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Help beginner with CMOY amp kit, please!

J

Johnny Blue

I made it to 'Member'!
Sorry to burden you chaps, with your £70 soldering stations, who are madly building the next Naim-slayer, but I have an embarrassingly basic question to ask:

I've just bought one of these and, despite requests to the seller for help, I've not got any response from him.

I recognise most of the components, but am not sure what certain of the items are. If you look at this photo, there are some things about which I'm not clear (circled in red). I've deduced by their number that the 3 tiny rectangular items must be the 'green=jumpers' (see circuit diagram) but I'm not sure what they're for: why can't I just use a bit of wire to connect the points on the PCB. And what is the long plastic section, with many pins along it: I presume they are link pins or may be to stick through the PCB, but don't know how or why to use them. Do they fit into the little black connectors (the 'green=jumpers')? Why are there so many of them? Presumably I snap or snip them off to use them?

And there are the wires in the resistor packet (above and to left of the red oval), without resistors on them: are they also for linking? Confused!

(I told you this was embarrassing!)
 
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I'm sure it's complete, that isn't my problem, it's just that I don't know what are the little pins and the black 'jumpers'! I don't see what the jumpers do that a piece of wire can't do...
 
The board probably has more than one application.

The open circuit jumper pins don't really need to be there at all for your purposes, and the closed ones could equally well be replaced with a piece of wire.

The jumper pin strip has been included purely to confuse you and probably only comes into play if you use the kit in some alternative way or as part of a larger kit.
 
Johnny blue. You do need to use the jumpers provided. This kit is a DIY version of the Banzai Blue Jelly.

Have a look at these links as they might help you. I have a Blue Jelly and have made my own CMoy's if you get stuck send it me and I will put it together for you.

http://rockgrotto.proboards.com/index.cgi?board=b&action=display&thread=4209&page=1

http://rockgrotto.proboards.com/index.cgi?board=b&action=display&thread=4209&page=2

http://rockgrotto.proboards.com/index.cgi?board=b&action=display&thread=4222
 
I've just uploaded this photo and there's definitely nothing other than a jumper connecting wire on these 'little black things'. They slide up and down on the PCB pins (assuming that's what they are) so I can only think they're designed to be removed on occasion, but why? Since it's a real cheapo set, I can't understand why they didn't cost-cut and stick in another few cms of wire.

Perhaps that's why the seller isn't responding: he doesn't know!
 
Puffin said:
Johnny blue. You do need to use the jumpers provided. This kit is a DIY version of the Banzai Blue Jelly.

Have a look at these links as they might help you. I have a Blue Jelly and have made my own CMoy's if you get stuck send it me and I will put it together for you.
Click to expand...

Thanks, very useful links! I knew it was the DIY version of the Jelly, but I read somewhere when researching it that it didn't have caps, so I thought the kit would be better (plus the fun of trying DIY, and saving a few quid!).

The pics help greatly, now I see how to use the pins, but I still don't see what the jumpers blocks are doing that a bit of wire wouldn't do?
 
Managed to build the amp last night, and (to my pleasant surprise!) it works.

However, I've discovered that removing the jumpers (about which I was enquiring in my OP) has no discernable effect!

Is there anyone here who can interpret the circuit diagram and explain why? (Also I managed to short out the lovely blue LED, so it doesn't work any more: anyone any idea of the specs it'd need for a replacement?)
 
Johnny Blue said:
Is there anyone here who can interpret the circuit diagram and explain why? (Also I managed to short out the lovely blue LED, so it doesn't work any more: anyone any idea of the specs it'd need for a replacement?)
Click to expand...
I'm no expert, but it looks like the jumpers are something to do with the 1K resistor(s) across the output (loudspeaker graphic) and tie it to V- Bias :confused:
I'm sure someone else here can explain why...

Sometimes jumpers are provided to allow different gain settings but I'm not sure if this is the case here.

The LED can be any normal type, suggest you avoid any super-bright ones as it might reduce battery life. If it's too bright, just increase the value of the 1K resistor (the one right next to the LED).
 
MikeInUK said:
The LED can be any normal type, suggest you avoid any super-bright ones as it might reduce battery life. If it's too bright, just increase the value of the 1K resistor (the one right next to the LED).
Click to expand...

Thanks, Mike. I assumed they'd come in different voltages and amperages, etc., like light bulbs! So they're all the same in this respect? Amazing!
 
Johnny Blue said:
I assumed they'd come in different voltages and amperages, etc., like light bulbs! So they're all the same in this respect? Amazing!
Click to expand...

They do differ, but in an application like this, any normal one should do.
Looking at the kit, it appears to be either a 3mm or 5mm diameter one, but you could go for other types - TBH, there are far too many types to choose from :)

Examples from Rapid for the 3mm are std and clear lens type
They typically need a low voltage of around 3.5v to work - hence the resistor.

I have some of these which should work fine. Not the cheapest, but nice ;)

Whatever floats your boat ;)

HTH
 
The two green jumpers going to the output 1K resistors is to bias the opamp into Class A. I presume they are jumpered to allow you to test how a particular opamp sounds when biased into class A. Different opamps will react differently to being biased that way, so use your ears to determine which way sounds better. There is a small penalty in battery life if the jumpers are on. Hard to tell the purpose of the other jumper from that diagram.

Info on biasing opamps
 
Many thanks for the useful and informative replies.

Since I expected the jumpers, if removed, to not allow the amp to work at all, I had initially assumed their removal had "no discernable effect!". Now I've seen the link from looser101, I realise that some more, finely tuned, listening is in order, to see if Class A operation is preferable or not. I LOVE a bit of A - B testing!
 
Do they all have the same 'tray', so swapping is just a matter of pulling out one and pushing in another, i.e., no soldering? I've a feeling it can't be so simple...
 
looser101 said:
The two green jumpers going to the output 1K resistors is to bias the opamp into Class A. I presume they are jumpered to allow you to test how a particular opamp sounds when biased into class A. Different opamps will react differently to being biased that way, so use your ears to determine which way sounds better. There is a small penalty in battery life if the jumpers are on. Hard to tell the purpose of the other jumper from that diagram.

Info on biasing opamps
Click to expand...

Spot on, looser101! I've just had this reply from the seller of the CMOY kit:

"The jumpers are rarely changed and you can just solder wired to close all 3 conections. I am working a new design that eliminates Bias and these will not be needed. That long plastic piece is what is used for the jumpers...break off two at a time."

Thanks to everyone for the guidance and advice. If you're interested, here's a peek inside.
 
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