Head Basket Shape - how it affects tonality

[MagnetoSound]

The 5Meg resistor is part of the roll off. It’s also written in the manual. If you want flat response down to 20Hz you have to unsolder that resistor else it’s -3dB at 40Hz.
But it wasn’t there in the very first version of the M49. But I would say the majority of M49’s were delivered with it.

You are right, I see it now. Given the high value of feedback resistor R3, C3 and R4 form a low impedance path to ground, with a rising impedance below ~80Hz. This attenuates much of the feedback above this frequency but allows feedback at LF into the capsule path.

If you want to compare this with the U47 rolloff, you only have to lift R3 and reduce R5 to 60M, which is easy enough to do.

 

[Murdock]

You are right, I see it now. Given the high value of feedback resistor R3, C3 and R4 form a low impedance path to ground, with a rising impedance below ~80Hz. This attenuates much of the feedback above this frequency but allows feedback at LF into the capsule path.

If you want to compare this with the U47 rolloff, you only have to lift R3 and reduce R5 to 60M, which is easy enough to do.

I just remembered, that the change from 100Meg to 60Meg and from 1uF to 0,5uF was also made at the same time as the new Bv08 transformer was used (which had Mumetal laminations instead of Permenorm). So the new Bv08 probably had higher inductance which could maybe also be the reason they changed the other two components as higher inductance leads to a lower cut off frequency.

To compare, one should also remove C4 in the M49 to disable the plate to grid feedback.

 

[RCAguy]

In the interests of usage of established terms, “tonality” refers to musical scales of notes, not to tone color or timbre.

 

[OneRoomStudio]

In the interests of usage of established terms, “tonality” refers to musical scales of notes, not to tone color or timbre.

That's certainly how the word used to be used (and still is in purely academic circles), but "tone" and "tonality" have evolved to mean timbre/"tone color" in general parlance. To quote Google Gemini, "Sound tonality is a measure of how humans perceive the tonal components of sound, and how well those components are reproduced. It's a psychoacoustic indicator that identifies tones in a sound spectrum and their contribution to the overall sound quality."

Just meeting pedantry with pedantry

 

[MagnetoSound]

I just remembered, that the change from 100Meg to 60Meg and from 1uF to 0,5uF was also made at the same time as the new Bv08 transformer was used (which had Mumetal laminations instead of Permenorm). So the new Bv08 probably had higher inductance which could maybe also be the reason they changed the other two components as higher inductance leads to a lower cut off frequency.

To compare, one should also remove C4 in the M49 to disable the plate to grid feedback.

Sorry, again I have to disagree. All the data I have indicates that the earlier U47 circuit had 60M at the grid, and this was later increased to 100M. This makes absolute sense, as they would much more likely have been seeking to extend the LF response, not attenuate it. The effect of C4 will likewise be shaped by the value of the grid resistor, and may well be wider in bandwidth than first assumed.

I think you are right about the coupling cap. According to Oliver Archut there were in total 5 variations of OPT, but the change from GN8 to BV08 did require reducing the output cap to maintain a flat response as the BV08 has better LF response (due, as you say, to higher inductance).

 

[k brown]

In the interests of usage of established terms, “tonality” refers to musical scales of notes, not to tone color or timbre.

??
In the audio world tonality is very commonly used as in definition #2 (from the Oxford dictionary); different timbres referred to in terms of 'tone' and 'color'.

Audio is definitely a 'sound picture'.

 

[Murdock]

Sorry, again I have to disagree. All the data I have indicates that the earlier U47 circuit had 60M at the grid, and this was later increased to 100M. This makes absolute sense, as they would much more likely have been seeking to extend the LF response, not attenuate it. The effect of C4 will likewise be shaped by the value of the grid resistor, and may well be wider in bandwidth than first assumed.

I think you are right about the coupling cap. According to Oliver Archut there were in total 5 variations of OPT, but the change from GN8 to BV08 did require reducing the output cap to maintain a flat response as the BV08 has better LF response (due, as you say, to higher inductance).

Sorry, but there are several schematics were it's clearly written, that older mics had 100Meg grid resistors and 1uF output caps...
And no, they were not seeking to extend LF response as can be seen with the later M49 and U67 where they deliberately cut the LF as the musicians and singers kept getting closer and closer to the mics and also to be less prone to floor vibrations and such.

 

[RCAguy]

That's certainly how the word used to be used (and still is in purely academic circles), but "tone" and "tonality" have evolved to mean timbre/"tone color" in general parlance. To quote Google Gemini, "Sound tonality is a measure of how humans perceive the tonal components of sound, and how well those components are reproduced. It's a psychoacoustic indicator that identifies tones in a sound spectrum and their contribution to the overall sound quality."

Just meeting pedantry with pedantry

I stand pedanted!…} ;<{)3

 

[k brown]

It's just sad that using words clearly and accurately, and in commonly-used ways, is these days considered "pedantic".

 

[Barry Hufker]

It is certainly fair to say that some words have a variety of definitions depending upon the profession. "Tone" can mean one thing in music and another in audio. Certainly "tone" has (at least) one meaning in audio, another in music, another in painting and yet another in politics. Here, we mainly discuss audio, so when speaking of sound quality, one could expect that definition to be the main one in use.

 

[rock soderstrom]

Sorry, but there are several schematics were it's clearly written, that older mics had 100Meg grid resistors and 1uF output caps...

The documents are really on @Murdock side.

 

[k brown]

It is certainly fair to say that some words have a variety of definitions depending upon the profession. "Tone" can mean one thing in music and another in audio. Certainly "tone" has (at least) one meaning in audio, another in music, another in painting and yet another in politics. Here, we mainly discuss audio, so when speaking of sound quality, one could expect that definition to be the main one in use.

Just one example is, when musical instrument amps are referred-to as 'tone cabinets', it's entirely timbre that refers to, and not musical scales of notes.

 

[Khron]

It's just sad that using words clearly and accurately, and in commonly-used ways, is these days considered "pedantic".

Speaking of which, the title should be "Affects"

 

[k brown]

Speaking of which, the title should be "Affects"

Yep

But there we go, being all pedantic . . .

 

[RCAguy]

I stand pedanted!…} ;<{)3

 

[Paul W]

Actually, "effects" could work if you parse things right.

To effect something is to bring it into action, like effecting a change, or effecting a plan.

Arguably, you could effect a tonality, i.e., bring that subtle tonality into action, with a headbasket that affects the tone.

(I have a black belt in pedantry.)

 

[k brown]

Actually, "effects" could work if you parse things right.

To effect something is to bring it into action, like effecting a change, or effecting a plan.

Arguably, you could effect a tonality, i.e., bring that subtle tonality into action, with a headbasket that affects the tone.

(I have a black belt in pedantry.)

Ouch

 

[MagnetoSound]

Sorry, but there are several schematics were it's clearly written, that older mics had 100Meg grid resistors and 1uF output caps...
And no, they were not seeking to extend LF response as can be seen with the later M49 and U67 where they deliberately cut the LF as the musicians and singers kept getting closer and closer to the mics and also to be less prone to floor vibrations and such.

I am grateful for the correction! Some fifteen years ago or so, it was pretty much agreed that 60M was the original value. My mic folders are full of threads on PSW and elsewhere with statements from contributors such as KH, Oliver Archut, David Bock and others, all of which steered me towards this belief.

Perhaps because these guys were deciding on even higher values (1G) for their ‘recreations’, it was assumed that the progression was always upwards in value..

I guess maybe folks back then either weren’t as honest with their ‘secrets’, or the strength of collective assumption simply overrode any doubt. Just shows we are always learning. Again, thanks.

 

[GeorgeToledo]

Some food for thought on the topic of headbaskets.

You can make the mesh inside of a large round headbasket have different angles to it, it doesn’t have to match the exterior shape.

—

An observation about headbaskets with very open mesh; if you put the optional (3 mesh layer) metal windscreen on a vintage C12, you will hear noisefloor go down; not environmental noise, but the same noise headbaskets stifle. The open grill on a C12 does work as a faraday cage, but not necessarily an ideal one.

 

[ricardo]

Some fifteen years ago or so, it was pretty much agreed that 60M was the original value. My mic folders are full of threads on PSW and elsewhere with statements from contributors such as KH, Oliver Archut, David Bock and others, all of which steered me towards this belief.

Perhaps because these guys were deciding on even higher values (1G) for their ‘recreations’, it was assumed that the progression was always upwards in value..

From the dates on the schematics, the less than 100M values might simply be availability of high value resistors.

Designers really wanted even higher values, not cos LF response, but for noise.

Circa late 70s, I had problems finding 1G resistors which obeyed Ohms Law for Calrec. Many high value 'resistors' were more like crappy diodes. Before we found a good source, we used HUGE 500M items.

Using 1G resistors for valve circuits is a risky as Grid leakage is higher than FET Gate leakage and somewhat variable. You might be OK with a genuine Mullard EF86 in good condition.