Getting better EQ on a Marshall AVT50

[Fr_3_aK]

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]

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]

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]

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]

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]

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]

You mean like this:

 

[DoctorJ]

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]

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]

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.

 

[Fr_3_aK]

I used paint to draw mine haha.

OK what value resistor for a 470pf cap? Or just get alot of them and see what works the best?

 

[DoctorJ]

I would use a trimpot of at least half of the volume pot's resistance.

 

[dnz.mtn]

i know it's 2008, been 2 years since you've made these conversations, but i happened to learn that you have avt-50 circuit diagram.
i'm planning to buy one, but i didn't like that clean channel doesn't have a mid control. is it possible for you to send me the diagram? and maybe your advise for the mid control modification...
thanks,
deniz

 

[GaryS]

Marshall AVT50

I'm new to the forum and this is my first posting. I was wondering if anyone can help me locate a schematic for an AVT50. Resistor r-58 is burn't beyond recognition. The amp is working but I need to know the reason for the burn and what part of the circuit the resistor's function. Thank's

 

[DoctorJ]

Hey Gary, welcome. Read the second post and let me know.

 

[vivis12]

Hello, I am new to the forum. I can't email anyone either. Any chance I can get a schematic for the AVT50?

Thanks!