Build This MoFo!

Mofo as voiced by three different preamps.

These are my thoughts on listening to the Mofo through the Pass BA-3 preamp, the AKSA-Lender preamp, and the Stuart Yaniger ImPasse preamp. All three of these preamps are capable of supplying the necessary voltage swing that the Mofo needs.
My music choices are a Pink Floyd song from their 1973 album "Dark Side of the Moon". That song is " The Great Gig in the Sky". The instruments are a piano, Hammond organ, pedal steel guitar, bass, and drums. The main vocals are supplied in an almost orgasmic way by Clare Torry. Her wailing reveals much about the preamps. Also I listened to the live version of Dave Brubeck's "Take Five" from the album "Concord on a Summer Night", from 1983.
Please keep in mind these are my thoughts using this three preamps and your listening experiences will vary, due to variances in the builds, you're listening space and choice of speakers.

BA-3 "The Great Gig in the Sky"
The pedal steel covered the width of the sound stage with the piano appearing in the upper right. Drums were centered to the rear. During Torry's second set of vocals the piano and bass dominate and appear balanced to one another. Her vocals throughout this song sound slightly veiled. Additionally the drums are not as defined to my ear. (I also have a pair of Pass F4 amps I built and from my listening to the same songs, I feel the F4 and BA-3 present a more defined sound image of this song).
"Take Five"
A wider soundstage than my F4 pair. The solo clarinet is front and center dominate. The bass is very nice against the other instruments. This amp/preamp combo is very satisfying on the low notes. The solo piano seems to have a slight edge to the sound, not as rounded as the F4 amps. I really like how the bass stays clean and recognizable throughout the song. Drums solo feels like I am there in person. The final wrap up, the piano and clarinet sound very balanced.

AKSA-Lender "The Great Gig in the Sky"
Lovely pedal steel with a wide sound stage. Piano is well defined and the drums and cymbals are distinct. In the beginning of the song Torry vocals are not as distinct. In the second bit the piano is nice and wide. Vocals are nicer now appearing to float in the background. For me the vocals are not best with this amp and preamp combination. However this setup had the widest sound stage of the three preamps.
"Take Five"
Solo clarinet not as dominate with a good balance with the piano and bass. Drums distinct during piano solo with individual notes more rounded. Drum solo felt like I was there, very three dimensional. Overall a nice blend and balance of all of the instruments. I also felt like the low end was fuller than the BA-3.

ImPasse "The Great Gig in the Sky"
Wide sound stage with the voice and pedal steel forward center. Hammond organ notes distinct. Torry's second vocals are nicely rounded, with the bass and piano having a good balance. To me it seems when the number of instruments increase my overall listening observation is they sound less defined/distinct.
"Take Five"
Another wide stage with the solo clarinet sounding from the front left. Very mellow/rounded sounding. Piano solo has rounded notes with nice overtones, not overly bright. Drums during that solo very realistic with nice sizzle on cymbals. Overall a rounded fat sound.

A while back I compared these three preamps using a pair of Pass F4 amps and found I had an easier time suggesting which preamp I would rank first. With the Mofo I am finding it's not as clear. So as I have listened to these two songs and others, I will say "it depends". By that I mean the genre, the particular piece of music, the artist. As I write this I am listening to an album by the Bruskers Guitar Duo, two Italian players through the ImPasse into the Mofo. This combo does a nice job with the acoustic guitars being played. For me I will keep on building and listening.
Thank you to all of the talented designers for making these circuits available to us mortals.
David
 
Mofo as voiced by three different preamps.
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These are my thoughts on listening to the Mofo through the Pass BA-3
Thank you to all of the talented designers for making these circuits available to us mortals.
David
Thanks David.....
I'll have to think about it ... but I think I'll look for an open-loop preamp.
Also mono component and also a buffer. A low impedance in out is very important to interface with the MoFo.
 
I built this MOFO, in a 19v version. My first DIY amplifier. For the file, I attached some photos.

The amplifier is medium in size, very friendly with the decoration and only weighs 12kgs. I used the heat receiver (recycled) as a chassis, since it had previous perforations, which I used. It has no bottom cover for better cooling. Very minimalist

I read all the pages of this forum !. A lot of useful and inspiring information for a novice like me.

The small black box they see at the center contains the two MOFO channels, built point-to-point.

As an inductor I used an MOT, which I removed the secondary and added another primary in series. I painted them with copper color, to match them. I used nail polish.

The heat sink weighs 6 kgs. Each choke weighs 2.5kgs. I think that they allow me a route of easy update to 24v.

Later I will give my impressions on the sound.

Thanks a lot Mr Michel Rothacher and members of this forum:)
 

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I built this MOFO, in a 19v version. My first DIY amplifier. For the file, I attached some photos.
..............................................................
Later I will give my impressions on the sound.

Thanks a lot Mr Michel Rothacher and members of this forum:)
Nice.....but....
there will not be too much heat under the cover of the sink?:confused:

pardon...
I saw the openings for the air.....good
 
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Very nice build JAGCH

One question: How did you do for the winding of MOT. Wasn't the iron welded?

Thanks!.:)

Yes, the MOT had solder joints. But it is easy to cut through the welding line. I used a metal saw. Then, removing the secondary with some hammer blows is relatively easy. I took the primary of another MOT of the same size, inserted it instead of the secondary one and connected them in series. I bought them used, at only US $ 2 each!

In this forum someone put a link to a similar job (I do not remember who or where, there are many pages...), but instead of taking the primary of another MOT, he´s built a coil and then inserted it. A lot of work for me! I chose the easy way.

I seem to remember that the author suggested that and I listened to him. Good advice!
 
more IPS experiments done

Inspired by all the well done real nice builds here i also will go forward.

Thank you drpro for very good (huge) comparison...wow.

Based on added(PDF) Nishiki Tube gain stage i have tested different tubes, to clear huge differences in tonality....:), there is.

First i have changed to FQA40N25 (2V on choke) with ECC82(250V on plate) what gives a wow, comparing to first try....very nice.
Than i changed to 6N6P (measured before.... on Rk ~5,6V, behind Rp ~ 110V)- that should work.
And the result is closer image to ECC, more accurat pointed, hmmm...

Next i changed to IRFP7430 (tip from Circlomanen, Johannes here).
That comes close to other, more darker typ....feels you losing a bit top end, first,
but all clean, detailled.
Than i highered the plate voltage on 6N6P to 300V(behind Rp now ~ 135V and 6,8V on Rk)
All fine like before, a nice tube.

Next morning on cold start the bricks died with big humm...bad...bad.
All checked crossed left-right and connected to big 12" woofer.... humm keeps on.
Now i change to C-L-C Filtering with HMD 159ZJ (10mH,5A) with 15VAC transformer, dives now 17,5VDC.Slightly humm is staying...needs work.

On this point i tested next with FQA16N25 (obsolete) with 1,8V bias and the
6N23P now.

I came closer to end of experimenting....but it's funny way to learn little diferences.

Nice listening weekend to all.
 

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front-end experiments for Mofo

to play with Mofo, I chose to start the front-end tests with an interesting pre by Juma.
I finished the construction today .... I'll have to think about feeding it with a shunt salas .... maybe.
this is the scheme and the realization on perfboard.
let's see ..... and let's listen
 

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