[rajesh]

I made my class D amp CDA254. Here. is the pic

Sad part is, there is not much gain. Also, the amp sounds thin and lean. LF content is very low. Moreover, the PCB area directly above the chips heats up quite a bit. Looking forward to comments and advices from the gurus here.

[srb]

You are using the linear power supply - it looks like you are powering it with a somewhat smaller transformer than the larger, more robust standard toroidal transformer.

The recommended transformer VA rating is 300VA and the required DC supply voltages for the CDA-254 are +/- 42 VDC to +/- 52 VDC, which would require a transformer with AC secondaries in the range of ~ 30 VAC to 36 VAC.

What is the VA rating and secondary voltages of your transformer?

Beyond that, although it's hard to tell from the photo, some of the wiring looks a bit on the small side, i.e. the transformer secondaries and wiring from power supply board to amp board.  The speaker wires also look a bit lean, I would recommend no smaller than 16 gauge, but again, hard to tell from the photo as well as not knowing what length they are or what speaker load you're driving.
 
Steve

[rajesh]

it looks like you are powering it with a somewhat smaller transformer than the larger, more robust standard toroidal transformer.

The recommended transformer VA rating is 300VA and the required DC supply voltages for the CDA-254 are +/- 42 VDC to +/- 52 VDC, which would require a transformer with AC secondaries in the range of ~ 30 VAC to 36 VAC.

What is the VA rating and secondary voltages of your transformer?

Thank you for the reply Steve. It is a EI core transformer, 35-0-35 & 400 VA. I'm posting some closeup pics which may give you a better view.

some of the wiring looks a bit on the small side, i.e. the transformer secondaries and wiring from power supply board to amp board.  The speaker wires also look a bit lean, I would recommend no smaller than 16 gauge, but again, hard to tell from the photo as well as not knowing what length they are or what speaker load you're driving.

Actually, I took the help of a guy who runs a AV repair workshop. The speaker cables are 14 gauge, the thickest possible which can fit into the slot. I tried 12 gauge but they won't fit in.

Are you saying that replacing the wires supplying current from power supply board to the amp with thicker ones would help in increasing the slam? Will try that for sure.

But what is the reason for generation of considerable heat on the PCB area just above the IR chips? Looking forward to your views.

Regards


Rajesh

[srb]

If the 400VA sticker on the transformer is correct and the secondaries are 35V-0-35V, that's certainly within spec.  I assume you got the 35V figure checking with a voltmeter?
 
As far as the supply to amp wiring, I would at least try to match the gauge of the transformer output wires, but they may already be of the same gauge.  (I didn't really do a great job of visually assessing wire sizes from the photo earlier).
 
I know this is just a test board hookup, but the RCA input wiring should probably be separated.  I would think the effect might just be some channel crosstalk, but maybe there is some kind of signal cancellation occuring?  Also, I'm not sure what I'm seeing at the elbow of that wire bundle.
 
None of this really explains why you may have higher than normal temperatures.  The heatsink is not quite as large or finned like the SDS series, so I don't know if it is somewhat normal.  Perhaps some owner's of the CDA-254 could report what level of heat they're experiencing.
 
Steve

[corndog71]

I would also recommend cutting those input wires down as short as possible and unbundled.  It should just be 2 nice, clean twisted pairs.

You might consider also upping the capacitance.

[Steidl Guitars]

The things you guys are suggesting about the cabling are useful, but are likely not going to make a real dramatic change. 

Like Steve, I'd start by making sure that transformer is within spec. 

[corndog71]

Today has been a great day for listening to music!

The stereo:
Rega P25 with Shure V15VxMR, Cambridge Audio 640P phono preamp, Bottlehead Quickie battery-powered tube preamp, Classdaudio SDS-258 driving my AV123 X-LS'.

Been spinning vinyl all day and it just sounds fantastic!

I may have to build another one of these amps for my other system.

[wushuliu]

How hot is hot? The heatsinks of my CDA amps were all too hot to touch, which is normal.

[rajesh]

Thanks for the suggestions guys. The wires from PSU Board to Amp are a little thinner than those from the trafo. The elbow of wires that you guys are talking is a pot which I inserted in the chain to control the gain into the amp's input to control volume. That photo was taken a while ago. The speaker cable is now of 16 gauge.

I've since made use of the kit as power amp. I've removed that pot and cut open a monster cable and am using it to connect to the source. Result is the same; lean bass.

Also, the heat I'm talking of is not on the heat sink but on the PCB which I've roughly marked.

This being my standby amp, I'm using it only once a while.

[Steidl Guitars]

I noticed that you have only a single lead going to the center tap on the power supply board; the toroids I've seen used all have two leads going to the center tap.

I don't know enough about transformers to know if how you have it is correct for your transformer, but I thought I'd point it out. 

[pelliott321]

I cannot comment on the xformer either.  I built mine from the full kit with the big toroidal supplied by TOM.
I still had the same problem, no gain, thin, lifeless sound.  I had to send the board back for a gain adjustment which Tom did cheerfully and quickly.  It mad a big difference in the gain but the amp still did not sound great.  I doubled the six PS electrolytics and by passed  with a poly and this helped but the just sounds totally non-involving and is now collecting dust at the bottom of a closet, hoping that some day I will find a use for the PS.

[rajesh]

I noticed that you have only a single lead going to the center tap on the power supply board; the toroids I've seen used all have two leads going to the center tap.

Don't know about that. I made another kit amp (based on LM 3886 designed by one Mr. Mauro Penasa and modified by one Mr. Shivchander) where I used a toroid. Even that had one wire for ground, one for + and one for -

I also do not understand the 2 taps each for the +, - & Gnd from the PSU whereas the amp has only 3 connectors.

I built mine from the full kit with the big toroidal supplied by TOM.
I still had the same problem, no gain, thin, lifeless sound.  I had to send the board back for a gain adjustment which Tom did cheerfully and quickly.  It made a big difference in the gain but the amp still did not sound great.  I doubled the six PS electrolytics and by passed  with a poly and this helped but the just sounds totally non-involving

The amp sound in mids is fantastic and highs are crisp; only lows are lean. I did a one-to-one comparison with the following setups.

Common components in the setup are Marantz CDP, 2-way Accoustic Portrait bokshelf speakers having Vifa drivers; 6.25 PP cone mid-woofer and 1" Aluminum tweeter and Cardas I/C.

1. The amp driving the speakers directly with pot controlling the gain
and
2. The amp receiving signal from Parasound P/LD 2000 Pre-Amp.
and
3. A vintage Luxman L80V SS Integrated Amp.

In the first setup, sound was thin and lean with negligible bass. Sound stage was not very wide.

In the second setup, Parasound improved the sound greatly, imparting it a lot of body but the bass was better but still lean. Sound stage was wider.

The third setup sounded superb with a wide and deep sound stage, oodles of bass and fantastic sound.

I think it is the case of amp-speaker mismatch. The speakers require a powerful AB Amp to sing I guess.

I also played the amp with Fostex single driver based speakers from Audere. Nice sound but sound stage was very narrow with razor sharp sweet spot; an inch here or there and the magic vanishes.

[srb]

I also do not understand the 2 taps each for the +, - & Gnd from the PSU whereas the amp has only 3 connectors.

The extra terminals are just for convenience if you are powering 2 amp modules.
 

I think it is the case of amp-speaker mismatch. The speakers require a powerful AB Amp to sing I guess.

It certainly could be a synergy thing with the speakers.  Maybe not even a Class A/B vs Class D thing.  Maybe a different Class D amp would drive them better.

I also played the amp with Fostex single driver based speakers from Audere. Nice sound but sound stage was very narrow with razor sharp sweet spot; an inch here or there and the magic vanishes.

Do you have any other 2-way speakers with passive crossover you can try it with?  It's just kind of surprising seeing how many people are thrilled with the amps.

Steve

[corndog71]

I'm driving my AV123 X-LS, a 2-way 6.5" ported bookshelf speaker, with my amp and getting unbelievable bass.

[wgscott]

My transformer arrived today.

It has a lot of wires on it.  I'd be grateful for a reality check, since the instructions are kind of vague to non-existant.  I've mostly pieced this together from the first 126 pages of this thread, so maybe it will be a good summary, if I got it right:

Input:

There are two red, two black and one purple wire.  From the diagram on the class D audio website, it indicates the two red wires connect to the AC hot wire (along with fuse and switch), and the two black wires connect to the AC neutral.  I hope I have that right. {Edit:  Yes, it is correct.} The purple wire says it connects to the internal shield.  Should this go to the ground? {Edit:  Tom verified it should.}

Output:

Do I ignore/cap off the orange and brown wires?  {Yes}

I see two blue and two black wires.  Since mine came with no wires taped together, I am assuming the wires in the #2 and #3 positions go to CT?  {Yes}


Covering:

Am I supposed to remove the clear plastic wrapping?  {No!}


Sorry if all of this is obvious to everyone but me...

[corndog71]

I don't know about the purple wire but it may not be a bad idea to ground it if your instructions say it's a shield wire. 

As for the brown and orange wires, I clipped off the exposed wire and wrapped each end with a little piece of electrical tape.  Then I taped them together for neatness.

You got the black and red primary leads correct.

Did you get this from classdaudio?

[wgscott]

Thanks.  Yes, but they drop-shipped it.

Should I leave the clear plastic wrap on it or take it off?

[corndog71]

Don't suppose you can post a pic?

Is it a bag?  Or is it tight like mine.





If it looks like mine I would leave it alone.  You can always email Tom to be sure.

[wgscott]

Looks identical to yours.  Thanks.

[IronForge]

You may want to check out Pete Schumacher's PCeiver build...


http://techtalk.parts-express.com/showthread.php?t=218374&page=7

Would the volume be controled by the "PCeiver" in this case?