Vox/Matchless Cut control

Vox and Hiwatt Discussion

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rooster
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Re: Vox/Matchless Cut control

Post by rooster »

pdf, OK, fair enough. BTW, there was a Hayseed 30 amp that was being built years ago - not sure if it's still being made - and a discussion came up about the brightness of the Heyboer OT he was using, that it did not mimic the original iron or the MM counterpart. The builder came up with a fix, apply a 280pf cap permanently across the coupling caps in parallel with the Cut Control.

Eh, just mentioning it because it pertains to the frequency of the Cut Control, and in this case the upper frequencies. I'm using a MM OT so I don't add the cap, but I thought this was interesting.
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pdf64
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Re: Vox/Matchless Cut control

Post by pdf64 »

Was there a crossline master volume on the phase splitter outputs of that Hayseed amp?
If so, and it was set for a low volume, then the cut off frequency would be pushed up.
Otherwise 280pF seems excessive to tame down a bright amp.
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rooster
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Re: Vox/Matchless Cut control

Post by rooster »

Well, I can only report what I've read. There was no MV involved, pretty sure about this.
Most people stall out when fixing a mistake that they've made. Why?
pdf64
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Re: Vox/Matchless Cut control

Post by pdf64 »

On plugging the numbers in, 280pF (across the LTP plates) is probably reasonable for taming down excessive brightness.
Would you like to have a go at working out the cut off frequency?
See my post from 10th Jan for an appropriate R value.
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JazzGuitarGimp
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Re: Vox/Matchless Cut control

Post by JazzGuitarGimp »

rooster wrote:For that matter, why do you write in your calculations:

'0.00000047' Where did this number come from and how is it relative to .0047uf, our target capacitance?

This confuses me still, sorry.
Oops! As pdf surmised, I slipped a digit. This is why my corner frequency disagreed with his by a factor of 10 (517Hz vs 51.7Hz). My apologies.

As for all the zeros, keep in mind that the capacitance factor of the equation must be entered in Farads. To convert 4.7nF to F, you need to multiply by ten to the minus ninth, so the decimal point moves nine places to the left:

4.7 x 10^-9 = 0.0000000047

Cheers,
Lou
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rooster
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Re: Vox/Matchless Cut control

Post by rooster »

OK, Lou, I understand....somewhat. :-) Thanks for the follow up!
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Masco
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Re: Vox/Matchless Cut control

Post by Masco »

pdf64 wrote:The track taper type and wiring of the control probably has as much affect on its operation as the track value.
eg is full CW the most or least trebley setting?
The old '60's JMI AC-30s were wired for least trebley at full CW, if anybody is interested. Has anyone noted how the Matchless type was wired?
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