Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on December 20, 2014, 08:14:46 am
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The D'Mars has been my favorite amp for some time. However, it was somewhat on the bright side using the OD.
NOTE: I am still using the original Hoffman style D'Mars turret board for this build and these mods.
I originally had a Hammond 1620 OT which is unusually large for a 20w OT and more like a typical 30w or 35w OT. However, I think the 1620 OT was a little too "hi-fi" for the OD channel even though it sounded great on the clean channel. I finally switched out the OT for a 40w OT (Doug's Bassman 5F6-A would be perfect for this).
What I discovered is that the larger OT seemed to give the amp a fuller tone and a smoother OD. So, I began experimenting with increasing the coupling caps. This proved to give the amp an even fuller warmer tone at lower volumes.
(I had tried larger coupling caps when it had the 1620 Hammond OT and that did NOT work well for me. The smaller OT needed smaller coupling caps)
The amp was originally 75% Marshallish/ 25% Dumblish in my thinking. It is now more like 60% Dumblish/40% Marshallish.
The amp sounds HUGE to me playing at very modest volumes and the OD is great with increased smoothness and sustain. The touch sensitivity of the amp is comparable to Geezer's HoSo56 which is one of the most touch sensitive amps I've played. The dynamics of tone dramatically changes with changes in how you pick.
This has very very musically sweet harmonics to it. I think it's a great option for someone looking for a channel switching amp that sounds good at modest volumes. I always use either delay or reverb in the FX. And the FX level makes a great master volume.
I am using an Emminence Delta Pro 12-A. It also sounds good with an Emminence Cannabis Rex and an Emminence Texas Heat.
With respect, Tubenit
EDIT: OD tone pot is 1MA not 250k
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Looks good! I think it may be time to go ahead and build this.
What did you use for the choke on this project?
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I used Doug's larger sized choke more for 6L6's and such.
I think it's a great amp! The original D'Mars (with 5879) was built in Aug. 2012 So this amp has literally two years of tweaks behind it. I have never spent this much time experimenting to get the best tone possible. For every tweak I kept, I probably tried 2 or 3 that I did not keep. Lots and lots of hours in on this one.
IF you build it, please post how you like it with some soundclips.
With respect, Tubenit
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Thanks. You got any gut-shots you'd like to share? I'd like to see how you laid it out with the switching relays and power supply circuit.
I just joined a blues band that I think this amp would work well for. I really would like a channel switcher to keep pedals to.a minimum.
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The chassis I used for the D'Mars had 5 other builds in it prior to the D'Mars and then I modified it for two years. so, the chassis interior is NOT very neat even though it is easy to service and has a logic to it.
Despite the messy chassis interior ........... The amp is amazingly quiet at idle even when the volume is set to be loud.
The other thing is I would do the layout very different if I built it again.
I would probably do a layout similar to the Dumblish clones BUT use Doug's turret boards and use Doug's grounding scheme since it has worked so well for me on every amp. It should be noted that the Dumblish clones have these rather large B+ filter cap boards that are not needed for the D'Mars.
Compare Normster's layout with an "edited version" that I would probably emulate IF I rebuilt this amp from fresh. Note that Normster's layout has some useful information about the FX controls and grounding on the back panel.
With respect, Tubenit
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Tubenit, you are the man!
FYI, going through and making a BOM and comparing layouts to schem, I noticed that the 250p cap from V1 pins 6 to 8 is missing from your layout.sch file.
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noticed that the 250p cap from V1 pins 6 to 8 is missing from your layout.sch file.
On the actual amp, there is a 250p cap from V1-6 to V1-8.
With respect, Tubenit
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Thanks, after going through the layout and comparing to the schematic, I noticed you left a lot of the on-tube and on-pot components off the layout. I figured must have been a conscious choice to help keep the layout printouts cleaner. I just penciled them in.
I usually get a decent amount of cash from my parents and my in-laws each Christmas. Hopefully tonight I'll have enough to finance most of this build and I can get crackin'! If not, I'll have to spread the component purchasing out over a few months.
Oh.... there are some odd cap values on the schematic. Like the .0013 in the tone stack. Do you just use a .0012 there? Also same for the .001? There's also a .022... just use the .02? And the .068 in the tone stack? I am basing this off of what AES has available in the PS series Orange Drops. Don't know if there is another source that has those exact sizes?
And all of the "pico value" caps... you are just using silver micas there or some of them ceramic disc?
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Drawing the layout with ExpressSCH was a challenge. I did the best I could so someone could follow it as best as possible. I don't have visio to draw layouts.
Oh.... there are some odd cap values on the schematic. Like the .0013 in the tone stack. Do you just use a .0012 there? Also same for the .001? There's also a .022... just use the .02? And the .068 in the tone stack? I am basing this off of what AES has available in the PS series Orange Drops. Don't know if there is another source that has those exact sizes?
Use an .0012 for the .0013. Use a .022 or .02. Use a .068 or .06 ............ etc....... doesn't make much difference honestly. Just get as close as you can.
I use mostly silver mica, I think there may be one or two ceramic but can't remember off hand? Not that critical to the tone, IMO. Sometimes a ceramic in a certain place can give a little more "vowel" tone but not in any place. You really have to experiment. I'd just silver mica everywhere. You can go back later and try ceramic if needed.
This really is a tweaker's amp. So you have to have a mindset to build it, and then tweak it to your own preferences.
With respect, Tubenit
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This really is a tweaker's amp. So you have to have a mindset to build it, and then tweak it to your own preferences.
With respect, Tubenit
:thumbsup:
Hopefully the tweaking will begin soon!
Yeah I wish I had Visio too, but man it's expensive. I've toyed with the Libre Office version of it, but I haven't spent much time with it.