Mesa Recto/FET Homemade

[Hyatt]

Hey, first post (just discovered the site).  A mesa style solid state project would be perfect for me.  I'd buy a pcb/layout too.

[rowdy_riemer]

Check this out: http://gaussmarkov.net/wordpress/circuits/dr-boogey/. I've built this one, and like it. There is also a variation of this build by Mensur, one of the users on this site. Do a search on Mensur's post, and you'll run across it.

[rowdy_riemer]

Holy *s!!t*, I didn't pay close attention did I. :loco

[J M Fahey]

Hi rowdy, I made the exact same mistake :loco, I directed him to Mensur's post  :lmao:
Then I erased my own message.
But now, come to think of it, I was misled by his choice of words, the same as you.
Fact is, he does not seem to have read the earlier posts (all two full pages of them). Well, he should.
It seems that a lot of people read only post headings or title, but does not read the answers.
Oh well.

[rowdy_riemer]

Hehehe, I'm glad I'm not the only one. Makes me not feel so silly.

I think he might just be looking to buy a pcb from someone. Maybe someone made a reply regarding this and I'm not reading all the replies. His choice of words are perhaps ambigious. At first read, it seems like he is saying "A mesa style solid state project would be perfect for me. (can you point me in the right direction)" where he might have meant to say "A mesa style solid state project would be perfect for me. (I'm sure glad I found this thread)".

[Hyatt]

Haha well my words made sense in my head.  I did read the whole 2 pages along with like half of the posts on this forum last night.  I still have the tabs open from all the links the various topics directed me to.

Thanks for the link rowdy, I like that site a lot, thats actually the same site I learned my switching and wiring from.  I build pedals and am looking forward to taking a go at an amp.  So the Dr Boogey is the preamp correct?  I can get a pcb of that.  And the tda7294 is the poweramp and you just make a pcb from the schem on the datasheet?  Then there's the power section which I have to look into.

I have a question though, what wattage would all of this come out to?  My goal would be to make around a 60 watt mesa style solid state head that has a good clean,  takes my pedals well, and run it into my 2x12 at 16 or 8 ohms.

Thanks.

[J M Fahey]

That's the idea.
A Dr Boogey should drive the chipamp easily; besides you can power it with 15 or 18V and it will work much better.
Want channel switching? Why not build TWO Dr Boogeys, with independent tone controls and switch between them?
(Or one Boogey plus one Tweed or whatever you fancy).
50W and a good speaker (or two) work in most places. In a stadium or open air venue, you'll be miked anyway.
I only frown on the TDA7294 (unless you can buy a professionaly made board), the pin assignation is *stupid*, you have to join pins which are 3-4 pins apart, forcing you to use double sided boards.
LM3886, on the contrary, is much more designer friendly.

[rowdy_riemer]

I think his version of the Dr. Boogie is just a little bit different.

[J M Fahey]

Yes, I think Mensur's version is his own, somewhat different from the Boogey one, but the basic sound is about the same, of course.
He also designed his PCB not for a Pedal, but more like a commercial amplifier type.
3886 Vs 7294?: a chipamp is a chipamp, clean and flat, no audible difference there. They are just big Op Amps.
In theory 7294 is slightly more robust, being MosFet, but don't try to pull more than 50W from any of them and they will last forever.
Marshall pulls (almost) 100W from them in their MG series, but they love to die spectacularly, so that's not a good idea.

[Hyatt]

I removed my last post by mistake  :grr

Alright so chipamp is clean and flat.  Good to know.  I ask because in the pedals, some opamps would drive them differently, some louder, some cleaner, some wouldn't work at all.  And yeah Fets have a nice characteristic.  But whatever its my first amp and 3886 is easier. 

You mentioned that I shouldn't pull 50W from a 7294.  Can I get 50W or better yet 75/80W from a 3886?  If not, how can I bring it up to that?  I did some more searching over at diyaudio and read some threads recommending a White Rogers transformer.  Checked that out and found a place to order it. 

I may mod the Dr Boogey as well with something like a "less gain" switch to have a pristine clean.  Mensur made his own board for the amp, how do you think its different from a regular guitar pedal board like rowdy's link http://gaussmarkov.net/wordpress/circuits/dr-boogey/ .

Forgive me if my questions seem ignorant, I just don't have much internet time these days and am trying to get as much info as possible.  Thanks again.

[rowdy_riemer]

It would be best to have a separate clean channel all together. High gain circuits, like the Dr. Boogie, are going to cut lower frequencies to keep the distortion from getting too muddy. If you simply bypassed a stage or too or attenuated the signal before the DB circuit, you won't get as good a clean sound as you would get with a different preamp optimized for a clean sound.

I've seen mensur's schematic, but can't find it any more, so I can't really tell you the difference. If I remember correctly, he had a buffer after the tone stack, and the tone stack had different value pots and caps. The DB uses j201's with a 9v supply while Mensur used 2n5754's with a 24v supply if I remember correctly. I don't remember the differences with the PCB layouts. Perhaps Mensur's isn't as compact, since he's not worried about fitting it in a stomp box. I know some Dr. Boogie layouts can have problems with oscillations. Perhaps his layout is less prone to such problems. Maybe Mensur will enlighten us.

[Hyatt]

*summons Mensur*

[mensur]

I used 24V PSU with 2N5484 FET's which are almost like 12AX7,or enhanced version of it
(low input capacitance like 12AX7, low output resistance, same current at lower voltages).
My layout is well designed, so it has no oscillations, star grounded, voltage ground is way out of the way of signal ground.The size of the PCB is only problem, but I'm not worried for that.
What else do you want to know?

[rowdy_riemer]

How does the tone stack differ from the Doctor Boogie tone stack? Can't find the schematic anymore, but it seems you had a buffer after the tone stack. Also, have you considered selling any PCBs?

[J M Fahey]

Hi Att (sorry, couldn't resist).
What I said is do not try to pull 100W rms from the 7294; 67-70W is fine.
I would use 3886 for a very reliable 50W, following the datasheet example.
Worst case, buy a double sized power transformer ( same voltage, double current), double the filter capacitors, and feed *two* 3886, each driving its own speakers.
Or build a 50W amp, and in the future, if you wish, a powered 50W box, driven from your preamp.
Don't worry, 50W and a good speaker make a lot of noise.