New Amp Design

MikeM

Hey guys

So I started working on this, was just wondering if anyone could take a gander to spot any mistakes yet (I'm pretty sure there'll be)

Basically the idea is to have 2 individual front ends, one being having a vox tonestack and switchable top boost and the other having a switchable fender tonestack. I then want to try and cascade theses channels for a 3rd hi-gain channel.

Anyway I have ordered a book on Vox amps to try and decipher it a bit better, but so far I have done the Vox front end, output stage, and power stages.

Mike

MikeM

Ok I've updated the post with a more complete schematic ?

Includes switching between the 2 channels and switching the tonestack out, again, any corrections because I am not sure if I have done it right :/

Currently I am on the 4th rev up. Been cross referencing a whole bunch of different Fender amps and another resource about general guitar amp design. So yea. Think I'm getting pretty close now. I still have no idea if the switching would work.

Also while I am on this quest for knowledge, what's the point of assymetric clipping/compression/distortion? Seen here..

Vick

The option of switching the tone stacks out is very nice... ?

MikeM

I'm rethinking this whole design now thought, probably not going to put the cascade in ☹

Also think I know how to do the switching of tonestacks ?

djpauw

MAYBE

IF

I have time sometime I'll help you check some of this. If I just weren't so busy.

Anyway, looks interesting so I'll be watching from the shadows.

FenderBender

MikeM wrote Also think I know how to do the switching of tonestacks

Well either the multipole switch we spoke about or a relay would do the trick

TomCat

Graeme Parfett wrote
MikeM wrote Also think I know how to do the switching of tonestacks
Well either the multipole switch we spoke about or a relay would do the trick

The relay option works well as it allows you to include as a footswitch option.....worked very well on my amp. One thin I learned was to switch the O/P of the tonestack only....somehow the switching of the input side did not fare well with relay contacts.....they started going intermittent after a while.

FenderBender

TomCat wrote somehow the switching of the input side did not fare well with relay contacts.....they started going intermittent after a while.

There is a danger of that with low voltage signals. A few years ago I made a lot of use of special relays designed for very low voltage switching. I used them to switch analog 0 to 5V signals over very long distances in factory environments and never had any issues. I'll have to try and think back to 1995 and figure out what I used. I remember that they had 9VDC coils as an option and that they had gold flashed contacts. They were completely sealed in a package about 20x10x10mm and PCB mountable, although those with a fine tipped soldering iron and good skills could solder the wires directly to the pins.

Gearhead

My vote also goes to the relays, but not soldered ones. I really like the fact that the relays in my Studio King are plug-in industrial ones, you can just take backups and they are designed for abuse. They also come in handy variants such as 3-way and all sorts of coil voltages.

The asymmetric clipping is going to happen anyway (to a small extent) on a class A with no feedback, because of the asymmetric behavior at the extremes of the tube curve. The picture you show can in my mind however only be from an AB or B class push-pull amp since it is very drastic. You could get to this by giving the push and the pull tube different power supply characteristics I suppose.

Even more of a personal opinion though is that crossover distortion is more desirable than asymmetric. It is easier to get to as well by playing with the grid stopper and coupling cap values until you get a hint of blocking. But I take it you want to stick to single ended so no crossover to distort.

TomCat

Graeme Parfett wrote
TomCat wrote somehow the switching of the input side did not fare well with relay contacts.....they started going intermittent after a while.
There is a danger of that with low voltage signals. A few years ago I made a lot of use of special relays designed for very low voltage switching. I used them to switch analog 0 to 5V signals over very long distances in factory environments and never had any issues. I'll have to try and think back to 1995 and figure out what I used. I remember that they had 9VDC coils as an option and that they had gold flashed contacts. They were completely sealed in a package about 20x10x10mm and PCB mountable, although those with a fine tipped soldering iron and good skills could solder the wires directly to the pins.

@ Graeme

Funny you should mention that....changed the relays to low voltage Finder relays and all has been well up to now....No failures yet.

MikeM

Ok ? I am starting to understand things better. I know that the OT is fine, the pi filter is really cool cause I'll be able to drop the V a bit more before I hit the 44uf caps which are only good or 500v - better safety factor there - however, would there be any negatives to using a metalized polypropylene cap or should I just get a Sprague 20uf/600v (Take note the first cap is hit with about 490v so I do need it)? Also it has more than enough power for the extra 12ax7. Still waiting on my Vox book though ☹

However these are some things still needed to be sorted out

5h choke - how many mA?
Going to get a new OT - instead of an oversized 15 watter, going for a regular 10watt. :? Was a TOUCH overkill hehehe..
How exactly the relays work. Same as the switching though, not TOO tough.
Layout drawing as well as the size of the head so that I can...
Order the bits.
Build the cab (Got some awesome flatsawn pine nehehhe.

I hope to do most of this next week (minus building the cab) as I've finished exams. Can finally knuckle down and get this baby going.