[wlai]

Hi:

I'm going to build a Tangent CMOY as a refresher soldering project, and been studying the parts list. I did notice that the schematic calls for two 9V, which works for a mint tin, but I'd like to use the recommended case from his parts list, which has one built-in 9V battery slot. Is there a different schematic for the one 9V config? I am afraid I wasn't able to find it on his site nor here in the forums.

And if there is such a config, what is the sound difference between them?

 

[wlai]

ah...further digging reveals the search term that I'm looking for..."virtual ground"...

Anyway, any pointers would still be appreciated. Thanks.

 

[mb3k]

Simply connect only one 9V battery to the Cmoy.
For me, it's not a significant improvement in sound... well to be honest I haven't listened to my CMOYs since last year when I had 'bad' headphones.

 

[mono]

Seek specs for the opamp you're using, some tolerate lower voltage better than others but it is do-able. Tangent has done some relevant testing, you ought to look at his recommendations for voltage vs opamp, "Notes on Audio Op-Amps"

 

[wlai]

Thanks all. I think I've got it now...The rail voltages is largely dependent on the op-amp's best performance zone. I also think I understand the virtual ground design.

I should have just *studied* Tangent's stuff top to bottom to begin with. Can't recommend it enough.

 

[Seaside]

wlai.
As you said, it is very important for any first builder to research about what he is building. You will have no problem making cmoy when you're following his instruction very carefully.
Cmoy certainly is not the finest amp available, but I still remember the joy I had when I first got my Cmoy working. So... It is worth to try... at least for the first project.

My recommendation for the parts is...

- use 0.47 or 1uF flim capacitors for input cap.
- use 470uF electrolytic cap for railsplitter.
- OPA2134pa will be a good OP for this project.
- Double check for cold joints and missing wires.

Good luck.

 

[picklgreen]

The opamps Tangent recommends for the CMoy are all usuable at 9V or 18V. I have built both versions, with 1 or 2 9V batteries. The most important thing is setting your gain to match your headphones correctly. Low impendance headphones (like ear buds) set gain low (i use 3 or 4). High impendance headpones (like Senn HD600's) set gain higher to your liking. And like i recommend for everyone who builds these CMOy's, change the .1uf and 470uf caps to 1uf and 1000uf caps respectively. This will give your CMoy better bass and more "body" to the sound. 9V battereis are fairly low current so and current reserves the 1000uf caps can provide the better!

 

[MisterX]

Quote:

but I'd like to use the recommended case from his parts list, which has one built-in 9V battery slot

Are you are referring to the Serpac H-65-9V?
If so I would suggest a Serpac M 6 series instead.
The H 65 is pretty huge for a CMoy.

Example:

Quote:

And like i recommend for everyone who builds these CMOy's, change the .1uf and 470uf caps to 1uf and 1000uf caps respectively. This will give your CMoy better bass and more "body" to the sound. 9V battereis are fairly low current so and current reserves the 1000uf caps can provide the better!

I would not go beyond 470uF without adding bypass caps in an amp that is powered by a single 9 volt battery.
I find the bass to be to slow and bloated without them when you go with that much rail capacitance.

 

[picklgreen]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif I would not go beyond 470uF without adding bypass caps in an amp that is powered by a single 9 volt battery. I find the bass to be to slow and bloated without them when you go with that much rail capacitance.

Would you recommend 1uf or .1uf for bypass caps. I have both these values in Wima caps. I also have some .06uf but i figure those are to small to be useful.

 

[mono]

For power rail stiffening slant to the decoupling, the 1uF would be better.

If (excessive) voltage droops are apparent from use of a single 9V, a cap might also be placed across it's +- terminals after the power switch.

It may just be my opinion but I think there is a diminishing return trying to tweak a CMOY, it's primarily meant to be simple and minimal, with more elaborate amps existing to gain some of the same benefits suggested by mere cap replacement.

No giant cap will allow an opamp to exceed it's reasonable current limit or change that it's still driving the load. We haven't even gone into the issue of which opamp is chosen but if you have one only capable of under 75mA output, that may be a more significant limit than capacitance over 470uF per rail-vGnd. It might help still, but I'm just suggesting a supertweaked CMOY is still just a CMOY.

 

[MisterX]

I think 1 uF is pushing it a tad so I would prolly use one of the smaller ones you have.

 

[picklgreen]

Bypass caps are not needed with the OPA2227PA or the 2107AP opamps. I am using both of these opamps with 1 and 2 9V sources with 1000uF caps with no bypass caps just fine! In fact after I read your post suggesting to use bypass caps I built another Cmoy just to try it out. I did one with 1 9V source and 1uf bypass caps on with the 1000uf caps. NO DIFFERENCE at all. Than i tried it with smaller bypass caps (0.1uf). Both were high quality caps (Wima MKS). AGAIN...NO DIFFERENCE!

I relise that using the 1uf bypass caps ought to provide some benefit...but in my test situation, and the Senn CX300 headphones used, I heard no audible difference. I am also not driving the opamp very hard (gain is only set at 3).

hehe....maybe I should start a new thread called "headfi DIY....MYTHBUSTERS?"

Ok im sure I just opened up a can of worms here...so let the replies begin!

Oh and BTW i did a search on EBAY to see what configs people are selling in their CMoy's and I did find some people selling them with 1000uf power caps and no bypass caps also.

I think the whole point of the CMOy was to desgin the best possible sounding headphone amp for mthe fewest possible parts...honestly the only reason i even moved from the 470uf caps to the 1000uf caps was because I heard an immediate difference which I was pleased with. Now I do have a CMoy 2 which uses 1000uf power caps, and 1uf bypass and input caps. It also uses cascading opamps and a buffer. I like the sound of the normal Cmoy much better.

 

[wlai]

pickle: I don't think the bypass caps is to enhance the sound, but to prevent DC offsets from entering the system and amp'ed and sent to the headphones, potentially overheating the drivers' coils. Look at Tangent's site and he explains that it's probably OK to not have the bypass caps, if you know that your source has an bypass cap on its output. Otherwise he recommends having one in input of the CMoy.

In your case I assume it didn't cause any problem for you, and that's fine. But I don't think that it is a "MYTH" to have one in the design, particularly since CMoy is so often recommended for first time DIYers.

 

[picklgreen]

no no no....the bypass caps in parallel with the power reserve caps are NOT there to filter DC offset! The power caps are there to supply a current reserve in times of need such as large bass passages for example. The bypass caps are there to help out the larger caps. In other words , yes you should be able to "hear" if the bypass caps are providing any benefit. They charge/discharge much faster than the larger cap and that is y they are there. The 1000uf caps would take 5*(RC) to charge fully. So the bypass caps if only 1uf would charge much faster. The caps we are referrring to are NOT in the CMoy schematic!!!!!

What your thinking of is C2 which with R2 forms a highpasss filter with R2 freq=1/(2piRC). It also filters out DC offset from the source. C2 is not what is referred to as a BYPASS cap. A bypass cap is always used in parallel with a much larger value and is usually only found in the pwer supply section, since this is where large caps are used. C2 is an INPUT SIGNAL cap.

 

[wlai]

You were right, I was thinking C2 due to the similar value. Apologies.