Dual rectifier schematic

Hey guys,

I started thinking about building a Dual rectifier and I found some schematics for the 3 channel solo head.

I decided to redraw them in KiCad both so they're easier to work with and also because eventually I would need to make the PCBs.

So far I've found one thing I don't quite get.

Can any of you wiser than me tell me where the " 1' bus " (down-right) is connected to?

preamp.png

It's totally possible that I am missing some stupid detail.

Thanks a lot.
Tomas
 
You´ve chosen a very complex amp to build, not only by the main circuit itself but because it incorporates all Mods possible, good o bad, made available to user through a very very complex array of switches, many controlled in a particular combination or another to provide certain sounds.

Hint: MOST users even "famous" ones (Metallica, Korn, etc.), do not bother trying all by any means but set up some basic killer sound and leave it there.

Suggest you choose which sound you prefer and simplify circuit by just hardwiring and using it.

Some variations are VERY subtle and not really sound changers in any significant way, not worth the extra complication, specially finding space to run crisscrossing tracks in the PCB.

In this case, V2a has its cathode going to ground through 1800 ohms, for self biasing purposes.
That resistor also adds some local NFB, so V2a has somewhat less gain, say 20-25X instead of possible 50X, around 6dB loss.

But it is bypassed by a 1uF capacior plus a *small*value 100 ohm resistor, so gain now is, say, 45X from 88Hz and above, which is the lower end of the Guitar band.
So far so good.

But MB offers an extra option:
you can now bypass both with a new 15uF capacitor, which is switched in/out by series JFet J175, which is switched ON/OFF by transistor 6426, which is triggered by voltage coming from 1´buss, which must certainly come from a switching matrix somewhere else, upload the full schematic, all 6-8 pages of it and I´ll show you where.

My beef with this Mod is that it´s useless.:rolleyes:

V2a is already at max gain, or almost.

New capacitor adds VERY VERY LITTLE gain because JFet in series is not a 0 ohm metal to metal switch but the JFet channel which has significant resistance, not much bypassingb the 100ohm resistor by it, but much worse, it´s adding that "gain" between 88 Hz and inaudible 5.9Hz ..... WTF?
NO Guitar signal down there.

My personal view on MBDR

1) they sound good.Not arguing that.

2) they are crazy uselessly complex.
NO user tries or uses all options, where to boot many sound very similar, they just set it up one way and play.
I mean sane players, that is :)

3) there must be a reason that many famous amps are offered in kit form: Fender, VOX, Marshall, Soldano, Traiwreck, Orange, Dumble, even "simpler" MB such as Mark 1 or 2 .... but no MBDR .... ever.

You´ll go crazy fitting everything inside that PCB first, and then debugging all ground loops .... serious.

I suggest you search models offered by , say, CERIATONE Home | Ceriatone (no affiliation) ,pick one model you like, and if you wish design your own PCB.
Their layouts work and can be a guide for an equivalent PCB.

Keep it FUN and doable :)
 
Hey!

First of all I have a very short answer to your very long (I appreciate it!) and informative one - Thank you and you are right!

I am still not sure if I am gonna build it so that might change - for now I just wanted to do the schematics...well...just for fun maybe. That said, I still have a lot of motivation to build it.
I mean ... for sure I am not gonna get even close to trying all the different settings but the complexity somehow attracks me.
I do electronic metrology equipment repairs so for some reason the batalion of relays and toggle switches makes me wanna build it :) .
(also because it's THAT amp)

I don't really like the idea of hardwiring some functions because in the end I would like to have "original" Double Rectifier.
If I had the money I'd be glad to go and buy it but DBs get pretty pricey around here :) . Considering that I've built my share of projects and I know that this approach likes to backfire and you end up spending more that if you would just buy that damn original...

Here is the schematic I am working off.
View attachment 3chSoloHead.pdf

Thanks for your reply.

Tomas
 
Probably. Didn´t follow it that deep :)

I guess your best bet is to print all schematic pages, say A4 or letter size each of them, and tape them together into a table cloth/bedsheet size "full" schematic (not exaggerating much ;) ) and join all relevant points, which will be on different sheets, using coloured markers or similar.
It will give you a clear view of what´s going on.

As of physical layout, Randall Smith (MB owner) is known for cutting a sheet of styrofoam the size of the chassis he will use and pricking all parts to it, not kidding, punching through with their own legs, in the proper positions, to see if they will ACTUALLY fit in the assigned space.

For me, state of the art design ;) , part "models" *sometimes* leave out some small detail which later bites you in the ankle.

One famous old example is DOS era Autotrax, their TO3 transistor case footprint was wrong (and nobody ever corrected it) and for ages those transistors simply wouldn´t fit.

No big deal if you are making a prototype at home, ironing PCBs or using photopositive boards, but if you ordered 50-100 PCBs ... may God help you.

PS: MB also started making PCBs in house until Rayven Smith (his wife) got a splash of hot etchant (a VERY corrosive and dangerous fluid by definition) in her eye.

Since then it become "outside order" only .
 
Now that I think about it ..it's true that with the effect the 15u cap has it's not really worth it. (Your explanation was real good btw.)

The styrofoam? No kidding :eek: . I was thought to do that when I was at high school! We would place piece of paper on top and then you could just connect the holes left by the legs with a pencil and you would get a final layout.

I am writing this reply while reaching over a stack of papers with the schematic printed on them :) . I think I am actually getting hang of it but there are few things that left me thinking.. Would you mind checking them with me?

1. On the switching matrix page there is supply labeled +2V ..and there is none in the power supplies so I guess that they ment the +1.5V (?!)
2. Is the amp supposed to be ground (PE) referenced?


I have a laser that I do prototype PCBs with ..or I go the photoresist route.

Thanks
Tomas
 
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Joined 2008
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I built the Red channel preamp long time ago. It was fun. Building the complete amplifier is not so much fun, good luck with it. I've heard about people who were able to do it, hats off to them. I cannot imagine how could one build the amp cheaper than a cost of a used one, especially the Single Recto which has the sound, can be had quite cheaply, but that depends on where you live of course.

After some years, I finally bought one. I've been using it for the last 16 years or so. My only complaint is the effect loop and the switching around it. It bleeds the wet signal to the other channel. That would need improvement.
 
^^^^^^^^^ THAT .
Thanks, pelanj.

This applies to your task:
what is this '1n760' diode? - Page 1

I couldn´t find a 2V supply either, but given the linked suggestion, "1.5V" might actually read about 2V

Sometimes designers try to get some voltage so they "think" the expected value, then get another but in their minds it´s still the "expected" one, only reality says otherwise.
Any of them might find its way to the written schematic, or one part might be corrected when sent to print, forgetting the other.

I´ve seen worse, and my own case: I make tons of SS Guitar amps and always refer to power rails as "+/-42V" since forever ... since that was the value for years.

But after about 2004-2006 2N3055 (my workhorse for decades) started steadily declining in quality, even from respected manufactiurers (ST) plus fakes appeared everywhere so I first downgraded that to +/-40V and currently to +/-38-39V .... yet on explaining something I STILL call them "+/-42V" ...... go figure.
So Techs repairing one of my amps in a remote Province or neighbouring Country sometimes ask: "hey Juan, there must be some problem, rails are low by about 4Volts!!!!!" :) :) :)

In a nutshell: unless proven otherwise consider "2V" and "1.5V" references the same point.

From another point of view: there´s a couple transistors with base connected to "2V" through 10k resistors so normally turned ON , which are turned OFF by grounding them through diodes at the footswitch area.
Circuit will work about the same whether fed 1.5V or 2V .

One particular beef is that they do NOT use Capital V for Volts, which is the universal convention, what originally made me think "2v" meant "connected to NET 2v" ,"2v" being a Label or NET name and not a Voltage.
Oh well.

As of grounding/PE, I am personally an ENEMY of floating circuit Earth from Mains/safety Earth through resistor/capacitor/diode networks "to save from poor Audio grounding and hum loops"

Nice until lightning falls on that Mains line or grossly miswired outlets are used or ... or ... or ....

I want a SOLID metal to metal "almost" zero ohm there, period.
 
I built the Red channel preamp long time ago. It was fun. Building the complete amplifier is not so much fun, good luck with it. I've heard about people who were able to do it, hats off to them. I cannot imagine how could one build the amp cheaper than a cost of a used one, especially the Single Recto which has the sound, can be had quite cheaply, but that depends on where you live of course.

After some years, I finally bought one. I've been using it for the last 16 years or so. My only complaint is the effect loop and the switching around it. It bleeds the wet signal to the other channel. That would need improvement.

Vidím dobře vlajku? :) .
I thought about (and it's maybe a little illegal to say this here :D ) doing a hybrid amp. So maybe a MESA preamp like you did and a LEACH power amp (?!). They are said to be pretty "non influential" soundwise... at least in the characteristics - they have flat frequency char. from almost DC to like 100kHz and very little distortion.
The idea is that you would get MESA(-ish) tone but with pretty easy, robust and compact power amp. I'd love to know your thought on that.

Well...the Dual Rectifier build is a scary topic indeed and I am not naive about it being an easy build..if i ever really decide to go that far.
The thing that even makes me think about trying is the fact that there are pictures of the internals of the amp so it's at least "some" reference for the PCB design.
 
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Yes, the flag is correct:) This was exactly my intention back then - I even replaced one cathode follower with a MOSFET IIRC. Forget about using a solid state amp for guitar. That simply does not work well. I found out that for good live guitar tone (to my liking), I need to have a tube power stage in the chain. I used to use a 15W tube amp with resistor load and a DI box as a giant distortion box - then amplified by a neutral SS amp with guitar speakers. That gave me 99 % of the tone at any volume. For practicing at home, I have a custom built preamp (by Gerhat) with built in 1W power stage.

A Recto digital sim through a tube power stage is very likely to sound better than a Recto preamp through a SS amp.

For recording, I almost exclusively use IR based box simulators (or a Kemper where available), which contain the interaction between the tube power stage, speaker and microphone - I use the IRs by Andy Sneap ever since I have discovered them.
 
JMFahey
Yeah..that makes sense. Well for now I am done with the schematics in Kicad.
I really don't know what to do :D .. I'm certainly listening to all the suggestions to not build it and I really do see the reasons but it also challenges me even more.
I am slowly gonna try to replicate the original layout and I'll see from there.

pelanj
Well...I mean there is probably a reason why there are still all-tube amps in use so that makes sense. The hybrid idea just sounds too good to be true.


To be honest if the components weren't as expensive as they are I'd probably just build the damn Mesa even if it would be hard - just for the experience and the challenge
 
I am very curious if this project will go ahead. I am also working on a DIY DR, but the 2 channel version.
DIY is not cheaper. Because individual components, and especially the transformers and optocouplers, are expensive.
But I do it purely for learning and entertainment.
Anyway, the 3 channel is a bit more extensive, so I'm very curious how that turns out as a DIY.
I also checked where the 1' BUS signal comes from. But in my schematics for the 3 channel version I also miss that page.. Or I have overlooked it.
In any case, good luck.