Guide to fix up a Cmoy 2

[jasonhanjk 0]

hi guys, went to Koba today to get some female jacks. the ones i bought were 'stero jacks' and they have 5 pins in them. however, I discover that only have OG, OL, OR holes. so can I still use those jacks or I have to buy those 3 pins ones? but the auntie say 3 pins jacks are mono jacks??? dry.gif

 

Jason, your schematic shows Vcc/2. so is the LM6171 outputs Vcc/2 and this Vcc/2 acts as the VG for the left and right opt -amp? cos quite confused when I saw both Vcc/2 are pointing outwards.

 

Yup, you should still able to use those jacks. The way to test it is in the first thread. Yes, it act as ground for left and right. The pointing does not mean anything significant, just means they are connected.

 

One word of advice...NEVER USE ANY FORM OF TIN WIRES (Are they tin?). The ones that tend be not so malleable and break. Especially if you're troubleshooting. I had to resolder all my jumper wires with multistrand copper. Of course, in the process, I burnt one e-cap. I singed the cap, and though now all my connections are solid, my sound is still crap.

 

I'm going to try replacing the lm6171 with the lm6181, and the opamp with a opa2228. Sigh....should I start over?...

 

Does the crap sound sounds terrible or just not up to par with other high end gear?

If you want to replace the IC, please do read thru the datasheet first.

[jasonhanjk 0]

Hi All,

Have just built my cMoy2 amp. Was all going great, first time worker, until i used 12v instead of 9v.

 

Parts I used

 

2x 1000uf 16v Pana's

5x 63v 1uf Wima Poly's

2x OPA2134

1x LM6171

8x 10kR 1% 0.4w

2x 10R 1% 0.4w

1x 50k log pot

 

Now, my left channel doesnt work. Only sound you get out of it is when turning the volume up to full, and then very faint left, whilst very distorted right.

 

I'm in the UK, so sourcing parts is fairly hard, Maplin is a joke, Farnell is decent but £20 min order.

 

Is there any way to check the amp with a multimeter to find out which component is kaput??

 

I soldered my opamps instead of socketing, and ive lost my solder sucker, compressed air seems to work quite well tho.

 

Any help will be much appreciated.

 

Back of Amp

Top of Amp

 

Thanks in advance

 

 

Matt

Hi Matt.

 

Good job on the soldering.

When you use 9V does the amp work well? Is you 12V supply regulated DC?

 

If you want to check whether the pot is working, short the 2 pin circle in red in the picture. Using a mp3 player headphone out (or line out) and slowly increase the volume. What do you hear?

 

[kross 0]

wow...$3. that's steep. i bought the five pins thing at only $0.50 each. anyway, i have tried Jason's method of the 'pop' sound and 2 of the pins produces the left and right sound while one is the ground. the other 2 pins seems to have no effect. so mayb I'll try out using the 5 pins ones first. if cannot then i go and buy the $3 one.

 

thanks.

[matt.pimm 0]

Thanks for the advice jason. I check the pot with a multimeter, it's resistance still varies correctly. At 9v, it was working perfectly, except when you turned it up high with the Sennheiser HD580's the bass would clip dreadfully.

 

The 12v was from a computer power supply, I know, probably not the best choice.

 

Now the left channel doesnt work at all. The only sound you get out of it is when the right is distorted, there is a faint sound.

 

I'm waiting on some new op-amps to try now, just realised how hard it is to remove them when soldered, so some sockets are coming too.

 

I think i may have pulled the PTH out of one of the holes so may need a new board now. If whoever still has supplies could led me know cost, including shipping to the UK.

 

 

 

Matt

[Kube 0]

Huh? If there's stub left in the hole, just do use a plier to take it out while melting the remainding solder, or juse use a toothpick to push it out when the solder's liquid.

 

Question to ask: How the Rubycon cap line differ? I went to buy an e-cap, it has the same values, but different product line. Can still use?

[jasonhanjk 0]

Thanks for the advice jason. I check the pot with a multimeter, it's resistance still varies correctly. At 9v, it was working perfectly, except when you turned it up high with the Sennheiser HD580's the bass would clip dreadfully.

 

The 12v was from a computer power supply, I know, probably not the best choice.

 

Now the left channel doesnt work at all. The only sound you get out of it is when the right is distorted, there is a faint sound.

 

I'm waiting on some new op-amps to try now, just realised how hard it is to remove them when soldered, so some sockets are coming too.

 

I think i may have pulled the PTH out of one of the holes so may need a new board now. If whoever still has supplies could led me know cost, including shipping to the UK.

 

 

 

Matt

Wait a minute.

 

Do you use the soundcard from the PC as source and power from the PC at the same time? That could cause the problem. Try to use the 12V from the PC but this time use another source like an MP3 player.

[jasonhanjk 0]

Huh? If there's stub left in the hole, just do use a plier to take it out while melting the remainding solder, or juse use a toothpick to push it out when the solder's liquid.

 

Question to ask: How the Rubycon cap line differ? I went to buy an e-cap, it has the same values, but different product line. Can still use?

To me, they are the same. To others, maybe different 'cos they can hear the difference.

[kross 0]

hi jason, i have some 1uf caps at home which are rated 100V, can i use them in place of the wima 1uF caps you used? also, can electrolithic caps do the job also?

 

you also mentioned changing the caps values increases the bass, am I right??

[jasonhanjk 0]

Yup, increasing the cap value will improve bass performance.

Elec cap can do also, face the positive towards the pot.

[Kippei 0]

Whats the max cap value to recommend

[kross 0]

thanks jason. what about the 100V 1 uF caps? i used them, and can work but I dunno whether they will affect the performance or not.

[Kube 0]

Ok...got round to getting a 2nd board and doing everything all over again, this time with more patience and experience, of course

 

Everything's set up for use (as in all connections made), flux cleaned the bottom thoroughly, jumpered the right and left channels where the pot's supposed to be...and still

 

Strangely, when I put my fingers underneath the connections, I can sometimes get clear sound. How's that? Also, LM6181 can work in place LM6171.

[xchagg 0]

hmm, look familiar anyone?

 

EBay CMOY2

 

Since when is the 2134 superior to the 2227, I always thought it was the other way round heh. Could be mistaken though

[Kube 0]

That amp has a nice knob

[heady 0]

LM6171BIN DIP-8 Hi speed, low power, low distortion volt feedback amp controller, commonly known as a "rail splitter"

 

Hmm, misinformation? The opamp is actually the ground driver, right? The rail spliting is done by the two resistors. Anyway, a good marketing job. US$40 and I nearly sold mine for S$50.