This is not just another gainclone

[Bricolo]

Which reminds me, Bricolo - did you ever manage to stop your GainClone oscillating?

You're right, of course. But the same is also true for a low-level interconnect. As I said, either approach is valid - just depends on your situation. If, as Peter suggests, you prefer to use no preamp then (assuming you want a single volume control for both channels), it's much better to use long speaker cables instead of long interconnects.

An approach that I think has already mentioned would be to put something like a PGA2310 in each GainClone. It would be quite possible to address them both from a common control circuit. Quite neat, assuming the thought of an active volume control doesn't worry you...

Nuuk, I'm slightly worried about your sparking GainClone! Have you fixed it?

Thanks Peter - my MUR860's just arrived - I'll install them tomorrow and report back

I added a zobel (but no case for the momment) and my amp is still oscillating at 666kHz, but 10mV pp, so I think it's reasonably low enough

 

[Guiness]

Another gainclone question...

I am getting ready to build my next gainclone, (the first one turned out great) but i would like to try something alittle different. I have a old JBL 2226H 15" woofer. It is a great woofer and would like to build a gainclone with the LM3886 chip, but my question is:

If I supply 28 - 35V to the chip can I use 40V (50V surge) caps on the power supply. Or do I need the 50V rated ones? I have some really nice 36,000uf 40V caps that need a home! (it does say 50V surge on the side, if that helps)

Thanks again,

Guiness,

one day my mind will start to work again!

 

[mhennessy]

I finished my cases today and mounted the amp circuits in them. Being a careful sort, I rechecked the offsets at the speaker terminals and noticed that when powering on or off I get about 1.5 volts momentarily, although it is normally steady at around 28mv.

Is this normal or do I have a problem to look for? Both channels are the same.

Thanks for all the suggestions on system set ups. The thing I like about this hobby is that you could spend several lifetimes trying things and still not run out of other possibilities!

So, the cute little cases have a fan club eh? I certainly won't junk them after all the time and work hand-shaping those front-plates!

Hi Nuuk,

Have you posted a schematic? I had a quick look but couldn't see one. I get 15mV, and nothing strange when powering up/down. In fact, I was very impressed with the silent behaviour - makes my setup a bit slicker, as the surround channels are only turned on by the preamp when you select the multichannel input.

Looking closely at your photo's, it looks like you've connected the non-inverting input to ground. If so, perhaps try using a 1K. I talk about this on my page, and I'd be curious to see if it makes a difference to your offset and power-on behaviour. (That said, do you get pops and clicks, or is the 1.5V peak slow enough not to cause them?)

I added a zobel (but no case for the momment) and my amp is still oscillating at 666kHz, but 10mV pp, so I think it's reasonably low enough

Oh dear... That's not good enough, IMO

Did you post a picture of your current setup? You should be able to get rid of that oscillation - even though it's only 10mV, it could still be causing you problems. What happens if you use a X10 'scope probe (with lower capacitance)? What happens with different lengths of speaker cable?

Cheers,

Mark

 

[Olle Bard]

god bless you people.
I shorted the orange and now have a lot of different voltages to play with.



and straight to another question: if i have a 60-0-60 supply that would not be appropriate to drive my little gainclone.

but can i put 2 amps in series to get 30+ and 30- on bothn amps?
if so, how do i do it? do i just connect the + to - on the gainclones and connect all the loose ends to the psu?(exept the input and output of course)

 

[Nuuk]

If I supply 28 - 35V to the chip can I use 40V (50V surge) caps on the power supply. Or do I need the 50V rated ones? I have some really nice 36,000uf 40V caps that need a home! (it does say 50V surge on the side, if that helps)

As a rule the voltage rating of a capacitor should be 1.25 higher than the highest voltage so for a 40v rated cap, 32 volts is the highest voltage it should see.

As regards my offset 'problem', I spoke to a friend who reminded me that with the output unloaded there is no path to ground and when I put a 10R resistor across the output, everything is back to 'normal'.

BTW - how many times do you have to say to yourself 'I'll just listen to one more track...' before the men in white coats come for you?

 

[Pan]

"BTW - how many times do you have to say to yourself 'I'll just listen to one more track...' before the men in white coats come for you? "

About a thousand times

/Peter

 

[Nuuk]

About a thousand times

Thanks Peter, I think that I'm just safe - for now

 

[breguetphile]

preamp parts

What is a good source for stepped attenuators and input selectors? (as well as knobs for them)

I'm thinking about building the preamp into the same case as my clone and was curious where parts are available for a fair prices (read: i'm a pseudo frugalphile).

Peter Daniel:

Where can you get 1" acyrlic? I really like that stand you built, but every hardware store employee looks at me like I'm wearing an "i love saddam" shirt everytime i ask.

 

[Matttcattt]

I'd use 10-100 ohms, and 10-100nF. YMMV

Happy listening! Soon, hopefully

what watt rating for the resistor? 1/4?

yes, hopefully when i get an input (i cant find my cheap walkman and i dont want to use my CD player)

i have inverting input connected directly to ground, should i use a resistor?

 

[Nuuk]

I completed my second PSU this afternoon (120 va/MUR860's/no caps) and connected it up so that each amp has it's own PSU.

I'm awaiting some aluminium boxes to house the PSU's (unless I find some scraps of 6 inch diameter plastic pipe )

The result is just more of that very euphonic sound, a little larger sound stage and perhaps a bit more space between everything.

I'm still listening in a small room with a less than ideal set up but soon I'll bring the clones downstairs and connect them up in my 'main' system to give them a thorough evaluation.

I'll try and borrow a camera tomorrow and get some finished pix up here.

 

[Guiness]

Conrad Cases...

So I really like the looks of the Conrad aluminum cases shown already in this thread. But I just noticed that conrad does not ship to the USA or Canada. Does anyone know of any other place that sell case similar to these. I notice Hammond has some extruded ones but I really do not like them and the height is only 2" max.

Thanks once again for the help
Guiness

 

[Matttcattt]

what is the limit for bridging and parrelleling gainclones? do i have to stop at 4 or can i have as many as i want?

 

[mhennessy]

So yesterday I fitted my MUR860 rectifiers. See my WWW for some more details - wasn't sure what difference to expect, but I think that the sound is clearer, more detailed, possibly a shade brighter. Not a huge difference, and I plan to revert to the old standard rectifiers in a few days time to convince myself that I'm not going mad

 

[Nuuk]

I made a couple of changes today. First off, I substituted the 100K pot for a 10K type and noticed that the bass tightened up a little. I had thought the 'flabbiness was due to the small square room and the speakers being in the corners but there was a noticeable difference.

Then I added 120 microfarad caps to the PSU. The bass got a bit tighter and the vocals came forward a bit. In fact the sound stage got a bit deeper despite the speakers being tight against a wall.

It's nice to be able to make these sort of changes so easily, especially as the PSU has no case as yet and I can just put the caps in, in a few seconds.

Now, here are some more pictures.

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An externally hosted image should be here but it was not working when we last tested it.

 

[vic2]

Hey man. I love that amp!

vic

 

[purplepeople]

Re: preamp parts

Where can you get 1" acyrlic? I really like that stand you built, but every hardware store employee looks at me like I'm wearing an "i love saddam" shirt everytime i ask.

To all,

Try GE Polymershapes (GE bought out Cadillac Plastics), or Tekra. Between them, they stock plastics from all the majors like GE, duPont, Bayer, etc. Also try surplus (especially for chunks of alum).

While acrylic is easy to machine and polish, I don't know what the dielectric properties are so that would something to check. I do know that they seem to hold a bit of a static charge. Stay away from acetate for that reason.

For cool factor, GE Lexan (polycarbonate) would be bulletproof in some grades at about 1" thick.

Bayer Makrofol (polycarbonate) can be had in some fire resistant grades that are also black.

You can also try using duPont Delrin (nylon), ABS or various UHMWs for impact and vibration resistance when mounting on subwoofers.

ensen.

 

[Nuuk]

A strange thing! I switched on my Gainclones this morning and found 285 mV on the speaker terminals of one amp. Everything had been working perfectly yesterday afternoon.

I carefully checked everything and resoldered the joints but now have 34.4 volts offset

After rechecking everything, I can only assume the problem is in the chip so have just ordered some replacements. Has anyone else experienced a chip failure with the LM3875?

 

[fedde]

I carefully checked everything and resoldered the joints but now have 34.4 volts offset

Probably the feedback resistor is not connected properly.

Originally posted by Nuuk
After rechecking everything, I can only assume the problem is in the chip so have just ordered some replacements. Has anyone else experienced a chip failure with the LM3875?

I once fried a LM3875 after a torture of heavy bass music on 82 dB/W speakers with mediocre cooling of the amp ;-)

Fedde

 

[Nuuk]

Thanks Fedde but...

I should write out a hundred times -

"If I check something and there are no problems with it, I must look for the problem elsewhere"

I had checked the voltage at the PSU and the amp circuit and what could go wrong with a simple lead joining the two?

Well, I had been moving the amp around to take those pictures yesterday and somehow, the negative supply had got disconnected (broken wire where it connects to Speakon connector). Not sure how as the cable is gripped tightly by a grommet but break it did and once reconnected 'normal service' has been resumed.

Now I have three more LM3875's on order and I can feel another Gainclone design coming on

BTW, I have located some 6 inch diameter tube but there's a problem it's sitting in a rabbit run in my mate's garden and he says that his partner would not see the priority of hi-fi over happy bunnies so the search is still on

 

[2Bak]

Speaker cables for GC

I would like to share the following experience: Today I connected my gainclone to my speakers using my DIY Cat5 braided cables, the FFRC, from the TNT website. This was the first time I tried these cables on the Gainclone.
The left side lenght of the cable is about one meter, the right side about three meters. Right side speaker made heavy distortion or something like that. It didn't sound healthy. I though the woofer was damaged, but it's not...!
My gainclone just didn't like this high cable with this lenght. With three meter cheap cobber speaker cable, everythings is OK.
Does anyone have similar experiences with speakers cables? Which types of speaker cables are best suited for Gainclones?

/Jan