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Author Topic: Restoring Vintage Gear Question  (Read 2705 times)

Big Bri

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Restoring Vintage Gear Question
« on: May 01, 2004, 01:34:19 am »

Dear John,

over the last few years our studio has accumilated a large collection of old Neve pre's, and compressors. I've slowly been recapping them as i get time but now more than ever am running into the problem of replacement caps at proper values.  Any suggestions on type (used to use panasonic HFS caps that are no longer made)and the proper way to combine caps to achieve proper values and what is acceptable if the proper value can't be arrived at reasonably.

Thanks in advance for your knowledge
Brian Baker
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John Klett

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Re: Restoring Vintage Gear Question
« Reply #1 on: May 01, 2004, 12:40:49 pm »

The easiest thing to do is replace the old caps with new ones of the same type...  Philips caps are now made by BC Components and the series you want are AML 138.  You can buy these from Digi-Key..  http://www.digikey.com

Nichicon VX is another possibility as well as a low impedance series from Lelan  but both of those are hard to find.  One of my associates is working on getting ELMA to do custom runs of a couple of the radial caps we buy lots of.  The minimum orders are in the 10,000's but in a lot of way's it's worth doing.  We are restoring several Neve 80 series desks now and this is going to keep coming up so it makes sense to just whack the axial cap availability problem on the lead and get on it...  the "whack a mole" approach to technical problems.

You can always go up in value and in voltage as long as the replacement cap fits mechanically - you don;t want to replace a cap with a lower value or voltage rating.  My own guideline/rule of thumb is that doubling the original capacitance is about as far as I want to go and if I can still fit a bigger cap I'l go to a higher voltage.  Once you have to start messing around fitting oversize caps to your boards you are asking for reliability problems.



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John Klett / Tech Mecca
http://www.technicalaudio.com

Big Bri

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Re: Restoring Vintage Gear Question
« Reply #2 on: May 03, 2004, 01:44:47 am »

John,

Thank you very much for the info...By the way do you or anyone you know have any gain pots for 1073/1066's.  I know they are hard to find and not cheap.

Thanks,
Brian
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thestudio

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Re: Restoring Vintage Gear Question
« Reply #3 on: May 03, 2004, 10:59:56 am »

John,

will you be selling the Elna capacitors? Rolling Eyes
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John Klett

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Re: Restoring Vintage Gear Question
« Reply #4 on: May 03, 2004, 03:40:49 pm »

The "gain" control in Neve 1073 (etc.) Channel Amplifiers is really a rotary switch.  Depending on what module you have, if it has only a single input for mic and line (like a 1063 module) or two inputs and input transformers for mic and for line or is a "Class A" modules (again like a 1073) or a "Class AB" module (like a 1081)...  the switch and the wiring of it (with resistors, bus wire and wire leads) will change.

For a Neve 1073 module you would need a 24 position switch with three "decks" so you end up with a 3 pole 24 throw switch...  actually you are using 22 positions of 24...  it's 15 degrees of rotation per switch position.

here's a drawing

http://www.technicalaudio.com/pdf/neve/EK20033-sensSW.pdf

and here is a 1073 so you can see how to wire it in

http://www.technicalaudio.com/pdf/neve/1073-EH10023.pdf

ELMA makes them

http://www.elma.com/us/products/rotary_components/

Look at Type 04

http://www.elma.com/us/products/rotary_components/Switches%2 0%26%20Encoders%20%3E%20Rotary%20Switches/6
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John Klett / Tech Mecca
http://www.technicalaudio.com

John Klett

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Re: Restoring Vintage Gear Question
« Reply #5 on: May 03, 2004, 03:42:54 pm »

I won't be selling those Elna caps but if my friend works it out I will post that info here...
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John Klett / Tech Mecca
http://www.technicalaudio.com

thestudio

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Re: Restoring Vintage Gear Question
« Reply #6 on: May 05, 2004, 04:41:54 pm »

You referenced Nichicon and BC caps but didn't mention Elna for Neve application? Is there a sound, spec, quality difference or?  Confused
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John Klett

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Re: Restoring Vintage Gear Question
« Reply #7 on: May 05, 2004, 07:49:47 pm »

The only ELNA caps you can get right now are radial.  Radials don't fit nicely in place of axials (laying flat - VR's they stand temp up) so I did not mention it.

The one axial cap Nichicon makes is hard to find.

The BC caps are good but a couple series of Elna caps sound better - the problem is the form factor.  Once I find out if a custom order can be done I will report back.  Right now it's only a concept.
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John Klett / Tech Mecca
http://www.technicalaudio.com

thestudio

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Re: Restoring Vintage Gear Question
« Reply #8 on: May 06, 2004, 01:23:49 pm »

The console I have has Elna's but I just wondering if there's a preference or quality difference. Also, on Elna's site they have caps made for audio (85C) and then general caps (105C) my question would be: should I go with a higher temp because I noticed on Neve V3's many tech's going with higher temp and longer life type.... Rolling Eyes
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Gold

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Re: Restoring Vintage Gear Question
« Reply #9 on: May 07, 2004, 03:49:07 pm »

john klett wrote on Wed, 05 May 2004 19:49


The BC caps are good but a couple series of Elna caps sound better - the problem is the form factor.  Once I find out if a custom order can be done I will report back.  Right now it's only a concept.


How do you evaluate the caps to find your preference?

Do you stuff two identical boards with different brands and listen?

Do you have a simple test circuit?

Do you also do measurements to check for things you might miss by listening?

ect?
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Paul Gold
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John Klett

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Re: Restoring Vintage Gear Question
« Reply #10 on: May 10, 2004, 04:46:45 pm »



This is a good question.  I've never written it up so I guess I can think about how to present this in some meaningful way but that won;t result in a complete answer now.

I have a couple circuits I test in.  

One is a virtual earth summing amplifier with a DC block cap right on the summing node but not "inside" the feedback loop...  that's just about the worst place for a cap but a it's good place for testing for differences.

Another circuit is an output amplifier driving a 200 ohm load resistive or a 150 ohm transformer primary (BIG 50% nickel output transformer).  

In both cases you are looking at large caps in low impedance applications.  The summing node is a good one because any non-linear aspects of the cap are placing themselves in between the summing buss inputs and the virtual earth node and degrading the buss and the quality of the virtual earth across the buss.

Listen and Measure.  

You'll find that, unless you have really been listening and tuning in to small differences like those you'll find from one cap to another that, you may not easily detect any differences...  so take four or eight of the same circuits and cascade them.  A/B compare between a cap and a wire (assuming you have no appreciable DC across the cap) or between a dried out cap and supposedly decent new cap.  Once you start picking up the subtleties it gets easier to compare one good cap to another better cap.  

Other tests

An impedance bridge is a good thing.

Simply driving AC current through a cap to ground and measuring across the cap at spot frequencies across the audio band while doing this...  The driving amplifier has be fairly stiff and drive the cap through a 100 ohm resistor.  You can also burn caps out pretty quickly this way...  it's kinda fun.  Any time you are measuring anything between the input of the cap and the grounded side you are seeing an indication of loss.  You can also have a single ended preamp amplifying whatever drop that cap has across it.

Various caps "score" better than others...  from there you do whole signal paths from input to output in a console and listen for what sounds better to you.  
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