miniHRM evolution

[10thTx]

Sorry late to this party..

I don't know if you have heard any of Mat's sound clips but this was one of my favorites of his:

http://www.soundclick.com/bands/page_so ... layer=true

I'm going to try a 5879 version of this with a CF 6BM8 triode going into a 6BM8 pentode. I like the CF following the 5879 prior to the passive FX loop. Should end up with about a 3-4 watt amp? I've had success using the 5879 as a switchable OD stage in some other amps I've built. I took some of Mat's ideas and brought them into the Tweed Overdrive Special amp design with a SE version.

With respect, 10thtx

[mat]

Sorry late to this party..Looks like a cool amp although I am not a big fan of the SE amps..I have messed around with this EF86 circuit and will add by changing the value on the 820k is a good way of playing around with the gain structure on that 86.. Mat...Did you play around with this and arrive at the 820..Just wondering..

Tony

Hi Tony,

Sorry for the late answer (building a dock at the sommer house..) I don't remember (or keep record) all of the changes I did for the amp. I did read few places where the EF86 has been used and tried different combinations/values of the EF86 on the OD section and the result is what worked for me. I don't have a scientific approach for the circuit, I just listen and keep when I hear/feel (playing feel) something I like.

On EF86-Special I like the playing feel because it is more forgiving than the straight D-style amp. There is Marshall nuances on the sound and playing feel + when maxing the drive pot my amp gets a fuzz face type of exploding tube kind of character (Neil Young) which I like very much.

To me the only speaker I've liked so far with this circuit has been the Emi Delta Pro 12A but Rog got a very good sound with his little combo having a 10" Emi Delta Lite in there. Also Rog has a switchable HRM circuit in his combo and that is something I might be getting back at also.

[talbany]

Mat
Thx for the shout back.. Always curious as to how one tweaks..You made a wonderful amp!

Rock on!!...Tony

[ER]

I've heard good things about the eminence legend 10", well balanced and response curve looks close to EVM12L in that same vain and a little cheaper than the pro speakers. Heard good reviews on these from Doveman.

Speakers really make a difference with low watt single ended designs, I recommend really experimenting here. My favorite so far is a pair of vintage 8" alnicos from a portable pa set up I got at a thrift store (probably used to announce bingo numbers), they're fragile cones but sound amazing. I keep them on life support with tacky glue and toilet paper it will be a sad day when they finally succumb to those 5 watts of monster power.

There are a lot of interesting 8 inch full-range speaker designs out there for the hi-fi guys that sound very nice for guitar.

-E

[10thTx]

I finally got the Mini-TOS build completed.

It has very nice sustain, & does the blooming thing well. It's very touch senstive, IMO. The amp is not as creamy smooth in overdrive as the Tweed Overdrive Special is.

There is actually nice contrast between the clean and OD channel on this amp. Both are useful.

I am using a 6BM8 pentode single ended, and the amp has more chime to it. Sustain and bloom similar to my Dumblish inspired amps but with more chime to it. I suspect the 6BM8 pentode is responsible for the chimey tone?

Despite the small chassis and messy wiring/layout, it is quieter at idle than the VibroChamp I used to own. It's a VERY loud cranked 3.5 watts!

The chassis had been my FX-Reverb unit, but with the CF after the clean and after the OD channels, my Boss digital delay sounds great to me with this amp!

THANKS to Mat and others for the inspiration for this amp!

Editable versions are here:
http://www.el34world.com/Forum/index.ph ... #msg107840

With respect, 10thtx

EDIT: I moved the passive effects loop between V1a & V1b which allows the Boss digital delay to be more transparent, with little to no white noise and NO volume drop. I previously had the FX loop after the clean/OD and prior to the 6BM8 and found that I had some volume loss and it colored the tone somewhat.

[da Geezer]

Great looking build!

This (Mini-TOS) will be 1st on my fall/winter build list.....putting it into a VJr box & using an EL84 or maybe 6AQ5/6005W.

Thanks for the update & schematics.

G

[ER]

Two thumbs up for 6aq5/6005

[mat]

Stunning looking build again ! Absolutely beautiful maple ! Congrats !

And Yes, me too looking forward for the clips

Thanks for the build report & pics.

[rogb]

Very nice work there, look forward to some gut shots and clips when you get a chance

[layupe]

Hi guys! Finished my try on the 86 special and have some trouble I just finished it and need to try it in deep yet but from now already i can tell something is not completely ok with it...

One of the things i noticed is that the bass pot seems to do nothing at all, i revised conections but did not found something wrong with that yet, ill work on it.

The other thing is that there is some werid noise when i play that is hard to describe, its not the "typical" noise if you know what i mean, ill try to upload an mp3 so you can understand what im talking about and maybe help me find the procedence...

Also i would like to ask you a couple of questions, sorry for my ignorance but can someone tell me what's the purposse of the 20M resistors on the PAB? What does they do exactly? And what would happen if i use half that value, say 10M? Is it correct the wiring of the PAB on the layout? I ask cause i think i see some diference against the schematic but its very probably i dont know what i see at this point!

[NEjoe]

Is it correct the wiring of the PAB on the layout? I ask cause I think I see some difference against the schematic but its very probably I don't know what i see at this point! [/quote]


I took a look and you're right; it seems that the 86 special duet layout doesn't match the schematic for the PAB switch. I edited the layout to what I think is correct and posted it over at el34world.

http://www.el34world.com/Forum/index.php?topic=11146.0

[Structo]

Layupe do you have the 10K resistor from the left Bass lug to the ground buss?

[layupe]

Yes Structo, i do have the 10k resistor from left lug of bass pot to ground, i changed the wiring of the PAB looking to the schematic instead of the layouts and the bass is back now...

NEjoe, ill take a look to the edited layout to compare it to what i did on mine, to me it seems to work ok now but im not very confident on my "skills" so i need to check and re-check everything!

Tomorrow i will have 3-4 hours with the amp and i will try to make some pics and an mp3, today i had just 30 minutes free and conected the guitar to it to test the changes on the PAB, enought to see the bass pot works ok now and also to connect the guitar on the "return" of the fx loop and notice the weird noise i was talking about on my last post was still there so i guess the problem is on the power amp section I have some "suspicious" points to check there, the NFB loop switch i installed there and the PPIMV are the first places to check, wish me luck!

Regards

[rogb]

Now you mention it, I'm not getting much bass action on mine, thanks for the heads up, I'll have a look at that PAB wiring and report back

[rogb]

Thanks! I have now got some good cut and boost on the bass, thought it was just my hearing before!!!

Just to note that the center lugs of the DPDT switch need to be joined so maybe another dot on the layout/schematic?