Connecting Revox to an external VU meter bridge

[pentoad]

Has anybody done this?
Could somebody advise me on the best way of connecting a Revox A77 to an external meter bridge
Would you hook it up to the terminal at the VU meters in the Revox or from the recording cards?

https://www.ebay.co.uk/itm/DC-12V-VU...kAAOSwvfRdqdgc

[Ted Kendall]

It's simplest to drive it from the line output, with suitable buffering. Bear in mind that the standard A77 drops its record level by about 1dB when the tape/input switch is moved from tape to input, as the record amplifier is loaded down by the monitor amplifier.

[pentoad]

I think that module I provided a link to is for a DC meter with a VU scale and is meant to replicate what a true AC VU meter with rectification and buffer achieves. Whether it actually does that is the question: will it have the correct VU ballistics or will the needles just flap about meaninglessly.

[TIMTAPE]

Pentoad, from reading your other thread I get the impression you want to use external record meters because one or both internal A77 meters are faulty and you want to avoid the cost of replacing the existing meter(s). Is this so?

Meters can sometimes be repaired. I've repaired A77 meters in the past. A small part in the movement tends to become unglued from the moving coil assembly. I've glued it back again.

Last week I repaired the failed record meter of an old Uher Report L portable. The top hairspring had become unsoldered from one of the meter input terminals. Tricky soldering job but I eventually managed it and the machine is now back with its owner.

Surely someone in the UK has experience in this and could at least inspect the meter(s) and offer an opinion. Perhaps a watchmaker.

External electronic type meters would work but of course need their own power supply. Repairing or replacing the existing meters would seem a simpler and more elegant solution in my opinion.

[pentoad]

Originally Posted by TIMTAPE

Pentoad, from reading your other thread I get the impression you want to use external record meters because one or both internal A77 meters are faulty and you want to avoid the cost of replacing the existing meter(s). Is this so?

Meters can sometimes be repaired. I've repaired A77 meters in the past. A small part in the movement tends to become unglued from the moving coil assembly. I've glued it back again.

Last week I repaired the failed record meter of an old Uher Report L portable. The top hairspring had become unsoldered from one of the meter input terminals. Tricky soldering job but I eventually managed it and the machine is now back with its owner.

Surely someone in the UK has experience in this and could at least inspect the meter(s) and offer an opinion. Perhaps a watchmaker.

External electronic type meters would work but of course need their own power supply. Repairing or replacing the existing meters would seem a simpler and more elegant solution in my opinion.

Yes that's correct those replacement ones from Australia cost a fortune with shipping!
I think that the Revox meter from what I have gathered, maybe irreparable as the needle has fallen off completely.
I expect the other one to go the same way because of the way it whacks against the housing from the surge when switch on. - is that normal?
I will have proper look at it at some point.

BTW I have recapped the A77 and replaced the trim-pots and it seems fine for the moment apart from the meter

[pentoad]

Originally Posted by TIMTAPE

Pentoad, from reading your other thread I get the impression you want to use external record meters because one or both internal A77 meters are faulty and you want to avoid the cost of replacing the existing meter(s). Is this so?

Meters can sometimes be repaired. I've repaired A77 meters in the past. A small part in the movement tends to become unglued from the moving coil assembly. I've glued it back again.

Last week I repaired the failed record meter of an old Uher Report L portable. The top hairspring had become unsoldered from one of the meter input terminals. Tricky soldering job but I eventually managed it and the machine is now back with its owner.

Surely someone in the UK has experience in this and could at least inspect the meter(s) and offer an opinion. Perhaps a watchmaker.

External electronic type meters would work but of course need their own power supply. Repairing or replacing the existing meters would seem a simpler and more elegant solution in my opinion.

Yes only needle is detached so it maybe repairable with care
The needle should be slid under the fragile coil spring and glued.
I'm quiet nervous about doing this as requires a great deal of dexterity/skill and the coil assembly can rotate easily during this operation
What type of glue would you recommend for glueing the needle back onto the carrier.
I'm thinking that super glue would be tricky and unforgiving and epoxy would be too thick and heavy.

[pentoad]

VU super glue repair seems to have worked out fine

[MeerKat]

The VU meters banging against the end stops is normal.

I have cured this on my A77, see post #43 of my thread 'Revox A77 refurbishment advice please.'

Let me know how you get on.

[pentoad]

Originally Posted by Andrew64

The VU meters banging against the end stops is normal.

I have cured this on my A77, see post #43 of my thread 'Revox A77 refurbishment advice please.'

Let me know how you get on.

I had a quick look at what's entailed however, I don't think I have the confidence to tackle that modification - could end in tears!

I had seen some time ago an additional mod to the record amps, which was a tiny pcb called a Revox vu meter patch.
Sadly they have become unavailable

[TIMTAPE]

I would only mod the circuit if it was clear the switch on caused the meter to fail. Maybe it's a contributor but these meters also fail due to the glued parts separating as we discussed.

[pentoad]

Originally Posted by TIMTAPE

I would only mod the circuit if it was clear the switch on caused the meter to fail. Maybe it's a contributor but these meters also fail due to the glued parts separating as we discussed.

Even if the glue they used was stronger or lasted longer it does seem like a design fault the fact that the meters clatter during switch on, it's strange that Revox never addressed that issue.

[Ted Kendall]

Like the Rifas and the motor run capacitors, this was seldom, if ever, an issue when the machines were current over forty years ago. The patch board looks like some sort of RC slow-start network, so not impossible to replicate or think out anew. What is needed is something to keep volts off the VUs until the 21v rail has settled down, and probably quite advisable given the eye-watering cost of replacements. Those for the A700 are even more pricey...

[lesmw0sec]

The earlier note about 'with a buffer' is apt. Remember that a standard VU includes diodes, and without a buffer in between, this can some times cause distortion due to diode action. I've never understood why people do not use peak programme meters...

[Ted Kendall]

Cost, plus the fact that you only need one PPM in a given chain, and the usual place for this is the mixer. Once the tape machine is adjusted to give the desired level with tone sent from the mixer, its meter dynamics are an irrelevance. The original VU buffered the half wave rectifier away from the nominally 600 ohm line with 3.6K in series, which was enough to prevent objectionable effects. An emitter follower costs next to nothing now, of course.

[jamesperrett]

Originally Posted by pentoad

it does seem like a design fault the fact that the meters clatter during switch on, it's strange that Revox never addressed that issue.

Plenty of other devices exhibit the same behaviour - on one mixing desk that I have you sometimes have to give the meter a good tap before it returns back to zero after switch on. You could also say that Revox did eventually fix the problem - they called it the B77.