D'Mars Overdrive Special

[EL34]

Cool beans
Two builds going on at the same time

Jeff, You add your parts to the board first and then wire up last?

I wire up the board in the chassis and add the parts last.

Just curious if you find it difficult to wrap wires around the lugs with the parts in the way?

[tubenit]

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

Hooray !!!!!!     Man, I am excited that it got that clear OD tone for you!  Mega cool!

Jeff, You add your parts to the board first and then wire up last?

I wire up the board in the chassis and add the parts last.

Just curious if you find it difficult to wrap wires around the lugs with the parts in the way?

Doug, you rascal !!!!!         I started laughing when I read that.

Sometime waayyyy back, I saw a populated layout board that you had done and figured you populated the board first and then wired it into the amp.  So,  I got the idea from you!
 

Anyhow, yeah that works fine and it's not been a problem wrapping wires around the lugs that way. I just use small needle nose pliars. No issue there.

Geezer,  I know you're a busy man .............. BUT I'd love to hear soundclips from you when it's convenient for you.  It's been a long time since I've had the pleasure of hearing your magnificent playing.  No rush, but I hope you'll share something at some point.

With respect, Tubenit

[EL34]

Sometime waayyyy back, I saw a populated layout board that you had done and figured you populated the board first

I am not sure where or when that was?

Anywho, just for the record, I always install the board in the amp, do all the wiring and then add the parts last.

Just my method, whatever works for you is good.

[tubenit]

I am not sure where or when that was?

You have really got me chuckling with this one .............

Always refer to the current Hoffman Library of Information!  

It's a marvelous source of information.   These pics are where I got the idea that you populated the boards first.  

With respect, Tubenit  

[Geezer]

I'll have to try & remember how to do sound clips....it's been a long time! 

I noticed that I had a LOT of gain on tap on the OD controls with the 5751 in V2, so I tried another 12AY7 (same as V1) & it gave me a great tone & alot more "headroom" on the OD controls. So far, I think the AY is gonna stay! So I'm running 12AY7's in both V1 & V2.

The amp sounds especially nice with the Telecaster.....chimey on the cleans & Robben Ford-like tones in MidBoosted OD mode! SWEEET!

With the MidBoost on the footswitch, I have 6x levels of Clean to OverDrive by just stomping on the pedal.

Going back to the shop to play some more!

Thx for the great design!
G

[EL34]

These pics are where I got the idea that you populated the boards first

Ah ok,
I can see how that would be misleading.
Those are the Hoffman board kits that I sold maybe 15 years ago and so I took pictures with the parts on them so people could see what they looked like when loaded. They arrived like that to the customer, but that's not how I installed them.

I never installed them with the parts on the board since it was so much easier to install the board without any parts.
But I found out that many people find it hard to do without looking at a part on the board for reference.

Hard to say after all these years if I have any instructions on how I actually installed the boards at my shop
Another plus to installing the board wires first is that you can clean up all the solder flux spots before you add the parts.

This makes the boards look really nice without tons of flux spots.
The flux seems to pop and spray everywhere as it heats up.

Again, this is just something I have in my brain because it's how I used to do it.

Probably the best info are the build pictures on the library page of some of my projects which show step by step how I build things.

Like the Revibe
http://www.el34world.com/projects/images/Img_6805.jpg

[tubenit]

I was thinking this could be a possible easy OD switching idea.  I have mentioned that there is this very clear OD tone  &  by changing the trim and level OD pots that you can dial in a FAT OD tone.

My chassis simply doesn't have room for any more pots. Geezer dual pot controls for the OD is ideal, IMO.   However, since that is not currently an option with this chassis, .......... it occured to me that I could the following:

place a resister between the trim pot and ground & then parallel a resistor across the level pot.  Let's say that the trim at "3" with level at "6-7" is a great clear OD tone and the fat OD tone  involves the trim at "7" and the level at "3-4".  NOTE: this means switching from clean OD to FAT OD withOUT boosting the volume.  Just a different tone. I can boost the trim from "3" to "7" with a resistor between pot and ground.

And I can reduce the level from "7" to "3.5" by paralleling a resistor across the pot terminals.

This could be done with relay switching.  So, the amp could have the following foot switch operated relays:

clean to OD
mid boost
clear OD to FAT OD  (keeping those two volumes the same)

Haven't worked out the values yet, but I can experiment and report back.  Doing this does NOT change anything on the D'Mars Hoffman board. The board would still work perfectly with this mod.

With respect, Tubenit

[tubenit]

OK, I had a chance to try playing the amp for over an hr to see IF the idea of a relay switching those resistors will work.  And the answer is yes! I marked where the trim and level pots need to be dialed to get the clear OD or FAT OD at the same volume.

I am really loving this amp & feel like this is the best tone that I've gotten. I'll offer these observations of the amp.

I am rarely changing the setting on the clean volume, clean tone controls or clean master volume. Those are pretty much "set and forget" for me.

Clean volume is set at about "6.5" about 95% of time and only occasionally boosted to "7.5" which does allow more blooming. The clean master volume could actually be removed for my purposes, but perhaps playing at quiet bedroom volumes could be useful.

I set the clean tone controls to what I like. Then adjust the OD tone control to how I want the tone on the OD to sound.  I set and forget those. Any further tone changes will be the 5-way switch on my guitar or guitar tone control.

I am finding it the easiest to change the volume using the PPIMV or the recovery pot on the active FX (D-lator).  or the guitar volume.

IF the FX is hooked up, then I use the FX recovery pot on it 90% of the time to control the volume of the amp & hardly touch the PPIMV.  However, the PPIMV is still useful without the FX and to reduce volume to recording levels.

The clear OD does sound comparably clear as the clean channel but with greater sustain. The FAT has a more pushed/overdriven and less clear tone.

Even with the clean volume only on "6.5",  I can get almost endless sustain & bloom on any note from 8 ft away from the amp IF my guitar is "9" and the PPIMV is above "8". There is an increase in blooming if the clean volume is up to "7.5", but I don't think it is as musically sweet, IMO.  This is with the FX box set at Send/6, Return/6 and Recovery/6 or higher. 

The FX box set at Send/5, Return/5 & Recovery/6 is pretty much the same volume as the amp withOUT the FX engaged in the loop.

The midboost on the amp is VERY functional and dramatically changes the tone.  AND I like the tone both with the midboost on .......... OR  off. The midboost plays a major roled in the blooming feature. Very very little blooming with the midboost off.  I can get some blooming with the clean channel and midboost on some notes but apprently not on all of them.

All of this is with the V1 being 12AY7 and the V2 being 5751. Obviously with 12AX7's the gain could be significantly increased but with the loss of musical "sweetness", IMO.

It is possible to match the volume levels between the clean channel, clear OD and FAT OD tones.

More later...................... With respect, Tubenit

[EL34]

Is that with the turret board or are you dialing in your first build?

[tubenit]

Is that with the turret board or are you dialing in your first build?

This is dialing in the first build.  However, I would expect similar if not identical results with the turret board.

(It should be noted that this original D'Mars OD Special was built with your turret and your board material.)

With respect, Tubenit

[Geezer]

OK, here's my final version (schematic attached)

FANTASTIC amp! I only made a few small changes to suit my taste....

Lowered the bright cap on the Clean Gain fron 470p to 270p to better suit my guitars. Ideally, a multi switch would be good for selection of different bright caps for different guitars.

Biggest thing I did was change from a "MidBoost" (.002 cap replacing the picofarad cap in the tonestack, to boost the mids) to a "PAB" (pre-amp boost or "raw" control) accomplished by lifting the mid pot slightly from ground to give a more subtle mid-boost.. This gave me a cleaner/clearer boost (again, to my ears & with my guitars....just a personal preference)

Everything else is exactly as Tubenit had as the "stock" values.

I am going to build the full-on amp this winter, including the tube buffered effects loop, using a nice 80's set of 100w iron I have, running 4x6L6/5881 cathode biased for ~50w

THANKS to Tubenit & Doug for all the work on this......having the pre-laid out & drilled board will be a HUGE help when I do the full amp build!

Geezer

[EL34]

Cool, sounds like it's another great design by Jeff

I would like to see a pic of all the realys and how you have them laid out if possible.

[Geezer]

Cool, sounds like it's another great design by Jeff

I would like to see a pic of all the relays and how you have them laid out if possible.

I cheat....

I use the Weber 4x relay board....very compact.

[EL34]

Haaa, no I meant as they sit in the amp itself.

I should have more specific.

I always like to see how long the signal wires are and where the relays sit in the actual circuit chain.

[moonbird]

Geezer -

As I understand it - you built a preamp. Is that right? If so - what power amp setups have you run your preamp with at this point? thx.

[kagliostro]

Tubenit's & Geezer's realizations are always Killer

this has also the contribute of Doug

what can we wish more ?

 

K

[Geezer]

Geezer -

As I understand it - you built a preamp. Is that right? If so - what power amp setups have you run your preamp with at this point? thx.

I'm running it into a 4x 6AQ5 (NOS Tung Sol's) power amp. So basically the same a 4x6V6 cathode biased.

[jazbo8]

Any chance you can post a schematic of the changes???  Maybe use one of the editable SCH ones I posted and change it to what you're doing.

I am VERY interested in visually seeing the changes.

The clean channel is so beautiful sounding, I liked the TOS 2 CF clean channel, this amp has even better sounding clean and clear channel.

THANKS of course for sharing the results!  I am glad you like the cleaner clean channel. I think it really does sound musically sweeter.

With respect, Tubenit

First, congrats on yet another great design. I am way behind on my builds - I'm not even done with the original TOS yet, and you guys are already onto TOS CF, D'Mar OS... But I noticed that the designs' topology stayed pretty much the same with some tube rolling and various tonestack, OD gain level tweaks. So my questions are - 1) is the 5789 primarily responsible for setting the tone for OD, 2) does whichever tube in V1 set the tone for the clean and 3) which version is the most suitable for classic rock/blues?

Thanks,
Jaz

[tubenit]

Q1  yes, the V1 sets the clean tone

Q2  yes, the 5879 is largely responsible for coloring the OD tone

Q3  I think either amp is great for rock or blues.   The D'Mars is closer to Eric Johnson clear tones.  The TOS is a great blues amp but
      can not match the clean tones of the D'Mars.  But the TOS maybe has a fatter OD tone.

      IF I was trying to play a ZZ Top blues heavily driven blues tone, I'd pick the TOS.
      Probably would pick the TOS for Gary Moore tones or Robin Trower tones also.

      IF I was trying to imitate Eric Johnson or the clear OD blues tones of Joe Bonamassa, then I'd lean toward the D'Mars.  IF I was
      wanting the clear OD tone of Larry Carlton playing with FourPlay, then I'd definitely use the D'Mars.

That's probably the best I can describe it, unfortunately. 

Hope that helps!  With respect, Tubenit

[jazbo8]

It definitely helps, it seems the TOS might be more suitable for me.

Thanks,
Jaz

[kagliostro]

Doug, you asked Geezer about relays placement

I hope you think it will be possible to you to add relays sockets (using your turret style) to the layout of the board as to have the versatile dual control version designed by Geezer

could you do such a thing ? 



I know, this will be a further effort, but I'm sure many people will be glad to you !

K

[EL34]

I have not studied the signal chain to see where realys would be located.
Still have not seen Geezer picture of where his are located

[tubenit]

With my chassis layout, I have the relay board mounted on the chassis top/bottom similar to how I mount the layout boards.  

The relays are between the layout board and the front panel & pots. The relay I am using is somewhat off center and to the side somewhat.

I currently only have one relay but I am going to change that to 3 relays for clean/OD, mid boost and clear OD/ FAT OD.

I attached Geezer's layout also, but I am not certain exactly where the physical location of the relay board is?  I am guessing it is similar to what I use and between layout board and pots.

Hope that helps.  With respect, Tubenit

[EL34]

Your relay location makes much more sense than having it on the turret board.
Having relays on the board takes up lots of space and means a longer board.

Then, some people don't want relays and so now what, have two different board designs?

Also, I like the idea of 3 relays in a row instead of how the weber board is laid out.

A layout end to end like this would take up much less space and would be a better fit into most chassis, IMO

[darkbluemurder]

Q1  yes, the V1 sets the clean tone

Q2  yes, the 5879 is largely responsible for coloring the OD tone

Q3  I think either amp is great for rock or blues.   The D'Mars is closer to Eric Johnson clear tones.  The TOS is a great blues amp but
      can not match the clean tones of the D'Mars.  But the TOS maybe has a fatter OD tone.

      IF I was trying to play a ZZ Top blues heavily driven blues tone, I'd pick the TOS.
      Probably would pick the TOS for Gary Moore tones or Robin Trower tones also.

      IF I was trying to imitate Eric Johnson or the clear OD blues tones of Joe Bonamassa, then I'd lean toward the D'Mars.  IF I was
      wanting the clear OD tone of Larry Carlton playing with FourPlay, then I'd definitely use the D'Mars.

That's probably the best I can describe it, unfortunately.  

Hope that helps!  With respect, Tubenit

Thank you very much for the description, this is very helpful.

Now I guess I have to build both ...

BTW: how important do you think is the IRF820 for the tone? I am thinking of simply omitting it since I have built a two stage preamp close to a plexi w/o a cathode follower, and that is a fine sounding amp indeed.

Cheers Stephan

[tubenit]

how important do you think is the IRF820 for the tone?

That is a very good question!   I am confidant that the cathode follower then the tone stack is VERY key to the tone. 

I am uncertain about the IRF820 mosfet specifically?  My guess is that the mosfet may possible create a more high fidelity tone than a CF triode, but I have no way of knowing that?  I am thinking the "high fidelity tone" may be useful in simply recreating a previous tone signal without coloring it much? I do like the clean tone on this amp very much.

Hopefully someone who actually knows can comment on this?

With respect, Tubenit

[kagliostro]

Thanks for replay

I was thinking to a board with relays on it a la Larry, I really like his constructions http://www.larryamps.de/



instead you were thinking to a separated board with the relays on line .............. a la Larry 



Two different solutions, both very elegant 

Can we hope for the layout of a small dedicated (turret or eyelet) add on Relays Board ?

K

[EL34]

Yes, that skinny little board in the bottom picture is more what I was thinking of.

[tubenit]

On the attached schematic, I am thinking that one would need a 4700uf cap for each relay?  Is that correct?

And the LED light would not be needed IF the footswitch already had one correct?  The LED is simply to show that it's on?

Can someone confirm that those particular relays are relatively quiet with no hum?

With respect, Tubenit

[EL34]

The 4700uf/16v cap in my relay diagrams is for the relay power supply.

You can share that power supply with more than one relay

That drawing I posted for two relays and one switch on one of your other post shows how that would work.

[kagliostro]

Can someone confirm that those particular relays are relatively quiet with no hum?

to which relay do you refer ?

I think that shielded relays are more safe than plastic case relays

but in my previous post you can see that a guru like Larry uses both type

so I assume that also relays like those posted by Doug are fine

Omron is a well known brand and many manufacturers use their products



K

[EL34]

On the attached schematic, I am thinking that one would need a 4700uf cap for each relay?  Is that correct?

No, that is in the relay power supply filter cap.
You can supply several relays with that power supply, so you just add more relays to the + and - leaving that power supply.
See my attached diagram below from your other post about multiple relays

You build the relay power supply and then supply the relay coils with power from the power supply
Each relay coil has a switch that switches the power to the coil on or one switch can switch on several relay coils.

And this page shows a few different ways to build that relay power supply based on what type of power tranny you have

http://www.el34world.com/projects/relay_switch.htm

And the LED light would not be needed IF the footswitch already had one correct?  The LED is simply to show that it's on

yes, the led is only there to indicate that the relay has been switched on.
You can delete the led and the 180 ohm resistor if you don't need them

Can someone confirm that those particular relays are relatively quiet with no hum?

Well yes, that's exactly why I stock those relays. They are Omron low signal switching relays

[Willabe]

On the attached schematic, I am thinking that one would need a 4700uf cap for each relay?

That cap is for filtering out the ripple from the PSU. As long as the PSU can supply the needed voltage and current you can add as many relays as you need.


                     Brad     

[EL34]

The signal switching relays I sell only draw 40ma for the coil so there's lots of power in that power supply

[tubenit]

THANKS for the info and responses regarding the relays!  I am going to work on drawing up a relay turret board and will post it sometime in the next few days.

Following Geezer's innovative lead regarding dual OD pots .........................

I have VERY limited chassis space, but I figured if I remove the clean MV (which I seldom use),  then put the OD drive on top of the chassis (set up more like a trimmer),  & then put 2 Trim pots and 2 OD level pots on the front ............. I can make this work.

This idea will work fine with the Hoffman style board.  No issues with that at all.  

IF I have time, I'll try to redraw the Hoffman layout to reflect this idea.

With respect, Tubenit

[proaudioguy]

Yes, that skinny little board in the bottom picture is more what I was thinking of.

I need a board like this too.  I bet a lot of folks do.  A long version we can cut the number of relays we need from would be cool.

[proaudioguy]

And this page shows a few different ways to build that relay power supply based on what type of power tranny you have

http://www.el34world.com/projects/relay_switch.htm

Is it possible to do this with the unused 5V(?) tap on the PT that would have normally been used for a rectifier tube?  If you use the 6.3V heater tap does that mess with the heaters?  IOW do you have to use a separate transformer (and find a place to put it)?

[kagliostro]

Is it possible to do this with the unused 5V(?) tap on the PT that would have normally been used for a rectifier tube?

Sure, there are type of Omron relays that has 3v - 4.5v - 5v ..... till 48v

see datasheet here

http://docs-europe.electrocomponents.com/webdocs/00b6/0900766b800b6042.pdf

K

[tubenit]

Building on Doug's previous work generously posted in the Library of Information,   I drew this up.

Can someone PLEASE look over the Relay Layout Board and confirm this is drawn up correctly and is consistent with Hoffman's schematic ?

Once this is confirmed as correct,  I'll try to draw up another board with multiple relay switching and a 5pin DIN plug.

With respect, Tubenit

[EL34]

I changed some things

You don't need two 4700uf caps
I think I did that on the stout because I was chasing a hum problem and so I made a two stage power supply with a resitor between the two caps
Turned out the relay was too close to the fuse holder on the Stout and it was not the relay power supply

The common on the relay is one connection point and either the normally closed or normally opened is the other
In your drawing 6 and 11 are the normally closed connections
9 and 8 are the normally open connections

[sluckey]

That circuit will be fine for one relay, but may not work as expected with 2 or more relays.

Consider this...

1. Doug's relay wants 40ma @ 5VDC. (It will work at less voltage and current but may not reliably operate)

2. 6.3VAC and a bridge will produce 8.9VDC unloaded. (Let's call it 9V to make the math easier)

So, we need to drop 4 volts across the resistor. Using a 100Ω resistor will do this nicely and will allow 40ma to flow (I = 4V\100Ω = 40ma). Thats perfect for one relay coil.

Now add a second relay. Each relay wants 40ma for a total of 80ma. This 80ma must flow thru that 100Ω resistor. The resistor will now drop 8 volts (.08ma X 100Ω = 8V) That only leaves 1V for the relays.

Add a third relay and the relays now want a combined total of 120ma. The resistor will try to drop 12 volts, but we only have 9 volts on tap. So, current will have to drop and this will probably drop well below the point to energize three relays.

The answer is to use a resistor that can automatically adjust it's resistance to compensate for different relay current requirements. That sounds like a series voltage regulator. A three terminal 5 volt regulator is the perfect solution and only costs $2 at RadioShack.

This is how I'd do it... Remove the 100Ω resistor and the bottom 4700µF cap. Install a 7805 regulator, input connects to the positive of the cap, common (or reference) connects to the negative side of the cap, and the output becomes your +5VDC that connects to the relay coil. And now you don't have to be concerned with how many relays you try to energize simultaneously. (Within reason of course. That $2 7805 regulator is good for one amp, or 25 each 40ma relays, so don't exceed that. )

[tubenit]

Sluckey,

THANKS as always for the reply!  Any chance you can edit this schematic to give me an idea visually of what you're suggesting?

Is this the voltage regulator?  

http://www.radioshack.com/product/index.jsp?productId=2062599


Doug,  

OK, good without the extra 4700uf, I can make it smaller. I added back (into the layout) the 150R resistor to drop the voltage. But with Sluckey's method maybe that's not needed?

Can someone put a pair of eyes on this and see if we're getting closer?

With respect, Tubenit

[kagliostro]

+ 1 for what Sluckey told

an LM7805 is a simple/low-cost implementation

there are 7805 rated for 1A and other for 1.5A, a lot of paralleled relays

K

p.s.: here datasheet with spec and schematics

http://docs-europe.electrocomponents.com/webdocs/0d25/0900766b80d25b92.pdf

[sluckey]

Yes, that's the regulator. Doug carries it's cousin, the 7812, but that's for +12V. Here's the schematic for what I'm talking about...

[EL34]

You guys can hash out a multi relay power supply

Mine was only powering one relay in my amps

I have 7805's also, but I don't thnk I added them to the catalog

Using the 7805 is a much better idea

Don't forget that the 6.3 volt source is different on some trannies

You have no center tap using two 100 ohms
center tap to ground
champ style with one leg going to chassis

[kagliostro]

Tubenit just add a 100nf cap at the output of the regulator (the closest to the regulator you can) as to prevent oscillations

about relay connection don't you think it will be better to duplicate the turret of the contacts as to have an easier way of connection (one turret for the relay pin the other for the connection wire) ?

Ciao

Franco

[Willabe]

This is how I'd do it... Remove the 100Ω resistor and the bottom 4700µF cap.

You forgot to take out the 180R. Your now using the 5v reg. inplace of it.

Tubenit just add a 100nf cap at the output of the regulator (the closest to the regulator you can) as to prevent oscillations.

Yep. You can go a lot bigger, KOC in TUT1 has a 2,200uF/10v on the input and 470uF/10v on the output. In another TUT book he has 1,000uF in both positions. And depending on how far away the input filter cap is from the reg. you my need to add a 2'nd small 1 directly to the input, again to prevent oscillations.

From page 23, figure 10 of the spec. sheet that K posted the link to;

2. CI is required if regulator is located an appreciable distance from power supply filter.
3. CO improves stability and transient response.

CI=0.33uF, CO=0.1uF. IIRC, distance is 2" or was it 4" at the max from the main/last B+ filter cap in the reg. PSU?

                    
                                  Brad    


Edit; K's link for reg. spec sheet;

http://docs-europe.electrocomponents.com/webdocs/0d25/0900766b80d25b92.pdf

[sluckey]

You forgot to take out the 180R.

What he said.

Don't forget that the 6.3 volt source is different on some trannies

Yes. Be careful here. If your filament winding has a CT connected to chassis, DO NOT CONNECT THE NEGATIVE SIDE OF THIS RELAY POWER SUPPLY TO CHASSIS! Doing so will poop the bridge or PT, maybe even both. Better to be safe and float this relay PS. There is no reason to connect the negative side to chassis. That means to also isolate any chassis connectors used to connect to a FS.

[Willabe]

about relay connection don't you think it will be better to duplicate the turret of the contacts as to have an easier way of connection (one turret for the relay pin the other for the connection wire) ?

Doug uses (and sells) a socket for the relay so I don't think that will be a problem?


                Brad     

[kagliostro]

May be I don't explained well what I mean

Quote from Doug

(1) I have added 4 lugs around the relay socket lugs so that I have better points to solder external wires to. Wires that lead to tube sockets, pots, etc are soldered to these extra lugs. It's much easier and better this way, it can be very difficult to solder to the lugs under the relay socket. Note that these extra lugs are jumpered under the board with short pieces of buss wire.

from this page

http://www.el34world.com/projects/relay_switch2.htm

Hope now you can understand what I was meaning

K