I need a second set of eyes to look at this layout, please!

[Baktown]

All,

Can someone take a look at this layout I made of a Marsha Valve with a Marshall tone stack and tell me if this is correct?  This is my first attempt at something like this, so please forgive the newbie request!

Thanks!

Axl Bundy

[Pushtone]

Can you post a schematic or link to one?


I do not see where VOLUME LUG 3 would connect.

[Pushtone]

I do not see where VOLUME LUG 3 would connect.

Oh now I see, TREBLE 2 to VOLUME 3


Thats when a schem would help.

[Baktown]

I'll see if I can find a schematic for the Marsha Valve.  I built it from a Vero layout I found in the gallery.

For the tone stack I plagiarized from Aron's Smash Drive, see below...

Axl

[Baktown]

Here's Erik Hansen's schematic for the Marsha Valve...

Axl

[ambulancevoice]

looks fine to me, the marsha valve part of the circuit anyway
im not gonna attempt that tone stack

[Baktown]

Thanks for taking a look.  The Marsha Valve was already on Vero, and it worked fine.  I wanted to add a tone stack on my own with no help, and it does work, it just sounds really weak and all the distortion is gone.

Axl

[ambulancevoice]

Thanks for taking a look.  The Marsha Valve was already on Vero, and it worked fine.  I wanted to add a tone stack on my own with no help, and it does work, it just sounds really weak and all the distortion is gone.

Axl

weak as in gain wise? or weak as in effect/tone wise?

[Baktown]

The amount of gain seems fine, but the tone is really thin and lacks punch.  Without the tone stack it sounded pretty similar to a JCM 800, but the addition of the tone stack seems to have robbed it of distortion.

Axl

[anchovie]

A passive tone stack such as the Marshall comes with a level of signal loss. The Marsha Valve is only an emulation of the input stage of a Marshall amp - the full preamp would have other gain stages after it, amplifying the signal to such a level that there is still plenty left after the losses of the tone stack. The Smash Drive chip has a very high output signal, which is why the tone stack works well with it.

The fact that the tone stack reduces your distortion level suggests that the JCM800 sound you were getting with the stack-less circuit was due more to it overdriving the amp you were running the effect into.

[Baktown]

Good point.  I'm a newbie, so I'm learning these things as I go.  The amp I use for test driving builds is a Vox Valvetronix, which has a tube preamp section.  I always set it on the Vox AC30 setting as clean as it will go.  Is this the right approach?  My gigging amp is a Kustom 72 Coupe hardtop, which is a sweet sounding amp, but it stays at our band practice room most of the time.

Thanks for the help!

Rock on!

Axl Bundy

[anchovie]

Setting your amp clean is a perfectly good approach. You may well find overdrives and boosters that give a great sound when run into a gritty amp too.

[Arfman]

Good point.  I'm a newbie, so I'm learning these things as I go.  The amp I use for test driving builds is a Vox Valvetronix, which has a tube preamp section.  I always set it on the Vox AC30 setting as clean as it will go.  Is this the right approach?  My gigging amp is a Kustom 72 Coupe hardtop, which is a sweet sounding amp, but it stays at our band practice room most of the time.

Thanks for the help!

Rock on!

Axl Bundy

First, I'm not much of a stomp box designer...built a bunch, but that doesn't mean anything. I do have a bit more experience with tube amps...so all I can do is throw something out here and see if theres enough here that someone else can pick it up...

Tone stacks are pretty sensitive the impedence of the preceding stage. In a tube amp you'll find big differences in the value of the slope resistor depending on whether it is connected to a cathode follower or a normal gain stage.

Your tone stack is pretty much a standard Marshall tone stack and anticipates the preceding impedence to be about 1.3k or so...is it possible the match here is so out of whack that it's contributing to the loss? I honestly don't know, but if you go into the Duncan TSC and raise the value of Zsrc you start losing a lot of signal...

[Baktown]

I know this is getting technical, but what's the formula for determining the impedance of the preceding gain stage?

If someone can point me in the right direction I can figure it out.

Thanks!

Axl