[breakfastchef]

Well, I took a stab at my first CMOY amp this weekend and was only partially successful. I surely do appreciate the technical craftsmanship and beauty of the rigs you folks build on this forum after venturing into this DIY headphone amp-building experience. Perhaps, I will grow another brain cell this week and my next attempt will be better.

I initially caught the bug after reading DIY Simple Headphone Amp Tutorial By Cmoy Design (Mini Pocket Amp) by William Neo on the Web (DIY Simple Headphone Amp Tutorial By Cmoy Design (Mini Pocket Amp): DIY Simple Headphone Amplifier for Beginner). I followed a few of his links and ended up on Tangent’s outstanding website – Audiologica – and eventually to here, head-fi. Tangent’s tutorials pushed me to try my first build.

The failed first CMOY was a valuable and expensive lesson. Being new to electronics and such, I, of course, needed a soldering iron, solder, desoldering items, lots of parts, a MM, and the most important thing for the vision-challenged – a magnifying visor. Wow, that was a lifesaver. This thing is tiny!!

I did many things correctly. The power circuit worked the first time. The amplifier section came together nicely and tested out with a hint of background hiss, but nothing that was alarming. I was hugely challenged trying to cram all of this into an Altoids Tin and find a place for the through components.

There are many things I did not do so well. First, I used a 20AWG multi-stranded copper wire I had laying around. It was a bit stiff so as I inserted pots, inputs, outputs, and moved the circuit board around, I stressed the crap out of the thin connectors to these devices. Hence, several wires broke free. I probably lost one of my Panasonic pots and one 3.5mm stereo jack trying to work with wire that was too stiff.

Second faux pas was ordering .062 solder. I think a thinner solder would have been easier to work with. I learned good solder technique by having to use all the desoldering stuff I purchased. Part of the learning curve, I guess. The .062 will work; I just need to be a bit more light-handed and get the iron a little hotter.

Thirdly, the volume control on the amp did nothing. So, frustrated, I removed the guts from the Altoids tin and broke off two contacts on my pot.

Lastly, I tried to fit too many connections on the short end of the Altoids Tin and had to put it into the recycling bin as unusable. Choosing panel mount locations is not easy.

After finally giving up on the cruddy hookup wire and broken terminals on a few connectors, I backtracked. All wires were desoldered from my board. I put on a few jumpers and used alligator clips to retest the board after its barrage of stress and repeated heatings and suckings.

This week I will start another CMOY attempt with the parts I have collected (in something WAY bigger than an Altoids Tin), but the first board may be salvageable. Here are its symptoms; any troubleshooting tips would be great.

1.The amp produces a very light hiss. I shorted out R5 per Tangent’s tutorial. I cannot hear the hiss when music is playing. Should I add some resistance to R5?
2.When testing the CMOY, I notice it picks up hum from hi-intensity lights or other RF generating sources. The amp also makes buzzing sounds (as heard through headphones) when I touch some wires, and those sounds disappear when I touch other hook up wires. Is this a problem or a trait of a CMOY?
3.I could not get any sound out of the right channel after the board was removed from the tin and completed my desoldering frenzy. By accident, I dislodged the right ground to the headphones and both channels came though as clear as could be. What does this tell you experts?
4.I still cannot get the Panasonic pot to make a volume change when rotated. Is it possible I fried it while soldering? Would a mis-wiring keep the pot from functioning?
5.I can test resistors with the DMM, but how can I test a capacitor? Feel free to just give me a web link, if you like.

Thanks all for letting me be part of this forum.

 

[jay sun]

chef,
I just built my first cmoy this weekend. I knew there would be issues so I went a little crazy to ensure success. First I purchased all the parts (including a cmoy pcb). The pcb made life rather easy and took all the guess work out of connectivity. Besides the fact that it leaves plenty of room in an altoid tin. The second preemptive action I took was to purchase a used cmoy cheap, for the sole purpose to test, compare and reverse engineer if needed. Everything works. There is a very noticeable hiss that both amps admit, but I am fairly sure it is the two meter interconnect I took off the pc speakers.
From reading your post I feel I missed out on quite a few lessons but saved myself some frustration. I myself can not offer technical advice because I am still completely ignorant, but I can assure you, with all the talent on this forum and a little tenacity you are guaranteed success.
Good luck

 

[steaxauce]

Hey guys, I just wanted to say that a little bit of hiss that's inaudible while music is playing is normal for amps like that. Jay sun, it's probably not your cable. But it's no big deal. Good luck!

 

[dgbiker1]

1. Use as little resistance as you can stand for R5, the higher R5, the lower the SQ.
2. This is common for circuits in general. When you get your case, ground the case if it's metal. If it's not metal and you have humming issues, line the inside with wire mesh or tin foil and ground it (see Farraday (sp?) cage)
3. Not sure what "right" ground is. You should only have one. If you dislodged THE ground, you shouldn't have any sound coming from your headphones since the current doesn't have a return path. Maybe you lodged it

4. You might have fried the pot while soldering, but you would know since you would have probably pushed or pulled the pins in/out. It is far more likely that you mis-wired it. You have the wiper (middle pins) going to the amp, one end to ground, and the other from line in. Resistance from line-in to ground should always stay constant. Resistance from amp to ground should change.
5. You can test caps if your DMM has a capacitor setting, it will probably say C or F. If not, you could test it in an R-C series circuit with an AC voltage source and measuring the voltage drop across R. I can give you instructions if you want.

 

[dgbiker1]

Sorry to double post, but I recommend doubling the power capacitor size from the Tangent tutorial. You can either use a bigger cap or, in my case, put a second 220uF cap in parallel with the first. The amp will have slightly better bass and impact with that setup.
I also found that his gain was way too high for the Grado SR225s I was using, the lowest volume where both channels were biased was way too loud. Reduce the ratio of R4/R3 to lower the gain. I lowered mine from the default 11 (100k/10k +1) to 8ish and it works great with 225s. Your mileage may vary though.

 

[breakfastchef]

Thanks, dgbiker1. Great information that I can use with my second CMOY, currently 'under the iron'. Cheers.

 

[fortney]

Most of the problems I had when first building a CMoy had to do with wrongly wired ground wires.

Since you made it work well at one point you can be assured the rest of the circuit and the opamp are OK.

Most of my mistakes have been very simple, in retrospect.

Follow all your wiring very carefully using the schematic to see what connects to what else and always look for solder bridges in non functioning units (not your problem since the unit worked well once).

Read Tangent's tutorial very closely.

It does not need to be put in an Altoids tin. Mr. CMoy used a plastic case. You might want to make wiring controls and connectors easier by using a larger case.

Note that there are grounding concerns using a metal case. This is described in Tangent's article.

Unless you are using high impedance headphones I would go to a much lower gain. I use a gain of 3 with 32 ohm phones and that is too much for me really.

Consider using .22 or .47 uF instead of .1 for the input capacitor for improved base response.

Good luck--learning experience-have fun!!

F

 

[breakfastchef]

Thank to everyone that replied to this post. I successfully completed two CMoys this week. You can see them at http://www.head-fi.org/forums/3734009-post2925.html. Cheers!

 

[fortney]

They look great inside and out.

Cases are a really appealing cosmetic feature too.

F

 

[SenjStevo]

I just finished mine last night and it sounds pretty horrible to be honest! Really weak and grainy, but i'm not bothered cause i learnt alot and i've got the parts for a second one

For some reason both of the 4.7k resistors in the power section have reduce to 3.7k(heat? bad soldering?) so i'm assuming that is the problem. I could be anything though, like the huge blobs of solder i made until i got the hang of it. I also ordered two potometers instead of a duel one by mistake so my channels have separte volume controls, i doubt thats the problem though.

I'm gonna salvage what i can and start again i think.

Edit: I turned the op-amp round and it became very very hot, i didn't realise it mattered which way it went round but ouch!

 

[breakfastchef]

Ouch, SenjStevo, hope you did not fry your opamp. Definitely match the notch on the socket with the notch on the op amp. As to performance issues, I am no expert, but look for solder bridges on the board. Review Tangent's tutorials closely for additional information.

If you not yet versed in the use of a solder sucker or desoldering braid, now would be the opportune time to develop these skills as you tear down one PCB and attempt another build.

 

[kuldeep1]

i build 2 Cmoy amps, based on the original circuit of Cho moy in headwize.com, but i felt the gain of 10 was too high. I build another miniature cmoy with 2 gain settings 6x and 10x using a DPDT switch

But i feel Cmoy is a basic headphone amplifier, now i am planning to make Mini3 based active ground headphone amplifier

 

[nsx_23]

I completed my first 2 CMOYs not too long ago, and it was an enjoyable and very educational experience.

I religiously followed the instructions on tangent, so luckily I didn't have to troubleshoot, but my 2nd build, which is a PCB build, wasn't as smooth because I tried using another type of solder, and my extremely simple iron wasn't hot enough to melt it properly.

 

[millwood]

Quote:

1.The amp produces a very light hiss.

the amp is oscillating.

you can build a simple RF probe to confirm it if you want.

the stock design does not have power supply decoupling - which is a must for an opamp amp. Put a 0.01u or higher cap, preferrably tantalum, or polyester cap, from the power supply pins to ground, as close to the chip as possible.

Quote:

2.When testing the CMOY, I notice it picks up hum from hi-intensity lights or other RF generating sources.

the amp has too high of an input impedance. change R5 to something < 47k - I typically make sure that it is 10 - 22k. if you do that, set R1 to 1k.

Quote:

4.I still cannot get the Panasonic pot to make a volume change when rotated. Is it possible I fried it while soldering? Would a mis-wiring keep the pot from functioning?

you just need to find the wiper on the pot. a multimeter will do.

Quote:

5.I can test resistors with the DMM, but how can I test a capacitor? Feel free to just give me a web link, if you like.

the quick answer is it depends on what you want to test the capacitor for. the leakage is fairly easy: just turn the multimeter to resistance measurement, and put the leads on the capacitors'. after a while, the reading should stablize, preferrably to "OL" (open loop).

capacitance shows up in how fast the reading stabilize. large capacitors take a while for the reading to stablize and smaller ones can stabilize in a flash. but that's just qualitative not quantitative.

 

[Fred_fred2004]

Unplug the headphones can you still hear a faint hiss if so its the same hiss you hear when you hold a seashell to your ear.