D'Mars Overdrive Special

[jojokeo]

You can use 250R/10w to 330R/10w on the power tube's cathodes.

tubenit, I've seen 250r, 330r, 360r all used/shown on various schems & layouts - which exactly are you using w/ the 5881s?

[EL34]

tubenit, I've seen 250r, 330r, 360r all used/shown on various schems & layouts - which exactly are you using w/ the 5881s?

Jeff, Got your most recent schematic and layout. I'll go over them.
As Joe pointed out, the schematic shows a 360 ohm and the layout shows a 250 ohm.

Just mentioning it because both should match to avoid confusion.

Going to match up the two right now
I'll be back

[tubenit]

I am actually using a 360R, but I have used a 250R also and don't hear much of a difference.  Since Doug carries a 250R, I'd just go with that. Measure volts and current and make sure there within what you want (which I would anticipate being fine).

The 360R idea was simply a hanging on left over approach from the first build design I attempted and like.

Again, the preamp and OD and LTPI volts are the critical focal points with this type of D-inspired amp, IMO.  I have run one preamp/OD into other amp's LTPI and power amps & still gotten "the sound".

With respect, Tubenit

[EL34]

Jeff,
I will change your schematic and layout so that they match the 250ohm
I'll post them back here when done.
Don't update your copies, use mine so that we both have the same changes

i'll be back

[DummyLoad]

Larry Carlton playing with FourPlay

love that band...

Earl Klugh Swamp Jazz

nice clip tubenit. definitely have some carlton influence happening in that clip.

--DL

[EL34]

Jeff,
The schematic and the layout that are attached should now match
Use these two to make future changes so we are all on the same page.

A few notes
The 330K section was still not right. I matched what the schematic showed. Double check it, it should be right now.
I changed the 1.2k and 1uf section around (at the tail end of the ground buss)
The 250P across the 82k plate resistor had a resistor body. I changed it to a capacitor body.
The volume pot is now a 500ka pot on the layout
Pots on the layout were updated to audio and linear to match schematic, but you had better double check them to see if they are correct.
.02's are now .022's
.002's are now .0022's
220p's are 250p
I added wires to E1 and E2
power tube cathode is now a 250 ohm 10w
power supply 250 ohm is now 10 watt

let me know if everything is ok

[tubenit]

The 330K section was still not right. I matched what the schematic showed. Double check it, it should be right now.

It looks right now!         (you're right, it previously wasn't drawn correctly)

I changed the 1.2k and 1uf section around (at the tail end of the ground buss)

That looks waaayy better to me.  Good job.

If you're good with it, let's call it a wrap.

Thanks!!! With respect, Tubenit

[moonbird]

Tubenit -
Between the two clips you have done a great job demonstrating the versatility of this amp - WOW  . Thanks so much for all you do and share with all of us!! You are a fantastic resource for anyone wanting to build a guitar amp!!!

Is this latest clip with the single 10" ragin cajin speaker? Thanks again!!

[EL34]

The 330K section was still not right. I matched what the schematic showed. Double check it, it should be right now.

It looks right now!         (you're right, it previously wasn't drawn correctly)

I changed the 1.2k and 1uf section around (at the tail end of the ground buss)

That looks waaayy better to me.  Good job.

If you're good with it, let's call it a wrap.

Thanks!!! With respect, Tubenit

I need to print out a paper template to make sure the spacing is right on all the parts.
Then I will know the exact lug hole placement

I'll print out a template and check the lug layout and then get back with you

[tubenit]

Doug,  thanks again for the help!  I know you're very busy and I realize you've put quite a bit of time on this. 

Is this latest clip with the single 10" ragin cajin speaker? Thanks again!!

Emminence Cannabis Rex on this one. I like the Red, White and Blues also. Having said that, I think there are a number of speakers that would well with this amp, IMO

With respect, Tubenit

[Geezer]

I just have to wire up the pots and relays, then mine will be up and running. Can't wait to get this thing going.

If my "preamp only" works out, I will probably build a full amp using the Hoffman layout.

Thanks for all the work on this!

G

[tubenit]

then mine will be up and running. Can't wait to get this thing going.

 

I can't wait either !!  

IF at all possible, and you've got time, please post a sound clip when you're done tweaking everything.  I'd love to actually have some actually good guitar work showing what this design is able to do. I think this amp is waayy better than my playing can show.

With respect, Tubenit

[EL34]

Jeff,
I looked at your 330k section, it's the same thing as what I have, just different.

I have already drawn up the lug layout in my CAD program, but I can change it.
The CAD program then creates the lug drilling file for the CNC machine

Here's an image file of what that board layout looks like
Check it out and see if it looks ok

I moved the 250 ohm 10 watt cathode resistor down to the last set of lugs and skipped one column
The 10 watt needs some breathing room from the cathode cap so the cap does not overheat.

[tubenit]

Looks excellent!   Great job!


I'm supportive of that being the final version. I think the board is laid out well and will be very tweakable if someone is wanting to do that.

I'll write up a Bill of Materials in the next day or so & post it along with the revised schematic and layout in the SCH files and then post on this thread that I have done so.

THANKS!  With respect, Tubenit

[EL34]

I'll send you a board with lugs so you can build it and see if everything is as it should be.

Let me know if I can go ahead and cut a board
I'll install the lugs

[tubenit]

Sounds great!  If I can get a board from you, I'll get it built!

Thanks, Tubenit

[tubenit]

I've attached a capacitor "guide" to show what caps that I would use where.

I'd used Orange Drop in the clean channel.  Use Mallory 150's everywhere else except the .1 where I'd used Xicon for size convenience.

with respect, Tubenit

[EL34]

I updated my CAD drawing for your cap colors

I stock a dual gang 250kl pot. Is that what you are using?

On your BOM, I think the .68 caps are supposed to be 1.68uf

If you want, you can update your layout digram to match my CAd
I moved the 330k and .1 lugs up to the top row
see Pic below

[tubenit]

I stock a dual gang 250kl pot

The PPIMV would be best being a 250ka.

Regarding the 1.68uf

I know it sounds kinda goofy.......... but I paralleled one of your 1uf with a .68uf.  I can imagine that it sounds picky; BUT for some reason, a 1uf sounded too thin and a 2.2uf was a little more "something" than what I wanted and the 1.68uf sounded spot on.  Others can either use a 1uf or 2.2uf and try it for themselves.

EDIT:  updated schematic and layout to reflect the 250ka PPIMV

With respect, Tubenit

[EL34]

I redid the mosfet section because the lug spacing would not have been right for a TO-220 body mosfet

The leg spacing is 5mm to the two outside legs and so I made that the spacing on the turret board lugs

The zener diode sits right next to the mosfet
Here's an update of how my CAD drawing looks and a bit of board with some test holes drilled

[tubenit]

Wow!  That looks fabulous! Very cool.

Thanks!  Tubenit

[EL34]

Going over the schematic and comparing to the parts list

These items differ from the parts list
1/2 of PPIMV still shows as 250kl on schematic
220r 3 watt shows as 1 watt on schematic and layout
68r should be a 680r

The quantities on the left are what I actually found and are different from the parts list quantites
2 - 1.5K 3 watt
2 - 100 ohm
1 - 820 ohm
1 - 6.8k
1 - 27k
2 - 68k
2 - 82k
3 - 1m
1 - 4.7m
3 - 1uf

[tubenit]

These items differ from the parts list
1/2 of PPIMV still shows as 250kl on schematic
220r 3 watt shows as 1 watt on schematic and layout
68r should be a 680r

The quantities on the left are what I actually found and are different from the parts list quantites
2 - 1.5K 3 watt
2 - 100 ohm
1 - 820 ohm
1 - 6.8k
1 - 27k
2 - 68k
2 - 82k
3 - 1m
1 - 4.7m
3 - 1uf

Thanks for helping and having a great eye for detail.  Should all be corrected.  New Bill of Materials attached.

Reference SCH information here :
http://www.el34world.com/Forum/index.php?topic=14302.0

 Tubenit

[EL34]

Thanks for helping and having a great eye for detail

That be one of my specialties  

I like ironing out details like the mosfet/zener lug section. The parts fit the lugs perfectly

BTW, how hot does the mosfet get?
Does it need to be heatsinked?

[tubenit]

BTW, how hot does the mosfet get?
Does it need to be heatsinked?

Does not need to be heatsinked from what I understand.  I did this on two amps with no issues not being heat sinked.

With respect, Tubenit

[Geezer]

Got thrown a "curve" today.......hooked up the relays & there wasn't enough current to run the 4x of them (plus the 4x tubes) so I had to install a dedicated 6.3v trannie (which I just happened to have on the shelf!)

Got the relays working, just have a few wires left to solder from the pots to the relays & tubes. Probably have it up & running by Saturday fer shur.....

[EL34]

Got thrown a "curve" today.......hooked up the relays & there wasn't enough current to run the 4x of them (plus the 4x tubes) so I had to install a dedicated 6.3v trannie (which I just happened to have on the shelf!)

Just curious about the rating on your main trannies heater winding?
Must be pretty low?

[Geezer]

Valve jr PT that originally ran a single 12ax7 & EL84, now running 4x tubes, one of them a 600 ma recto

[EL34]

Ah, ok, that makes sense

[EL34]

Ok Jeff,
Your D'Mars board is done and is going out with your parts today

I am still not happy with the 1.2k to 1uf section below the phase inverter lugs
The 1uf body is too large to span the lug gap.
It may be better just to go from the 1.2k right down to the ground buss lugs at an angle.
You can see how that goes when you load the board.

The wire that goes from the drain on the mosfet is under the board, which makes more sense
I am changing that on my CAD drawing to a dotted line and a note that it goes under the board.

I added the two main ground wires
I included 4 screws, nuts and standoffs

Here's a shot of your board and my cad program layout

[EL34]

After building the board and lacing up the lugs, I updated my CAD drawing with these two changes

Dotted line for under the board wire that goes from mosfet drain to the power supply rail
1uf body seems to be a better fit by mounting it at an angle from the 1.2k to the ground buss lug shown in my screen shot.

[tubenit]

EL34,

THANKS! That board looks fantastic! Very cool.   

Looking forward to populating the board.  I'll definitely do my best work & post some good pictures when done.

Again, I truly appreciate the generousity of your time and effort helping all of us out on the forum.  I know you're busy and that you put some significant time in on this.

This is going to make it much easier for others who are interested to do this build. Schematic (editable), layout, parts, Bill of Materials and a Hoffman style board is a good foundation to work from.

I'm looking forward to hearing reviews by others who build this on how they like this amp and what tweaks/mods they might add to theirs.

With respect, Tubenit

[EL34]

I added my CAD program layout to the post up above

[SILVERGUN]

Doug, if you're ready, I'd love to get one of those boards...I need some other parts, so just let me know how I can add it in my shopping cart.
Thanks again for all of your hard work.....you guys have made this idiot proof.

[EL34]

I would like to wait and see if it requires any changes
Once Jeff builds it we will know.

You can't really tell if a lug layout is perfect until the board has been poulated

[SILVERGUN]

Ok, no problem, and no rush....I'm excited to get going, but you guys are saving me about 72 hours of triple checking all of this stuff....It's really the part of the project that makes me craziest and just takes ME way too long...I worked on my last layout for 2 weeks and my wife thought I was nuts....maybe she's right.

Jeff, thanks so much for all of your work and the sound clips that tie it all together....priceless

[EL34]

BTW, the boards don't come with the lugs installed and laced together like in the picture shown above.

They will be a drilled board like the ones you see on this page
http://www.hoffmanamps.com/MyStore/catalog/parts12.htm

You have to install the lugs, lace the lugs and drill the four mounting holes.

[SILVERGUN]

I knew I should've put that in there...I was gonna say," I am aware that the board will come bare"...but, as usual, you are very clear in your description

I am assuming that when it's ready for sale, it will appear on the boards page in the store.........in the meantime, I'm gathering some backing tracks in preparation

[EL34]

I'll post back when they are added to the catalog pages

[tubenit]

Just got the mail & the layout board is in it!  Yeah!

Guys, I placed the parts order yesterday morning!  How is that from prompt service!!  Hands down, Doug's got all of them beat.

This board looks fantastic to me.  I have somewhat of a busy wkend ahead, but  I'll start on it this wkend and do my best work on neatness.  Probably will post pics next wkend hopefully of the completed board.

EL34, the lug lacing looks incredible. Remarkably neat and organized job. Very impressive.

THANKS & with respect,  Tubenit

[EL34]

I am the fastest ship in the shipping business.

Stole that line from UPS, but it is true.

Have fun with your new build

[sluckey]

He laces boards by day. And steals down from the mountains by cover of night to put little jewels in our mailboxes.

[EL34]

No, I lace one board by day and drink beer by night while the slave elves do all the hard work.

"Back to work you lazy little grub eaters"

[Willabe]

No, I lace one board by day and drink beer by night while the slave elves do all the hard work.

"Back to work you lazy little grub eaters"

        

Watch out that the little buggers don't go on strike for gold and silver instead of grubs, just like Santas little guys did.


                         Brad        

[EL34]

The elves must polish my Gold and Silver stack in the sub terranian vaults

[Willabe]

The elves must polish my Gold and Silver stack in the sub terranian vaults.

               

[sluckey]

You know I'm gonna come see you one day. And we'll bash some elves and drink some beers. And hopefully swap some tunes.

[Willabe]

Man you guys are mean!



              Brad       

[tubenit]

A big THANKS to EL34 for making this board!!

It is laid out quite well & was very easy to wire up.  He got the spacing "spot on" for the components.  

Board is 10" x 3 &1/8".

The board in the picture is not quite finished  and needs a mosfet, different B+ resistors, .033 post LTPI coupling caps and 220R/1w resistor going into the mosfet.   (while I don't have the mosfet installed, EL34 posted a pic in an earlier post showing that the spacing he used works well with the mosfet)  

However, it does show how well the components fit.  About a 2.5 hr wiring for me. I installed the components into the turrets and then came back and soldered them in short order.  I made a component bending jig out of wood to help facilitate ease of bending the components to fit the spacing.  Only took about 5 minutes to make the wood jigs.  

With this predrilled  Hoffman D'Mars layout board, the schematic and layout drawing ......... making this amp should be reasonably easy.  

As an FYI,  I don't have a drill press, but the boards I've built have been easy to install turrets using his staking instructions
(search "tools" and Hoffman Library of Information  http://www.el34world.com/Forum/index.php?topic=9800.0).

I will repost again after I get the remaining parts and finish the board.  

Ordered the board parts Thurs am, got the board and parts Fri, got it populated in a few hrs on Sat ...............  how's that  

With respect, Tubenit

[Geezer]

Alrighty......mine is up & running!  

Worked perfectly from the 1st startup, and sounds fantastic! I haven't even started "tube rolling" yet, just stuck a 12AY7/5751/5879 in there & she took off!

The tone of the clean has a Fender sparkle at lower gain settings, & gets a nice Marshally grunt as you turn up the gain. The MidBoost used with the clean channel gives a convincing pentode-like tone.

The OD is indeed the "clearest" I've gotten yet, and a wide range of tones is available with different control settings.

Build it just as Tubenit says, with all his values & voltages. I had made some changes to the "Red" channel of my OD section (changed some limiting resistor values) but reverted to match the original values, which is what I used on the "Blue" OD channel, which sounds perfect. So both of my OD channels are now "stock" and give any variation of OD tone I want at the click of a foot-switch.

I am attaching an updated schem & layout. Use this as a reference ONLY IF you want to do the multi-channel OD switching like I have done. If that's what you want, then refer to the pots & relay wiring to see how that was done. Use the Hoffman board for the best possible layout & just add the switching mods. Otherwise, adhere strickly to the Hoffman schem & layout that is posted.

I'm off to try some different tube combinations to see if any improvement (to my tastes) can be had.......

G