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Question: Amphenol 7 pin connectors on old mic pre. Pls Help
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wolffproaudio
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Joined: 19 May 2016
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Location: Brooklyn, NY

PostPosted: Sun May 22, 2016 3:50 pm    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote

Test metered the amphenols with the unit powered up. Very, very similar to the LEMO pinout except I think the pin 4/5 duties are different. Definitely glad I metered it as I'm seeing 120v on one of the pins! Not going to hook that one up to any of my mics, needless to say. lol.

Im going to make some test leads to try the potential inputs and see if we get anything back out. Stay tuned and thanks for all the info!

~Dorian
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Nick Sevilla
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Joined: 03 Mar 2008
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PostPosted: Mon May 23, 2016 2:18 pm    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote

Thanks Dfuruta. Good to know I was wrong.

So, why the "no heater" label then? for evil antarctic lairs?
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dfuruta
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Joined: 08 May 2009
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PostPosted: Mon May 23, 2016 8:33 pm    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote

Beats me! Possibly something tube related?
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wolffproaudio
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Joined: 19 May 2016
Posts: 10
Location: Brooklyn, NY

PostPosted: Sat Jun 04, 2016 6:00 am    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote

First of all, thanks so much to everyone here who offered advice and helped me get on the right track! This thing is modded and passing signal now. Smile

After bouncing email with Bruel & Kjaer, they confirmed that this was built in their old Ohio division. Sometime in the late 70's or early 80's (Their HQ is in Denmark now). They have no further info on the unit, other than that it was likely for wide frequency range measurement microphones that use polarization voltage.

After metering voltage, impedance, and potential ground faults between chassis and every pin combo on the Amphenol inputs, I eventually isolated what I hoped would be the microphone signal input and ground. Success!

Leap of faith: modified the chassis for XLR in and 1/4" out. Safetied off the power supply feeds that went to the original mic connections. Currently running unbalanced (if anyone has a better idea, please tell) as due to the mysterious pinout readings on my meter, I couldn't verify a negative input.

4 out of 6 channels pass clean, crisp signal, testing with a cardioid vocal mic.

Racking it up in the studio this Monday to compare it to our other preamps! (Neve 1272 clones, Chandler, etc).

Thanks again and stay tuned.

~Dorian

















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dfuruta
re-cappin' neve


Joined: 08 May 2009
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PostPosted: Sat Jun 04, 2016 10:52 am    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote

Looks good! Have you looked at the board much? Might be possible to tell if it's balanced by looking at the input stage. Otherwise, process of elimination: are there any connected pins that you're not using that aren't ground?
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Scodiddly
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PostPosted: Sat Jun 04, 2016 6:57 pm    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote

Very cool!

The obvious answer to a single-ended input is a transformer.
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wolffproaudio
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Joined: 19 May 2016
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PostPosted: Sun Jun 05, 2016 5:49 am    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote

Scodiddly, forgive my n00bness, but please explain? I'm no electrical engineer.

~D
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wolffproaudio
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Joined: 19 May 2016
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Location: Brooklyn, NY

PostPosted: Sun Jun 05, 2016 5:57 am    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote


images hosting
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Scodiddly
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PostPosted: Sun Jun 05, 2016 7:08 pm    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote

wolffproaudio wrote:
Scodiddly, forgive my n00bness, but please explain? I'm no electrical engineer.

~D


Most old mic preamps only had a single-ended input, but used a mic transformer to make the input balanced.
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wolffproaudio
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Joined: 19 May 2016
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Location: Brooklyn, NY

PostPosted: Wed Aug 31, 2016 7:56 am    Post subject: Hi All! ~ Update Reply with quote

Pardon the slow update- right as we got these mystery Bruel & Kjaer pre's in working order we also opted to reconfigure our space for a Rupert Neve Designs 5059 summing mixer. Smile This past week has been a gauntlet of soldering work to convert our Mogami snakes to the required connections on either end. Testing all signal paths later today!

So- The Bruel & Kjaer is a very interesting beast! I haven't put it on any scope or analyzer since the conversion, but have been trying it with different tracking duties. First favorite: toms. Vocals and guitars seemed a bit too bright and harsh in the 3-6k range, but worked very well for a dark drum set, as well as bass. The low mids and stick attack for toms were naturally accented as most would want for rock.

I want to run some pink noise in to get a better idea of what the circuit is really doing. These pre's seem useful and unique. They can be pushed on the input side for some nice crunch & energy.

Still running unbalanced on the outputs, due to my lack of expertise, but they push a pretty hot, clean signal overall.

Ideas or advice? You all have been so helpful Thanks.

~Dorian



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Drone
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PostPosted: Wed Aug 31, 2016 10:20 am    Post subject: Re: Question: Amphenol 7 pin connectors on old mic pre. Pls Help Reply with quote

If you like 'em, leave 'em alone Laughing

Seriously, if it's working, sounding good, and not really a problem in your signal flow, don't do a thing.
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