as with all subjects
Knowledge is everything

too many questions !

Soldering - practice makes perfect

Parts - many many place will have what you want
very basic answer
resistors - %1 tollerance metal film
caps - electros 105 deg types
other caps MKT is a good filter type
POTs - very hard to get quality these days

it would be much easier to take the question one at a time with some specifics to refer to

For parts, I like Digikey for a good selection of components:

http://www.digikey.com/

Good selection and stock. Doesn't mind small quantity orders.

Thanks Mike. I'll contact them.

Okay, so my first evening of tinkering was successful.

I replaced the tubes with Mullards from GT (12AX7M) and already the unit sounds quite a bit better. Also, the distortion is WAY down.

Next, I checked the resistance of the attenuators.

They are marked:

Threshold - C10K (I measured 4.8K ohms though. It is also hooked to a resistor, but I did not check the value - my color:number memory wasn't good, so I figured I'd check it out later.)

Ratio - B100K (I measured 74K ohms)

Output gain - B10K (I didn't get to measure it, my son got cranky).

I also got a new soldering iron - it's in the form factor of a soldering gun but with the fine tip. 30W. I find it SO much easier to use!!!

So, here's the next problem - P&G potentiometers come in values of 1,5, and 10K. Could a simple resistor in the path fix this, or is there another solution?

J.

A torch? That sounds crazy. I would probably kill myself. I don't know a lot about their heating properties, but I would think it wouldn't be able to heat joints as quickly and non-destructively as the soldering iron. And I would personally prefer a pencil iron to a gun, but different strokes.

I've seen a few other people have similar ideas about the VLA, but few people get farther than changing the tubes and perhaps caps. I don't know but maybe it would need to be basically redesigned to change its character too much from what it is. Everything has its use I guess. You should build a G*S*S*L as a learning guide. and as a kick ass comp. It's too easy.

Reggie wrote: A torch? That sounds crazy. I would probably kill myself. I don't know a lot about their heating properties, but I would think it wouldn't be able to heat joints as quickly and non-destructively as the soldering iron. And I would personally prefer a pencil iron to a gun, but different strokes.

You'd be surprised. The torch actually heats the joint very quickly, since it's output is as high as 1200 degrees farenheit. I'm quite used to using it on very precise jobs. Trust me, when I hit my $10,000 french horn with a torch, I'm sure to hit it EXACTLY where I want it and no where else. It takes a bit of practice, but they can be VERY precise.

Also - the gun I just got is only a gun in form factor, the tip is just like a pencil iron. I just have a far easier time manipulating the gun. Obviously, a regular gun's tip is WAY too broad. Just practicing tonight, I was easily able to unsolder two potentiometers and 4 capacitors and resolder them from a broken POS headphone amp I had laying around.

I've seen a few other people have similar ideas about the VLA, but few people get farther than changing the tubes and perhaps caps. I don't know but maybe it would need to be basically redesigned to change its character too much from what it is. Everything has its use I guess. You should build a G*S*S*L as a learning guide. and as a kick ass comp. It's too easy.

I'm hoping to take what is a decent or even usable limiter for "ghetto" mastering and make it a viable mastering tool. I don't doubt that this may be a hell of an effort, but I'm willing to learn and work on this.

I figure or $300 to start and then maybe $500 or so in mods, if I can make it sound THAT much better, it might be worth it.

Once I'm done, I might send it over to John Scrip and see what his opinion is. I think he has one unmodded and could give me a good impression as to whether it was worth the money and efforts.

J.

Kev wrote: POTs - very hard to get quality these days

For potentiometers, I've been looking at all sorts.

The output needs to be an attenuator and the threshold and the ratio need to be potentiometers, no? Or am I stupid and they all need to be the same thing, just different resistance values?

J.

PS - God DANG stepped attenuators are expensive. 24 position switches are around $130 and up per piece! That would be $1000 upgrade just for the stepped attenuators! No wonder mastering gear costs so much!

if you are really interested in DIY

http://www.groupdiy.com

http://www.diyfactory.com
ask me for direct links to things hidden at the Factory

my home site for some interesting DIY links
The GSSL is a fine compressor ... even in it's standard form

walk before you try running

Jeremy,

The DIY bug will bite you! Be careful! I started building stompboxes then moved on to an SSL based compressor, and I'm now tackling the Pultec, LA2A, and some Neve stuff!

When I don't need "quality" parts I normally go through http://www.futurlec.com because their prices are fractions of DigiKey and Mouser, but their selection is smaller.

Good luck on the ART....you can go to Blacklionaudio.com and contact the guy that runs it because I believe he has mods layed out for this unit.

Thanks Art! You're the bomb!

I've just been bitten. I started taking apart shit last night that wasn't broken, just so I could practice soldering. So far, my USB hard drive enclosre has been field stripped and put back together and to my amazement, still works!! (I didn't get nuts and take chips off, just some caps and some resistors...)

J.

kev wrote:

POTs - very hard to get quality these days

i am not totally shure if today but it was usually not a problem (at least in europe... the last time i ordered some was about two years ago) to get penny & giles pots 'n' faders, they cost a fortune, but they are simply the best. just the question if it makes sense to stick a few hundred euro / dollar pot into a DIY, to save money (i mean with DIY-ing)

sorry, just talking a whole lot-a-rubish.

therecordingart wrote: ... you can go to Blacklionaudio.com and contact the guy that runs it because I believe he has mods layed out for this unit.

:shock:
unbeleivable

you have to pay for the info ??
but
this stuff was all discussed at both Tech Talk and now the LAB
I hope those prices do include the parts.

just do a search !!
http://www.prodigy-pro.com/forum/viewtopic.php?t=12550&highlight=art
http://www.prodigy-pro.com/forum/viewtopic.php?t=9800&highlight=art
just two of many at the LAB

Yep. I just talked to Dale Manquen - the US distributor for P&G. He would have no problem getting me some new pots. But, they only have them in 5K and 10K values. Two of the pots (out of all six) are 100K. I would probably have to go to ALPS for that.

They are around $160 each!!! ZOINKS. I don't mind dropping the $$ if it's worth it. The fact is, I actually dig the ProVLA as it is, but hear room for considerable improvement. I'm thinking I could really polish this turd into something quite nice if I keep working at it.

Does anybody have any recommendations for lesser expensive but still high-quality pots. (Given the unit's original price and it's total potential, I'm deciding whether $900 of upgraded pots is really going to make sense...)

J.

If you were here I could take you to my local shop and show you and chose a pot for each job

BUT
it's my experience that lets me do that

you need a pot that fits the physical location
otherwise you will need to do some metal work
what hole size do you have ?

Then there is the shaft size and type and whether you want to re-use the original knob.
what shaft size and type ?

Then there is value and type ... say Log 100K
what value and type ?
the hardest is the reverse log pots

JLM have some detented reverse dual log pots in a couple of values and can be set up for a variety of situation.

AS I SAID
take things one at a time and give some specifics

Torch and soldergun?... forget about it.

Once you try a quality iron and solder, you will understand why. Making a good solder joint is key to making good electrical connections while avoiding damaging circuit components. Get a Weller WTCPT with an assortment of tips (600, 700, 800 degrees). Silver bareing solder like Wonder Solder is also worth the price.

Good pots are hard to find. But it is easy to replace them with stepped attenuators. Repeatable and better sonics.

Quality part sources:

percyaudio.com
welbornelabs.com
partsconnexion.com

Kev wrote: If you were here I could take you to my local shop and show you and chose a pot for each job

BUT
it's my experience that lets me do that

you need a pot that fits the physical location
otherwise you will need to do some metal work

what hole size do you have ?

Then there is the shaft size and type and whether you want to re-use the original knob.

Then there is value and type ... say Log 100K

the hardest is the reverse log pots

JLM have some detented reverse dual log pots in a couple of values and can be set up for a variety of situation.

AS I SAID
take things one at a time and give some specifics

Thanks Kev.

I pretty much am taking things one item at a time. Right now, it's the pots. Next, it will be the caps and the opamps. The tubes are already a done deal.

As for the size, I'm not concerned in the slightest. The chassis has so much room behind the knobs, anything will work. (even the REALLY big ones). Also, the pots can bypass the small daughter circuit board as they are wired (not traced) to the motherboard from there.

The resistance factor and the tapers are easy. I've already detailed those. The thresh and ratio are linear tapers (standard, not reverse) and the output is log.

As for knobs, I'm not worried. If I have to, I'll cut new ones - machining ain't a problem.

J.

Zilla wrote: Torch and soldergun?... forget about it.

Once you try a quality iron and solder, you will understand why. Making a good solder joint is key to making good electrical connections while avoiding damaging circuit components. Get a Weller WTCPT with an assortment of tips (600, 700, 800 degrees). Silver bareing solder like Wonder Solder is also worth the price.

Good pots are hard to find. But it is easy to replace them with stepped attenuators. Repeatable and better sonics.

Quality part sources:

percyaudio.com
welbornelabs.com
partsconnexion.com

Thanks Scott!

Don't get me wrong - the torch I've only used in the past cuz I'm good with it and only on cable jobs. (And I'm talking a precision torch, not some huge Benzomatic... :wink: )

The gun is not a traditional gun. It is a true soldering iron with multiple tips. It's just held like a gun. The tip is still the fine point soldering iron type tip.

I already dropped the cash on the good solder. (Lead free, silver). I have tons of that laying around. I use it for musical instrument repair. Lead solder is a BAD idea when it comes to brass instruments...

I'll check out the sources.

Thanks!!

Most of my stuff uses the simple pots I find at Jaycar
... even so, I hand pick them based on feel
I very rarely have to change them
and some items have been in service for 10 years +

when I need stereo or recall I'll use a rotart switch
Lorlins are fine for a start and they have a 1 pole 12 position
beyong that comes the Elna's

For minature PCB switches and pots ... Farnell, RS, WES Digikey all have extensive catalogues to choose from.

I would change the hole or Knob if I didn't have to
so again
what holes size, shaft size and type ??

I really don't mind modding the hole or the knobs (in fact, I'm getting new knobs regardless. The existing ones are plastic. I'll be making milled aluminum or epoxy lacquered bronze ones).

But the hole is .3" in diameter. Using my trusty micrometer, I got .294 but was able to "stretch" it to .3" In reality, .275" would be a good fit without too much wiggle room (room for dirt) but still enough that I won't have a tough time mounting it.

J.

mmm
:roll:
my catalogues are in mm
for example the Lorlin switches are M9.0 for hole cut out and 6.35 mm(1/4inch I s'pose) for shaft

I think they come in both flat and round but not splined
the PCB mount rotary that JLM uses is a splined shaft and so is his pots

but the pots are very small at 16 mm and have the 41 detents

Okay, so after doing A LOT of reading and chatting with some folks here and elsewhere, here's the plan.

Replace the output gain pot with a P&G RF15 log taper. To do so, I will need to replace a pair of resistors which are in place to make non-log taper faders approximate a log-taper fader. I will replace these 4.99KOhm resistors (5%) with 50K Ohm (1%) devices.

The other controls are only passing DC and therefore no signal - no sound improvement will happen by replacing these. However, I am still looking into affordable pots with detents (I've found few. Kev, I'll check on the ones you posted above - thanks!) The problem is, as you pointed out Kev, that one of the pots (threshold) is a reverse taper. So, I guess I'll have to dig up one of those somewhere. Finding one with detents and cheap may be a REAL challenge.

Next, I'm going to replace the OpAmps. I've already ordered a set of Analog Devices OP275s and will have to track down a pair of Burr Brown OPA2604s...

I'll keep ya posted...

J.

FYI, detented pots are not accurate enough be considered "repeatable". Also if you are trying to match two stereo channels, a 5% pot is not going to cut it. Only switches with hand picked resistors achieve true repeatablility and tight stereo matching.

Zilla is right

the pot I showed above IS reverse tapper
JLM also has the 2604 chips

I will replace these 4.99KOhm resistors (5%) with 50K Ohm (1%) devices.

why !! ?
what are these resistors for ?

A %1 resistor is not inherently better than a %5 resistor

IN FACT for tube work and bias adjustment the %5 may be just perfect when you DON'T want exactly 50Kohm

:roll:
as I said

is stereo and repeatability important ?
are these opamps signal path or control
are they unit gain or gain ... some hi class opamps don't like being at unity

if in doubt use machined pin sockets

phew ... :cry:
too much of a hurry
good luck
one thing at a time and some details

Kev wrote: Zilla is right

the pot I showed above IS reverse tapper
JLM also has the 2604 chips

Good - I need one pair of reverse tapers...

Kev wrote:

I will replace these 4.99KOhm resistors (5%) with 50K Ohm (1%) devices.

why !! ?
what are these resistors for ?

A %1 resistor is not inherently better than a %5 resistor

IN FACT for tube work and bias adjustment the %5 may be just perfect when you DON'T want exactly 50Kohm

Why - cuz they are there to put a load on the gain output attenuator to make its output approximate a logarithmic taper. To take the load off of new pot, I will be raising this. There is no effect from these resistors on the tube circuitry - only on the pots.

Kev wrote:
is stereo and repeatability important ?

Stereo - no - each channel seperately. Repeatability - Yes.

Kev wrote:
are these opamps signal path or control

are they unit gain or gain ... some hi class opamps don't like being at unity

all 6 are in the signal path. 2 are at unity, 4 are not. I'm only using these opamps after spending a LOT of time yesterday researching their specifications and speaking with engineers at both BB and AD.

Cucco wrote: Why - cuz they are there to put a load on the gain output attenuator to make its output approximate a logarithmic taper. To take the load off of new pot, I will be raising this.

yes to approximate
so which value is the best ?

http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

just one of many pages about this stuff

There is no effect from these resistors on the tube circuitry - only on the pots.

No Effect ??
... if it were no effect there would be no need for P&G or Alps faders and Vishay Resistors.

So I can't agree with you there
... this is a signal path and not just control circuitry.

A simple opamp in a unity gain circuit ... like a 5534 doesn't lend itself to a change to an OPA or AD opamp ... and bring night and day changes to the audio.
It can actualy cause some problems.

as I said use quality machined sockets
and you can experiment

Okay, update time..

I replaced four of the OpAmps and at Kev's advice, I used a board mount socket so I could try out a few different ones.

I'm sticking with the BBs for a while as they did make a noticable difference (in a GOOD way...)

Now I'm off to try a few more things.

I'm thinking of these: (12 step models)
http://www.marchandelec.com/att.html
for my threshold and ratio

and these: (24 step models)
http://www.goldpt.com/index.html
for my gain.

After a lot of digging, the power supply seems to be up to par more or less, so I think I'll leave that alone for a while.

All told, the replacment of 4 OpAmps took me just under an hour from removing the board from the chassis to screwing it back in.

Not too bad I guess.

J. 8-)