Akitika GT-108 Stereo Amplifier Kit Review

[restorer-john]

This amp appears to have a unipolar PS, hence the need for the large C13 coupling to the speaker to remove the DC offset of about half VCC. To avoid a loud "thump" and speaker overload upon power up, K1 is likely in the O position so that C13 can charge through R35 and R38 to about half VCC. Then K1 is switched to the S position, at which point the internal resistive load (to keep C13 charged) changes to R40. But it seems that the speaker is connected to the OUT terminal, not the L1A point. If so, the 10 Ohm / 1 Watt R35 is kept in series with the speaker, which does not seem a good thing even if negative feedback is connected to L1B. Am I reading the schematic incorrectly?

You missed the inductor (wound around the cap can) that sits in parallel with the resistor...

The rest is anti-thump due to the 10mF cap which would otherwise make a huge bang at turn on.

 

[ta240]

.....

But, gotta agree with @amirm, the instruction manual is the highlight. It's a seriously well done manual. 56 pages full of photos and details. Nothing like the B&W kit manual on 20th generation photocopied & folded-up rat-paper like I had growing up.
....

It is a really fun build. A modern Heathkit.

 

[ta240]

It looks like the GT-102 measures better

AkitikA GT-102 power amplifier Measurements

Sidebar 3: Measurements

www.stereophile.com

The GT-108 was designed to fill the gap when the LM3886 chips weren't available.

 

[restorer-john]

Is that capacitor inductor for feedback?

No. The capacitor is for DC blocking and the inductor/resistor is impedance compensation when connected to a typical load, to ensure stability.

10,000uF will give a decent low end rolloff (~2Hz@8R). But there's a huge inrush (thump) to charge it, that's why the relay shunts that current to ground at turn on- so you don't damage a voice coil or scare the dog/wife.

 

[Mikig]

I don't go into strictly technical issues, it's not my job
I do notice one thing, however: all the power amplifiers and integrated amplifiers that I own and most I've seen have inputs above or on the side of the outputs.
This strangely is the opposite; I find it very inconvenient, especially if you use bananas. Normally the amplifier is placed at the bottom and the sources gradually rise...
However, it goes without saying that if you read the data sheet and look at the price you might find it interesting.
Then he looked at the measurements, and everything falls apart….

thanks for the review Amirm!!

 

[Doodski]

The capacitor is for DC blocking

This I am aware of and the capacity of it if for setting the corner frequency.

the inductor/resistor is impedance compensation when connected to a typical load, to ensure stability.

This is a new one I have never seen other than a old Marantz although I was not up to speed as per it's function. Very intriguing operation.

10,000uF will give a decent low end rolloff (~2Hz@8R). But there's a huge inrush (thump) to charge it, that's why the relay shunts that current to ground at turn on.

The charge discharge cycle is a big thought that crossed my mind. That relay might operate at shutdown too to prevent sizzle and frazzle @ the speaker at power OFF<?> I'm not looking at the schematic right now and am just asking.

 

[Sokel]

I voted great not for the finished amp but for the person behind it.
Not for the schematics,not for the components,not for nothing.

But for his ability to forget what he may have learned as an EE and put himself in the complete amateur's shoes writing this masterpiece (the manual) .

Pure respect,only people who know exactly what they're doing can break things down to the complete amateur level.

 

[restorer-john]

This is a new one I have never seen other than a old Marantz although I was not up to speed as per it's function.

It only looks different to you because a) it is capacitor coupled and b) the inductor is wound around the cap, instead of sitting on the speaker terminal PCB as it is in millions of other amplifiers.

 

[Doodski]

It only looks different to you because a) it is capacitor coupled and b) the inductor is wound around the cap, instead of sitting on the speaker terminal PCB as it is in millions of other amplifiers.

As in a zobel network at the emitter resister? This stuff I usually just meter it out and if it meters OK I go on to other circuitry troubleshooting...LoL. HeHe.

 

[JasonC331]

I bet the owner would build you one to test the installer. He's a nice guy, I own a bought Z4 version of this amp, made by him, and one of the best-sounding amplifiers that I have brought to compete with many amps and it comes out on top. I think there maybe an issue with the build.

 

[restorer-john]

It is a really fun build. A modern Heathkit.

I agree. If it gets people into building HiFi again, that's a good thing, regardless of whether it's a fantastic performer or not.

I think of the first amplifier kit I built. It was a long time ago. Almost brings a tear to my eye.

 

[restorer-john]

.

 

[Doodski]

I think of the first amplifier kit I built. It was a long time ago. Almost brings a tear to my eye. See here:

I built a flip flop circuit LED lapel pin and then assembled an analogue large sized multimeter from parts, had to solder it all together, assemble the assemblies and stuff it all in a case and button it up. I gave it to my father who thought it the bees knees because he did not have a multimeter and he dug the meter in the display for some reason. I hated the meter because it was analogue and I did not appreciate at the time it's special capabilities. I was veryy pleased when I got a digital meter. That was cool. I wore the flip flop circuit led lapel pin and thought I had mastered electricity... LMAO... After that I did not do any kits and just focused on destroying gear and attempting to make speakers with home made coils without capacitors and again thought I mastered speaker crossovers... LoL. I was advised clearly by my family to stop wrecking gear in the name of science... gg*

 

[JasonC331]

.

This is from Dan the owner:

Some of what they say is true...I've limited peak currents to limit power dissipation to make it pretty bulletproof. I'd be curious what ASR's thoughts are on the GT-102 Z4 version. It's also hard to say as to whether the unit might have a problem or not.

All the best...

Dan

 

[ta240]

I agree. If it gets people into building HiFi again, that's a good thing, regardless of whether it's a fantastic performer or not.

I think of the first amplifier kit I built. It was a long time ago. Almost brings a tear to my eye.

Having built at least a dozen amps, this was by far the most fun. I built one as a gift and liked it enough I built one for myself. Come home from work, sit down at the bench and solder for awhile on this kit; it is almost meditational. Soldering, sanding wood, anything like that, you don't let your mind wander so you are in the now.

I'm not familiar with many other all inclusive amp kits (and I don't consider just bolting a premade amplifier board into a case a kit). Having everything there, in one box, is such a big plus over trying to source all the components for the many designs that are out there as PCBs or Gerber files.

Some people enjoy finding appropriate heatsinks, power supplies, cases, matching components, finding replacements for discontinued and back ordered components and although the challenge can be fun sometimes it can also be draining.

And this thing has already outlasted 3 Topping DACs that I bought when they first became all the rage.

 

[phoenixdogfan]

I kind of see this as a poor performer. Not powerful, not performant, and not inexpensive. And you get to put it together yourself, because you're still not over making lop-sided ashtrays in high school shop.

If you want to feel better about yourself by expending all that sweat equity, at least make sure you come out with a Purifi Eigentact at the end of the process.

 

[restorer-john]

I don't consider just bolting a premade amplifier board into a case a kit

Like that ridiculous Hypex preamplifier "kit". No soldering iron required- that is NOT an electronic kit- it's LEGO for 8 year olds.

Where are the "options"? In the future. 1 Year on, still nothing. LOL.

 

[brunes]

The GT-102 was my gateway drug to diy hifi. Amazing manual, super support and at the end a pretty decent amp. I can't really tell the difference between this and my vidar to be honest but that's a whole thread in itself. The satisfaction of a working amp you soldered yourself is pretty cool.

Also this kit includes EVERYTHING to make it, you don't need to hunt for a case or drill holes in metal. Cases can have significant cost and effort to make.

 

[Rick Sykora]

Like that ridiculous Hypex preamplifier "kit". No soldering iron required- that is NOT an electronic kit- it's LEGO for 8 year olds.

Where are the "options"? In the future. 1 Year on, still nothing. LOL.

View attachment 357809

While deserving some criticism for not delivering any options (yet), if the Hypex kit sparks an 8-year old's interest enough to take the plunge into a more serious kit, seems a good thing to me! The most equipment they might need is a multimeter to check their work and have a great performing product with a 5-year warranty.

While like that Akitika offers some warranty, not many DIY kits do. If the build does not go perfectly, you will need equipment to troubleshoot. If you want to be sure your amp is meeting spec, you will need more equipment. In any case, there is no Heathkit anymore because the tech and the market have moved on. Future geeks are even less likely to have access to DIY kits. When I see the power of contemporary design sim tools, am more envious and not lamenting that they will not be exposed to electric shock, flux fumes or nasty cleaning solvents.

 

[ta240]

... Some of what they say is true...I've limited peak currents to limit power dissipation to make it pretty bulletproof. ....

Which is nice because then it won't be likely to add to the mountain of e-waste the world is dealing with like so many current offerings

UN says e-waste from trashed electric devices is piling up​