I just killed another ribbon mic

[Ben M]

So do you just try it out and see what sounds good for that particular mic?

I get good results using the vari-Z knob on Joe's pre with my R84 or old U87... either to mellow the tone or spark/brighten it up.
Great for electric gtr tone and drum OH with a Coles 4038 or R84. I've really come to love that little extra flexibility.

Variable phase is hard to do and do well and has distinct sonic impacts and also is not the same as time delay, such as the delay resulting from moving a mic

I'd be really interested to hear more about this black magic voodoo knob/circuit Rob. As a case in point the Radial company use terms such as "time adjustment" and "adjusting the time differential" with their Vari-phase product.
I don't own one, nor have I used one but..the concept is there.
Could you please give uz some skooling on what's going on in this circuit when you have a sec.

aaannd still off topic...

[Barney Loveland]

I think the 48V with high preamp input impedance would only be a problem with mics with very high output impedance. And designing a mic with high output impedance isn't a great idea as the mic will be susceptible to loading effects as well as series resistance creating noise voltage that would only be amplified by the mic pre.

I have used the AEA RPQ and it really is a good bit of kit.

Self promotion warning (Rick please delete or advise if this is unsuitable).

On another note the 'Pickstone High Voltage Preamps' are in production. The prototypes have been in use for some 5 years now. The input impedance is >100k, I will advise exact specs when measured. The noise floor is incredibly low as well, (specs to come). Gain is 20-60dB or with boost switch in 35-75dB, usual 20db pad, 48V, phase.
They have a brushed aluminium front but for you Rick I can make the sonically superior black faced model . As for the sonics I don't really wish to start internet folklore but they have been used widely by a pop/contemporary engineer/producer through to a classical recording engineer. I will be in Syd a couple of times during August so could bring up a demo set.

[rob]

good work Pickstone!

Just to clarify my statement about the limitation on input Z and having phantom available, the standard phantom feed resistors are 6K8 each on the hot and cold leg; when either the junction of these resistors is connected to the 48V voltage or switched to ground, which is the common approach when phantom is turned off, these resistors appear in parallel to the mic input, thus regardless of the intrinsic input Z of the following preamp place a 3K4 load across the mic. If you want a higher input Z than this ( which is largely only of sonic benefit to ribbon mics ) then these feed resistors need to be completely switched out of circuit when phantom is turned off.

[Chris H]

Rob, do you think the Byer / Rola preamps to be a good option for ribbons? Also I like my Optro silver preamps for ribbons but can you shed light re technical aspects on the two options for gain adjustment on them, the stepped gain pot and the other pot just above?

[Wiz]

good work Pickstone!

Just to clarify my statement about the limitation on input Z and having phantom available, the standard phantom feed resistors are 6K8 each on the hot and cold leg; when either the junction of these resistors is connected to the 48V voltage or switched to ground, which is the common approach when phantom is turned off, these resistors appear in parallel to the mic input, thus regardless of the intrinsic input Z of the following preamp place a 3K4 load across the mic. If you want a higher input Z than this ( which is largely only of sonic benefit to ribbon mics ) then these feed resistors need to be completely switched out of circuit when phantom is turned off.

Timely, very timely.

I just, right now, I mean in the last two minutes... put two 6K8 resisitors and phantom on my mic pre build.

I was sitting there thinking, man, how cool would it be if I could wire up switches to take the caps and resistors out of circuit so they aint there when I dont need em... 8)

[rob]

re the Byer / Rolas. I've never measured the input Z on these but i'd hazard a punt that they are lowish, say 600 ohms.
So the benefit of high input Z on ribbons to open and extend the top end isn't there.

[Alistair]

Haven't really spent much time with them on ribbons, but the Pickstone does sound great! Highly recommended.

[Barney Loveland]

Rob, 'the thinking man's thinker'.

[The Tasmanian]

A question from the electro dummy...

I have a Byer Mic pre that is 50 ohm - Rob, you put pad/ service etc on it (it had 110 db gain!)
I'm still trying to work out what the mic pre was expecting in the 1950's.
When I originally bought it many years ago, I just blindly presumed it would be great on ribbons at the time.

Byer.jpg

Question is - what sort of mic's would work best (if any) on it at 50 ohm's?, and can this be changed easily for more modern mic's? - or is this a design limitation?

These were the pre's from the 1956 Olympic's - what mic's were they using?

[rob]

ok, thats a deep question Chris.

first up I can't say for sure that the input on that unit still is 50 ohms and I certainly doubt that with the pad engaged it is. I frig around with these old sorts of things when I have them on the bench to wrangle them into something that makes sense to me at the time.

back to your question...

when using a mic transformer on the front end of a preamp there is a direct relationship between input impedance and gain. A high turns ratio tranformer will give more gain but also reflect the load on the secondary side where it connects to the first amplifying valve back to the primary side which is what the mic sees as its load.
ie. The V72 that was on the bench today has an input transformer with a 1 to 10 turns ratio. Thus the transformer supplies 20dB of gain. On the secondary side is a 500K resistor. This is reflected back to the mic as 500K divided by the square of the turns ratio, ie 10 squared, so 500K divided by 100 which equals 500 ohms. ( note this is a simplication.... there are other factors involved but it gets us into the ballpark )

back in the day, you had announcers talking in measured tones into ribbon or dynamic mics.... they needed lots of gain to get to the nominal line level standard of the broadcast industry of +8dBm, easily 60 to 70 dB.

A high turns ratio transformer helps get the gain required.

Many mics had a nominal output impedance of 50 ohms, even many condensor mics such as the U47 and C12 could have their output transformers strapped for either 200 ohms or 50 ohms.

The thing about high turns ratio transformers is that the high frequencies get wonky, roll off, peaks and dips. It is real hard to have them flat beyond 10 KHz.

In 1958, we weren't too fussed about what happened above 10KHz. AM radio fell away beyond 9KHz...

Today we can easily get 70 dB of gain without transformers or with low ratio transformers that are flat to beyond 50KHz that also have an noise floor within fractions of a dB of the theorectical limit.... so we can now pursue the few dB of "air" that you can squeeze out of a ribbon mic through placing a very high impedance load on it.

and note the reason why ribbon mics high freq response is so load dependent is because they all contain a very, very high turns ratio transformer ..... it comes full circle.

Thats it ... I'm off to bed, got a V76 and a pair of V376 to rack tomorrow ...

[The Tasmanian]

OK - now I understand the relationship after all these years...
That is very good info.
Thanks in heaps !

[Chinagraf]

So in these days of space age alloys and the unobtanium mines the government is keeping secret, is 99.9999999 aluminium still the best material we have to make a ribbon from?

[rick]

No
Rosewelite foil is the new kid on the block
It's now owned by shure and it is serious
Engineering medical foil made out of clusters
Of nano metals ..
I really have to get around to checking out those
Shure and Crowley and Tripp naked eye mics
That use it

I have read the entire online background to them
And besides being diametrically opposed to Bobs
View on how to record a vocal
Which speaks volumes about his recording expertise

I believe nearly everything outside his repeated sales pitch spin
And when I finally hear the mics maybe I will believe that too !

He and his team are obviously uber smart types
The world needs more like them .

[Lee]

That was a great read thanks Rob. That's the kind of stuff I miss about reading AT.

[Djembe]

Rick, I have a Shure KSM353 (same as K&T El Diablo) with Roswellite.
You are welcome to borrow it anytime.

[rick]

Blair

Can I make a pre listening judgement based on your experience

What's it like ..?
Is it dull ?

Is it easy to use ?


Why don't you use it

Why do you use it ?

[Djembe]

Not dull at all. In fact, for a ribbon it's fairly bright.
It's easy to use and has the normal attributes of a ribbon mic. i.e. low output, figure of 8 etc but without the paranoia of worrying about blasts of air ruining the ribbon. Its certainly not as warm as a 4038 but seems to fit somewhere between a ribbon and condenser
My experience has been that on some things it doesn't work so well but when it works, it really shines. For example, I tried it on a djembe and it was just OK, but on tabla it was absolutely beautiful. Tried it as a side mic in an M/S setup on a flute with a DPA 4011 as the mid mic and it was great. Used it on a cello - also great. Haven't used it on a vocal yet but I think it would work well on some voices.