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Author Topic: Studer A810 with unbalanced preamp...  (Read 3610 times)

Offline Guglielmo

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Studer A810 with unbalanced preamp...
« on: February 13, 2014, 04:03:31 AM »
Hi to all!

Last night I connected a Studer A810 with XLRs output to my McIntosh C28 RCAs with a dedicated cable (XLR -> RCA). I utilized the C28 rear inputs REC in. I didn't connected the REC out because I was interested in playback only.

The C28 is freshly refurbished and serviced so fully functionally and within specs. And then I realized a severe hum even without signal and even disconnecting the tape machine and just leaving the cables... The hum is important and intolerable with the preamp volume pot beyond 12 o' clock. I checked the cables and I noted that all the 3 pins of XLR are isolated between them. I conencted another cable (always XLR to RCA) but with pin 1 nad 2 of XLR connected and the hum is still present even less loud...

May be the cables are not suitable and leading to unwanted ground loops?

Should I need this?

http://www.ebay.it/itm/Jensen-Transformers-PC-2XR-XLR-RCA-Audio-Converter-Balanced-to-Unbalanced-/400456028519?pt=US_Signal_Amplifiers_Filters&hash=item5d3d0a1167

Thank you for expert help!

Guglielmo


Offline High and Outside

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Re: Studer A810 with unbalanced preamp...
« Reply #1 on: February 13, 2014, 01:11:31 PM »
Guglielmo,

You are getting good advice from Richard Hess over on one of the Studer lists.

I would add a couple of things:

First, figure out the best way to plug in your power cord. Since the preamp has a two prong plug it can be plugged in either way, and one way will give lower leakage current than the other. Connect a meter between the chassis of the preamp and the ground post on the back of the 810, set it for AC volts, and try both orientations of the plug. The one that gives the lowest reading is the one to use.

Now hook a wire between the chassis of your McIntosh and the ground post on the back of your 810. Do this BEFORE you make any signal connections. Make some shorting plugs for the inputs that you will be using on the preamp--that's just RCA plugs with the two terminals shorted together. With the shorting plugs installed, the ground wire connected and everything powered on your system should be noise-free. If not, you have some problem in the preamp that should be fixed first.

But if it's quiet at this step then remove the shorting plugs and connect the 810 to the preamp using cables made according to Richard's advice: pin two to RCA center pin, pin three to RCA shell, and start with pin one connected to the shield of your cable but not connected to anything on the RCA end. If it's quiet, you're done.

If it's almost quiet but not quite, then try connecting the shield to the RCA shell.
Paul Stubblebine
Managing Director, The TapeProject

Offline Guglielmo

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Re: Studer A810 with unbalanced preamp...
« Reply #2 on: February 14, 2014, 04:05:31 AM »
Thank you very much for extended trouble shooting procedure. I shall follow that accordingly.

In the meantime I checked my available two sets of cables how they are connected inside:

Cable #1

XLR pin1 together with pin2 and connected to RCA outer
XLR pin3 connected to RCA central (hot)

Cable# 2

XLR pin 1 connected to RCA outer
XLR pin3 connected to RCA central (hot)

Both cables just plugged to my vintage preamp unbalanced inputs and without source load (Studer A810) generate a lot of noise, mainly the Cable set #2.

Actually none respects the internal pin connection as suggested by you or Richard... These cables need some reconfiguration!

Cheers,

Guglielmo

Offline gamve

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Re: Studer A810 with unbalanced preamp...
« Reply #3 on: February 14, 2014, 07:36:02 AM »
Thank you very much for extended trouble shooting procedure. I shall follow that accordingly.

In the meantime I checked my available two sets of cables how they are connected inside:

Cable #1

XLR pin1 together with pin2 and connected to RCA outer
XLR pin3 connected to RCA central (hot)

Cable# 2

XLR pin 1 connected to RCA outer
XLR pin3 connected to RCA central (hot)

Both cables just plugged to my vintage preamp unbalanced inputs and without source load (Studer A810) generate a lot of noise, mainly the Cable set #2.

Actually none respects the internal pin connection as suggested by you or Richard... These cables need some reconfiguration!

Cheers,

Guglielmo

Yep should be pin2 Hot
Graham Van Essen
(Living in the past in an analogue dream)

Offline HDVS

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Re: Studer A810 with unbalanced preamp...
« Reply #4 on: June 13, 2014, 04:26:29 AM »
Thank you very much for extended trouble shooting procedure. I shall follow that accordingly.

In the meantime I checked my available two sets of cables how they are connected inside:

Cable #1

XLR pin1 together with pin2 and connected to RCA outer
XLR pin3 connected to RCA central (hot)

Cable# 2

XLR pin 1 connected to RCA outer
XLR pin3 connected to RCA central (hot)

Both cables just plugged to my vintage preamp unbalanced inputs and without source load (Studer A810) generate a lot of noise, mainly the Cable set #2.

Actually none respects the internal pin connection as suggested by you or Richard... These cables need some reconfiguration!

Cheers,

Guglielmo


Guglielmo,

the cable #1 is ok, but the absolute phase is inverted. You should swap pin 2 with 3.

The cable #2 can't work without introducing noise and limiting the bandwidth because the signal path is left open. Pin 2 and 3 must always be connected in balanced cables. At least you can leave floating pin 1.

My suggestion:

- swap pin 3 with 2 on the first cable.
- connect the ground of the RCA to pin 3 and the hot pin to pin 2 on the second cable

Have Fun!
Giorgio
Ampex ATR102 1/4" & 1/2" - Nagra T Audio (2 units, one set for NAB, the other to CCIR EQ) - Nagra DII - Stellavox TD9 1/4" & 16mm perfo - Telefunken M15 - Telefunken M5 mono - Digitec F500 - ABE AG31 - Studer D820X - Studer 961 - EMT 100 - Crookwood Paintpot MkI

Offline newrant

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Re: Studer A810 with unbalanced preamp...
« Reply #5 on: June 13, 2014, 06:08:14 AM »
be it so !