[OliG]

Hi Everyone,

Well well well, there it is, I've been drawn into the DIY. Even if I dont know a lot about electrical circuits, I will try to build headphones amps. I will first build a Cmoy to learn the basics, folowing the excellents instructions at tangentsoft.com and then I will try a CKKIII.

I have 2 questions for you guys :

- I read at amb.org that I will need an a "Amveco TE62033 15V+15V toroidal with wire leads" to build the CKKIII. I went today to a local store that was selling a transformer +15v -15v but it was not toroidal, it is like a square box. Do I really nead a toroidal transformer or do any 30v transformer will do?
(I'm trying to order parts from a single place and buy local if I can) What should I look for when buying a transformer?

- I've bought a ac/dc 24vDC adaptor today for the Cmoy I will build, as I want to get it working from the wall plug instead of batteries. Do I really nead a power supply like the THREAD available at tangent or can I feed the amp directly from this adaptor? Any suggestions others than the THREAD?

I hope thoses questions do not sounds too stupid, even if I read a lot ont the subject, all theses specs can be confusing...

Thanks for your help !

Oli

 

[tomb]

Power supplies for high-fidelity audio is an extensive subject.

It's been awhile since I looked at the CKKIII, but I'd take the recommendation for two secondaries at 15V each very seriously. A +15V and -15V transformer is not the same thing. As a matter of fact, +15 and -15V implies a DC output, which is not appropriate at all. As for whether you need a toroid, IMHO that's really dictated by whether you want to locate the transformer in the same case as the amplifier. Non-toroids work fine (and are cheaper) as long as you have adequate distance from the amp (a separate box, for instance) They are not as quiet as toroids and you will probably run into noise/hum issues if you locate a non-toroid in the same case as the amplifier.

For your CMoy, one of the best and cheapest ways to guarantee best sound quality is to use the typical one or two 9V batteries. If you go for a power supply, you should use a linear-regulated one. Those are not very common, hence the TREAD that tangent sells. With one of those, you can use a transformer or a very inexpensive AC-to-AC 24VAC adapter. Chances are, what you picked up is a switching adapter - probably 90% of the ones on the market are switching supplies. Those have a tendency to throw a lot of trash into the signal and a CMoy is not sophisticated enough to filter that noise out.

 

[nightanole]

The shape of the transformer doesnt really matter. However you do need a 15v+15v unit. That means 2 leads in and 4 leads out. It uses this to make a virtual ground later on (what does 15v + -15v get you?).

As for your cmoy i think you are half way there. there are several ways to tell what you got.

if its a wall wart its probably unregulated. So all it is, is a transfomer, 4 diodes, and a cap or 2. If it gets kinda warm you might have lucked out and there is a regulator in there.

If its a brick type like something that would supply power to a notebook computer, its probably a switching type and not very good for audio


Heres what i would do. First i would hope its a wall wart that you can take apart (destroy the case if you have to, you can make another cheap). Then check out what kind it is. If its got a regulator you dont need to do anything, just feed your cmoy. If its got just 4 diodes and some caps, well then your half way to a tread.


http://tangentsoft.net/elec/tread/misc/sch-v1.1.pdf


You have the transformer and 4 diodes allready. Now you can buy a tread board or if you want to save maybe 5 bucks you can just hobby board it.

If you buy the tread then just use the transformer and throw the rest away.
If you make a tread then first thing is to put the 4 caps in the bridge rectifier and hopefully put the case back together. Then you would have to hobby board the rest of the circuit in another box. This also helps keep the noisy parts away from the regulator parts.

 

[jnewman]

Also if you get a different transformer, make sure you get one with enough power capacity. The specified Amveco is 7 VA (30V * .233A = 7VA).

 

[dBel84]

Just wanting to clarify what tomb said above - although this amp end up with a dual 15V supply , it does not use a center tapped 30Vac transformer , thus the one you describe is not appropriate

The power supply uses each 15Vac secondary to generate the appropriate rail voltage with a common ground. The shape of the transformer does not matter as stated , could be a torroid, EI- or R-core but it must have dual 15Vac windings.

..dB

 

[OliG]

Thanks for all thoses answers guys !

Following your advices, I ordered the transformer recommended in the parts list at amb.org. This will be my second project, so I will follow the part list blindly... I might try some tweaks on laters builds

but for now I'm not confident enough to pick locals parts... I knew I needed an AC transformer 15v + 15v but I could not saw the difference on the shelf from a +15v -15v DC output... I'm gonna learn with time but for now, the copy/paste method suits me.

Concerning the Cmoy, I will add a THREAD power supply to regulate my cheap switching wall adaptor. I know that the easiest way would be to run the amp from batteries, but this amp will be used at the office, so it will probably be running all day and I dont want to change batteries every morning. I ordered a THREAD kit from tangent.

All my parts are now ordered, except for the metallized polyester capacitors and the metallized polypropylene capacitors needed for the CKKIII. they are back order at mouser and digikey. Any advices where I can find them here in Canada? And one last question, I think I ordered some ceramic capacitors with higher voltage tolerance than needed (10pF 200V instead of 10pF 100V) is this a big issue?

Thanks again for all the help !

Oli

 

[OliG]

Forget about the 2 last questions... I just ordered everything I needed from mouser.

I will begin the assembly when I receive all parts !

Oli

 

[Skubasteve]

I had my ckkiii up and running, but dismantled it to redo some of the wiring. When I put it back together, one of the power supply halves no longer worked - I got a loud buzzing through both channels. The +15V rail was reading -3V (the -15V rail looked fine), so I removed VR1 in order to isolate the power supply from the rest of the circuitry. I put a 200 ohm resistor across the rectified output in order to insure some current was moving through the rectifier diodes, and when I apply the 20V AC I only measure .15V or so. Can I conclude from this test that my rectifier is shot? If so, what should I replace - all the diodes, all the little caps, etc.?

 

[FallenAngel]

Check AC from transformer and DC after diodes, should tell you what's going on.