Pvy AMR 800 Restore / Mods

[Sturoc]

Recently acquired a Peavey AMR 800 24 channel 8 buss, Split console w/ 16 tape monitor returns, Full LED Meter bridge, Rack Power Supply .
Am in the process of pulling channel strips/ monitor/ master section and tape return modules for cleaning and inspection.
Overall its a very clean console, save for a thin layer of grime on the top which is easily coming off.
The modules PCBs look like they just came from the factory ! Faders while being the cheap Junk poon Korea brand are still functioning for now
Not bad for a 34 yr old console.

Questions for those who know these mixers :
Apprently some or all of the pots and switches were custom made per this model ? Who made them ?
Where were the knobs sourced from ? Am considering changing the style / color scheme.
Meter Bridge LEDs were sourced from ? In case any are burn out.

Since my AMR 800 appears to have been built in June of 1990 (based on the handwritten inspection stickers with names and dates on each PCB channel strip) I am presuming it has the Junk Poon 10k faders. What fader law are these using, Logarithmic? I need to start sourcing replacements so they are on hand if /when the Junks fail.

The meter board rotates back for servicing, its hinge adds some support for all modules or vis a vers. Since the hinge does not tie into the side cheeks I am considering adding a small diameter metal strut to further strengthen the sides. There is enough clearance when the meter bridge is rotated into position to do this. This will also keep the cheeks from pressing in on the meter bridge as its a very tight fit between them.. Reason is I may have to store the mainframe (empty or full) for a while standing up on one end and dont want the frame to tweak out of square. There shouldnt be an weird electronic interference with being close to the meter bridge pcb ?

At the 'rear' end of the channel PCB, nearest the inputs, Red 4 pin connectors are labeled in groups of 8, being numbered 1 thru 8 on the connectors as opposed to 1 thru 24. Any reason for this?
After pulling channel #16, I noticed the last 8 channels 17 thru 24 are not connected via the individual red 4 pin connector - one per channel from the cable loom running along the tray near the rear inputs. Pic is showing the cables w/ red connectors that plug into the 4 pin conn on pcb shown here on channel 9
Cables from this run connect to each channel module 1-thru 16 . However those cables w/connectors are missing for channels #17 thru 24. The schematic/block diagram says it - conn labeled as J112 - feeds the"Monitor" section ?

I've read some older Gearspace and GroupDIY posts etc about swapping ICs out for more modern ones. Seems the general thinking is there wouldnt be much of an improvement, if any ? Seems kinda subjective. Someone also opin'ed that a 2 stage preamp design would have been better but my own jury is still out on that one.

Finally, from my ever adventurous mind, Was wondering how hard it would be to incorporate several channels from a different console ? Swapping out 2 or 4 of the AMRs channel modules for a higher end strip from say an API, Neve, or any other top quality console. if the incoming channel strip is a close fit physically with minimal fabrication and if its power needs can use the AMR PS 19v + - voltage and seamlessly rout into the AMR busses and master section. .

Of course, its easy to say 'just use outboard racked channel strip etc instead', But am thinking to make the console more unique and custom to my studio.

The overall condition of this AMR 800 is really excellent, PCBs and all parts look brand new for a 34 yr old mixer. But anticipate some recapping.. Once she is up and running for a few days, we'll do a more in depth check.
In the late 1980s into the early 90s Peavey created a separate division called AMR- Audio Media Research, attempting to break into higher end market and make their name known for pro quality $10k to $20k range consoles. They didnt succeed no doubt due to their name being more associated with lower end gear, some say customers would see the "Peavey " badge and walk away. Also the profit margin for mid to high range pro consoles is not great so ole Hartley canned the product range. Yet these consoles are a sleeper, being very well designed. A number of small and regional studios are still operating AMR 32 and 36 trk consoles to this day. The cult following these have, its reputation for fairly 'clean' preamps and versatile Eq plus the myriad of ins/ outs routing along with nice layout and ease of access maintenance makes this console range a keeper.

Appreciate any help per all the questions especially from John Roberts if active here in the group.

 

[JohnRoberts]

We did make an 8 "bus" split, Production Series 800...

A 1990 build is fairly early so perhaps used jung poon faders. They are pretty fragile, be careful about pushing side to side (plastic wiper housing breaks if you look at them crosseyed.) The alps K faders should drop in and are more reliable.

I'll look at your specific questions tomorrow morning (of course I have thoughts after a couple decades). Somewhere I have a pdf of the OM I'll try to find you a copy. I tried to load it up on one of my websites a while back and the file is somehow corrupted and would not transfer. But I can open it and read it locally. Somebody posted it to the Gearslutz website thread about these consoles several years ago, thats where I got it.

That's a little un... try lifting the 36x24 bus.

JR

 

[JohnRoberts]

Recently acquired a Peavey AMR 800 24 channel 8 buss,

bus. That series had 8 bus, 16 bus, and 24 bus versions

Split console w/ 16 tape monitor returns, Full LED Meter bridge, Rack Power Supply .
Am in the process of pulling channel strips/ monitor/ master section and tape return modules for cleaning and inspection.
Overall its a very clean console, save for a thin layer of grime on the top which is easily coming off.
The modules PCBs look like they just came from the factory ! Faders while being the cheap Junk poon Korea brand are still functioning for now
Not bad for a 34 yr old console.

Alps K-faders should drop in... IIRC 10KA tapers

View attachment 128210


Questions for those who know these mixers :
Apprently some or all of the pots and switches were custom made per this model ? Who made them ?

Custom pots were all second sourced by two makers, Alps and Bourns (IIRC). I am not aware of custom switches.

This set of special components were shared across two console programs inside Peavey. My AMR split recording console, and Peavey's Mark VIII live sound console.

Where were the knobs sourced from ? Am considering changing the style / color scheme.

Knobs were custom designs tooled up and supplied by Rogan

Meter Bridge LEDs were sourced from ? In case any are burn out.

those were some common LED strips from a Chinese vendor no doubt tooled to work with the off the shelf LED meter drivers.

Since my AMR 800 appears to have been built in June of 1990 (based on the handwritten inspection stickers with names and dates on each PCB channel strip) I am presuming it has the Junk Poon 10k faders. What fader law are these using, Logarithmic? I need to start sourcing replacements so they are on hand if /when the Junks fail.

Audio taper, we used Alps K faders in later production

The meter board rotates back for servicing, its hinge adds some support for all modules or vis a vers. Since the hinge does not tie into the side cheeks I am considering adding a small diameter metal strut to further strengthen the sides. There is enough clearance when the meter bridge is rotated into position to do this. This will also keep the cheeks from pressing in on the meter bridge as its a very tight fit between them.. Reason is I may have to store the mainframe (empty or full) for a while standing up on one end and dont want the frame to tweak out of square. There shouldnt be an weird electronic interference with being close to the meter bridge pcb ?

The meter bridge is inside its own metal box to not contaminate sensitive audio paths.

Have no suggestions about modifying the mechanical design. That console chassis base plate uses monocoque construction, similar to aircraft wing, so it is rigid and strong.

At the 'rear' end of the channel PCB, nearest the inputs, Red 4 pin connectors are labeled in groups of 8, being numbered 1 thru 8 on the connectors as opposed to 1 thru 24. Any reason for this?
After pulling channel #16, I noticed the last 8 channels 17 thru 24 are not connected via the individual red 4 pin connector - one per channel from the cable loom running along the tray near the rear inputs. Pic is showing the cables w/ red connectors that plug into the 4 pin conn on pcb shown here on channel 9
View attachment 128214Cables from this run connect to each channel module 1-thru 16 . However those cables w/connectors are missing for channels #17 thru 24. The schematic/block diagram says it - conn labeled as J112 - feeds the"Monitor" section ?

Let's see how good my memory is.

Each monitor section module has 3 feeds to the L/R bus. Two get feeds from a flip switch in the input strips. So an 8 bus console will support feeds from 16 input strips.

I've read some older Gearspace and GroupDIY posts etc about swapping ICs out for more modern ones. Seems the general thinking is there wouldnt be much of an improvement, if any ? Seems kinda subjective. Someone also opin'ed that a 2 stage preamp design would have been better but my own jury is still out on that one.

Argh... The console uses adequate op amps while there may be a few sockets where one could throw more money at it.

I will come back and revisit while I have more free time (I have a few specific thoughts).

Finally, from my ever adventurous mind, Was wondering how hard it would be to incorporate several channels from a different console ? Swapping out 2 or 4 of the AMRs channel modules for a higher end strip from say an API, Neve, or any other top quality console. if the incoming channel strip is a close fit physically with minimal fabrication and if its power needs can use the AMR PS 19v + - voltage and seamlessly rout into the AMR busses and master section. .

arghh You will not find any strips that seamlessly interface with the AMR master section and architecture.

Of course, its easy to say 'just use outboard racked channel strip etc instead', But am thinking to make the console more unique and custom to my studio.

Do what you want, don't expect me to bless it.

The overall condition of this AMR 800 is really excellent, PCBs and all parts look brand new for a 34 yr old mixer. But anticipate some recapping.. Once she is up and running for a few days, we'll do a more in depth check.

My general advice is start by characterizing each strips performance. A simple frequency response sweep should help identify and dried out DC blocking capacitors. I tuned most poles to be very low, so path performance might still hold up. If you find one or more dead caps, replace all of the same value as they are probably in similar shape.

BE CAREFUL those strips use single sided PCBs so overheating pads while recapping can lift traces.

In the late 1980s into the early 90s Peavey created a separate division called AMR- Audio Media Research, attempting to break into higher end market and make their name known for pro quality $10k to $20k range consoles. They didnt succeed no doubt due to their name being more associated with lower end gear, some say customers would see the "Peavey " badge and walk away.

Since I lived that history I have a slightly different reality based version.

Also the profit margin for mid to high range pro consoles is not great so ole Hartley canned the product range.

I was trying to sell $40k big split consoles for only $20k. Simultaneously Greg Mackie was marketing small inline consoles for something like $4k with massive advertising support. Since Peavey did not rely on advertising, Mackie won that battle in the marketplace. Being under the Peavey corporate umbrella did not help market perception. I got my best reception from serious professionals who knew what they were seeing. The mass market was influenced by advertising.

Yet these consoles are a sleeper, being very well designed. A number of small and regional studios are still operating AMR 32 and 36 trk consoles to this day. The cult following these have, its reputation for fairly 'clean' preamps and versatile Eq plus the myriad of ins/ outs routing along with nice layout and ease of access maintenance makes this console range a keeper.

IMO the mic preamps are still SOTA by today's standards. The EQ topology is low noise and low distortion. I voiced it to have similar bandwidth/Q to a popular API EQ but I gave mine more boost/cut. This console series has lots of input capability. The 24 bus platform has well over 100 inputs to the L/R bus.

There are a few areas that IMO could be improved, but right now my rain ditches need trimming before the temperature rises too high.

Appreciate any help per all the questions especially from John Roberts if active here in the group.

more later...

JR

 

[JohnRoberts]

Here's a link to the production series OM I just uploaded... https://groupdiy.com/threads/amr-production-series-console.87391/

JR

 

[Sturoc]

Thanks for the link to the OM upload
I have been doing my homework since your last reply.
Digging deep finding an old thread which had a ton of info

Sourcing Replacement Pots ( if needed) still a search in progress and buying a few 'donor' channel strips may be a possible solution as there are a few available online.

Caps/ OpAmps are still available as most resistors So I am planning to build up a stock pile of those so they are on hand when needed.

Per the Caps I am thinking to do a few channels at a time. I dont see any visual evidence of failure but since they will undoubtedly fail at some point due to age ( 34 years is a long time !) and that the modules are out of the frame right now, then why not. I have alot of experience in soldering PCBs especially older boards slow and steady hands wins that race.

As for only 16 of the 24 channels going to the 8 bus Was this a cost aspect as having the option of any of the 24 to route to bus would have made a more expensive build /selling price ?

I understand your bit of frustration when users talk about modding the channel preamps etc. I actually did some reading up on the OpAmps you used and they are still regarded as very good. I will leave the channels as is !
There was some consensus among a few that modding the master section resulted in an improvement.

Whenever you have time to reply.....Your thoughts per what, if any, other improvements you might suggest.

Its not often one gets to dialogue with a vintage console's designer, I appreciate your help.

 

[JohnRoberts]

Thanks for the link to the OM upload
I have been doing my homework since your last reply.
Digging deep finding an old thread which had a ton of info

Sourcing Replacement Pots ( if needed) still a search in progress and buying a few 'donor' channel strips may be a possible solution as there are a few available online.

+1 some of the pots like the 557 sweep EQ pots are surely unobtanium now, so a couple old donor strips could be wise.

Caps/ OpAmps are still available as most resistors So I am planning to build up a stock pile of those so they are on hand when needed.

Per the Caps I am thinking to do a few channels at a time. I dont see any visual evidence of failure but since they will undoubtedly fail at some point due to age ( 34 years is a long time !) and that the modules are out of the frame right now, then why not. I have alot of experience in soldering PCBs especially older boards slow and steady hands wins that race.

I am surely repeating myself but I advise running frequency response sweeps to identify any problem caps (from weak LF response). If you identify a problem cap value, replace all of them but I wouldn't advise doing any rework to those old single sided PCB unless required.

As for only 16 of the 24 channels going to the 8 bus Was this a cost aspect as having the option of any of the 24 to route to bus would have made a more expensive build /selling price ?

It's not an inline architecture, but there are different trade offs. If working into a 24T recorder you could patch say 8 upper inputs into 17-24.

I understand your bit of frustration when users talk about modding the channel preamps etc. I actually did some reading up on the OpAmps you used and they are still regarded as very good. I will leave the channels as is !

I know exactly where the skeletons are buried.

There was some consensus among a few that modding the master section resulted in an improvement.

The L/R bus summing amp is clearly an area where today's op amp technology has eclipsed the off the shelf parts I had available back then. There are more complications with the L/R bus including lots of stems feeding the bus. Even that minimal 8-bus configuration has 24 feeds to the L/R from the input strips, +3 feeds to the L/R bus from each sub-master strip for another 24, then a few over in aux/efx return. IIRC there was also a way to trick more line level inputs to the L/R bus using sub master fader insert jacks. But 50+ is not bad for a modest 8 Bus.

Whenever you have time to reply.....Your thoughts per what, if any, other improvements you might suggest.

I was never happy with the L/R master sum amp. It has a -6dB gain trim so you can bang the bus hard and trim down the bus gain for a lower noise floor.

I tried rolling my own bus amp using the low noise mic preamp transistors we had in the system but it was a bit of a kluge. These days there are some nice 1nV/rt Hz off the shelf op amps I would use instead.
======
I have more thoughts but not for right now. I was working on an engineering change order for the sub-master strip but that never happened when the series was cancelled. I describe that another time.

Its not often one gets to dialogue with a vintage console's designer, I appreciate your help.

I don't think we made a dedicated 8 bus power supply so you probably got an 16 bus PS with some extra capacity.

JR

 

[JohnRoberts]

I may have mentioned in passing that I had an engineering change circuit tweak to the sub master strips almost finished and ready to go when this SKU got cancelled. This tweak corrected a major issue (L/R bus noise). To explain let me back up and discuss the sum bus topology/philosophy. I first described this in my 1980 console performance limits article in RE/P Magazine. By using "current source summing" one can in theory completely eliminate the N+1 noise gain factor in bus sum amp.
I have addressed current source summing multiple times here over the years,
https://groupdiy.com/threads/summing-large-amounts-of-channels.75435/page-3#post-957252
https://groupdiy.com/threads/summing-large-amounts-of-channels.75435/#post-956742
https://groupdiy.com/threads/balanced-summing.55980/page-2#post-714492

Long story short I crafted a synthesized bilateral current source using a Howland current pump (name?). The combination of positive and negative feedback around a high performance op amp can bootstrap the output impedance to be very large. This output impedance depends on the close matching of the feedback resistors and driving the inputs from a low stable source impedance and the feedback resistors themselves. All the typical examples use megohm size resistor values. I figured out I could get more than adequate benefit using more sensible precision resistors down in the 10k-20k range.

The weak link in the production series was driving the synthesized bilateral current sources directly from the pan pots. Adding op amp buffers to the pan pots could have corrected this issue but would have resulted in adding 2 op amp sections per pan pot or 72 more op amps into the 24 bus production series monitor section. My calculus was that the degraded source impedance of the bilateral current sources was not an issue in use...... BUT with all of these current sources sending to the L/R bus 24x7 could be audible in WFO listening tests.

The evidence of the current sources sensitivity to source impedance can be revealed by this simple test. Center all the pan pots in the monitor section (24 pan pots in your 8 bus). This is the worst case for source impedance. Alternately hard pan all those pan pots hard left or hard right and listen again. This shows how well the bilateral current sources can work. Seriously do that, hard pan everything not in use. In use this with lots of stems in use this noise floor is well below the program noise floor but perception matters.

My engineering change that elegantly(?) dealt with this was to disconnect the current sources from the L/R bus when the sends were muted. I don't recall the details of the final design solution but there was several prototype cuts to get the mute switching quiet. The bad news is that this is not simple enough to implement as a DIY tweak (especially since I don't remember the details).

So for now I will try to stick to more practical mods if you have too much money burning holes in your pockets. The 24 stereo bilateral current sources in your 8 bus monitor section use TL072 bifet op amps. These are typically 3uV of input noise. Modern high performance bifet op amps can beat the 3uV ein figure by a comfortable margin. Caveat: don't expect this to make a huge difference but it is something you can brag to your clients about.

Next potential noise floor improvement is to swap out the 5532 op amps used in multiple bus summing amps. These are respectable enough for summing modest numbers of inputs, but is money is not object better is always better.

Finally the master section. The first thing is to disconnect/remove the little midi controller. It was a selling hook back when midi was the new thing, now it's just a source of digital clock noise.

The L/R bus master socket deserves the best uber op amp you can afford. In the owners manual schematic it shows a 5532 but I tried several different variants. I would just remove that rats nest and KISS. Return to the original schematic design but using a seriously low noise uber op amp.
======
Repeating myself,
#1 I wouldn't go crazy replacing old caps until after making measurements.
#2 keep all unused pan pots in the monitor section panned hard right or left.
#3 turn the master bus trim down (this improves bus noise floor).

That should keep you busy, and give you a place to start.

JR

 

[r2d2]

We did make an 8 "bus" split, Production Series 800...

A 1990 build is fairly early so perhaps used jung poon faders. They are pretty fragile, be careful about pushing side to side (plastic wiper housing breaks if you look at them crosseyed.) The alps K faders should drop in and are more reliable.

I'll look at your specific questions tomorrow morning (of course I have thoughts after a couple decades). Somewhere I have a pdf of the OM I'll try to find you a copy. I tried to load it up on one of my websites a while back and the file is somehow corrupted and would not transfer. But I can open it and read it locally. Somebody posted it to the Gearslutz website thread about these consoles several years ago, thats where I got it.

That's a little un... try lifting the 36x24 bus.

JR

The midi mute section is like various others available on Soundcraft Ghost, Soundtracs PC Midi etc.. ?
thanks.

 

[JohnRoberts]

The midi mute section is like various others available on Soundcraft Ghost, Soundtracs PC Midi etc.. ?
thanks.

The midi gadget in the master section was only capable of generating midi outputs like song start, or program changes. It had absolutely zero connection to audio paths inside the console.
====
For a little story about that midi dohickey, it's digital content lowered the import tariff rate for selling the consoles into Canada. So that is the only good thing I can think to say about it.

JR

 

[r2d2]

The midi gadget in the master section was only capable of generating midi outputs like song start, or program changes. It had absolutely zero connection to audio paths inside the console.
====
For a little story about that midi dohickey, it's digital content lowered the import tariff rate for selling the consoles into Canada. So that is the only good thing I can think to say about it.

JR

Ops,

really no midi mute option ?

Is there any particular reason why it was not included,
while the midi imterface was there ?

 

[JohnRoberts]

Ops,

really no midi mute option ?

Is there any particular reason why it was not included,
while the midi imterface was there ?

Midi mutes were not designed in because of cost /complexity.

The midi gadget was there pretty much as a gimmick (It wasn't my idea).

JR

 

[Gord Bestwick]

Hello everyone. I know I'm a bit late to this thread, but if you're looking for parts I'm about to pitch what amounts to an entire AMR 800. If you would like parts, you can contact me through here, or answer this thread and I'll find a way to contact you.

Gord

 

[JohnRoberts]

If it has the good alps "557" parts in the channel EQ sweep pots, those may be of value for servicing other old soldiers. Those consoles were built with two different versions of the EQ pot (71190557 pn?). The CTS version of that pot suffered from some wiper bounce that could sound sometimes like a scratchy pot. The Alps version used custom tooled wiper that didn't suffer from wiper bounce.

JR

 

[Sturoc]

Hello everyone. I know I'm a bit late to this thread, but if you're looking for parts I'm about to pitch what amounts to an entire AMR 800. If you would like parts, you can contact me through here, or answer this thread and I'll find a way to contact you.

Gord

Hey Gord
I am interested in :
Master Module section ( with that useless midi thingy)
Several monitor modules
Several channel strips
A bank or two of the LED meter bridge
Depending on which fader package you have : early version Junk Pung or Alps K fader which is what I am looking for am be interested in several banks of those .

Basically its for the pots and stacked EQ Pots as John R mentioned since they were a custom order for these consoles and pretty much an unobtanium part these days.
The Alps Faders if they are still moving well.

Master section so I can mod one and have an intact spare.
A few channel spares in case one of mine poops out they can easily be swapped.
LED bank just to have in case...
Maybe the Power supply cable w/ conns

Be better to buy the entire console intact from you...BUT you're in BC, CAN and I am currently in NY for several months - home base is in Colorado

 

[Nele]

Just to chip in. I also have one of these consoles, the 32-16 version.
The biggest problem I have is that sometimes channels drop out. I have to really crank up the gain to get them to work again. I did frequency sweeps on all the channels and these look ok.

I did recap some channels and indeed be very careful when desoldering. I at first used a Hakko 909 desoldering gun but this teared the solder pads right of. In the end I used my Hakko soldering iron set to a low temperature and desoldering braid. This worked fine but you still have to be gentle.
Also some of the regulators on the channels were broken. Easy repair.

I didn't do any mods except to the master section. Here I swapped the opamps in the main audio path for LM4562 and I disabled the Midi-module.

The main issue that still remains is the dropping out of the meterbridge, but this is not a big issue.

Great desk!

 

[JohnRoberts]

Just to chip in. I also have one of these consoles, the 32-16 version.
The biggest problem I have is that sometimes channels drop out. I have to really crank up the gain to get them to work again.

That symptom sounds like an oxidized switch contact like perhaps in an insert jack switch..... turning up the music punches through the oxide layer.

I did frequency sweeps on all the channels and these look ok.

I did recap some channels and indeed be very careful when desoldering. I at first used a Hakko 909 desoldering gun but this teared the solder pads right of. In the end I used my Hakko soldering iron set to a low temperature and desoldering braid. This worked fine but you still have to be gentle.
Also some of the regulators on the channels were broken. Easy repair.

I didn't do any mods except to the master section. Here I swapped the opamps in the main audio path for LM4562 and I disabled the Midi-module.

The main issue that still remains is the dropping out of the meterbridge, but this is not a big issue.

Great desk!

Good to hear about another old soldier....

JR

 

[Nele]

That symptom sounds like an oxidized switch contact like perhaps in an insert jack switch..... turning up the music punches through the oxide layer.

Ah yes, I forgot. I also replaced some of the jacks.

 

[Newmarket]

That symptom sounds like an oxidized switch contact like perhaps in an insert jack switch..... turning up the music punches through the oxide layer

+1. I had this on an Insert Point (fwiw on my A&H GL2). Oddly on Channel 1 that you might think less likely as more use than the higher channels. What surprised me was the repeatability - crank the channel gain and note would get through find and sustain that performance for a set amount of time before failing again. I think I solved it with IPA/Deoxit/Cotton Buds but always aware and regularly crank channels to mitigate. Cleaning this particular case not so easy as connections are on the back panel so more or less vertical - like working on a car whilst avoiding drips

 

[jensenmann]

Look at the self-cutting Molex connectors (2nd picture, post #1). Many console manufacturers used to use these. Over the years both the contacts and copper get oxidized. Rip the wires out, shorten them and re-fit them. There´s a punching tool for that purpose, but it can be done without if care has been taken. That will solve many contact problems. If you still can find these connectors then it´s a good idea to use new connectors. I went through many consoles and these Molexes very often were the source of trouble.

 

[JohnRoberts]

+1. I had this on an Insert Point (fwiw on my A&H GL2). Oddly on Channel 1 that you might think less likely as more use than the higher channels. What surprised me was the repeatability - crank the channel gain and note would get through find and sustain that performance for a set amount of time before failing again. I think I solved it with IPA/Deoxit/Cotton Buds but always aware and regularly crank channels to mitigate. Cleaning this particular case not so easy as connections are on the back panel so more or less vertical - like working on a car whilst avoiding drips

This was decades ago so I may not recall all the details precisely but as I recall this switching jack problem occurred to a Switchcraft TRS switching jack commonly used in inserts. As usual I only get dragged into these field service situations after they become a problem. It ended up being blamed on the plating used for those switch contacts.

This was not Switchcraft's first rodeo and real (?) engineers were involved in the plating change. Of course such changes require approval by engineering but I never heard about it until after it turned into a widespread service problem. These switching jacks were used by several engineering groups so either one of the three of us could have approved it.

I still don't recall the details but there may have been a cosmetic issue with previous silver plating that "looks" bad (silver oxide tarnish is black), vs some other plating media that "looks" better. Of course this too passed..... Just another day in the life being manager over all mixers. When you use truckloads of components you find their weak links.

JR