[Antique shop find] Rack of 8 Valley People trans-amp LZ pres? (PICS)

[Aj]

Thread starter here... riveting conversation.  I follow what the veterans are saying.  Capacitors often last a really, really long time.  So old ones should be tested properly before replacing them. Makes sense, and I'll reference this thread when I read otherwise.

But what would you guys recommend, given I'm a relative beginner?  My goals are twofold - (1) get this thing working; and (2) actually learn something.  I don't know if my skills (heck, tools even...) are up to the task of properly proving out the condition of aging caps.  With apologies to the late DeForest Kelley - I'm a musician, not an electronics technician.  I am learning though.  That said, I suspect the quickest path to results (for me) may involve swapping in some new parts.

Anyway, I need to get this thing on the bench again and try it out.  It's been two years since I tried using it, and that was only briefly to determine it's relative condition.  Now that I know recapping isn't standard procedure, I'll report back when I have more info on what exactly is happening with the problem cards...

Again: thanks everyone for your help.  And dirtyhanfri, I love that cheesy Illuminati logo too!  If you've got any documents to add to this discussion, by all means post 'em, if you get a chance..

 

[JohnRoberts]

Thread starter here... riveting conversation.  I follow what the veterans are saying.  Capacitors often last a really, really long time.  So old ones should be tested properly before replacing them. Makes sense, and I'll reference this thread when I read otherwise.

I would expand that to include if you find a clearly bad capacitor, replace all that appear to be from the same production batch (same value, same MFR, etc). If one is bad, other identical caps may also be in similar condition  This does not mean one bad cap means all are bad, but it suggests more may be bad.

But what would you guys recommend, given I'm a relative beginner?  My goals are twofold - (1) get this thing working; and (2) actually learn something.  I don't know if my skills (heck, tools even...) are up to the task of properly proving out the condition of aging caps.  With apologies to the late DeForest Kelley - I'm a musician, not an electronics technician.  I am learning though.  That said, I suspect the quickest path to results (for me) may involve swapping in some new parts.

I like to compare similar paths with null tests. You can do null tests without any test equipment, just sum two otherwise identical channels into adjacent mixer channels with the polarity inverted on one. If they don't null out, figure out why...

Anyway, I need to get this thing on the bench again and try it out.  It's been two years since I tried using it, and that was only briefly to determine it's relative condition.  Now that I know recapping isn't standard procedure, I'll report back when I have more info on what exactly is happening with the problem cards...

Again: thanks everyone for your help.  And dirtyhanfri, I love that cheesy Illuminati logo too!  If you've got any documents to add to this discussion, by all means post 'em, if you get a chance..

There is more Paul Buff  lit over at Wayne's forum.

http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=12&t=114&p=2914&hilit=transamp&sid=55a5b973cc6d8ffe33632483d1aaa6b2#p894

Enjoy.. Last I heard Paul still lived in Nashville but was making strobe flashes for photography.

JR

 

[gridcurrent]

An article on capacitors worth reading.
http://conradhoffman.com/capchecktut.htm

of interest:
"Sprague 30D cap that's well over 30 years old,
It has lower losses than the fresh and well respected Panasonic FC"

 

[Aj]

Interesting article... thanks for posting it.  Over my head in places, but a worthwhile read.

Here's the bottom line/conclusion, a good addendum to this thread's discussion:

The Bottom Line

    Test caps in the same frequency range they have to perform in.
    Consider whether losses are important for the circuit in question.
    You should have a schematic or at least know what part of the circuit the caps are in.
    Reject caps with excessive losses for the application.
    Reject caps with excessive DC leakage for the application.
    Reject caps with low capacitance.
    Reject caps with unusually high capacitance.
    Reject caps with visible leakage, corrosion of the leads, deep dents or bulging.
    Reject caps whose similar neighbors have failed.
    Keep caps, regardless of age, that don't exhibit the above criteria.

 

[Brian Roth]

Caps hanging across power rails "lived" a rough life.

Fortunately, those Kemet "bullet" Tants were excellent to begin with.

BUT tantalums on PSU rails always seem to get old and cranky...like ME!  LOL  They fail as a short circuit.

If I see ancient tants hanging on PS rails, I replace 'em with decent/new 105 C lytics.

I can't tell you how many times I've seen old tants short and then take out a series PS resistor and/or burn circuit board foil.

New 105 degree C lytics are a cheap insurance on PS rails....maybe 25 cents apiece at WORST.

So, 50 Cents per card...and less chance of nasty smells next time you turn on the rack....

My 2 cents....

Bri

 

[analogguru]

Caps hanging across power rails "lived" a rough life.

Fortunately, those Kemet "bullet" Tants were excellent to begin with.

BUT tantalums on PSU rails always seem to get old and cranky...like ME!  LOL  They fail as a short circuit.

correct.

If I see ancient tants hanging on PS rails, I replace 'em with decent/new 105 C lytics.
.....
So, 50 Cents per card...and less chance of nasty smells next time you turn on the rack....

My 2 cents....

Bri

Obviously you neither had a look at the pcb itself nor at the schematic, because in this case there are no "tantalums hanging on PS-rails".  So no need to waste 50 cents.

My one cent....

 

[Brian Roth]

Oops....I was making an ASSumption about those tants.

Bri

 

[CJ]

the technical papers on this amp are better than the sound of the amp itself,

clean but sterile, headroom is a problem,

transformers will help get you some tone out of this thing,

so will different input caps, not only type of cap but value,

imagine using a burr brown instrumentation amp for audio and you have the VP trans amp,

cool looking modules, but that is about it,

better off with API, Quad 8, Jensen 990, Forsell, etc

or WE 407a, which will give you the VP high end clarity but with some vacuum tube mojo,

 

[Aj]

clean but sterile, headroom is a problem, transformers will help get you some tone out of this thing, so will different input caps, not only type of cap but value,

better off with API, Quad 8, Jensen 990, Forsell, etc

Hey CJ, which input caps (brand/values) would you recommend trying? 

I have plenty of other pres I like (neve/trident/benchmark) so this is mostly a fun science experiment/learning project for me.  But I'm sure I'll find some use for it when it's done!

 

[emrr]

Oops....I was making an ASSumption about those tants.

Bri

You did say, generically, "if I see". 

 

[JohnRoberts]

the technical papers on this amp are better than the sound of the amp itself,

clean but sterile, headroom is a problem,

transformers will help get you some tone out of this thing,

so will different input caps, not only type of cap but value,

imagine using a burr brown instrumentation amp for audio and you have the VP trans amp,

cool looking modules, but that is about it,

better off with API, Quad 8, Jensen 990, Forsell, etc

or WE 407a, which will give you the VP high end clarity but with some vacuum tube mojo,

Opinions vary... The transamp IMO was the state of the art at the time. But even back then there was push back and resistance against the sterile (another word for accurate) mic preamp path. I was consulting on a fully transformer-less (input and output) console back in the late '70s, and we were in the minority, and not universally embraced. 

Since then there were better (lower noise transistors), marginally better opamps, etc. At this point we can buy standard off the shelf chip sets that match or beat that SOTA discrete preamps from several decades ago. Now even those lower noise transistors are no longer being made. 

JR

 

[CJ]

if you have the rack space, then there is nothing wrong with having a VP in there,

kind of a specialty amp that can be teamed up with other amps to get better definition on maybe an acoustic guitar or maybe capture the high end off a hi hat,

as far as a vocal amp, i think there are better options,

there are not that many amps without transformers, so it is nice to have at least one option if non linear circuit components get on your wick, Bill Yacey was a big fan of the VP but i have not seen him around lately, i hope he did not fall thru the ice up there,

as far as input caps, just plug and play, bass can be improved a bit by going up to 100 uf, 250 uf, of course this means lytics, which would irk the designer, i do not know if it is the increased C or increased L of the cap that improves bass, might be both,

you can also hang a 600:600 xfmr off the end to get better isolation, you can run into problems when combining this amp with other equipment if your grounding schemes are a bit off,

beware that some opamps do not like to drive a 600:600 with low input inductance, maybe a 10K:10K would be an option,

 

[abechap024]

Very interesting link about how to measure caps. Seems an in depth but rewarding process...

Hmmm.

For something like this, especially DIY...the cost of caps VS. time, VS eventually you will want to replace them all anyway. I would just replace them all, save the time it would take to measure and test each one, but hey it is pretty interesting, be my guest.

Since I chimed in last, I fixed one piece of equipment that was totally dead because the Tants had all shorted to the power supply rails...luckily when I replaced them all, it now works like a charm.

Also replaced the caps in a vintage DBX 160vu, they were leaking DC causing the power supply to overheat and eventually fail.
Replacing ALL the caps, saved me time in the long run, saved the owner time (he shouldn't need it serviced again for a long while) and it now has lower noise, and I would say sounds better (ghasp)

I did recap a channel on an JH-600 (hi brian) and surprisingly did not hear as large of a difference as I was expecting! (it was a lot of work too)

So....I'm sure its true that not all caps need to be replaced...and I'm thinking for the console, I am only going to replace the ones I need to...unless under further testing I find it does infact sound and measure better.

Sorry to get side tracked. But rack em up! Clean, but if you don't like em, give a couple to me