Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: wolf_papa on July 12, 2019, 04:20:03 pm

Title: I need some help with the D'Mars ODS
Post by: wolf_papa on July 12, 2019, 04:20:03 pm

I've assembled the pieces for the 5751 version of the D'Mars amp, but the only schem I can find is for the 5879 version. Does anyone have a good schematic for the 5751 version? A good layout would be even better. Thanks

Title: Re: I need some help with the D'Mars ODS
Post by: SILVERGUN on July 12, 2019, 05:38:16 pm

This is my guess:
https://el34world.com/Forum/index.php?topic=15406.0

Title: Re: I need some help with the D'Mars ODS
Post by: wolf_papa on July 12, 2019, 07:50:49 pm

Thank you, that really helps, but I'm having problems decoding some of the symbols. They weren't on the BOM. This is my first foray into modern electronics, my only experience comes before JFETs, MOSFETs, etc. What part numbers should I be using for the solid state parts? There is also an unfamiliar symbol between tubes 2 and 3, as well as rectangles with 3 or 6 circles in them (look a lot like Legos).
                  Again, thank you,    Bob

Title: Re: I need some help with the D'Mars ODS
Post by: SILVERGUN on July 12, 2019, 08:54:57 pm

The Legos are designations for switch terminals. You can use panel switches or relays or both. I would highly suggest sticking to whatever info you can gather off of the build threads.

The IRF820 is a common Mosfet and the part marked 12V is a zener diode.
Doug sells both of these parts on this page:
https://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Lamps&ORDER_ID=!ORDERID!

Title: Re: I need some help with the D'Mars ODS
Post by: tubenit on July 12, 2019, 09:04:08 pm

Silvergun gave you correct information.   You can use relays for the switching & Doug sell the relay boards and there is a lot of info on relays in ARCHIVES.  OR you can use simple mini-toggles for the switching IF you don't need/want it footswitchable.
You could also build it with the mini-toggles and leave room to add relay switching later.  Just look at Doug's relay board dimensions and plan accordingly.

Doug sells the mosfet and the 12v Zener diode also.

Here is a D'Mars sound clip (built by DaGeezer) who used to be a moderator on the forum:
https://soundcloud.com/dageezer/dumars-noodles1-0

https://www.soundclick.com/html5/v4/player.cfm?songID=11842172

With respect, Tubenit

Title: Re: I need some help with the D'Mars ODS
Post by: wolf_papa on July 13, 2019, 04:09:05 pm

Thanks, I think I need to know now most of what I need to know, but how do I tell the polarity on the mosfet and zener diode. I don't want to burn one up or spend hours trying to trace down a mistake.

Title: Re: I need some help with the D'Mars ODS
Post by: shooter on July 13, 2019, 04:14:58 pm

Quote

how do I tell the polarity

Um.. google mosfet datasheet?  ya might want to add the mosfet number like 2n2222a - ya I know, bipolar transistor, but  :icon_biggrin:

Title: Re: I need some help with the D'Mars ODS
Post by: tubenit on July 14, 2019, 04:24:40 am

Maybe this will help?  This is on an amp I built maybe 6+ yrs ago and the amp has worked flawlessly since I first built it. It typically gets played several hours every week. The picture is of a D'Mars where the mosfet is being used as a cathode follower.

" mosfet follies" article    http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm

With respect, Tubenit

Title: Re: I need some help with the D'Mars ODS
Post by: wolf_papa on July 14, 2019, 02:06:03 pm

Great, thank you very much,      Bob