Hi I've trying to create a recording chain of

Chandler Abbey Road TG Channel > ADR Gemini Easy Rider > Tape Deck

for hours without success. 

I'm pretty sure it's because of the pigtail connections at the back of the ADR Gemini Easy Rider compressor which is similar to an old Urei 1176.  At first I was advised to just connect the red to + and blue to - for input and output and then leave the ground wires alone, which gave good sound but also a loud hum plus lots of electrical noise.  The hum went down when I connected the input ground to - with the red wire (see photo), but then the LED stopped working and the sound became quieter. 





Should I be connecting anything to the "chassis"?  Are my DIY pigtails terrible?  I'm pretty lost and would appreciate any help.

Many thanks!


MeToo2

No one else has replied so I'll give this a go. Your kit looks generally untidy, which is not going to help mains hum (although it may not be the cause). You may want to invest in a small rack to save you some set up time and frustration in future.

You have a mix of balanced and unbalanced gear.

Doing a web search: the Chandler does look as though it has both input and output transformers so I guess that won't be the problem.

As far as I can see on the schematic: http://www.moonpony.net/images/Gemini_schematic.jpg the Gemini Easy Rider does NOT have balanced outputs nor balanced inputs. 0V really is 0V, and will probably be connected to the chassis (somewhere). It is no way similar in output circuitry to a 1176 (which has an output transformer, and generally electrically balanced inputs). Looks like a really cheap design to me, but if you like the sound then fair enough. You can check if there is a connection between chassis and 0V using a multimeter on resistance setting. So one thing to try would be to explicitly try disconnecting 0V to chassis on the Gemini Easy Rider box (e.g. the tag strip to the left, ground lift switch, remove other screened connections etc.) but I doubt that will help because I don't see any jumper there on the photo anyway between chassis and 0V.

Two signal wires should be enough between the Chandler and the Gemini Easy Rider, but you will probably want to only connect ONE end of the overall screen on the interconnect cable (at the output of the Chandler since the Easy Rider isn't balanced). Do not connect the screen to the chassis of the Easy Rider.

For the Gemini to the tape you have unbalanced to unknown (you didn't mention the type of tape deck) So the tape could either be balanced or unbalanced. See for example http://scopeboy.com/balance.html for a description of the various combinations. Or maybe clearer is this white paper http://www.rane.com/pdf/ranenotes/Sound%20System%20Interconnection.pdf

Anyway, if you've got two channels of Easy Riders connected to the same pieces of source kit as it appears in the photo that to me also looks like a recipe for a hum loop (two pieces of unbalanced gear in parallel).

Therefore putting a 1:1 galvanic (transformer) isolation box between the Easy Rider and the tape machine would certainly be something thing to try, and may be the only true solution.

Also make sure your kit is all plugged into the same phase of mains at a common well-grounded outlet, and that your cabling is tidy.
« Last Edit: March 04, 2011, 04:06:28 AM by MeToo2 »

tmuikku

Also the Good Old Rane Notes might provide handy ;)

http://www.rane.com/library.html
- check especially the section about Wiring, Interconnection & grounding

Thanks for the response.

Sorry I forgot to mention, my tape is either a Nakamichi 680 (via a Alice Matchpak for swithcing balanced XLR to unbalanced rca, then an old Sansui AU 7900 amp) or a Tascam 424 mk III.  At the moment I'm hooked up to the Tascam.

I'll have a look at the notes you guys have suggested, I guess I've got some learning and tidying to do tonight.

 

MeToo2

Thanks for the response.

Sorry I forgot to mention, my tape is either a Nakamichi 680 (via a Alice Matchpak for swithcing balanced XLR to unbalanced rca, then an old Sansui AU 7900 amp) or a Tascam 424 mk III.  At the moment I'm hooked up to the Tascam.

I'll have a look at the notes you guys have suggested, I guess I've got some learning and tidying to do tonight.

 
Well your 424 mk iii has both balanced and unbalanced in and out, but it can only cope with -20 dBu on the balanced side and -10dBu on the unbalanced side, so it's easy to overload. Your Nakamichi can also only run unbalanced (50mV @ 50K = -26dBu), but is probably much much higher quality than your Tascam 424. Obvious place to me to put the Alice Matchpak would be immediately on the output of your Chandler to avoid overloading your -10dBu unbalanced (jack or terminal block) inputs..... (and not between the Gemini and the tape) and then run the other stuff unbalanced. YMMV.
« Last Edit: March 04, 2011, 08:12:12 AM by MeToo2 »

Cool I'll try that.  Also I've got a DBX 160x and ART ProVLA, both (I think) can work with unbalanced signals so maybe they can go between TG and Gemini.  The Alive has XLR in and RCA outs which is a pain.

The Tascam actually sounds better for mixes because I use High Speed and then turn the pith control to max so it's running much faster than Nakamichi.  But Nakamichi sounds more faithful to the source though, even though it does have a subtle Nak sound.
« Last Edit: March 06, 2011, 09:49:40 PM by Farringdon »

I tried making it unbalanced after the Chandler TG and before the Gemini but there's still noise.  But when I connect the ground wire of the pigtail to the - (negative) of the input of the Gemini instead of leaving it unconnected, the sound goes away.

Can anyone explain why that works and if it is recommended?  The main drawback is the the LED stops working when I connect the groundwire to the -.

Many thanks in advance.
« Last Edit: March 06, 2011, 09:49:01 PM by Farringdon »

MeToo2

Sorry, not understanding your banter old boy. Don't mean to sound facetious, but your description does not seem to be very enlightening. Could you try to clarify.
I tried making it unbalanced after the Chandler TG and before the Gemini but there's still noise.

Exactly how did you try to "make it unbalanced?"
With the Alice Matchpack, or with a cable, or some other way?

What sort of noise? hiss? mains hum? Your signal?

But when I connect the ground wire of the pigtail to the - (negative) of the input of the Gemini instead of leaving it unconnected, the sound goes away.
Which '-' input. Don't want to sound dumb, but there doesn't appear to be a connector marked '-' on the back of a Gemini. Only '+' and '0V' input and output and "chassis"

When you say ground wire, do you mean pin 1 from the XLR on the output of the Chandler?

Thought if you truly were using unbalanced (from the tulip connector of your Alice Matchpack), there would be no separate ground.

Which sound goes away? The mains hum? Your recording signal?

Can anyone explain why that works and if it is recommended?  The main drawback is the the LED stops working when I connect the groundwire to the -.

Many thanks in advance.
Sorry can't explain it.

Which "LED stops working?" As far as I can see there are 20+ LEDs on the front panel. There's a GR meter, a clip LED, and other indicators.
Do you mean the 20 LED's of the GR meter stop working? The power LED? The clip LED?

If it's the GR meter, that's a bad sign, because that would sound like there's a DC offset somewhere, or something else stopping the box from compressing at all (FET not properly biassed?).
When you connect the ground wire to the input it would suggest that ground ref of the psu is being shifted.

Can you measure any DC offset on the output of the Chandler (pin 1 to pin 2 of the XLR and pin 1 of the XLR to pin 3) without the boxes connected?

Can you measure any DC offset on the input of the Gemini ("0V input" to chassis, "+ input" to chassis) with and without the boxes connected?

Does that change when the boxes are connected? Does that change when the ground wire is connected?

Hi Metoo2,

Thanks for your help.

The LED I'm referring to is the GR meter, sorry I should have been more specific.  However today I started the unit up and the GR meter is working again even though I still have the ground wire (XLR from Chandler) connected to 0v.  The compressor sounds like it's working and the noise/hum has gone.  It might be a less hot sounding but maybe that's how it's supposed to sound without the noise.  As soon as I remove the ground wire (not the blue or the red, pin 1) from 0v, the noise comes back.  I have nothing connected to the "chassis" side.

To make it unbalanced someone adviced me to put a unit that can be both balanced and unbalanced between the Chandler and the Gemini.   In my case I have a ART Pro VLA and a ADR Compex 2 that I think can do that.  At the moment I'm using the Compex 2 as suggested by my friend.  I also just found 2 XLR (male and female) to 1/4 adaptors that might be helpful.  My Alice Matchpak only converts XLR balanced to RCA unbalanced, so it's hard to use without extra cables and adaptors that I don't have.  Anyway so far I've found two things that lower the noise:

1) Connecting the ground wire as well as the blue wire to 0v at the input of the Gemini

2) Disconnecting the spdif out of the Lavry convertor sometimes lowers the noise

I understand why 2) works, but not 1).   Hope this makes more sense.
« Last Edit: March 08, 2011, 05:24:37 PM by Farringdon »

 

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