[hugeshows]

Hi Patrick,

You're totally right about the non-linear response of guitar amps in general, they're notoriously curvy when you plot the response.

When you examined the response in your experiments, did you use a speaker or a dummy load? The reason I ask is because the 'full range' single driver type setup most common in guitar amps leaves a lot of room for the impedance curve of the speaker to effect overall frequency response, often showing reduced or exaggerated efficiency at certain spots.

If you haven't already tried the speaker variable in your listening, I'd perhaps start with at least ruling out the possibility that modern drivers aren't more to blame than modern electronics.

Maybe A/B the two amps with a signal sweep and across a resistive dummy load? Pink noise can also work but often loading at all frequencies changes response across the spectrum in some areas, which can be misleading since guitar signal (hopefully) rarely approaches pink noise in terms of spectrum use. Response curves with pink noise bight be quite different than with a single sine or sqaure sweep. And as much as I hate to suggest tube rolling, there's always that variable to consider as well.

Regards,

-forkinthesocket


On Saturday, February 15, 2014 5:20:44 AM UTC-5, Patrick Turner wrote:
I've been asked by a couple of locals in my town to make their guitar amps sound better. One has had 20 years as a working muso and the other teaches music and plays at gigs often. d

How they perceive sound is often difficult. It varies between individuals, and if I had a cent for each time I heard musicians talk about amp sound quality, or for each time I read utter BS about guitar amps online,

and all without the slightest technical appraisals, I'd be STOINKINGLY RICH!

The teacher said he had a slight buzz from one amp he brought, and it wasn't obvious, but sure enough there was a loose spade connector on one of two speakers in the cab.



But a month ago one customer brought in an old 1965 amp plus his guitar, and demoed to me why he liked it in comparison to a newly made Fender re-issue of the same model number. The re-issue he said, was bloody awful, and indeed even my tired old ears could hear exactly what he was saying about the sound. The 1965 sound was just so much better than the 2013 sound.



So I explored F response. Its anything but flat, and it seems the best sound comes when the response shows 100Hz at say 0dB, then a dip in response of -5dB at 400Hz, then rising to 0dB by 1kHz and rising at 6dB/octave above 1kHz to 5kHz, then ending op at 0dB at 20kHz.



For most guitar amps, if the controls are adjusted widely for the best square wave possible 1kHz, usually it sounds dull and lifeless. So flatness in response isn't wanted.



I came across the tone control calculator at Duncan's amp pages.

Its the best attempt at such a thing I have seen, but after building a couple of sample "tone stacks" and measuring the responses, I often could not get the same curves. In general, Duncan's tone stack calculator gives far more optimistic boost and cut than appears to be possible, and there does not seem to be adequate means of inputting the measured resistance of pots used in the 1, 5 and 10 positions, so one doesn't know what effect a log A or log B pot might have, or what assumptions about pot have been made by the program.



Remarkably, many guitar amps have very poor F response with inadequate bass levels and no way of much boosting them much. Sound is tinny, harsh. There's poor treble boost, and almost non existent benefit of a "middle" which if at least done basically, should be able to create a -10dB dip at between 320Hz and 1,000Hz which seems to give the best sound, by amplifying the highest string harmonics the most.



Is there a better calculator around for tone controls which allows any combination of R&C to be used? I don't wish to use a circuit simulation program.



I have the offending Fender Deluxe on my and will eventually figure a decent mod so it sounds better - I hope - and as a result of applied science rather than applied BS.



Patrick Turner