Active AMZ Presence Control?

Mr. Lime · Post by **Mr. Lime** » 03 Apr 2016, 09:09

Hi guys,

I've seen a DIY project with an active BMP tone control which seems pretty cool as you save one gain stage because it's placed in the feedback loop.
So there is no need for a recovery stage respectively a buffer.
Guess this could be very interesting for a view pedal builders..

I like the BMP tonestack a lot but would like to add the "Body" control of the AMZ Presence Control to alter the mids.
Not sure about the values,what a pity I'm not into spice..

Just imagine what a killer tone control this could be, simple, efficient and nearly none tone sucking!

Here's the schematic:

Can I ditch the yellow circled resistors?
Does replacing the red circled resistor with a pot, let's say 50 to100k, work the same way like the body control?
How do I have to change the other values to get a similar response to the presence tone control?

Thanks in advance

Nocentelli · Post by **Nocentelli** » 03 Apr 2016, 15:20

I think you want to keep the resistors, and R9 can be replaced with a pot for a body control (maybe replace it with a pot + smaller resistor).

Mr. Lime · Post by **Mr. Lime** » 04 Apr 2016, 08:16

You are sure to replace R9 with a pot and not R11?

I put both values in the duncan tonestack calculator and it seems as the AMZ (red one) version has a loss of about 7dB compared to the other one (green).
Then I played around with the values hoping getting some similar response with less loss (blue lines).

Maybe in the active implementation the losses aren't that critical..

phatt · Post by **phatt** » 04 Apr 2016, 12:05

You are dealing with two completely different circuits! Although they might look similar on paper they function differently. If you want a contour you will likely need another stage to do that.

Duncans cal is Only meant for the passive tone systems

so I suggest you download some kind of simulation and spend the time learning how it works. Trust me I'm a dummy and I worked out how to use the software so If I can do it,,,,you can

Sims will open doors,, slowly at first but will dramatically speed up your understanding of how these circuits effect the tone. For what you are trying to work out even a basic sim can do it.

Another point; I've messed around with many types of tone circuits and just because there is no insertion loss does not automatically improve tone/sound.
I have built passive tone circuits that can even out perform a more advanced parametric EQ. so don't be fooled,, passive loss is not a bad thing in fact it can be an advantage over active tone.

Phil.

Mr. Lime · Post by **Mr. Lime** » 04 Apr 2016, 13:23

I know that the circuits are basically two different animals but I guess they do work in the same manner because the Duncan calculator shows pretty much the same range as the graph from the active circuit.
I wish I had time to dive into LT spice but I'm afraid that will take a view months more

My purpose is to use only one stage to keep the parts count low and the layout simple. The active baxandall / james stack like used in a xotic AC booster could work as well but I found the BMP control more pleasing.

The problem is my next two projects require a buffer stage so one half of a double IC chip is already used and I wouldn't like to add another stage just for a mid control. The more soldering I gotta do, the more issues come up..

Maybe someone would be kind enough to do a simulation as I'm sure it's not only interesting for me.
Sooner or later I will simulate those things myself but as already mentioned, this will take time.

anselm · Post by **anselm** » 04 Apr 2016, 17:18

sim'a'little
-the op-amp schemo works pretty different from BMT
it has a flat responce, and will never sound like BMT, AMZ PC or somethin with dipped middle freq
to get somethin alike you should change C9 to 15n, C10 - to 22n, and a pot value should be 10k
-about mid control
for about half an hour i was tried to achive this feature with some variable resistance
and i failed
not pretty sure, is it even possible

but
changing of capacistance of C9 does the job jast well
with three position switch you can get:
15n - mid dip
about 1kHz, if output impedanse of previous cascade as low, as op-amp
15+6.8n - flat responce
15+15n - mid peak
at 750Hz, about two dB
more capacistance - more dB

not exactly what you wanted, but i can't do more so

have fan
xqz my engl

Nocentelli · Post by **Nocentelli** » 10 Apr 2016, 20:54

Just to continue this discussion, I found this over at DIYSB:

https://www.diystompboxes.com/smfforum/ ... c=112900.0

... this Tilt circuit seems to be a similar arrangement, and there are frequency plots for different values.

Mr. Lime · Post by **Mr. Lime** » 13 Apr 2016, 10:38

Thanks for the link!

Great information in there, the treble roll off could be useful.

phatt · Post by **phatt** » 14 Apr 2016, 08:42

Treble roll off is a given for guitar amplification,, Full bandwidth is the enemy of great tone.

It's a case of what you *Don't Hear* that makes it sound so good.

One only has to see how the tone shape is manipulated as it passes through each stage of the classic Valve amp designs to understand that good guitar sound is a world away from HiFi flat DC coupled circuits.

A tone control is just for fine adjustment of the system tone.
Of course if the overall *System tone* is already down 50dB at a given frequency and your tone knob can only boost that same freq by say 5 or 10dB it becomes obvious the tone control is not the issue.

This is where simulation can save hours if not months of wasted solder trying to find the offending section that is robbing the tone.

Phil.