Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => PC Express and JSchem - Schematics and Layout diagrams => Topic started by: tubenit on April 14, 2010, 05:10:41 pm

Title: Mini-HRM (Mat's amp)
Post by: tubenit on April 14, 2010, 05:10:41 pm: 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
Title: Mini-HRM (Mat's amp)
Post by: tubenit on May 10, 2010, 05:38:51 am: 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
Title: Re: Mini-HRM (Mat's amp)
Post by: tubenit on February 12, 2011, 08:28:25 am: 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
Title: Re: Mini-HRM (Mat's amp)
Post by: tubenit on March 27, 2011, 03:51:35 pm: We now have some voltages from Mat on his single ended 86Special. These reflect what he has posted.

With respect, 10thtx
Title: Re: Mini-HRM (Mat's amp)
Post by: tonewood on March 30, 2011, 10:09:15 pm: I can't seem to find a sound clip for the 86 special. Can you point me to it?
Thanks
Title: Re: Mini-HRM (Mat's amp)
Post by: tubenit on April 04, 2011, 08:48:59 am: 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
Title: Re: Mini-HRM (Mat's amp)
Post by: arjepsen on August 18, 2014, 03:15:12 am: 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???
Title: Re: Mini-HRM (Mat's amp)
Post by: sluckey on August 18, 2014, 06:33:10 am: Quote from: arjepsen on August 18, 2014, 03:15:12 am
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
Title: Re: Mini-HRM (Mat's amp)
Post by: toneseeker on September 22, 2014, 09:07:44 am: 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!
Title: Re: Mini-HRM (Mat's amp)
Post by: tubenit on September 22, 2014, 09:45:59 am: 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.
Title: Re: Mini-HRM (Mat's amp)
Post by: toneseeker on September 29, 2014, 03:27:21 pm: 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_SE/AX84_20W_SE_Poweramp_Schematic.pdf)
http://ax84.com/static/corepoweramps/20W_PP/AX84_20W_PP_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?
Title: Re: Mini-HRM (Mat's amp)
Post by: sluckey on September 29, 2014, 03:54:56 pm: Quote
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.
Title: Re: Mini-HRM (Mat's amp)
Post by: toneseeker on October 01, 2014, 01:28:09 pm: 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.?
Title: Re: Mini-HRM (Mat's amp)
Post by: tubenit on October 02, 2014, 07:39:26 am: 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
Title: Re: Mini-HRM (Mat's amp)
Post by: sluckey on October 02, 2014, 09:06:13 am: This is how I would do it...