parts are added to assure performance in unknown environments.  So something like an RF filter is good practice, but may not always be necessary.

Knowing what I know about Peavey's sharp pencil mentality I doubt there were any superfluous circuit details. If a part was in the design it was probably doing something useful.

JR

 

[Winston OBoogie]

It’s the Reichenbach RE-115k-e which I think is the equivalent of the the Jensen JE-115k-e 

Yes, it's exactly the same part as the Jensen.  In every way but the first prefix on the part number.

 

[JohnRoberts]

Yes, it's exactly the same part as the Jensen.  In every way but the first prefix on the part number.

and the cost....  8)

JR

 

[Winston OBoogie]

and the cost....  8)

JR

;D  Yes, that too of course,
Cheers 

 

[john12ax7]

Does this schematic of the circuit give a better idea?  Thanks so much for your help.

The 100pf cap is most likely there to assure stability at high gains.