LITTLE BOOGA AMP

[TIMBO]

HI guys,I'm wanting to embark on a learning adventure, as i have been able to construct a few amps ( the TOS , Plexi 50 and a couple of smaller ones) but i still do not know some of the technical reasons that make these amps work. I do not have any training so i am relying on you guys to do the thinking.
What i have learn't so far is that with valve amps their are no real limits to their constructions other than electrical requirements. I do enjoy surfing the endless schematics and being amazed at the also endless ideas and methods of construction.
In my travels i have found the Mesa Boogie Dual rectifier, 2 channels.Looking through the schem at first it look somewhat involved but that made me more eager to learn of it construction, lots of digging and internet surfing i have been able to nut it out so far.
There are lots of interesting parts to this amp and some have been posted (Tubenits active FX Loop)although MB has their own version.
With all the aspects of this amp i though it great learning for us Level 1's, so please all you Techs and seasoned amp builders throw your 2c in to help us Level 1s.
I'll start with the schem, i have added parts the the original schem which i hope we will discuss later on but for the moment the schem i have drawn is just the starting point. I have made a project board to allow me to make changes along the way.I also have no need to have 100w of power and i do have 2x EL 84s and OT and PT to match. I did some calcs and i hope the PT(120ma) is able to take the load.
The power amp at this stage is based on Sluckeys November Project which also has some interesting parts to it.The reverb is Tubenits as you can see which is slotted in after the TS and before the FX loop which has also been discussed.
I have acquired some parts, all resistors are 1w carbon film ( accept power) and caps are orange drops (although i might use Mollary's in the TS.
First question is can orange drops be used throughout the whole amp?( accept the power filtering of course)
Please look over the schem and i look forward to any input, good or bad!!! Thanks

[tubenit]

Wow!  My hats off to you for having the patience and ability to draw that. I think you did an excellent job with it.

Some thoughts ...........

I don't see why you can't use Orange Drops? I think that would be fine, IMO.

I would NOT even consider building that amp until you have a layout completed and posted it on the forum for some eyes that are more knowledgeable than mine. I definitely would want others to critique my layout and offer thoughts or suggestions.

You have a paralleled 1st gain stage into multiple gain stages into a cathode follower into reverb into switchable FX loop.  It will be amazing to me if you don't end up with oscillation problems or a very noisey amp at idle.

The dual switchable tone stack after the cathode follower seems to be redundant in places and have alot of "stuff/clutter" around it. I tend to set the tone controls and not change them so having alot of options there wouldn't be useful to me personally.

It's not always true,  but (at times) the more stuff you put in the signal path, the less touch sensitive and articulate the tone and playability of the amp is. I think it (at times)  can lead to a less expressive amp.

I think you will need a very large chassis to build that in to avoid oscillation. I think there is a chance you will end up with  an amp with lots of switches and that it might just sound "OK".

Just an opinon (and I am not a fan of EL84 amps overall),  I think the EL84 tube has a unique tone & that perhaps it does not lend itself to different tones as well as other tubes? Some of this is because of how quickly that tube breaks up and the glassy/chimey nature of the EL84 tone.  And if that is true, then all the switches might not really change the tone as dramatically as you may be anticipating?

Lastly, do you really like the way Mesa Boogie amps sound?  If so, go for it & good luck.

With respect, Tubenit

[TIMBO]

Thanks Tubenit, To answer the first question of the parallel first gain stage was because the MB used only half of the 12AX7 in V1, Other than using a tube that is similar to half the 12AX7 what could the other half be used for ( any suggestions)?? Yes i assumed that this project would be subject to all sorts of problems. I have done a setout of my own and was able to get it into an area of about 2'x 8".It has taken me about a month just to get to this stage but i'll start working on a layout :huh:I have listen to some sound clips of the 18 watters and i don't mined their sound as this amp is going in another direction to the warm and bluesy sounds.One of the things you mention was that the EL 84 do break up early which was why i went that way to try and simulate the 100w at a lower level. I was also wanting to tweak the power amp end so that it was working on the edge. The tone stack will be done on separate PCB's with the pots mounted on then ( this is to free up space on the main boards) the original schem shows the two stacks to be similar which i assume that they can be set and channels switched in flight. At the moment the switching will be done via a number of switchs but i was hoping later i would be able to come up with my own switching matrix (possible use of LDR's). Thank and please keep the comments comming.

[tubenit]

Sounds like your clear with your goals and have a particular tone in mind. Very cool. When you get your layout done, just post it for a critique. I will look forward to seeing what you come up with.

I used to build kinda simple amps with a bunch of switches but really got more dependent on using a resistor and cap substituion box to determine what I really wanted to hear. And I found some switch I almost never used.

My guess is that IF you had the amp completely built and working OK that you'd use some switches more than others and even possibly find some that you never switched out of a preferred value.

And if that is true, I'd encourage you to think thru and just ponder considerations such as .......... IF I could have only two switches which would be the most important to me?  In other words, approach it from different angles to be sure it continues to head the direction you want it to.

Please keep us posted in how all of this evolves.   With respect, Tubenit

[FYL]

IF I could have only two switches which would be the most important to me?

Zen and the art of amp building.
 

I would use <ON> and <TALENT BOOST>.

[TIMBO]

Hi guys, Thanks for the feed back. I do like the sound of the DR and the sound clip provided by MB does have a good range of sounds. I agree that there are a lot of switches, but for the moment i am going to have indivigual  switches for 4,7,10,16,19 ,20, 3a &3b and as i see it these set the gain as per the cheat sheet and 1&2, 5&6, 8&9, 14&15 on a 4pole, 2 position rotary switch select the colour channel . My idea for this if it ever flies, I can get a 8pole 5position rotary switch that will set all the gain switches for each mode. Thanks   

[TIMBO]

Got some updated schems and layouts. Thanks
I think i just found what i can do with my spare 1/2 12AXY