Guide to fix up a Cmoy 2

[ClieOS 0]

They are from Farnell, but made by WELWYN. Here are the three type of resistors used:

 

9341145-RESISTOR, 0.25W 1% 10R; RoHS Compliant:YES; Resistor element type:Metal Film; Resistance:10R; Case style:Axial; Power rating:0.25W; Tolerance, +:1%; Tolerance, -:1%; Temperature, operating max:155°C; Temperature, operati...

 

9497994-RESISTOR, 0.25W 0.5% 10K0; RoHS Compliant:YES; Resistor element type:Metal Film; Resistance:10.0kR; Case style:Axial; Power rating:0.25W; Tolerance, +:0.5%; Tolerance, -:0.5%; Temperature, operating max:155°C; Temperatur...

 

9501061-RESISTOR, 0.25W 0.1% 20K; RoHS Compliant:YES; Resistor element type:Metal Film; Resistance:20kR; Case style:Axial; Power rating:0.25W; Tolerance, +:0.1%; Tolerance, -:0.1%; Temperature, operating max:155°C; Temperature,...

 

The board is semi-attached to the box by a 3M Command tape at one end (only about ~3mm). The volume pot also help to hold it in position. It can be removed at any time i want to.

[RancidM 0]

80p resistor.... thats not cheap is it...

nice looking mind you.

[jasonhanjk 0]

You can try to get those 1% type. You shouldn't spend too much on beginners amp though.

[ClieOS 0]

Wel, since this is the first amp i made myself, i decide everything should be as good as possible. Consider the money i already spent on my headphone, i guess the amp still come in at a reasonable price tag. I do like the sound alot, currently the best among all my amp...and a not so important point, black resistor make it look cooler:)

[BlakeN 0]

I have a completly noob question

 

when I am looking at opamps there are letters after the model numbers can anyone explain what they mean? I am guessing it has to do with socket type

 

OPA2227P

OPA2227PA

OPA2227U

OPA2227U/2k5

OPA2227UA

OPA2227UA/2k5

 

 

 

Also if I want full bass extension what is the minimum uf capcitors I should get for the electrolitic caps c6, c7. I was going to try to use black gate caps like the guy in post 226 but the recommended cap is 1000uf and he only used 330 I assume thats fine but I wanted to make sure. BTW I might listen to movies so I dont want to block any bass out.

 

Thanks

[ClieOS 0]

~P is for normal DIP 8 pin socket. ~U is for SOIC SMD (surface mounting). For cmoy2 you want the ~P variation. Also, the ~A variation has larger input voltage offset max(200µV), vs. non~A (75µV), the rest in almost the same. Just get a opa2227pa if you are not sure. For more technical detail, here is the offical TI PDF file: http://focus.ti.com/lit/ds/symlink/opa2227.pdf

 

In my understanding, larger cap results in better sound in general (My pengamp (cmoy with 2xLM6171) uses a pair of 3300µF) but only to a certain extend. You will be better off rolling some op-amp to see which one give you better bass respond than keep increasing your cap. I had rolled opa2227 and opa2134 from TI(BB), and op270 and op275 from Analog Device. OP270 give better respond on mid/low range with warmer sound, while Ti chip tend to be more balance out. I like op270 better, but it eat alot of power and more $$$...

[BlakeN 0]

Thanks ClieOS.

 

Power is not an issue this going to be 100% desk amp so I am going to use adc wall wart.

 

What is the full part number of the op270? I tried to find it on mouser and found opa2705PA but that was the closest thing to it and of course they don't have that in stock anyway. I am trying to get everything from mouser if I can. It seems to be a bit cheaper then farnell and I live in the US so it just makes sence.

 

 

[ClieOS 0]

I have op270ez (the one i am using) and op270gpz, different in input voltage offset 150µV vs. 0.25mV. Sound wise they are very difficult to tell apart. But i feel ~ez has stronger output.. I bought all my op-amp from Farnell, maybe mouser didnt carry them. Newark USA (Farnell?) does have it, here is the link: http://www.newark.com/NewarkWebCommerce/ne...=AFC-TL10000001

Edited September 6, 2006 by ClieOS

[BlakeN 0]

Thank you for the link! I am so new to this I didnt know about newark. I kept going to farnell.com and clicking on U.S. which was no good.

 

I will be looking arround the site today

[BlakeN 0]

This is my current BOM if anyone wants to take a look and confirm it.

 

Part Description - Qty - Price - Per Store - Part number - Brand

1. 10ohm Metal Film Resistor - 4 - 0.23 - newark.com - 83F1618 - Vishay Dale
2. 10k Ohm Metal Film Resistor - 8 - 0.42 - newark.com - 83F1561 - Vishay Dale
3. 1.2k/3k ohm RLED - 1
4. Pot Alps 290070 - 1 - 4.05 - newark.com - 70C0151 - Alps
5. OpAmp OP270EZ - 2 - 12.39 - newark.com - 05F8617 - Analog Devices
6. LM6171BIN - 1 - 2.83 - newark.com - 41k6219 - Nat Semi
7. 1uf WIMA Cap 63v - 5 - 0.54 - newark.com - 1049119610 - Wima
8. 1000uF Electrolytic Cap - 2 - 0.33 - newark.com - 01E9247 - United Chem-con
9. 1/8th Stero Jack female - 2 - 2.33 - newark.com - 35RAPC2BV4 - SwitchCraft

I can't seem to fromat my post correctly sorry for the mess. I still need a switch, LED, and LED holder but I can probably get them localy. I guess I am most worried about the Electrolytic cap. Is that a good brand? Edited September 6, 2006 by BlakeN

[Guest strumluff]

Seems cool BlakeN but I'm a DIY newbie so dont take my word for it!

 

Guys I need some advice. I've completed my amp and I have a penguin tin I want to mount it in. Could any of you give advice on how you mount your amps and what tools you use and if there are any tips or tricks to it, thanks

 

 

[ClieOS 0]

I guess I am most worried about the Electrolytic cap. Is that a good brand?

 

The cap seems ok. I use Panasonic, it has a smaller Dissipation Factor than your (loss of charge by heat,etc). Try to you can get one with smaller Dissipation Factor, if not, i dont think it will affect too much.

 

For mountiing into a tin, the tool you need is just a drill the can work with metal. Do remember to insulated the base.

[BlakeN 0]

hmm I might just get some black gate caps if I can't get good ones from newark. If I am going to have to pay seprate shipping for 2 silly caps I might as well make it worth it Could you explain what stat Dissipation Factor is and what a good value would be?

 

Celios are there any other changes I need to make to the cmoy 2 to use the OP270EZ? or is it just a drop in?

 

If anyone has any other mods to suggest let em rip I want to make the best cmoy 2 possible (within reason under $100 hehe)

 

Edit:

 

Ok I have been browsing arround the newark webiste some more and found a few more caps that will fit the specs.

 

Vishay makes this one

 

"2222 150 65471" 470uF 10x12 here is a link to the data sheet if one of the experts can take a look at it.

 

United Chem-con makes 2 series of caps that also fit the specs the KME and the SMG if anyone wants to look at those data sheets.

 

Thanks for all the help so far guys.

Edited September 7, 2006 by BlakeN

[heady 0]

For mountiing into a tin, the tool you need is just a drill the can work with metal. Do remember to insulated the base.

 

I am not sure about mounting it in a tin. I know that most 3 channel amp won't allow it since the input ground and output ground is different and in a metal enclosure, the input and output ground is connected via the tin. Will the experts please confirm this? Jason?

 

CORRECTION: It is ok to connect input ground to output ground for the CMOY2, so a tin is fine as long as you insulate the bottom of the pcb.

 

Edited September 7, 2006 by heady

[ClieOS 0]

I will give you a stardard wiki answer:

"Dissipation factor (DF) is the ratio of a capacitor's resistance ® to its capacitive reactance (Xc). DF is usually expressed as a percentage.

DF will vary depending on the dielectric material. In low dielectric constant (K), temperature compensating, ceramics DF of 0.1 to 0.2% is typical. In high dielectic constant ceramics DF can be 1 to 2%. However, lower DF is usually an indication of quality capacitors when comparing similar dielectric material."

from http://en.wikipedia.org/wiki/Dissipation_Factor

 

The lower the DF is, the less likely the charge will be lost due to non-electrical factor, in general. I am not an electronic engineer so i cant say how low is good, but i will say get the lowest you can afforted. Also, you can just drop the op270ez in.

 

The other question about mounting in tin is: you should use isolated audio jack and switch to avoid ground problem. they are more pricy but better in quality and have less interference. (or you can isolate them yourselve.) I do connect the two together before and notice no difference.