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Author Topic: Ashdown MAG tonestack - please help me mod (or ruin) my amp.  (Read 1633 times)

Kobaia

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Hello all,

I have an Ashdown MAG 300 head that has a very boring tone. I would like to re-tune the EQ to match the frequencies that an Ampeg SVT has. The amp will not suddenly sound like an SVT I know, but I always feel the controls are better placed in an SVT in terms of the tonal spectrum.

I've found a schem for my amp here at the bottom of this page;

http://music-electronics-forum.com/t28046/#post307779

On the Ashdown, there are five EQ controls. They are, and their frequencies are;

Bass - 100 Hz
Mid - 650 Hz
Treble - 7 kHz

Lo Mid - 340 Hz
Hi Mid - 1.6 kHz

This doesn't seem like an ideal spread to my ears. I always feel that Ampeg gear has a sweeter mids response.

Ampeg frequencies are;

Bass - 40 Hz
Midrange (switchable at) 220 Hz, 450 Hz, 800 Hz, 1.6 Hz and 3 kHz

Treble is at 4 kHz

Ideally I would have the Ashdown 'retuned' so that the bass control was at 40 Hz, the mid control at 800 Hz 'lo mids' at 300 Hz, the 'hi mids' at 1.2 kHz or so and the treble at 4 kHz.

Is this possible just from substituting the caps and resistors affiliated with each control on the schematic?

Thanks in advance,
Kobaia
« Last Edit: June 24, 2014, 02:00:24 PM by Kobaia »

phatt

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Re: Ashdown MAG tonestack - please help me mod (or ruin) my amp.
« Reply #1 on: June 25, 2014, 08:33:59 AM »
Hi Kobaia,
Yes doable but Could end up a pointless exercise. :-X
Have you tried different speakers?? 8)

Take a peek at the speakers driven by the Ampeg SVT ,, now Buy some of those before you explore the insides of amplifiers.

Speakers Make or Break even the best brandnames.  8|
Phil.

nashvillebill

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Re: Ashdown MAG tonestack - please help me mod (or ruin) my amp.
« Reply #2 on: June 25, 2014, 09:20:25 AM »
I'm not sure we can draw a lot of conclusions from the numbers from either amp.  We really would need to see a plot of the frequency response...those numbers you gave are too "simplistic" IMO.  Merely saying one EQ is "100Hz" doesn't tell us a whole lot.

Not only that, you are comparing an active transistor-driven preamp to an all-tube amp!  Can we say comparing apples to oranges?

In theory, yes of course the EQ on the Ashdown could be modified, but given that it's active, it's going to take a lot more than just experimenting with different resistors and caps. Running a SPICE simulation for what you've got, then tweaking it, while maintaining correct operation of the circuit.

I agree with phatt, I doubt the usefulness of messing with the tone stack on the Ashdown.  Maybe try some different speakers, then if that doesn't work, go buy the Ampeg.   No offense to the Ashdown owners but that Ashdown isn't in the same league as a SVT.

Roly

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Re: Ashdown MAG tonestack - please help me mod (or ruin) my amp.
« Reply #3 on: June 27, 2014, 04:44:23 AM »
nashvillebill makes an important point; if one amp uses passive EQ (the valve one), and the other s.s. amp uses active EQ, then the short answer to your question...

Quote from: Kobaia
Is this possible just from substituting the caps and resistors affiliated with each control on the schematic?

...is basically, no.

Active controls employ frequency selective feedback (and gyrators in graphic EQ) and this gives them a different set of response contours to passive controls used in valve amps.

In short the passive James (valve) has a fixed hinge frequency and alters the slope radially from there.  An active like the active Baxandall (solid-state) has a constant slope but slides it hinge frequency left and right.  Fixed frequency variable slope vs. Fixed slope variable frequency.  Their inherent actions are quite different.
If you say theory and practice don't agree you haven't applied enough theory.