Gainclone building thread based on BrianGT's boards

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#241
Tomorrow's another day... alas, too funky and wet for sailboat commissioning work.


But perfect for DIY audio!


The wife's workin', the stereo's workin'. Life is great!

Check out my "line array V2.0" on "Loudspeakers". Better without the Onkyo 5 cent tweeters...

Those things stomp!
 
#242
Now offering Dual Monoblock upgrade for kits

By popular request, I am now offering a monoblock upgrade for the kit, consisting of a pcb set, 8 - MUR860 diodes, and 2 - 4.7uF capacitors. This will allow you to add an extra power supply unit to your kit to run a dual monoblock setup.

The pricing is:
$18 for the upgrade with 4.7uF Panasonic FC capacitors
$24 for the upgrade with 4.7uF Blackgate N capacitors

The ordering page is here:
http://www.BrianGT.com/order

Drop me an e-mail, or make a post in this thread if you have any questions.

Note: I am unable to offer just the power supply pcb, since the pcb set is combined on a single pcb, with scoring to easily break them apart.
Picture of pcb set:
http://www.briangt.com/gallery/nigc-kit/build001

--
Brian
 
#244
Re: Gain Question

ultrachrome said:
Can I lower the gain of my gainclone to compensate for the high gain of my foreplay? Or will I just end up over driving it?

I'm still using the stock attenuators that result in a hair trigger volume control with "normal" amps.
Click to expand...

Yes, very easily.

Change the value of R3 (the blue Riken resistor for the premium kits).

The formula is:
Gain = 1 + Rf/R3, where Rf is the 20-22k feedback resistor. The default gain is around 33.

Partsconnexion.com sells Riken resistors if you want to replace it with a higher value Riken. Any resistor will work fine here for testing.

--
Brian
 
#245
Finally eliminated the noise.

Of all the things that could have possibly caused it, I think this was one of the strangest. It seems the coax cable going to my cable box and then to my tv was picking up a lot of AC mains noise from my surge supressor, which it then carried into the tv input. From there it "swam upstream" through the component video inputs on the tv to the component video outputs on the DVD player (my source), and somehow made its way from there to the analog audio outputs to my amp. The solution was as simple as disconnecting the regular tv cable and running a video cable from the rca composite out on my cable box to my tv. It's all better now, but I wish I could have figured out what the problem was earlier. It only took a few seconds to fix.
 
#246
Re: Finally eliminated the noise.

tpenguin said:
Of all the things that could have possibly caused it, I think this was one of the strangest. It seems the coax cable going to my cable box and then to my tv was picking up a lot of AC mains noise from my surge supressor, which it then carried into the tv input. From there it "swam upstream" through the component video inputs on the tv to the component video outputs on the DVD player (my source), and somehow made its way from there to the analog audio outputs to my amp. The solution was as simple as disconnecting the regular tv cable and running a video cable from the rca composite out on my cable box to my tv. It's all better now, but I wish I could have figured out what the problem was earlier. It only took a few seconds to fix.
Click to expand...

That is actually a very common problem ... there are cablevision isolation transformers specifically for that problem.

dave
 
#249
Just built a gainclone today w/ BrianGT's boards given to me by another member on this board. Before I finished the case, my father and I fired it up. Its got a 25-0-25 transformer and a single bridge rectifier (not BrianGT's boards) w/ 2 lm3875 chips. I put the boards together identically and hooked them up the same as well, one output has 40mV dc offset, the other has -30V on it!:devilr: bad chip? i haven't seen this w/ nationals chips yet, and i've been reading these boards for a long time now... did everything identical between the two boards...and checked voltage at V+ and V- in ...and both capacitors are seeing the correct rail voltage. Should I just get a new chip...? I was gonna post pics this weekend but

:bawling:

-Matthew K. Olson
 
#255
Heres my progress so far on mine. I made one small change to the design, but I doubt its a big deal so I wont mention it 😉

I used what I had. Dale's (1K,22K), Vishay's(44.3K), the supplied 680R resistor. Samsung caps (4700). And Xicon (2.2uf) on the power board.

Still waiting on case, so it will be a while 🙂

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This how I used larger than expected resistors

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#256
Unless you have a pretty tricky heatsink scheme, I'd suggest breaking the board into it's 3 pieces before populating it.

It might have been cool for Brian to design the board so it could be used in one piece more easily by mirroring the amp boards so that the chips would be outboard on each end.
 
#258
Fuses blown

I did finalize today the first stereo amp.

I am still waiting for the transformers.

Just give it a try with an old Yamaha scrapyard trafo.

The +19/0/-19 V AC gave a nice -27 + 27 DC, the centre AC wire, wirde to both the bridges.

Filtered and fused with 2*500mA on the 220V AC side.

I did had music for about three seconds then both the fuses were blown. Music was to short to recollect whether both channels were playing.

I would think that 500mA should suffice?

Is the wiring of a centre tap then wrong after all. I have read the thread discussing this isuue and opted for given the layout a try as indicated above. I could not think of any problems with doing it like this.


Brian and all the others allthough I am not really up and running yet I stil think it is a marvelous design. It was very easy to solder (something I had not done for an odd 15 years)

Wiring the thing in a small box is the time consuming elelement.

I will post pictures as soon as my daughter (and wife) return from Paris. My daughter has the digital camera.

If there is someone out there with further thoughts on the centre wire transformator setup I would be pleased to hear.

I will recheck all the wiring wether no normal shortcuts are made.

Regards
E&E
 
#260
A anectode to the group:

I built my 3rd Brian GT amp in an all aluminum case, with a single 3A fast fuse between the input switch and the Tranny input (as opposed to my usual double, one per channel).

After I plugged it in, the fuse immediately blew. I checked all the connections for shorts and values, couldn't find anything wrong. Again, I tried it and the fuse blew. I decided to use a variac to isolate the problem, and brought it slowly to 90VAC. It worked fine, I brought it to full power, still good. I tried it without the variac, again, it worked perfectly, as it has been for a couple of days. I tried many times to turn it on and off, everything works great. It seems that bringing the power slowly for the first time did the trick.

BTW, I'm using all black gate caps 1000mF @ 50V that are twice the size of the panasonics.

Jam
 
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