VSP Labs Trans Mos Gold Series amp measurements

[mrwasabihead]

Greetings, I purchased a VSP Labs Gold Series Trans Mos amp a while back and luckily it's in pretty decent cosmetic and functional shape. I started looking for technical info on this unit, but like most, found little. At this point I'd like to mention a little about the designer of this amp - Juan Velazquez. Apparently Mr. Velazquez passed away last summer - his obituary can be found here: https://obits.mlive.com/us/obituaries/annarbor/name/juan-velazquez-obituary?id=52550447
Even though VSP Labs was located here in Ann Arbor, MI, where I currently live, I was surprised to find that at the time of his passing, Mr. Velazquez was living in Saline, MI, barely 10 minutes from my house. I wish I had known this long before this week when I found out. I almost certainly would have attempted to contact him. Not just to inquire about some of the VSP amp technical info that seems to be much needed, but to also give respect where respect is due. It's not often that audio engineers of note are found basically living right next door. I was saddened to read that Mr. Velazquez had passed, but remain grateful for the contribution he and his crew made to the pantheon of quality audio components we all enjoy. RIP.




As I mentioned, the VSP Trans Mos Gold Series (200W @ 8 Ohm) I have is in pretty good condition and I've read several posts from those with non working amps that have no idea about where DC offset, bias and the like, should be set once they do get their amps safely powered up. I've yet to find docs that specifically show or denote that they are for the Gold Series, but there is a bit of documentation online, and here in the AK archives, for the Trans Mos 150 (150W @ 8 Ohm) - some of which may transfer to the Gold Series as well. Having compared my amp to images of other Gold Series amp there also seems to be multiple revisions of this and the TM 150 amps - as is common for just about every amp out there. When I decided to check this amps functionality the first thing I did was power it up on a DBT - it passed. Then I checked the DC offset at the speaker terminals - and after about an hour of on time with no load, my amp measured:
[119VAC Supply]
Rt Ch: -164mV (Pos. lead to Pos/Neg to Neg)
Lt Ch: -111mV (Pos. lead to Pos/Neg to Neg)
The VSP TM150 Instruction manual states; "DC Output Offset: +/- 50mV or less, typical 5 - 10mV, internally adjustable." I've found no info yet about DC offset for the Gold Seris amp and don't have the bonifides to make assumptions about what it's offset should be for this amp. Any input and opinions would be appreciated.



There are only 2 trim pots per amp board in the amp section of any of the available TM150 schematics. There are 4 trim pots on most of the amp schematics, but I believe that two of the trim pots are on, and for, adjustments at the NE5532AN OpAmps on the input board - one trim pot pair per chip, per channel. [US Patent diagrgm cir. 1984] My input board also has a TL072CP, low-noise FET Input OpAmp - which may be part of the "T-Sense" (clip/mute) circuit. A circuit that exists on both versions of the TM amps but the TL072CP isn't on the TM150 schematics. One TM150 schematic shows an "RTS" (trip sense) variable resistor - so I believe that that is what the 5th trim pot on my TM GS input board may be for.



The two trim pots on the TM150 schematic's amp section are connected to the two Differential pair's emitters (2N4401 / 2N4403) on the amp boards.
There are 4 trim pots on each of my TM Gold Series' amp boards; The amp boards are PN: [L] 10-0255B1 / [R] 10-0258B1. I assume that two of the trim pots are for each of the differential pairs that also exist on the TM GS boards, but I'm not sure as yet what the other two are for.




It seemed safe to take the amp off of the DBT, so I did, and then I pulled each of the two 10A fuses that are each of the amp boards, one at a time, and measured current. The two fuses, when looking at the amp boards face on are: Left side Negative supply and Right side, Positive supply.
The current was measured after the amp had been on at least an hour;
Right Channel: Negative supply Fuse: 282mA Right Channel - Positive supply Fuse: 280mA
Left Channel: Negative supply Fuse: 351mA Left Channel - Positive supply Fuse: 351mA
These current readings settled down to these measurements within a few minutes, stabilized quickly, and remained stable and consistent.




I decided to hook the amp to a load and scope and run a signal through it. Even with my limited knowledge I'd consider the results encouraging. No odd artifacts or oscillations and a pretty balanced output. This scope is capable of displaying other measurements, which I should have initiated, but I just wanted to see what I'd get - DC and current measurements being what they are.




I figured it was OK to run program material (music) through the amp, which I did, and the results were fab. It sounds great. At moderate volume for about an hour the heat sinks are only just slightly, but evenly, warm. I believe that do much else would require me to seek the assistance of those that have a better idea than I do of if and how to proceed with any adjustments or service. With no specific TM Gold Series schcematics to go on I kind of feel comfortable leaving this amp the way it is, but at the same time it can obviously be risky leaving an amp built around 1983 to it's own designs.
I hope that not only will this thread and these measurements help anyone else working with a VSP Labs Trans Mos Gold Series amp, but also invites those interested in and experienced with working on quality amps with little documentation and a large fan bases, to offer their valued opinions. I'm really interested in knowing what people think in regard to dealing with an amp in this condition and of these circumstances. I just finished restoring a pair of Infinity Quantum 3 speakers which have been looking at this amp over my shoulder and drooling every since I took it off the shelf. Their favorite food, I'm told, are high current amps that'll laugh at a 2 Ohm load. I'm beginning to become worried that I'll come into the shop one morning and they'll have hooked themselves up while I was sleeping! Things are cool for now, but I look forward to any and all opinions, info and recommendations. I'm eager to get it back into service, which I'm sure, is something Juan Valezquez would be happy to hear.

 

[specialcase]

schematic for the transmos gold 200 seems to be a white whale. i’ve scoured the internet pretty hard and never seen one turn up. bit of theme that. there’s several threads scattered across diy audio, here, and a few other sites going back 20 years looking for info on the 200 and, particularly, a schematic. @hamrules had a post a year or two ago while he was going through one. if i recall correctly, he ran into some sort of roadblock. don’t know where that landed.

it’s a really good amp imo, great sound, and i doubt there’s a speaker load out there that can outmuscle it. maybe someone with documentation will come along. be nice to know the dc offset at least.

bummer to hear velazquez passed. vsp labs was located in ann arbor and i’m fairly certain i read somewhere he retired from wadia. makes sense he was right down the road from you.

 

[hamrules]

I moved on from it, I didn’t have what I needed to get the output assembly apart. I’d probably set the current as your left channel showed, if it was mine anyway.

 

[mrwasabihead]

schematic for the transmos gold 200 seems to be a white whale. i’ve scoured the internet pretty hard and never seen one turn up. bit of theme that. there’s several threads scattered across diy audio, here, and a few other sites going back 20 years looking for info on the 200 and, particularly, a schematic. @hamrules had a post a year or two ago while he was going through one. if i recall correctly, he ran into some sort of roadblock. don’t know where that landed.

it’s a really good amp imo, great sound, and i doubt there’s a speaker load out there that can outmuscle it. maybe someone with documentation will come along. be nice to know the dc offset at least.

bummer to hear velazquez passed. vsp labs was located in ann arbor and i’m fairly certain i read somewhere he retired from wadia. makes sense he was right down the road from you.

A "White whale" indeed, Sir. Arrr! But I'll do me best.

 

[mrwasabihead]

I moved on from it, I didn’t have what I needed to get the output assembly apart. I’d probably set the current as your left channel showed, if it was mine anyway.

I think I remember your thread and the trouble you were having getting the output transistors de-soldered from the double sided amp board. The pins on my amp's output transistors are connected with wires soldered to the pins. Must be an earlier board. Probably a bit easier than dealing with a double sided board, but a bit of a pain just the same. As part of "necessary" updating I'd like to replace the output's insulators - but I won't be doing anything until I have a better understanding of what's what. Thanks!

 

[mrwasabihead]

And now for a rather startling (to me) piece of information about Mr. Velazquez. About 2 1/2 years ago a friend informed me about an estate sale in,...you guessed it, Saline, MI. - where there was apparently a lot of electronics equipment. I was, I think, the first one there. There was quite a bit of audio and electronics equipment there indeed. It's there that I bought the VSP Labs amp outlined in this thread, along with some other things. Today I kind of wondered if Mr. Velazquez had a surviving spouse or children living in the area, and while I was looking up info, I found the address for the late Mr. Velazquez. Yes, you guessed it again - it was the same address that I had gone to when I bought this VSP Labs amp! This amp, and the other things I purchased, belonged to Juan Velazquez! You never know where the questions you may have will lead, and in this case, when all the pieces came together it was actually kinda impactfull mentally, and a little emotionally. I realize now that had I known of VSP Labs and Mr. Velazquez a little better at the time, my "estate sale" meanderings through all manner of his things at the sale would have been done much more purposefully. When I found the amp at the sale there was a home made wire "harness" connected to two of the main filter caps and sticking out of the side of the lid of the amp, and I thought, "what the heck was this guy thinking, and more so, what the heck was he doing with this amp?!" I purchased it, and then removed the make-shift harness when I got home. A DBT test was performed when I got home and the results were the same as is detailed above - but at that point I just popped it up on the shelf next to the other things that would need further attention - until the day I started this thread, almost three years later. Life is strange, bro, life is strange. (...or maybe it's just me ; )
My writing about Mr. Velazquez in relation to this amp my seem strange to some but I, personally, have a great deal of admiration for those more technically adept at electronics than myself, as well as those designers that have created some of the more "unique" products and methods that have since become a part of audio history. I'm not school or Armed Services trained in electronics and only know what I know by reading, doing, the kind help of friends, and those here on AK - many of whom are admirably adept indeed. For me, audio electronics servicing, repair and restoration has been a hobby that I've enjoyed immensely for about 13 years or so, and the more I learn the more I admire those who've invested so much time and effort to the craft and are also willing to share their time and experience with others.

 

[michigannick]

outstanding write up and effort!

 

[BuckRogers]

Today I purchased a set of Gold Edition amplifiers and the Straightwire II pre amp, the seller stated that he purchased them from Steve Eberbach son 7 yrs ago, I just got them home and I'm going to inspect them and clean them first.
I've heard in a Video with Steve Eberbach speaking that they used these amplifiers while DCM LOUDSPEAKERS was operating.
PS all 3 units are missing common stickers on the rear panel and no serial numbers are present.
Thanks for the write up!

 

[mrwasabihead]

I saw those for sale here in S. E Michigan.
I seriously thought about buying them but I've already got amps sitting setting not being used. Good luck with them. I hope they turn out to be in good shape! Let us know how things go.

 

[llwhtt]

Made in Ann Arbor, that's where DCM was originally. I still have my DCM QEDs I bought back in 80/81 timeframe, pun intended. Steve E. and Bob Waterstripe had a good thing going back then.

Craig

 

[mrwasabihead]

They did indeed. I had a pair back in the early 90's, and a tweeter went out - I called DCM and went out to their place by Ann Arbor airport, I showed them the bad tweeter and they handed me a brand new one....free!
That's my kind of audio company.

Made Ann Arbor, that's where DCM was originally. I still have my DCM QEDs I bought back in 80/81 timeframe, pun intended. Steve E. and Bob Waterstripe had a good thing going back then.

Craig

 

[llwhtt]

Philips tweeter?

 

[mrwasabihead]

Not sure. The speakers were the original time windows - about 4.5" feet high, with the semi oval wood caps at the top and bottoms.

Philips tweeter?

 

[llwhtt]

Small dome with a plastic cap over the dome?

 

[mrwasabihead]

I only remember they were square, ferro- fluid filled type tweeters. I think the ones in the timeframe (600) series were the same. I restored a pair of those several years ago that had similar tweeters.

 

[BuckRogers]

I also have 2 Gold Edition amplifiers but they are not consumer editions, they have different Capacitors, Dual transformers a they lack any rear badging and serial numbers, it was reported to me by the seller that he had purchased them from Steve Eberbach son and they were his father's units.
The transformers look like the ones that are in the TM150.
I also have the Straightwire II preamp but the buttons on the panel need attention.

 

[mrwasabihead]

Yeah, I noticed the dual transformers in the earlier pics. I wish we could find someone that worked at VSP that could shed light on some of the going's on at the company. Like most companies I'm sure there were lots of iterations of all their amps that were not meant for sale but where instead gap versions that tested new boards, designs and such. If you're in the Ann Arbor area I'll PM you with my number. I've got a shop here at home and would be happy to assist you with your stuff as much as I can. My amp works really well and you can get measurements off of it if you need to.
Mark

 

[BuckRogers]

Yeah, I noticed the dual transformers in the earlier pics. I wish we could find someone that worked at VSP that could shed light on some of the going's on at the company. Like most companies I'm sure there were lots of iterations of all their amps that were not meant for sale but where instead gap versions that tested new boards, designs and such. If you're in the Ann Arbor area I'll PM you with my number. I've got a shop here at home and would be happy to assist you with your stuff as much as I can. My amp works really well and you can get measurements off of it if you need to.
Mark

I'm going to replace the fuse holder and see if the 2nd amp fires up, I've been auditioning the 1st amp all weekend.

 

[Jeanpaul56]

Today I purchased a set of Gold Edition amplifiers and the Straightwire II pre amp, the seller stated that he purchased them from Steve Eberbach son 7 yrs ago, I just got them home and I'm going to inspect them and clean them first.
I've heard in a Video with Steve Eberbach speaking that they used these amplifiers while DCM LOUDSPEAKERS was operating.
PS all 3 units are missing common stickers on the rear panel and no serial numbers are present.
Thanks for the write up!

I also have a VSP good purchased new in 1983. Still sounds amazing. Dc offset at each channel is 25mv. Driving JBL L300.
I also have the preamp but it is an early version with many blue wires on the main and switch boards. I had a failing switch or two as well as relay issues so put my efforts on another preamp. These parts are available if someone is interested.

 

[BuckRogers]

I also have a VSP good purchased new in 1983. Still sounds amazing. Dc offset at each channel is 25mv. Driving JBL L300.
I also have the preamp but it is an early version with many blue wires on the main and switch boards. I had a failing switch or two as well as relay issues so put my efforts on another preamp. These parts are available if someone is interested.

My next project is to replace all 10 of the function switches on my Straightwire II Preamplifier, I found a surplus sales outlet that had the same switch but with a different face cover, I'm hoping the original covers will mount to the new switches.