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Author Topic: V series noise level  (Read 10778 times)

Jonas as

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V series noise level
« on: January 03, 2005, 03:23:21 PM »

My experience with these pre-amps is limited to the Telefunken V72 and the Mercury audio  "remake" the M72.

I find the V72 to be an amazingly sounding amp, it like it very, very much!
However, i also like ribbon mics very, very much.
Recording acoustic instruments with ribbon mics trough an V72 (or M72 for that matter) is simply too noisy, but GREAT sounding.

Is other V series amps less noisy,-would an V76 be better suited noisewise?

Thanks for any info, hope this is the right forum for this!

-Bora

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RMoore

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Re: V series noise level
« Reply #1 on: January 03, 2005, 03:35:33 PM »

The v77 mic pre is well suited for ribbon mic duties due to its high gain,
I use one all the time..
Have no experience w V76
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Oliver Archut

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Re: V series noise level
« Reply #2 on: January 03, 2005, 04:21:31 PM »

Hello Bora,

the historic stock V72 is not the greatest choice for a ribbon mic due to its 34dB (EMI/Carl Lindstroem versions 40dB)of gain.

As Ryan pointed out the historic stock V77 is better, but the historic V76 works best.

Regarding noise, a proper rebuild and modified historic V72 gives you about 60dB of gain, with a self noise of approx. -88dB weighted, that translate to approx. -110dB noise at max. gain.

Please take a look at the historic specification (see attached pic) with AC heating, if you heat the filament with DC you get a signal to noise ratio that touches the physical limits.

A proper rebuild V76 has a self noise of - 120dB AC or DC heating.

Putting this in proper perspective, most historic American mic pres in the same league than the V72, RCA, Westrex, etc; the best of them has a self noise of -60dB....
The best A/D converter today is approx. -75 dB (last time I checked company specs..)

I can not talk about the M72, it might be just an V72 inspired unit, but if this units is noisy you want to check the self noise, and make sure there is nothing wrong with it... If it is a V72 type pre, the noise specs should apply too.

Regarding historic V7x units, if your Telefunken V72 is noisy it probably reminds you that it is in desperate need of service..

From the statistic, 90% of all units that were send to me last year did not even meet the historic specs. just passing signal.

Biggest problem, 48V use/damage (see 48 volt info)  http://recforums.prosoundweb.com/index.php/t/3244/1288/?SQ=1 ea6ac25558ae22943a72e719101fbde

2nd problem, over heating of the filaments due to wrong mains 230V/240V vs. 220V or wrong improper step up x-former, that will fry your tubes and power x-former.
I ripped out step ups with mains as high as 250V out of home made and so called professional racks...

3rd problem, improper removal and/or modification on cost of S/N ratio as well as sound.

4th problem wrong tubes to save some money other tubes than the EF804/806s tubes were installed.

Hope that answers your question.

Your info indicates that you are located in europe, if you need a good V tech, I can give you some suggestion via PM.











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Oliver Archut
www.tab-funkenwerk.com

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Jonas as

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Re: V series noise level
« Reply #3 on: January 03, 2005, 04:44:24 PM »

Oliver,
Thanks for your very prompt and informative reply!

I have huge respect for people with this level of specialised knowledge, great! Very Happy
Seems like we'll be looking into getting an V76 , when we can afford one.


I would definately be interested in knowing which techs in europe you can suggest for V72, it seems quite a bit more noisy than the M72, altough i don't think they are meant to be comparable in that realm.

(edited to remove inappropriate unscientific second hand content that i posted about a pre-amp)

Again, thank you for your helpfull info!

-bora
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Oliver Archut

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Re: V series noise level
« Reply #4 on: January 03, 2005, 07:06:29 PM »

Hello Bora,

yes, it is inappropriate...

over the years I put down several offers about hosting/moderation, etc. due to the fact that I always have the conflict building gear, so what shall I do, use this forum as a showcase for my work? I do not think so.

I agreed to be a guest moderator, to talk and exchange info on technical issues or recording related problems. Bringing up my or other people products directly (sometimes it is hard to avoid) is not appropriate.
I am more than happy talking about facts, so please post some hard data like S/N ratio specs, with reference how they were measured, etc. Not just a nice sale pitch story.

I have no problem talking about design fields like the historic V series, x-former design, etc. or maybe just some experience on being a small business owner in a corporate america run market. If you want we can talk about how the magnetic field of the earth is compromising electron flow in audio tubes, thats fine as well,  but please do not use this forum for sale links or pimping.

I do not want to edit nor delete messages, working out issues is a big part of social interaction. I hope I made myself clear.

I will PM you a very reliable tech in europe.

Regarding your noise issue I double checked with a tech that worked on a M72, the self noise of the M72 is -65dB (shorted input 600 Ohm strapped output), so it appears that your historic V72 lost some sparkle and needs some TLC....
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Oliver Archut
www.tab-funkenwerk.com

We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.

Jonas as

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Re: V series noise level
« Reply #5 on: January 03, 2005, 07:23:27 PM »

Thanks for setting me straight, Oliver, I Edited my message. Shoul be OK now, i think.

Thanks
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dcollins

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Re: V series noise level
« Reply #6 on: January 03, 2005, 09:29:03 PM »

Oliver Archut wrote on Mon, 03 January 2005 13:21


The best A/D converter today is approx. -75 dB (last time I checked company specs..)


It must have been a while, as todays converters are like 40dB greater than that, unless I'm misunderstanding you

http://www.asahi-kasei.co.jp/akm/en/product/ak5394a/ak5394a. html

DC

Oliver Archut

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Re: V series noise level
« Reply #7 on: January 03, 2005, 10:45:44 PM »

Hello Dc,

you pointing out the theoretical specs of a chip manufacture, and not the real life specs of a intergraded product, XLR or 1/4 inch, maybe RCA in, via soundcard/converter onto the digital domain.

I am talking about the self noise of any given four pole with a shorted input, only measuring noise that is introduced by itself, in form of the active device, like transistor, tube or op amp and power supply. The lowest self noise is limited by the electron movement through a conductor by a given impedance.

I didn't even go as far as interference noise, you are close to a EM/RF source and you are not sufficient shielded, etc. This is in most cases a bigger problem than the self noise.
(the historic V72 is protected by a magnetic shield approx. 70dB, in form of 300 gram of Mu-Metal)

If I understand the spec sheet right, you have the actual A/D chip, with an op amp/earth free input, but in order to feed it a line signal you need to buffer the input with either passive pad (introduces noise and phase shift), an electronic impedance converter (introduces noise) a transformer (price factor comes to mind) or and electronic amplifier with high negative feedback (you end up with phase shift and either high or low spectrum noise).
Otherwise you will overdrive the chip (with standard mic pre outputs) to kingdom come, due to the fact that all standard inputs of converter have a very simple but effective peak stop limiter (two anti parallel diodes to protect the chip of destruction.

The last time I looked (about a year ago or so) every manufacture published the digital specs, that look great on paper, but the analog self noise is approx. about -75dB. I even measured a few but gave up on the cause...  

Up to today there is no acoustic digital converter, even some so called digital mics are out there, they still have a buffer in form of an electronic amplifier build in, so we still deal with the basic rule of four poles established at the beginning (to be precise in 1906)of the last century.
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Oliver Archut
www.tab-funkenwerk.com

We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.

jfrigo

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Re: V series noise level
« Reply #8 on: January 04, 2005, 12:36:47 AM »

Oliver Archut wrote on Mon, 03 January 2005 19:45

The last time I looked (about a year ago or so) every manufacture published the digital specs, that look great on paper, but the analog self noise is approx. about -75dB. I even measured a few but gave up on the cause...


Hi Oliver,

It great to have you here. I'm looking forward to absorbing some great info over the next month.

I'm probably getting in over my head as I'm a user, not a designer, but here's a quote and some published specs from Dan Lavry's converter:

Quote:


the AD122-96MKII features -127dB dynamic range (unweighted)

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Oliver Archut

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Re: V series noise level
« Reply #9 on: January 04, 2005, 10:43:01 AM »

Hello Jefrigo,

I would be happy to get more up to date input, for myself, I find my way around in the analog world, linear/nonlinear and controllers, etc. digital I understand but never got into it...

I always get confronted by customers that use my product to "warm up" the signal before they go digital; what ever that means.
But up to today I did not found or hear any converter set up that I could recommend, if somebody ask me what I think about it...
The ones that sounded O.K. are noisy as hell and the once that have good noise specs sounded like a can. (those ones are user quotes from several of my customers!)

On the other hand it is hard to recommend going the analog way, the vinyl age is commercially over for two decades and the Magnetic Tape age is nearly gone too, if no entrepreneur steps in and takes over the last remaining factory that still has original equipment...
http://recforums.prosoundweb.com/index.php/t/3243/1288/?SQ=4 a085268878d7047e1f6d013277dd26c

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Oliver Archut
www.tab-funkenwerk.com

We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.

Bob Olhsson

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Re: V series noise level
« Reply #10 on: January 06, 2005, 12:30:37 PM »

Preamp specs can be very misleading with ribbon and dynamic mikes because the noise spectrum has a huge impact on the subjective noise level. The RCA and Western Electric preamps that were the contemporaries of the V series for ribbon mikes were amazingly quiet subjectively although they measured worse than many subjectively noisier preamps.
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