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Patrick Turner Patrick Turner is offline
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Default Guitar amp tone control calculators

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
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hugeshows hugeshows is offline
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Default Guitar amp tone control calculators

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


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jh[_2_] jh[_2_] is offline
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Default Guitar amp tone control calculators

Am 15.02.2014 11:20, schrieb Patrick Turner:
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


Hi Patrick,

whhy not measure the values of the aged components of the tonestack and
"clone it"?

second - the big variable in "Sound" is the speaker. It changes more
than a little bit. Especially with the DRRI.

AFAIK the TSC is the only readily available software. And it only does
the tonestack. It does not cover the "bright switch" - or cap, nor the
cap across the isolation resistor of the reverb and so on...


regards

Jochen


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Patrick Turner Patrick Turner is offline
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Default Guitar amp tone control calculators

hugeshows
Feb 16
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.

I understand that, and most 12" drivers used in an open backed cabinet make a lot more SPL between say 500Hz and 2kHz than at F outside these F.
Impedance isn't a huge concern because most guitar amps do in fact have maybe 10dB global NFB which is enough to reduce the pentode output stage Rout to
sensible levels.

The problem is to get meaningful amounts of boost and cut, and a lack of interaction between the bass and treble and mid control if there is one.
The r s control NFB applied, fct Ha mts

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.

Possibly old drivers are more sensitive than more recent mades, so all the more reason why a greater variability of bass, treble and mids is needed.


Maybe A/B the two amps with a signal sweep and across a resistive dummy load?

I done all that, and the older one had much more bass than newer re-issue, and had more treble boost.

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.

Tone controls offer a varying load to the tube driving them. It seems best sound and tone variability occurs with 1/2 12AX7 gain tube anode direct coupled to 1/2 12AX7 as a cathode follower. The Fender Deluxe has tone stack driven from anode circuit, while the Early Fender Twin Reverb has the CF - and the better sound by far.

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.

Different brands of 12AX7 make very little difference with what I measure, although sound may change a little.
Its the engineering and numbers that make the most difference and the curves of response with sine waves and variability. 99% of BS artists online who have a lot to say about guitar amp mods often have no clue what they are talking about.
The owner of Fender Deluxe I have here asked me to reverse the R&C parts change he did himself after reading a long winded article online by a wannabe guitar amp "specialist" He said the changes made no difference or made it worse.
When I analyzed, I could see why.


Regards,

-forkinthesocket

I found that first need for guitar amp tone stack is to have low Rout tube driving the "stack". While it could be a 12AX7 CF, when there isn't one, one has to think of putting in an extra socket and tube OR using a BJT direct coupled as emitter follower. Maybe MJE340 will do.........
Collector to B+,
Base to gain tube anode,
Emitter to 56k to 0V so that Ic = 3.5mA approx.
This can be done easily, and the sound is determined by the gain triode,
as followers are very neutral sounding ( very low THD)

The Baxandal tone control gives the MOST tone variability.
The Deluxe has 260k log bass pot and when set at No5 level, midway rotation, there is 21k below wiper and 240k above. The treble is also a 260k "log" pot but with 50k below wiper and 210k above at 1/2 rotation.

The Baxandal passive tone control is the easiest to build to get a flat
response with B and T settings at 5. Unlike most other tone stacks designed by penny pinching accountants, the Baxandal gives the most cut and boost and steepest curves closest to 6dB/octave maximum possible.
Just what is possible as a mid control boost and cut remains to be seen
when I send another day on Wednesday making experiments.
But the Baxandal must be made carefully. I have 47k in series with bass pot,
then no usual shunt between top and wiper. Wiper goes to 200k to treble RC array.
But when set at 5, bass should be flat from 1k down to 50Hz. To ensure this,
the ratio of 47k : 240k above pot wiper must be the same as the grounding R and the 21k below wiper, so I found R = 3k9.
This means that for say 10V input, you get 1V output at 5, and max boost and cut
is over +/- 12dB, enough. The 2caps used to shunt wiper to each pot end must have the same XC ratio of 240k : 20k, and if R or C values are more than 10% inaccurate, then you get much poorer max boost or cut, or vice versa, and the best performance is given with the correct R&C values and correct ratios.
The feed to treble boost/cut pot wiper probably will have 220k that connects to 850k log volume pot. Some small C will be put from top volume pot and wiper to at least neutralize the Miller of following 12AX7, and perhaps give slight presence.

I have yet to figure out a mid adjustment which puts a dip up to -10dB in response at 400Hz with Q a bit over 1.

The simplest things can trap me in a shed for days, but then I like to give my best input before asking the owner to tray it out to see how it sounds.
Patrick Turner.
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Patrick Turner Patrick Turner is offline
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Default Guitar amp tone control calculators

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


Hi Patrick,

why not measure the values of the aged components of the tonestack and
"clone it"?

The older good Fender pots usually don't change R values much.

I plotted the response carefully though.

second - the big variable in "Sound" is the speaker. It changes more
than a little bit. Especially with the DRRI.

Well yes, but Its worth a shot to re-engineer the tone controls.
I have heard fabulous music from modern speakers, even though they have a bad reputation with many musos who I sometimes think have irrational fondness to items from the "good old days". Not all their opinions are wrong though, and this time the amp owner was dead right about what he hears. OK, let me try something rather than blindly copying, and if the guy is happy, then mission accomplished and I am the wiser for it.


AFAIK the TSC is the only readily available software. And it only does
the tonestack. It does not cover the "bright switch" - or cap, nor the
cap across the isolation resistor of the reverb and so on...

Yes, seems like TSC is all there is, and was made up by a Mr Woodgate who seems non-contactable. I may be FORCED to learn how to simulate with R&C and a decent simulation program that accurately predicts response of any R&C network one is likely to compose.

Ampeg have a Baxandal type of tone control, no cheapy silly "stacks".

I'll have another look at Ampeg circuits. ,have

regards Jochen

Patrick Turner.


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Default Guitar amp tone control calculators

On 17.02.2014 10:18, Patrick Turner wrote:
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


Hi Patrick,

why not measure the values of the aged components of the tonestack and
"clone it"?

The older good Fender pots usually don't change R values much.

I plotted the response carefully though.

second - the big variable in "Sound" is the speaker. It changes more
than a little bit. Especially with the DRRI.

Well yes, but Its worth a shot to re-engineer the tone controls.
I have heard fabulous music from modern speakers, even though they have a bad reputation with many musos who I sometimes think have irrational fondness to items from the "good old days". Not all their opinions are wrong though, and this time the amp owner was dead right about what he hears. OK, let me try something rather than blindly copying, and if the guy is happy, then mission accomplished and I am the wiser for it.


AFAIK the TSC is the only readily available software. And it only does
the tonestack. It does not cover the "bright switch" - or cap, nor the
cap across the isolation resistor of the reverb and so on...

Yes, seems like TSC is all there is, and was made up by a Mr Woodgate who seems non-contactable. I may be FORCED to learn how to simulate with R&C and a decent simulation program that accurately predicts response of any R&C network one is likely to compose.

Ampeg have a Baxandal type of tone control, no cheapy silly "stacks".

I'll have another look at Ampeg circuits. ,have

regards Jochen

Patrick Turner.


Hi Patrick,
don't laugh - I deleted some lines about those old ampegs and the
Baxandall... Did I really delete them? =

the components I'd consider to measure and clone ain't the pots, but the
caps, the slope resistor and the cathode caps (them throughout the whole
amp). It's the whole system - not just the tone stack. Differnces might
be subtle. You are dealing with - humans - worse: artisans

For me the speakers themselves don't need to be "old". IMHO the
particular OEM-Emi in the DRRI is simply a piece of ****. It does not do
any justice to the capabiliies of the amp.
New speakers ain't generally bad. You've got a hunch of choices
nowadays. IMHO there are some Speakers to consider with a DR:
EMI RedFang,
Celestion Alnico Blue,
Jensen Electric Lightning,
the WGS Blackhawk,
Celestion G12-65;
EV-12L
et al

It's simply a matter of taste.... Myself, still opinionated, that
"better" is not always necessarily "BETTER"..... But I hav e to confess:
I'm a convinced player of an old 5E3 Deluxe Repro with an 12" Alnico
Blue RI - far away from technically perfect, but a real fun machine ;-)

regards

Jochen
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Patrick Turner Patrick Turner is offline
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Default Guitar amp tone control calculators

Hi Patrick,
don't laugh - I deleted some lines about those old ampegs and the
Baxandall... Did I really delete them? =

the components I'd consider to measure and clone ain't the pots, but the
caps, the slope resistor and the cathode caps (them throughout the whole
amp). It's the whole system - not just the tone stack. Differnces might
be subtle. You are dealing with - humans - worse: artisans

For me the speakers themselves don't need to be "old". IMHO the
particular OEM-Emi in the DRRI is simply a piece of ****. It does not do
any justice to the capabiliies of the amp.
New speakers ain't generally bad. You've got a hunch of choices
nowadays. IMHO there are some Speakers to consider with a DR:
EMI RedFang,
Celestion Alnico Blue,
Jensen Electric Lightning,
the WGS Blackhawk,
Celestion G12-65;
EV-12L
et al

It's simply a matter of taste.... Myself, still opinionated, that
"better" is not always necessarily "BETTER"..... But I have to confess:
I'm a convinced player of an old 5E3 Deluxe Repro with an 12" Alnico
Blue RI - far away from technically perfect, but a real fun machine ;-)

regards

Jochen

Well, I guess I should leave all that you said alone because probably it makes a lot of sense to the muso brigade.

BUT, I had a look at a few Ampeg pre-amps and they all have just bass and treble and no mid to make a big dip at around 400Hz. The tone "stacks" are NOT stacks as such but are stock standard Baxandal which give the widest possible range of bass and treble variation. Pots are 1M so network RL is all high enough ohm load to be driven by ****-week 12AX7 anode power. I'm not going to put in 1M pots to replace what's there but will stay with 260k pots and try for a Marshal type of Mid dipper pot and C. But I'll put a follower in to drive the tone network which will better preserve gain, and give the wanted curves with highest possible slope.

I downloaded a Tina90-TLen program for simulations of R&C networks and much more. It took an hour to learn how to use it, and its clumsy and slow and you have to keep closing pages and re-opening and starting new ones to see what changing C or R properties does to response. But the response of what I measured yesterday were exactly reproduced so I have faith that it works OK to simulate such things.

BUT, Suppose I tried to draw a response line I wanted, then enter an order for program to tell me what R&C to use, the program would be quite useless at telling me what R&C I should use to get that specified response.
As soon as one expects the PC to act like a human, its ****ed. Like, OK, we want passive, no extra tubes or NFB & PFB loops, and we want it NOW, and no more than 20dB insertion loss, and whatever it thinks up must be as close as it can get to the wanted curve. Hmm, I reckon I can guestimate faster than involving a dopey 3rd party.
Its not hard for humans to think up stuff that a PC cannot answer.


So, I have a bit more trial and error of pot values and C values to use to try to create an adjustable 400Hz dip, so that the tone control can give the same response as the good sounding amp - but with a lot more to play with..

Are the people on the nearest planet to us outside the Solar System purple, with yellow stripes?
Nah, PC and Google is useless.

Patrick Turner.
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Quote:
Originally Posted by Patrick Turner View Post
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.
Patrick Turner
Try this one http://demonstrations.wolfram.com/FenderToneCircuit/

May be an improvement?
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Patrick Turner Patrick Turner is offline
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Default Guitar amp tone control calculators

Patrick Turner;976155 Wrote:

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.
Patrick Turner


Try this one http://demonstrations.wolfram.com/FenderToneCircuit/

May be an improvement?

Maybe it is, maybe it isn't. I went to the link and downloaded the 190MB program which was supposed to allow tone control inspection without building it. After the download, I checked it for threats, non were found. I could not get it to set up right and to start after getting the Wolfram icon to desktop, so OK, nothing I know ever fixes software dud instals. I find it had been automatically saved in Program files, but the when I tried to use the program to add/remove programs it wasn't listed as a program. But opening the program folder showed it was present. OK, can't un-install it. So I just deleted it.
So another hour entirely wasted with another dud instal.

I got a fairly good response graph yesterday just by adjusting R&C values.
Patrick Turner.
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