Guide to fix up a Cmoy 2

[heady 0]

Hi, I answered you in headfi. I used the pot from Tangent in my CMOY2. Works fine as switch and volume control. Of course you can't mount it on the PCB, I just use some short leads and turn it 90degrees to fit into casing.

[69CamaroSS396 0]

Just completed my first CMoy2 yesterday. I was so disappointed and frustrated when I tried it out and had severe distortion and/or oscillation. Read through this thread and found out that maybe my power supply was lacking. I am using the LM6171 and was testing with 2 AA batteries. After changing to fresh 9V, sweet music to my ears. I used default values for every position on the pcb. Input caps are Vishay/Roederstein, resistors are Vishay/Dale RN55s, Nichicon Electrolytics. I ended up using the switched Alps RK097 because of the pcb mountable version being unavailable. Now to get it cased up. In USD I have less than $30 invested. First impression is very favorable. With Grado SR60s and a very nice CD transport with true line level outputs, it is very loud and clean. Not so great on the headphone output of my cheap portable player. Need to upgrade my portable source unit. Any recommendations would be appreciated.

[xchagg 0]

You might need to change R2/R3 if you're using it with a portable source. The standard values give a gain of 2, which is a little on the low side. If you're using the SR60s as your portable can, a gain of 3-4 should be sufficent.

 

I built my CMOY2 with a gain of 2 and it was perfect with IEMs, but a slightly higher gain would still have been preferable. A gain of 2 isn't enough for high impedance phones like the Senn 650's though. They still sounded good, just not loud enough

 

Another suggestion would be to remove the input caps (C1&C2) and jumper them for improved bass. The input caps help block any DC offset in your source from frying your phones, but they can induce bass roll off, unless you chuck in a bigger value film cap like 2++uF, which isn't quite possible given the small space.

Edited February 20, 2006 by xchagg

[heady 0]

Well done. This little amp is good value considering the effort and cost.

[arc_sine_squared 0]

Help, need to remove the BASS ----

 

My grandfather wants me to change the amp I made for him.

 

Several months ago I build him a cmoy2 so he could watch DVDs and TIVO with his wireless headphones. He has really bad hearing so I really cranked up the gain. Anyway, He loves the amp, but wants to be able the remove the bass so he can hear the talking during a movie.

 

What is the best solution for actually trying to get rid of the bass?

I was thinking about adding a switch, where he could choose no bass, some bass, or lots of bass.

 

So if it was something simple like changing a resistors value, then have three different values for each leg would accomplish my need.

 

My personal amp is something like this, except it is on r2 and r6 so I can change my gain with a 50k dual control pot.

[huangyong 0]

lower the value of input cap.

[squalle 0]

a good solution would be baxandall equalizer

go and take a look at headwize

[jasonhanjk 0]

Help, need to remove the BASS ----

 

My grandfather wants me to change the amp I made for him.

 

Several months ago I build him a cmoy2 so he could watch DVDs and TIVO with his wireless headphones. He has really bad hearing so I really cranked up the gain. Anyway, He loves the amp, but wants to be able the remove the bass so he can hear the talking during a movie.

 

What is the best solution for actually trying to get rid of the bass?

I was thinking about adding a switch, where he could choose no bass, some bass, or lots of bass.

 

So if it was something simple like changing a resistors value, then have three different values for each leg would accomplish my need.

 

My personal amp is something like this, except it is on r2 and r6 so I can change my gain with a 50k dual control pot.

Reducing R4 and R8 would increase the low frequency roll-off.

 

Currently if C1 = C2 = 1uF and R4 = R8 = 10kohm, the -3dB roll-off is 16Hz.

 

If you don't change the cap and reduce the resistor to 1kohm, roll-off will be 160Hz. That should take care most of the bass element.

 

[jasonhanjk 0]

UP

[RancidM 0]

Hi yas....

 

i managed to totally mullar a go at the project once allready...

my own fault for taking parts advice from the chap in maplins.

never again will that idea go thru my mind

 

so im starting from scratch again and would like to make a decent job of it.

i have a new PCB on route (UK seller on ebay) afraid to say my de-soildering skills suck and for the sake of a tenner id rather start with a new PCB.

 

i do however have a few questions (cheers in advance Jason)

 

the set up is simple to take a feed from my PC's onboard soundcard and drive a set of Senn HD500's

i do suffer from a little deafness so im looking to get some decent bass out of this little amp.

 

so if i can ask...

 

1. is it going to be better to use a 12V +/- Dual PSU or will i get the same performance from just using a 9V DC PSU in place of a battery pack ?

 

2. if it is better, did you make a post on how to build a Dual PSU jason ? if not are they cheap to purchase ? (farnell code if one exsists?)

 

3. i do suffer a little deafness and im concerned that +2 Gain might not be enuf with the HD500's (are these high impedance headphones ?) so im thinking i might need to adjust the resisters to get extra gain.

what is a sensible ammount of gain ?

 

if i suggest +4 Gain then the resistors would be

R1: 10

R2: 30k

R3: 10k

R4: 10k

R5: 10

R6: 30k

R7: 10k

R8: 10k

 

G = 1 + 30/10 = 4 ?

 

or is +4 gain too much for headphones ?

 

cheers in advance.....

gonna take a little time and car over this project, im not the most skilled soilder, but i do like little projects of this type.

 

Cheers.....

[Guest strumluff]

Hey all!

I read through this entire thread. Just like RancidM i got my cmoy 2 from that UK ebay seller (2 of them), and just like RancidM am having no luck with crappy Maplin.

I ordered in most of my parts through Farnell, but now stuck in a situation as Farnell only accept a minimum order of £20.

 

I'm most of the way through the soldering, and now just have to hook up my panel components to the pcb.

 

The question I'd like to ask is about the current limiting resistor for the LED.

 

The LED I'm after is a blue mountable one with these specs:

 

Source Voltage: 9V

LED forward voltage (Vf) : 3.5V

LED operating current : 30mA

 

This works out to 183 Ohms, which means i'd need a 220R 1/4W resistor right?

 

If this is so then I'm stuck because the only one i can buy easily here in the UK (through dear old Maplin) is a metal film 220R 0.6W resistor. Is that okay to use? Or can you recommend another that has a 0.6W spec as that is the lowest wattage that Maplin sell

 

As I'll be popping into Maplin the only other component I need is the stereo sockets. Can anybody recommend which I need from this page please, http://www.maplin.co.uk/search.aspx?MenuNo...Menu=y&doy=30m8

 

Thanks a million for your help!

Edited August 29, 2006 by strumluff

[RancidM 0]

all mates together....

 

 

i think i got my head around the LED situation.

i found this web page which has some very usefull info for use less exsperianced chaps (NEWBS)

http://www.kpsec.freeuk.com/components/led.htm

 

i would deffo wait for a second opinion but as i read it.

 

Source Voltage: 9V

LED forward voltage (Vf) : 3.5V

LED operating current : 30mA

 

so the formular will be

R = (VS - VL) / I

 

so

 

R= (9v-3.5v)/0.03a (30mA is 0.03A)

R= 5.5/0.03

R= 183.3 Ohm

 

so it would seem we agree on the 183 Ohms..

 

it says to use a carbon 1/2 W resistor.. i cant see any carbon resistors on the Maplins website and i would imagine a 0.6W in place of a 1/2W would be ok for the LED.

 

then again ive allready managed to bork one attempt so it may be best to wait for confirmation.

 

with a bit of luck jason will come online and share out some wisdom.

i want to know about the dual PSU as it effect what stuff i order from farnell.

 

concerning the stero jacks i got the very same ones from maplins (code FK03D)

they seem to be just fine if lacking any documentation.

 

good luck to us all....

 

 

 

 

[heady 0]

Seems Jason must be busy as he is not answering. So, let me give you what I think:

1. Your calc of the RLED resistance value seems right to me.

2. 0.6W is larger than 1/2W so you are fine there too.

3. The CMOY2 has its own rail splitter (2 resistors), so you don't need a dual power supply. If you still want to use a dual supply, you will need to omit the 2 resistors and also connect the power supply to the pcb differently from the default.

[RancidM 0]

Hi heady...

 

cheers for the advice...

im still a little confused over the dual PSU thingy.

 

 

the instructions at the start seem to suggest using a +/- 12v dual PSU.

and then leaving out the LM6171 (shorting out the LM6171 socket with some caps)

 

i do however have a 9Vdc PSU avalible for this..

would it be easier just to use a LM6171 and this 9vdc PSU in place of a bettery..

 

my concern is that Jason appears to suggest for use at home the dual PSU thingy provides a better solution ?

 

as i really am only a novice at these things then i like to try and find clear instruction from people who do know better.

 

Cheers.

R.

 

 

[heady 0]

Hi, since you have said you are a novice, I will strongly advise you to keep things as simple as possible and thus allow you enjoy the amp as soon as possible.

 

Since the amp will only be used at home, it makes sense to use an external power supply rather than batteries. To do so, you just need to get one of those DC power connectors and a wall wart (AC-DC convertor) to connect to the DC power connection.

 

For most amps, a higher voltage will give a better sound quality. However, you have to read the data specs to be sure you don't over-do it and burn the chip instead. Opamps have different max voltage, so there is no standard max voltage. 9 volt is the lowest voltage which an opamp will sound reasonably good.

 

In my opinion (FWIW), the CMOY2 will not benefit greatly from a dual power supply. And the cost of that supply can be very high. Infact, in Singapore, it is hard to find a wall wart supplying more than 15volts. And they won't be as cheap as the common 6-12V types.

 

So, use a DC power connector and a 12V wall wart and you are home free. Spend the time enjoying the music instead of trying to squeeze the last bit of goodness out of a basic design. If you really crave for quality sound, then you need to go higher up the DIY ladder and build yourself a PPA2 or M3. (if you can get a SOHA pcb, it is very good too.)

 

So that's my opinion. You don't have to agree with me.

 

Edited August 30, 2006 by heady