Getting better EQ on a Marshall AVT50

Fr_3_aK · 24th September 2006, 03:43 PM

Hey,

On my Marshall AVT200050H the distortion channel sounds really hollow or empty. After playing about 7 guitars through it, i figure the EQ needs a bit of a boost.

So how would i, on my Marshall AVT200050H, mod it so the EQ on the distortion channel puts out (and cuts) a few more db's?

Thanks.

DoctorJ · 24th September 2006, 06:26 PM

Marshall and most any amp manufacturer use a shelving eq which merely takes a certain frequency or range and dumps it to ground. The Marshall eq typically has almost no mid control, meaning the mid control makes little difference in the mid output. It would be very easy to change the caps and such for a different frequency on the three knobs, but a shelving eq does not offer much control anyway - ie no boost at all. You could replace the circuit with a active eq which will improve the control, however it may be easier to insert an eq pedal into the fx loop.
Email me for the AVT50 schematic if you like.

Fr_3_aK · 25th September 2006, 08:25 AM

Hmm i was worried about the "buy an EQ pedal" response. I think i knew it was coming.

Yeah sure, i'd love the schematic.

Thanks.

Fr_3_aK · 25th September 2006, 08:25 AM

Oh and i cant access your email, i think its due to the 'probation' im on, being a new member.

If you'd be so kind to email me

fr_3_ak@hotmail.com

Fr_3_aK · 26th September 2006, 07:15 AM

Thanks for the schematics.

On the EQ circuit, is the pot like the tone knob on a guitar? Can i just change the value to alter the sound?

The treble knob is 200k, so should i change it to 500k or 1M to make it brighter?

DoctorJ · 26th September 2006, 12:44 PM

Your right the tone stack works similar to a tone control in a guitar. However if you want the sound to be brighter like a bright switch, then add a low value (1000-470pf) cap through a resistor across the volume control. At lower volumes it will be brighter and as the volume increase it will decrease much like a presence in older amps.

Fr_3_aK · 26th September 2006, 01:47 PM

You mean like this:

DoctorJ · 26th September 2006, 02:14 PM

Not exactly. Tie the cap lead at the bottom to the sweeper or middle terminal. You will need a resistor in series or else you will end up with too much! You could also use a pot versus a fixed resistor so you could vary the amount.

Fr_3_aK · 26th September 2006, 02:32 PM

Would you mind putting that on the schematic and take out any guess work?

I only have limited theoretical knowledge of this sort of thing, but i can follow a schematic pretty well.

Enzo · 27th September 2006, 12:53 AM

You drew the cap from the top to the bottom of the pot. He suggested wiring it from the top of the pot to the wiper of the pot. The classic brightness cap. SInce he feared that might be too much, he suggested adding a resistor in series with teh cap to soften the blow. I'd draw it but I got no way to.

24th September 2006, 03:43 PM	#1
Fr_3_aK diyAudio Member Join Date: Sep 2006	Getting better EQ on a Marshall AVT50 Hey, On my Marshall AVT200050H the distortion channel sounds really hollow or empty. After playing about 7 guitars through it, i figure the EQ needs a bit of a boost. So how would i, on my Marshall AVT200050H, mod it so the EQ on the distortion channel puts out (and cuts) a few more db's? Thanks.

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24th September 2006, 06:26 PM	#2
DoctorJ diyAudio Member Join Date: Mar 2006 Location: Georgia	Marshall and most any amp manufacturer use a shelving eq which merely takes a certain frequency or range and dumps it to ground. The Marshall eq typically has almost no mid control, meaning the mid control makes little difference in the mid output. It would be very easy to change the caps and such for a different frequency on the three knobs, but a shelving eq does not offer much control anyway - ie no boost at all. You could replace the circuit with a active eq which will improve the control, however it may be easier to insert an eq pedal into the fx loop. Email me for the AVT50 schematic if you like.

25th September 2006, 08:25 AM	#3
Fr_3_aK diyAudio Member Join Date: Sep 2006	Hmm i was worried about the "buy an EQ pedal" response. I think i knew it was coming. Yeah sure, i'd love the schematic. Thanks.

26th September 2006, 07:15 AM	#5
Fr_3_aK diyAudio Member Join Date: Sep 2006	Thanks for the schematics. On the EQ circuit, is the pot like the tone knob on a guitar? Can i just change the value to alter the sound? The treble knob is 200k, so should i change it to 500k or 1M to make it brighter?

26th September 2006, 12:44 PM	#6
DoctorJ diyAudio Member Join Date: Mar 2006 Location: Georgia	Your right the tone stack works similar to a tone control in a guitar. However if you want the sound to be brighter like a bright switch, then add a low value (1000-470pf) cap through a resistor across the volume control. At lower volumes it will be brighter and as the volume increase it will decrease much like a presence in older amps.

26th September 2006, 01:47 PM	#7
Fr_3_aK diyAudio Member Join Date: Sep 2006	You mean like this:

26th September 2006, 02:14 PM	#8
DoctorJ diyAudio Member Join Date: Mar 2006 Location: Georgia	Not exactly. Tie the cap lead at the bottom to the sweeper or middle terminal. You will need a resistor in series or else you will end up with too much! You could also use a pot versus a fixed resistor so you could vary the amount.

26th September 2006, 02:32 PM	#9
Fr_3_aK diyAudio Member Join Date: Sep 2006	Would you mind putting that on the schematic and take out any guess work? I only have limited theoretical knowledge of this sort of thing, but i can follow a schematic pretty well.

27th September 2006, 12:53 AM	#10
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	You drew the cap from the top to the bottom of the pot. He suggested wiring it from the top of the pot to the wiper of the pot. The classic brightness cap. SInce he feared that might be too much, he suggested adding a resistor in series with teh cap to soften the blow. I'd draw it but I got no way to.