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 1 
 on: Today at 01:02:34 am 
Started by duskb - Last post by afterlifestudios
Are the halogens running at line voltage?  (110VAC?)   Or are they something else, like 12V running off an included transformer? 
If line voltage, then just add up the total wattage in the chain of bulbs and divide by 110(Voltage) to get your current (AMPS).  Leave yourself some head room.

 2 
 on: Yesterday at 05:42:26 pm 
Started by klaus - Last post by klaus
The writer of the OP added the following:

"Think about it this way:

If you had to run a balanced audio signal through (Gotham cable) GAC-7, and there were no other signals, what wires would you choose?
I would choose the heavier gauge because of the higher strand count, lower Z, and durability.

Now take each signal:

B+ = <10mA usually, no need for heavy gauge

Pattern Voltage: <5mA, no need for heavy gauge.

Negative Grid bias: <5mA, no need for heavy gauge.

Filament: 0.1-.2A:
First look at the wire: Thin wire in GAC-7 = 0.14mm^2

According to standard wire gauges: (https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes)

(...) All the reading I have done says the capacity has to do with cross-sectional area at DC, as frequency goes up, the strand performs better than solid.  The chart I initially reference use the numbers 2.2A for 26ga, 3.5A for 24ga.
This equates to roughly 25 gauge (not listed), so looking at the numbers and taking worst case (26 gauge at 60 deg C), that would be 1.3A. 

Double that = 2.6A, compute over-rating for common tube filaments:
AC701 i=0.1A over-rating = 2.6/.1= x26

6072 i=0.15A over-rating = 2.6/.15= x17.3

6267 i=0.2A over-rating = 2.6/.2= x13

The actual over-ratings for the thin wires in GAC-7 will be higher than these.
Any tube that uses more current than 0.2A like an EF14 I wouldn't do this way.  Given the U67 only needs 4 inner conductors, you can triple the wire.




 3 
 on: May 25, 2020, 12:31:38 pm 
Started by Glenn Bucci - Last post by David Satz
When well-known people endorse products, it can be valuable for the seller of the product. But it's also promotion for the endorser, which may be even more valuable than whatever fees and free stuff they get as part of the deal. Their public persona is like a brand in itself, and the more prominently it's displayed, the more valuable it becomes for them in other, future deals. In an extreme version of that scenario, some people worry that some day, an unfit person could even find their way into public office by using the techniques of celebrity salesmanship. (I rather doubt it; people are rational, and aren't swayed by their feelings where something so important is concerned.)

--As for the useful role that a recording engineer could play in capsule design, my experience may be relevant, since I've been a "beta tester" for two capsule types. I recorded concerts with them and gave my observations to the company involved--even sent them samples of my recordings in the more recent case. There was real back-and-forth discussion, and I know that I wasn't the only (nor, frankly, the most prominent) engineer testing these capsules. Neumann has mentioned their version of this process quite openly, e.g. in their origin stories for the TLM 103 via the short-lived model TLM 171, as well as one or another of their modern-day offshoots of the M 50 (I can't remember which one), regarding the way its membrane material was chosen. I would frankly be very surprised if any microphone manufacturer in the world would risk introducing a new capsule or microphone without asking at least one outside recording engineer to try it out first--and before that happens, they will almost certainly have made their own test recordings with it.

But giving our observations and opinions is really all that we sound engineers can do. The actual acoustical and mechanical design of capsules, particularly for directional microphones, is a highly specialized field. To say that "it isn't widely understood" would be an extreme understatement. Even reverse-engineering and copying a known, good-sounding capsule gets you only partway there if you don't know what you're doing in the first place--which very few people do. And they generally keep some parts of that knowledge to themselves, at least in the "old school" way of doing things.

This can create real problems for an established manufacturer (say, in a musical capital of Europe) if there's demand for one of their older designs, but it's been so long that all the people who originally worked on it are gone, and no one who is still in the company knows what made it work, or even exactly how it was assembled. They may have all the old drawings and some leftover, original parts--but in the end they simply become one more imitator of their own original, and not necessarily the most successful at it, either. It's not an enviable position to be in.

--best regards

 4 
 on: May 23, 2020, 12:14:08 pm 
Started by klaus - Last post by afterlifestudios
Does capacitance also come into play when using thicker wire?  I know lower capacitance is favourable in high impedance situations (guitar pickup to amp) and as you increase the diameter of the conductor, the capacitance goes up.  But I don’t know if capacitance has much effect on audio frequencies in low impedance situations like microphone to mic pre.

 5 
 on: May 23, 2020, 09:15:33 am 
Started by klaus - Last post by RuudNL
As far as I know, 'skin effect' isn't of any importance for audio frequencies.
It only plays a role at frequencies in the MHz. range.
Also 'characteristic impedance' can be neglected for audio, unless your microphone cables are longer than 15000 meters...

 6 
 on: May 23, 2020, 02:44:12 am 
Started by klaus - Last post by RadarDoug2
A bridging load is typically at least ten times the driver output impedance. In line level signals, a 600 ohm output drive (which could be 100 ohms source impedance) with a load of 10,000 ohms would be typical. Most mike preamps are arranged to supply a 1K load to a 200 ohm microphone, so not completely bridging.
With regard to using the thin wires for filaments. Most 6.3 volt heaters in small tubes draw 300 mA. While this is not a huge current, the idea of using the thin wires when you can use the thick ones is not good engineering. Perhaps someone from Neumann can chime in? They designed the product and specified the cable. They used the thick wires for filament based on good engineering practice.

 7 
 on: May 22, 2020, 08:37:15 pm 
Started by klaus - Last post by klaus
His whole theory is incorrect. While the output transformer is low Z, it will typically feed a bridging load.

Could not find a definition for "bridging load" anywhere. Did you mean the common 1:5 ratio of mic output to pre-input impedance?
Please explain in simple language what you mean, and how the theory of using thicker wire gauges for a balanced audio signal yielding better audio is incorrect.
Thanks.

 8 
 on: May 22, 2020, 05:02:26 pm 
Started by klaus - Last post by RadarDoug2
His whole theory is incorrect. While the output transformer is low Z, it will typically feed a bridging load. The filament draws the most current in the microphone, and so voltage drop on the cable will be the most significant. The thick wires should be used for the filament supply.

 9 
 on: May 22, 2020, 04:54:23 pm 
Started by klaus - Last post by klaus
I no longer post or respond to discussions (or allow them here) where people question the fact that audio cables between audio components contribute a sound. I know from decades of experience that different construction of cables  connecting between condenser mics, power supplies and mic pre's will have a more or less significant influence on the sound. 

What can and should be discussed are factors that may contribute to a cable's transmission properties, especially when they can be scientifically explained.

Below I am copying a stimulating opinion about the topic. The writer, a respected audio professional, believes there is an advantage to terminating seven-conductor tube mic cables, historically and still manufactured for companies like Neumann, Schoeps, Brauner, Bock etc. differently than was customarily prescribed by the German broadcast system, Neumann, and others in the tube mic era: Back then, ground and heater were terminated to the two thicker conductors, and the thinner conductors to audio (+), audio (-), B+, and variable polarization voltage.

Here is the poster's theory why we should try it differently (unedited):

I figured someone would challenge me on this, historically I always did it the way you do as well, but here is my argument for using the thick wires for signal:

1.  The audio output is a low Z system, the DCR (DC resistance. KH) of a mic output transformer is typically 30-50ohms from my experience measuring them.  So at low frequency, having low Z on the audio lines is especially important.

2.  The thinner wires are not spec'd in their data book as a "gauge", but by rough calculation they should be able to handle a  minimum of 2.5A, upwards of 4A.  For the filament I double 2 because there are extra.  For an AC701, I should have at least 5A/0.1A = 50x over rating.  So there is ample current carrying capability in the thin wires, especially if I double an unused one for the filament.

3.  b+ at most carries 40-50mA in a U47, other than that its typically a few mA, so the thin wire easily handles both situations.  For the U47 I double up the b+ with 2 wires.

4.  Ground current is not separate, so audio and filament grounds are carried in the shields (most mics).  Ideally you would want the filament ground separate, and run through heavy wire also.  But this is not the way most mics operate.

5.  This scheme favors the audio, considering it the most important signal, and provides the lower Z between the transformer and the output jack on the supply.  The thick wires are 252 x 0.05mm stranded, the thinner wire 72 x 0.05.  So there are more strands = more surface area i.e. less skin effect, the higher the frequency, signals penetrate less into a conductor.  Dc flows through an entire conductor, RF only on the surface. 

I welcome your thoughts.  I have only been doing this for about a year, but have thought about it for a long time.  I kept asking myself, which more more important, the DC power or the audio signal out.  If the wires are more than capable of handling the DC, then why not give the audio a better signal path?  Eventually I decided to do it, and take whatever heat came along with that decision.


 10 
 on: May 21, 2020, 03:02:53 pm 
Started by klaus - Last post by klaus
I have been getting so many requests for this, and rather than keep sending people on a Google Search, I've made it a Stickie:

- Remove all three head screws completely

- If you are right-handed: grab the (upside down positioned) grill with your left, and hold the head assembly with the fingers of your right hand, by pressing on three sets of 
  two adjacent head pins as follows:
  thumb between pins 3 and 4,
  index finger between pins 5 and 6
  ring finger between 1 and 2.

- Slightly lift and angle ONLY THE FRONT of the head assembly by gently wiggling it back and forth, until the purple pattern selector barely clears the rim of the head basket 
  (do not yet lift the rear of the capsule assembly!)

- While still keeping the back of the assembly (and its 2 fragile attenuator switch nipples) in its original position, move the slightly angled front of the capsule assembly
  forward, as far as you can, until the purple pattern selector is positioned beyond the rim of the head basket. This is the greatest distance you can obtain to finally be able to
  clear the attenuator nipples, barely past the rear rim of the head basket.

That's it. It's also the only way how you can remove it without breaking the nipples. Reassembly is in reverse order.

Best of luck,
Klaus Heyne
©2020

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