A snubber for my Akitika GT-101 (2 x LM3886)

[Mark Johnson]

I thought other diyAudio members might be interested in the modification I made to my Akitika GT-101 power amp kit. I added a snubber on the Power Supply Unit PCBoard, to reduce/eliminate RF interference by damping out any transformer secondary ringing that may occur when the rectifier diodes turn off.

The GT-101's PSU board already includes capacitor C5 (0.01 uF) across the secondary; the snubber components I added are (0.15uF in series with 110 ohms) for 115VAC operation, or (0.15uF in series with 120 ohms) for 230VAC operation. These are shown in a dotted rectangle on the attached schematics, and are indicated by yellow arrows in the "After" photographs.

Measured scope waveforms using the "Quasimodo" test jig (link) are also attached. You can see that the transformer secondary is critically damped (zeta = 1.00) in the red traces, corresponding to 109 ohms and 120 ohms.

The GT-101 uses an Avel Lindberg Y236602 toroidal transformer. It is rated 230VA, has dual primaries for 115VAC / 230VAC operation, and dual 35V secondaries which the kit connects in series. This 70VAC is rectified, filtered, and then feeds a DC voltage regulator (rare in a chip amp) which applies +72VDC to the LM3886 ICs.

Hoping this is helpful,
-MJ

 

[maty tinman]

Akitika GT-102 review

Yesterday, a new review.

Review: AkitikA GT-102 Power Amplifier, Part I LS3/5A vs Linn Kan

Doctorjohn Cheaptubeaudio: Audio Reviews and More: AkitikA GT-102 Power Amplifier, Audiomaster LS3/5A, Linn Kan, LM3886

…With a tube preamp, vocals are naturally even better. Shirley Horn’s priceless You won’t forget me (CD, Verve) was so utterly compelling that I just had to listen from start to finish (which never occurred before). Not only were the fine modulations of Horn’s voice as well rendered as I have ever heard, the piano (herself) and the solos of the guests (a starry cast, including Miles) had startling definition and realism, as did the ambience and audience noise (little). On Richard Galliano’s Bach album (CD, DG), I too could not help just sampling, and had to listen to the entire Violin Concerto. For either album, I was not at all sure I’d exchange the amp for even the best tube amps.

Sonic Assessments Overall, there is little question that the AkitikA is an overachieving amp. The most gratifying thing is, no matter what I played, I was gripped and could not stop listening. I am likely to keep it and the LS3/5A for a quick listening system, such is the synergy between them. The LS3/5A works well with UK classics integrated amps like the Naim Nait, but here it is taken to a wholly new level. Rhythm and Pace The AkitikA even trumps the UK amps in PRaT that the flat-earthers so covet.

Solid State? Although the AkititkA is just a little warm sounding but, lest you misunderstood from the listening notes above, it is not tube-like. Although vocals and instrumental timbers are alluring, the treble, though not lean, is not quite as harmonically fleshed out as a tube amp. Tube die-hards may demure, but the AkitikA compensates by its enticing performance in other areas...

Stereophile review:

AkitikA GT-102 power amplifier | Stereophile.com

Measurements: AkitikA GT-102 power amplifier Measurements | Stereophile.com


Mark, can you tell us more about the GT-101? Sound impressions vs others SS amps. Class A or not.

How much NFB usually have the LM3886 amps? And your Akitika GT-101 too.

 

[nigelwright7557]

I thought other diyAudio members might be interested in the modification I made to my Akitika GT-101 power amp kit. I added a snubber on the Power Supply Unit PCBoard, to reduce/eliminate RF interference by damping out any transformer secondary ringing that may occur when the rectifier diodes turn off.

-MJ

I had a problem with very bad diodes switching noise on a valve mixer.
The noise on the output was terrible.
I just changed to Schottky diodes and the problem went away.

A snubber across the transformer is a good idea anyway to stop nasty spikes getting in off the mains.
I had an amp blow up an output transistor when I turned off my soldering iron. The spike down the mains got into the amp and blew up the transistor.

 

[Panelhead]

I have always connected a snubber with the capacitor connected to ground. The resistor connected to the rails.
Not sure if it makes a difference.

 

[asuslover]

Akitika gt 101/102 is a Great amp , very affordable and delivers great sound and no speaker protection needed.

 

[Jungstar]

There is also an AC scraper that can be added if you have asymmetric AC power in the house. 25 USD.

 

[nigelwright7557]

It doesnt take many components to kill the DC.