The Clone wars: for and against !!

Oh yeah, absoltutely, the fundamentals.  My sister is currently at a high ranked culinary school, and that's the same thing they are telling her.  Focus on the techniques, the basic requirements like salt, cooking time and all that.  It's maybe a little to easy to get distracted and miss the point.  If you wanna get fancy you better have your basics covered to a point.

Hmm.. Beer clones - only 50% off topic.

I've been a wannabe oenophile for the last 20 years so I'm a bit late to the IPA dating scene, so call it young love but damn, even the "mediocre" IPA's bring something worthy to the table for me.  Granted, I'm not sampling much of the cheap stuff.  Maybe I need to go there to get a base-line.

For LDC microphones nothing beats a vintage Neumann. If you get a good one there is something about their engineering that no other mic captures. I've owned nearly every 47 clone short and long body Neumann U47s and at the end of the day the mic you will will have to pry out of my dead hands is a vintage 1976 U87 that just happens to be the best vintage U87 I have ever owned and I've been through 4 of them over the years. Nothing beats a good Neumann or a good Neve.

Which Inner tube U87 mod do you have?T he Inner Tube mod has changed over the years. It started out as a cathode follower circuit. I heard the more recent incarnations are not as good.

Just take a trip north of the state line and grab some New Glarus!😁

 Hi Ragan, The problem is indistinguishable to which original?  Which microphone did Stam or Slate "clone". 

The original U87 had a double sided separated K67/87 capsule and the polarization voltage was lower at 47 volts plus the original transformer had a 5:1 or 10:1 turns ratio(50 ohms/200 ohms).  The polarization was passive and they swapped the polarity on each half of th capsule to get the FIG 8.  All U87ai microphones made after 1988 had a voltage tripler circuit that placed 60v on the double sided K67/87 capsule's back-plates which are tied together.  Instead of swapping the polarity of the two halves, the U87ai had 120 volts on the rear diaphragm for FIG 8 and 60v on the back plate.
This higher polarization voltage increases the output a few db decreasing the headroom and it increases the upper mid rise a couple of db.

The U87ai is brighter than the original U87 plus the U87ai has a single 7:1 ratio wound transformer.

We have service many original U87 microphones and they always sound mellower/smoother to our old ears than the U87AI.

Cheers, Dave

Hi Guys, that was what I was pointing to.  A 1976 U87 is a different animal than a 1988 or later U87AI.  

We had two U87's at Ocean and 3 later version U87ai's.  In critical listening tests the majority of folks preferred the original U87.   When folks state, U87 which one are they referring to?

In 90% of the time the U47's, C414eb, C37a microphones were preferred over the U87 on vocals.  However, we often used the U87's on horns, strings and for room miking.


Neumann used tantalum capacitors across the power supply and in the audio chain of the U87.

Tantalums are twice as fast as electrolytic's but they are more partial to early failure.  I have repaired several U87's with a failed (shorted) C12 and the odd C10.  

I have also found older U87's with a failing C7 or C8.  I recently repaired one where C8 measured 800 ohms and there was absolutely no gain.   Usually, tantalums get noisy before they fail but not always.

If you use an electrolytic to couple the audio then you need to bypass it with a .1-.01ufd metal film.  

The circuit requires the use of a 20ufd at C8 but C7 in the U87 is a 1ufd.  Metal film capacitors which are over twice as fast as tantalums can be found in a small enough size to fit the circuit board.

However, the 20ufd C8 either has to be an electrolytic bypassed or a tantalum.  Also, the power supply capacitors can be replaced with electrolytics to improve reliability.


In our CM87 we did not copy the U87 circuit.  We used a more reliable, more efficient capsule, that has a response we really like, without de-emphasis.  

Its has the same rise in the upper midrange as the original U87 but is on average 2db brighter at 12khz without the de-emphasis.  It has the same polarization circuit as the U87Ai.

However, it has a 2-stage emitter follower Class "A" transformer coupled circuit with 14db more headroom than the U87.  

There is 20db of loss in the U87 with a 10:1 ratio transformer, 17db of loss with a 7:1 ratio transformer, 14db of loss with a 5:1 transformer ratio. 

Simply by adding another transistor configured as a emitter follower, the output transformer can have a 2:1 ratio (6db loss).  So, we drop the gain of the first stage by 14db compared to the U87 at 10:1.

This increases the headroom of the circuit and reduces the circuit noise by approximately 14db.  So, I never found any reason to copy or clone the U87 build.


However, to get the "mystical" sound of the U47 one has to "dumb" down the circuit compared to our CCD circuit which can drive the transformer from 600 ohms. 

1) The reactance of the drive circuit must be the same as a VF14m would be, driving an original BV8.  The output capacitor should be .5ufd in order to "react" correctly with the Bv-08's inductance.


2) The VF14m had an input capacitance of <9pf.  

Newer tubes have an input capacitance <4pf and to match the VF14m a small capacitor must be fitted to "dumb"  down the amplifier so it has the same HF turn-over point as the VF14m circuit.

3) Also, the U47 had much smaller value, input resistors compared to newer circuits.  


The original few U47's had 60 megohm but later they were 100meg today we use 1G but to get the same LF roll-off curve as the original they should be lowered to 100m.



Between, the lower value input impedance, the correct reactance in the output stage, matching the gain and current draw of a VF1m, the circuit should react like the average U47 did.


I have a working VF14m arriving in the New Year and I will be able to calculate the plate resistance and gain when it is wired as a triode configured like the U47 circuit.  



IPA is a bit like the U47 circuit which was a magical "work around" to buid a "HiFi" circuit in 1947.  


Indian Pale Ale was shipped by sailing ship from Britain to the colonies and by the time it reached India it was going bad.

So, they increased the HOPS content in later shipments which is a natural preservative and it made the trip but increased the alcohol content and that made it popular.



Cheers, Dave

Hey markfouxman, your mics are a work of art. Keep up the good work.

http://instagram.com/p/BMw_HsYgXNu

If it's an AML 1073 DIY kit for the 500 series under $300 then yes, absolutely. :-D

Yeah had the same conversations over the years and lots of hope, it was disgusting how many guys ordered the new 451 and were disappointed, I bought a pair and well it did look like the old one with a fixed Capsule!
I haven't had the D12vr but have heard mixed reviews some say it's got it others hate it.

I have a better relationship with the people from Senn. / Neumann.
What people don't get is they are all about quantity and efficiency, they make more mics in a day than companies like Flea makes in a year!

Actually, I have no doubt that Steven's stuff sounds "indistinguishable" to people who have little experiential frame of reference and spend all their time listening to plugins. But it ain't me, babe.