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Author Topic: U87Ai vs. U87: What's Really Behind The Difference in Sound?  (Read 15831 times)

Kai

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Re: U87Ai vs. U87: What's Really Behind The Difference in Sound?
« Reply #15 on: April 25, 2013, 04:39:38 pm »

...these are Field Effect Transistors which perform the equivalent of a tube...
I wouldn't subscribe that a FET does perform like a tube.
When FETs originally were introduced, this statement was often heard from those who found it was easier (and cheaper) to build a circuit using a FET instead of a tube.

There are some similarities, but there are even great differences.
E.g.:

- Most tubes are much more linear and the transition to the nonlinear range is softer.

- A tube works with and can handle much higher voltages (up to several hundred volts on common types). If used with high supply voltages, they have a greater dynamic range.
Tubes can even stand much higher voltages without breaking - in fact you almost never will find a tube that failed due to overvoltage at the input. This means you don't need to take care for that in a mic.
For a FET it's deadly coming in contact with the polarisation voltage.

- Most important for us: tubes do sound different to FET's, as a result of all the differences in their characteristics plus the necessary differences in mic design.

- Tubes give a nice heating to the mic, which helps to keep the capsule dry.


Regards
Kai
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klaus

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Re: U87Ai vs. U87: What's Really Behind The Difference in Sound?
« Reply #16 on: April 25, 2013, 05:08:49 pm »

I agree with your distinctions. That is why I wrote "perform the equivalent functions" rather than "are comparable in the outcome of these functions..."
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Klaus Heyne
German Masterworks®
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Jim Williams

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Re: U87Ai vs. U87: What's Really Behind The Difference in Sound?
« Reply #17 on: April 26, 2013, 11:44:22 am »

That is interesting to hear from you. I have experimented with lower noise JFETs* in the past, but always found them wanting in headroom. Please elaborate.

One example is the LSK series from
www.linearsystems.com

Those are very low noise jfets, an "upgrade" to the 2SK170 jfets commonly found in modern fet input condenser mics.

As for their headroom, they will output within about a volt or so of the power supply voltage, if set to 10 volts these will do 9. If that is not sufficient, one can increase the voltage the fet sees a few more volts by re-arranging the power feeds.
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klaus

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Re: U87Ai vs. U87: What's Really Behind The Difference in Sound?
« Reply #18 on: April 27, 2013, 01:39:05 am »

Thanks, I will look into these and test.
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Klaus Heyne
German Masterworks®
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Sage

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Re: U87Ai vs. U87: What's Really Behind The Difference in Sound?
« Reply #19 on: December 26, 2013, 11:56:20 pm »

Has anyone here ever attempted to mod a U87Ai back down to the lower capsule polarising voltage of the U87/U87i by disabling the DC to DC converter?

If so, is it a straightforward mod?

And...I know I know...why...right?

Apologies for dredging up an old thread, but I have the exact opposite question.  Is it possible to update a vintage U87 circuit (or a facsimile like this one) to the newer U87ai, in order to achieve the lower noise and higher sensitivity of the later version?  If so, what would it require?  Is it just a matter of adding the DC-DC converter into the circuit somewhere and swapping the capsule, or is there more to it?
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Uwe

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Re: U87Ai vs. U87: What's Really Behind The Difference in Sound?
« Reply #20 on: December 27, 2013, 09:24:15 am »

'upgrading' an U87 to U87A is theoretically possible, but would be more expensive than purchasing a new U87A. So what would be the point of retaining only the original basket, chassis rails, bottom assembly with connector, threaded cap and some minor hardware? Upgrade would require minimally replacement of the capsule, capsule mounting base assembly, microphone head socket assembly, amplifier pc-board assembly complete, DC-DC-converter board, output filter board assembly and housing tube. You can see the cost adding up beyond reasonable feasibility... Some afficionados do prefer the more vintage U87 over the U87A, and you may be able to sell the older version and get more than enough for a substantial down payment toward the U87A.
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hasbeen

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Re: U87Ai vs. U87: What's Really Behind The Difference in Sound?
« Reply #21 on: January 02, 2014, 04:42:33 pm »

If you have an old U87 with the 'Gotham Pads' you can restore it to European output specs. Do you have a red or blue dot embossed next to the XLR connector?
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klaus

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Re: U87Ai vs. U87: What's Really Behind The Difference in Sound?
« Reply #22 on: January 02, 2014, 07:14:37 pm »

That mod, however, does not turn the U87 into a U87Ai, but, where applicable, increases the output of a Gotham-padded U87 (50Ω, pads in) up to 12dB (pads removed + 200Ω strapping).
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Klaus Heyne
German Masterworks®
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