Mini-HRM (Mat's amp)

[tubenit]

I occasionally visit other amp forums and saw this amp and sound clips on the Amp Garage under the D_mble discussion.
I was VERY impressed with the sound clips and would like to build the amp.  Mat (the designer of the Mini-HRM EL84) and Colossal (who drew the schematic of the amp) both gave us permission to post an editable schematic and layout version of it.

http://ampgarage.com/forum/viewtopic.php?t=10913

Colossal occasionally visits the Hoffman forum and was aware of DaGeezer's Little Wing & HoSo56 ...... and some of the other innovative builds here. Anyhow Colossal and Mat both seem to be very cordial individuals and I am grateful for their willingness to share this.

http://soundclick.com/share?songid=8895338

http://soundclick.com/share?songid=8927753


With respect, Tubenit

[tubenit]

OK, I was going to do a 5881 SE version but that was not successful. So keeping with a low wattage amp, I am going to try Mat's preamp into a poweramp similar to the 56T using 6BM8's. This should be about a 9 watt amp.

DaGeezer tried this with his HoSo56 with 6BM8's and gave it a positive review.


With respect, Tubenit

[tubenit]

Mat's mini-D amp has evolved. This is just an idea based on his latest information and soundclip.

Mat switched the V2 12AX7 out for a EF86.  He is calling it the 86-Special.

CHECK for errors and compare schematics to layouts.

I also included what I'll call Matt's mini-D hybrid.  This was based around Geezer's TBM which has an incredibly sweet clean channel.  I typically use the mid and PAB switch on ........... so I don't really need the bass and mid pot. This idea uses a 5879 pentode.

NOTE :  CHECK to make sure you are using the correct type of rectifier!!
With respect, Tubenit

[tubenit]

We now have some voltages from Mat on his single ended 86Special.  These reflect what he has posted.

With respect, 10thtx

[tonewood]

I can't seem to find a sound clip for the 86 special. Can you point me to it?
Thanks

[tubenit]

Tonewood,

There are a bunch of soundclips spread over the pages of this thread:

http://ampgarage.com/forum/viewtopic.php?t=13854&start=150

With respect, Tubenit

[arjepsen]

Im a bit confused...
There's a 70 pf on the clean master. However it is going from wiper to ground.... Is this correct?
Usually there would be a "bright cap" from wiper to the signal side, but is this a different function? Maybe a sort of "dark cap" to bleed off a bit of treble???

[sluckey]

Im a bit confused...
There's a 70 pf on the clean master. However it is going from wiper to ground.... Is this correct?
Usually there would be a "bright cap" from wiper to the signal side, but is this a different function? Maybe a sort of "dark cap" to bleed off a bit of treble???

Tubenit prefers a smooth tone to a bright tone.

I/Tubenit do prefer a smooth tone to a bright tone, but this was actually Mat's choice.   with respect, Tubenit

[toneseeker]

I am interested in building the 86-special. Has anyone completed this build? If so, could you please post some pictures of the build. Is this the current layout and schematic? Is there a BOM around?
Thanks!

[tubenit]

There is no BOM.  I don't know of anyone on the Hoffman forum who has built one?

I think Mat's amp has gone thru several mods & I am not sure exactly where it is now?  The original however is an incredibly good sounding amp, IMO per Mat's soundclips.

With respect, Tubenit.

[toneseeker]

Is there any way to integrate the 86-special into one of the AX84 core power amp?

http://ax84.com/static/corepoweramps/20W_SE/AX84_20W_SE_Poweramp_Schematic.pdf
http://ax84.com/static/corepoweramps/20W_PP/AX84_20W_PP_Poweramp_Schematic.pdf

Could I go from E2 to Pin 1 on the volume control of the SE or E2 to R27/100K on the PP? There must be a better way since the 86-Special already has Vol and Mst Vol. Can it just not be done because the B+ voltages are to high?

[sluckey]

Could I go from E2 to Pin 1 on the volume control of the SE or E2 to R27/100K on the PP?

That should work.

[toneseeker]

I am trying to make a board for the filter section coming off the transformer. I don't understand the 22uf under the B on the schematic attached to the 1K/3W. Is the 1K/3W the same resister shown on V3-9 or a separate resister? Is this board layout correct? Where do I add the 1K/3W and the 22uf cap.?

[tubenit]

I understand it to be like this.

Please be sure to post pictures and a tone review of the amp on the Tweaks forum when you are done!

Tubenit

[sluckey]

This is how I would do it...