[909]

The Si2A3 that were originally made by Moth aren't optimized for low impedance headphones, though, most people that I've heard from say once the music starts you can't tell. Now some may have been modified with an out-boarded power supply, which Craig did on the handful of Si2A3-H as those are ideally suited to drive both low and high impedance headphones.

 

[Karo]

Quote:

Originally Posted by s1rrah /img/forum/go_quote.gif I'd buy one just because of that fine logo. (sucker for good branding)

It reminds me of the Slingerland badge from the late 50's, right before they moved to Niles. Congrats Aura. *

photo

 

[foo_me]

Quote:

Originally Posted by Zanth /img/forum/go_quote.gif I've always loved the look of Moth amps and if only they were compatible with Grados and Sony R10's I'd be all over them, but by their own advisement they recommend Senn Z levels or above. K1000's + Moth 300b must be heaven!

I actually prefer Craig's new Balancing Act with my RS1s over the Senns when I recently auditioned them. Something about transformers matching very well with low impedance cans. With the Zana, I favored the senns. Not sure about the R10 but would be interesting to find out!

 

[nghows]

OOOoooo someone nearly made a BIG mistake. Withdrawing a Si2A3 from the FS listings......

Imagine the eternal regret if he'd gone through with it......

Good save Jussei, in case you're reading this.

 

[recstar24]

Quote:

Originally Posted by Zanth /img/forum/go_quote.gif I've always loved the look of Moth amps and if only they were compatible with Grados and Sony R10's I'd be all over them, but by their own advisement they recommend Senn Z levels or above. K1000's + Moth 300b must be heaven!

That has been sort of a misnomer. Speaks to Craig's brutal honestly, and no BS straightforwardness, probably cost him sales back then if anything.

The output from the s2a3 and si2a3 runs directly off the transformer secondary tap. Default it is 8 ohm. Running 32 ohm grados off a 8 ohm transformer tap coupled from a 2a3 tube sounds absolutely fantastic, in my opinion. 3 watts into 8 ohms is under a watt or so into the 32 ohm load, maybe 750 milliwatts or anything. That is plenty of power, and listening to grados on moth gear is fantastic. RS-1's sing on transformer coupled amps.

The issue was hum. The s2a3 and si2a3 have the power transformer inside the main chassis in somewhat close proximity to the output transformers. The magnetic field from the 50/60 hz hum from the power tranny is close enough to be induced into the output transformers, so you hear the low pitch B in your cans which represents that frequency. It is typically low enough to be covered in the natural background and noise floor of 95% of most recordings. But it exists and for some people they cannot even notice it. I did with my s2a3 but the sound quality made up for it.

Now, craig did produce a set of si2a3's that were modified by placing the power transformer and inductors in a separate chassis, eliminating the hum completely. Power supply caps were upgraded as well to all polypropylene film caps. Some of these upgraded models also used 6j5 tubes for the input, which are basically single plated 6sn7's, and sound fantastic. Most of these were also modified to run 45 tubes in addition to 2a3's. I believe only 5 were made...and yes I have one of them

Moth si2a3/45H running Emission Labs 45 solid plate tubes going into vintage RS-1's = _____________________ (insert adjective here)

 

[Karo]

Somebody just snagged a good one ...

Moth Audio Corporation s2A3 Tube Amplifier - eBay (item 390036166036 end time Mar-16-09 11:55:46 PDT)

 

[IceClass]

Quote:

Originally Posted by s1rrah /img/forum/go_quote.gif I'd buy one just because of that fine ass logo. (sucker for good branding) Congrats on the amp, Bryan. Hope to hear it someday (so keep this one a while already!)

I would love a T-shirt with that logo splashed across the front.

 

[Sanderman]

Quote:

Originally Posted by recstar24 /img/forum/go_quote.gif That has been sort of a misnomer. Speaks to Craig's brutal honestly, and no BS straightforwardness, probably cost him sales back then if anything. The output from the s2a3 and si2a3 runs directly off the transformer secondary tap. Default it is 8 ohm. Running 32 ohm grados off a 8 ohm transformer tap coupled from a 2a3 tube sounds absolutely fantastic, in my opinion. 3 watts into 8 ohms is under a watt or so into the 32 ohm load, maybe 750 milliwatts or anything. That is plenty of power, and listening to grados on moth gear is fantastic. RS-1's sing on transformer coupled amps. The issue was hum. The s2a3 and si2a3 have the power transformer inside the main chassis in somewhat close proximity to the output transformers. The magnetic field from the 50/60 hz hum from the power tranny is close enough to be induced into the output transformers, so you hear the low pitch B in your cans which represents that frequency. It is typically low enough to be covered in the natural background and noise floor of 95% of most recordings. But it exists and for some people they cannot even notice it. I did with my s2a3 but the sound quality made up for it. Now, craig did produce a set of si2a3's that were modified by placing the power transformer and inductors in a separate chassis, eliminating the hum completely. Power supply caps were upgraded as well to all polypropylene film caps. Some of these upgraded models also used 6j5 tubes for the input, which are basically single plated 6sn7's, and sound fantastic. Most of these were also modified to run 45 tubes in addition to 2a3's. I believe only 5 were made...and yes I have one of them Moth si2a3/45H running Emission Labs 45 solid plate tubes going into vintage RS-1's = _____________________ (insert adjective here)

I found a mint Moth Si2A3 from a reviewer a friend on mine knows who has been hanging on to a pair of the things forever. He sold me one for $1,200 that still had the plastic film on the Moth logo plate! Problem was it hummed. I had a Zana on order and so I reached to Craig and asked what could be done. He then proceeded to walk me through upgrading the amp to outboard power supply and beyond.....

First up the mint stock Moth:

And peeling off the logo cover film....

First up you move the power tranny out of the amp into an external project box I sourced form an electronic supply company....

Then you get the two Hammond heater trannies he specifies (not inductors actually) and put them in that box too....

Then you have to build an umbilical cord with all of the appropriate connectors and drill a hole in the chassis of the Moth and mount it....

The inside of the chassis starts to get a bit bare then so you fill it with other stuff. Like the film caps he specifies in place of the electrolytic cathode caps....

Which you put where the power tanny used to be....

And then you start wiring it to handle 45s by drilling holes to mount a few switches....

And you wire in the appropriate resistors....

And drill and touch up holes in the top plate for those 2A3 / 45 mode switches....

Then he sells you a pair of new JJ 100/100 caps to replace the old LCRs that have started to dry out.....

Which you then swap out....

And bypass with copper foil and oils....

But you're not done

Joe

 

[Sanderman]

...who can't live with unlabeled switches. So you really go all out and make your own custom 2A3 / 45 switch plates to match the main Moth logo plate....

And you end up with a Moth Si2A3 that doesn't hum, has far greater image specificity, transparency and palpability.

And you're right about it locking in with Grados. With 45s and the new Grado PS1000s it sounds freaking transcendentally phenomenal.

Joe

 

[Zanth]

Brilliant! I so want; you have no idea

 

[IceClass]

Brilliant Joe!
Thanks a bundle for sharing and what ingenuity!

 

[uberburger101]

Amazing job there Sanderman. It looks absolutely gorgeous.

 

[Karo]

Nice patina dude.

You did the end-grain block as well ?

These units go outside the norm. Bravo, Sir.

 

[EnOYiN]

Wow! If that sounds half as good as it looks it sounds amazing.

 

[Aura]

Glad to see this thread revitalized.

Sanderman - amazing job. I'm not sure what your additional costs were for transforming the amp completely into the /45H variant, but the price you paid for the amp (in mint shape nonetheless) is mind-boggling.

My EC2A3 currently has an issue that needs to be remedied, but I think I'm going to take advantage of the situation by making a few upgrades inside the amp while I'm at it. The big disadvantage (in theory) of the EC2A3 compared to it's Si2A3 brethren is that it's got a single capacitor in the signal path, so I hope to change out the stock cap to something a little bit better (Craig suggested Black Gate). I should probably grab some better output tubes while I'm at it

.

~ Viva la Moth ~