have a second speaker jack in parallel? a technical musing
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have a second speaker jack in parallel? a technical musing
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Last edited by matt h on Fri Mar 27, 2015 2:21 am, edited 1 time in total.
Re: have a second speaker jack in parallel? a technical musing
rather elegant thinking outside the box
thanks for the suggestion, will give it a whirl
thanks for the suggestion, will give it a whirl
Re: have a second speaker jack in parallel? a technical musing
You might have a product there. Would have to built in China to be profitable though.
One caveat: some amps (Fender 135s, Hotrods, and others) use switching jacks to connect a different impedance tap when both jacks are used. Won't work quite the same in that case.
One caveat: some amps (Fender 135s, Hotrods, and others) use switching jacks to connect a different impedance tap when both jacks are used. Won't work quite the same in that case.
Re: have a second speaker jack in parallel? a technical musing
(deleted)
Last edited by matt h on Fri Mar 27, 2015 2:21 am, edited 1 time in total.
Re: have a second speaker jack in parallel? a technical musing
By coincidence, I posted something along these lines to the EL84 conjunctive filter thread.
My quick (& very dirty!) version consisted of 3 x caps (0.68u / 1u / 2u2) and 9 resistors (10R to 100R) because I happened to have a 3 way and a 12 way switch.
The first amp I used it on was a 18W type of circuit with 2 x EL84 and a Hammond 125E OT.
It had a nasty harsh edge when pushed deep into distortion. I couldn't see anything amiss driving a dummy load, but when I plugged in a speaker, I saw the ugly spikes on the leading edge of the waveform come in as the harshness came in. These were totally absent driving a dummy load. (Not cross-over distortion, either.)
I looked at all sorts of possibilities, and to cut a long story short, ended up experimenting with conjunctive filters & 'Zobel' filters. I built the little switched substitution box after going through a few cycles of testing the amp on the bench, deciding it was *just right*, buttoning it up, and then a week later wondering if it wasn't still a little bit mufffled / harsh* (*delete as appropriate).
I found that it is possible to sweeten the sound considerably without killing the high end of the amp, but the values were critical for this. If the capacitor isn't big enough, you can't get to the sweet spot before also rolling off the highs. I think the maths that govern it are related to critical damping, etc. rather than frequency roll-off - just a hunch.
The photos below shows the effect of the network optimised by 'scope. In practice, I think it sounded better with just a little of the peak left.
I suspect that the root cause of the spike is a poorly designed OT. It might depend on the speaker cabinet, too but I've only got a single 1x12 cabinet, so can't really comment.
I think this is a useful weapon in the armoury, but would be at the bottom of my list of things to try (after searching for other sources of parasitics, etc.).
My quick (& very dirty!) version consisted of 3 x caps (0.68u / 1u / 2u2) and 9 resistors (10R to 100R) because I happened to have a 3 way and a 12 way switch.
The first amp I used it on was a 18W type of circuit with 2 x EL84 and a Hammond 125E OT.
It had a nasty harsh edge when pushed deep into distortion. I couldn't see anything amiss driving a dummy load, but when I plugged in a speaker, I saw the ugly spikes on the leading edge of the waveform come in as the harshness came in. These were totally absent driving a dummy load. (Not cross-over distortion, either.)
I looked at all sorts of possibilities, and to cut a long story short, ended up experimenting with conjunctive filters & 'Zobel' filters. I built the little switched substitution box after going through a few cycles of testing the amp on the bench, deciding it was *just right*, buttoning it up, and then a week later wondering if it wasn't still a little bit mufffled / harsh* (*delete as appropriate).
I found that it is possible to sweeten the sound considerably without killing the high end of the amp, but the values were critical for this. If the capacitor isn't big enough, you can't get to the sweet spot before also rolling off the highs. I think the maths that govern it are related to critical damping, etc. rather than frequency roll-off - just a hunch.
The photos below shows the effect of the network optimised by 'scope. In practice, I think it sounded better with just a little of the peak left.
I suspect that the root cause of the spike is a poorly designed OT. It might depend on the speaker cabinet, too but I've only got a single 1x12 cabinet, so can't really comment.
I think this is a useful weapon in the armoury, but would be at the bottom of my list of things to try (after searching for other sources of parasitics, etc.).
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