70's Console, noise (6k to18K hiss) troubleshooting help?

I have a 1976 Raindirk Console with Audio Design 760 Compressors on the 2 of the busses. The pre's sound thick and as friends call it "creamy" sounding. The inserts for each channel are Long Frame 1/4" which I have been using as DO. Anyway, it has been minimally recapped (just a few specific caps). I have noticed the noise floor has been raising, there has been an increasing 6k to 18k hiss on every channel, the more gain, the louder the Hiss. It does not matter if I use the Long Frame insert out, the busses, or main out; its still there on every channel.

I spoke to John Klett about it and he seems to suspect its a Balanced and unbalanced transformer problem. John only had a minute to talk (busy guy), so I didn't get a chance to ask him how I could troubleshoot the noise issue.

I spoke to Raindirk, they said that even the units back in the 70's were very quiet. roughly -120db

Today the level is around -20 to -40db

First question: what would you suggest and where would you to start for trouble shooting the noise? I would like to test down the resistors, After all everything in the console is 30 years old.

Second Question: Can input and output Transformers go bad after 30 years? Could the age of the transformers contribute to the noise increase?

Thanks Cannikin
aka David

Do you have a schemo for this mixer?

I would not suspect resistors or transformers to become bad in the first place. Do you get this hiss on every channel at the same level?

Samuel

Unfortunately, I don't have the schematics, although I have been talking with raindirk people and they are trying to find them.

The Hiss is approximately the same on every channel, although channels 8 & 9 its about 10db louder.

[quote author="cannikin"]Unfortunately, I don't have the schematics, although I have been talking with raindirk people and they are trying to find them.

The Hiss is approximately the same on every channel, although channels 8 & 9 its about 10db louder.[/quote]


wierd....and it's everywhere, including the sub/master modules (with nothing assigned)? maybe it's time to look at your power supply, or perhaps the grounding overall..... if the modules are removable it might do you some good to go through and clean/DeOxit/ProGold connections first, just to make sure a flaky connection somewhere isn't propagating the problem everywhere else....

the thing is, to troubleshoot you need to try and check things out in isolation, and remove the usual suspects from the lineup. check the console out with no other gear (including patchbays) connected. if it's still there, a good clean of the internal connections (i.e., where the modules mate to the console frame or wiring harness, etc.) is probably in order if it hasn't been done already. make sure everything's seated/attached properly. try with just one module and see if it makes any change, then add them back one by one. if that still doesn't take care of things, then maybe make sure all the grounds are securely connected, maybe run through and measure with a voltmeter to make sure that all the points that are supposed to be grounded are truly measuring very close to 0 ohms. if everything looks normal, maybe going through and measuring the voltages from your power supply would be the thing to do.


if it were me, that's the way i'd start (i might be missing some obvious things here that someone else could point out). you want to avoid blindly trying fixes untill you're pretty sure where the problem is originating from, because that can get expensive and time consuming.

Thanks that really helps, I will disconnect all the modules and start from there.

I have a feeling its the power supply, I believe its only using +38V. There's no phantom power for the mics I think the power was modified at some point



The fuses that are lit say +18v +12v and -8v
But for the first step I will Clean all the connections with deoxit and ProGold

Thanks

Here a little photo album of the guts if my Mixer.

http://homepage.mac.com/cannikin/PhotoAlbum5.html

And its not for sale

If it's on every channel, everywhere, I'd try adding a bunch of decoupling on one channel and see if it goes away. If so, the noise is coming from the power supply. That's one point where it will affect every channel.

One other option is something on the really noisy channels is oscillating somewhere in the 100kHz to 30 MHz region (you need a nice scope to check this out). Try putting a scope on the power rails, no signal, but set the sweep to maybe 1 us per div, and auto trigger just over 0, and AC input. Probe and see if you see that kind of oscillation. This kind of oscillation can manifest itself as noise everywhere, as it travels around on supposedly ground busses, mixing busses, and power busses.

I had this happen on an old Audiopro powered PA mixing board.

Good luck!

_Dale

[quote author="cannikin"]Thanks that really helps, I will disconnect all the modules and start from there.

I have a feeling its the power supply, I believe its only using +38V. There's no phantom power for the mics I think the power was modified at some point



The fuses that are lit say +18v +12v and -8v
But for the first step I will Clean all the connections with deoxit and ProGold

Thanks[/quote]


is there an indicator light for the 24v & phantom power? don't see them....i would check the power supply legs (+18v, -18v, 12v, 24v & 48v) just to be sure that things are hunky dory. probably is, but you never know especially if the PSU was "modified".... a lot of things people do to "modify" equipment turn out to be a bad idea. check it out -carefully, with a voltmeter while the console's powered up (so that you are checking it while the power supply has it's usual load). the cleaning thing is still a good idea if it's not been done.

Nope no lights for +24v or +48v

The lights it has is for +18v , +16v, -8v.

So from what people are telling me, this is what I'm going to do tomorrow:

I am going to pull all the modules out (faders, input channels, busses), leaving only the main outs. Then power the gutted beast up.

Listen if the noise still exists, if so its most likely a power issue, right?
then take a voltmeter to see if and where there are fluctuations in the voltage and ground throughout the board.

while the modules are out I'm going to clean them with DEoxit and ProGold.

but If the console is silent with no modules in it, then using only one module test it on every channel.

Does this sound right to you guys?

its a start.

[quote author="cannikin"]Nope no lights for +24v or +48v

The lights it has is for +18v , +16v, -8v.

So from what people are telling me, this is what I'm going to do tomorrow:

I am going to pull all the modules out (faders, input channels, busses), leaving only the main outs. Then power the gutted beast up.

Listen if the noise still exists, if so its most likely a power issue, right?
then take a voltmeter to see if and where there are fluctuations in the voltage and ground throughout the board.

while the modules are out I'm going to clean them with DEoxit and ProGold.

but If the console is silent with no modules in it, then using only one module test it on every channel.

Does this sound right to you guys?

its a start.[/quote]


yeah - i would then add at least buss module and see so then you'll have a path for the input module to go to...i guess you could assign right to the master as well. shut off the power supply before adding modules just to be on the safe side in case it doesn't like hot swapping.

if it's still crapola with just the master in then it's likely your not-quite-stock power supply. if not carry on until you run into problems. that should narrow things down considerably.

It's an old Raindirk.

It Hisses.

I'm very tempted to say "get over it", but I suppose that it would be more constructive to say that this is just a noisy piece of gear. The Pots and switches are cheap carbon track, it's going to be a bit crackly, crunchy and so on.

Raindirk were never very high quality. You can spend a lot trying to improve it, but it would be a lot like spending money on a Ford Escort in an attempt to make it beat a Ferrari 308. Of course it would be possible, but you could buy a new Ferrari for less than it will take, and what you will end up with will still be a Ford Escort, with rather limited resale value.

You could spend a lot of money replacing a lot of things and still end up with a cheap, noisy Raindirk console, that for some reason you sank a lot of money into.

Never been a fan of Raindirk. When they were being advertised we used to wonder who was buying them...

Keith

I always thought Raindirk was quite a classy console....never used one though.

@SSL tech: I can buy a Sony mxp2900 for cheap. What do you think about that one?

SSLTech, thanks for the kind words and opinion.

Though its no SSL or Neve. Its a really wonderful small console, no there is no crackle crunchy pots everything is smooth. I have had amazing results tracking drums, guitar, and bass. I can get it to be punchy and fat. Using the raindirk with ribbons, forget it - nothing has compared. Sure The transients are not ideal to capture acoustic guitars and some vocals and yes it can get mushy sounding if I track the entire album with it, but thats why I have a bunch of outboard gear. The Audio & Designs 760 comp/lim on it sound amazing. the Pre amps, are very open and lush. It may not be an A Class console (ferrari or Porshes) but I don't expect it to be.

In the end, I enjoy results and the people I have recorded enjoy it. I'm not trying to make this anything else.

All I want is to get peoples thoughts on how to troubleshoot, if it costs me money than thats my business.

Cheers
Cannikin

a -40 to -20 dB noise floor means something is very wrong somewhere, even for an allegedly mediocre design. i have never been anywhere near a Raindirk so i don't know anything about them - wasn't that Dick Swettingham's company, the guy who built the Helios consoles?

I guess I have to apologise for the hijack as well...

[quote author="radiance"]I can buy a Sony mxp2900 for cheap. What do you think about that one?[/quote]
I only ever worked on the MXP3000... is the 2900 a discounted 3000? :wink:

The 3000 was decent enough. The preamps were replaceable modules, as were the EQs, which had several different plug-n-play options. The power supply was a nightmare. The company which made them (Deltona Power Supplies) are nearby and refuse to have anything to do with them... (they were made to MCI's specification and they're hideously troublesome!)

Cannikin, if you like the sound of the console don't change it. If you don't like it, change it. If you want to get rid of the hiss, replace it.

I reckon the PSU rails should be +18V, +12V and -18V not -8V... you might want to check again.

Don't get me wrong, SSL E and G series aren't exactly stunning sounding boards either, nor are the Neve V series. J series are good SSLs and some older Neves are good, but I'm not a big fan of earlier SSLs or Later Neves, with the possible exception of the 88R, which I've never had the pleasure of working on in person. Focusrite inlines and 9098i's are benchmark consoles, but I've made great sounding albums on Allen & Heaths before now.

I have worked on Raindirks though, and after the first encounter, I only went to the studios that had them if there was no budgetary option. The noise and crunchiness is something you'd have to put up with if you like other aspects of the sound, for example.

Keith

[quote author="blakbeltjonez"] wasn't that Dick Swettingham's company, the guy who built the Helios consoles?[/quote]

Yes I believe it was.

Cyril Jones was Mister Raindirk I believe; not Dick Swettenham.

I know that Cyril and Dick Swettenham worked together on a helios upgrade/rebuild, but I'm not aware of Dick ever having any association with Raindirk. The extent of their collaboration (to my knowlege) was that Cyril did the console rebuild with Dick working as a consultant.

Keith

ah, ok.... i know i had seen the Raindirk/Helios names together somewhere, you're absolutely right.

Here are the Results of a series of tests I performed try and isolate the noise.

1. I removed all the modules (channel strips, Faders & Busses), leaving only the master out. When I powered it up everything was good, all knobs cranked all the way up.
Right Channel: -128dB to ?124dB @1kHz
Left Channel: -127dB to ?123dB @1kHz

2. Powered it down, added the busses(760 Comp/Lim) and Buss faders. Powered it back up. Master Output knob at max, Faders at +10
Right Channel: -120dB @1kHz
Left Channel: -120dB @ 1kHz

3. I switched the 760 Comp/Lim ON.
Right Channel: -123dB @1kHz
Left Channel: -123dB @1kHz

4. Turned the input and output of the 760 Comp/Lim to Max.
Right Channel: -83dB @1kHz
Left Channel: -123dB @1kHz

5. I took one channel strip and fader and put it on Channel 1. (Output gain and bus faders at maximum, no 760 comp/lim). Channel Strip fader +10 and channel gain turned all the way up (no group assignment).
Right Channel: -119dB @1kHz
Left Channel: -113dB @1kHz

I assigned the channel to group A (left channel) - 67dB @1kHz
I assigned the channel to Group B (right channel) -73dB @1kHz

6. On Channel 1 I took the Long Frame 1/4? channel insert out (the insert is pre fader).
The signal scope reads: -90dB @1kHz

7.I took the same channel strip and moved it to channel 9 of the console and performed the same tests. Trim and fader at max. (No group Assignment)
Right channel: -120dB @1kHz
Left channel: -116dB @1kHz
Group A (left channel) -65dB @1kHz
Group B (right channel) -71dB @1kHz

Another thing I noticed, There is also a 10dB spike at 60Hz. So if my noise floor is ?130dB, at 60Hz it reads ?120db.

With the given information what are your thoughts, in regards to the issue. I think its 2 fold.