$175 Class D amp--120 wpc

raindance · « **Reply #1960 on:** 11 Sep 2010, 01:25 pm »

OK, some pictures. I've built the CDA254 kit with the low profile power supply into a chassis from a ghastly Chinese preamp that has finally found a good use... I changed the fuse on the power module to a 6.3A slow blow to allow for toroid inrush. I added a heavy duty mains power switch at the rear to ensure that back emf from the toroid didn't destroy it on turn off. I added two LME49710 buffer stages to transform the input impedance to something usable (50K) and added a home brew shunt balance control (currently mounted at the rear) that works great although it looks a bit scruffy while I optimize resistor values to suit my requirements. Volume is currently a cheap 100K dual log pot, but I have a motorized Alps with input selection relays on the way. Other controls on the front of the preamp are for decoration only... Volume and power are the only controls that work right now. Power controls the housekeeping circuit only. The tube in the front window is for show and I am powering its heater.

Please note I used a partial center point grounding scheme and have the mains ground connected at the inlet. Details are in the photos. This grounding scheme gives me zero hum.

I am driving Vandersteen 2CE's with it - check out "my system" gallery. It is a match made in heaven with the Vandersteens.

Oh, dimensions: (1) transformer 5" x 3-1/4" including mounting bolt.
(2) PSU board 4-1/2" x 4-1/2" x 1-3/4".
(3) CDA 254 amp board 4-1/2" x 4-1/2" x 1-3/4".

Board dimensions INCLUDE stand-offs as supplied.

My chassis is 16-3/4" x 11-1/4" x 4" (including feet) to give an idea of space requirements. It looks OK now, but once I have the remote volume pot, input relays and logic board installed, plus a tube preamp stage, this is going to be packed. I'm not even sure I want to add the tube stage any more as I'm enjoying the quietness of the amp so much. We'll see, I'm always trying to squeeze a bit more out of everything.

hottuner · « **Reply #1961 on:** 11 Sep 2010, 01:34 pm »

raindance, looking forward to your info on grounding.

OK I've got another WOW experience to report. last night I spent the evening setting up a pair of Acoustat 1+1's in my living room, running full range bringing a sub in to match. I spent a lot of the time dialing in the sub and room mode notch, got it sorted out pretty good, with a known decent amp. This morning I stuck the SDS-4 in and jaysus I never heard 1+1's sound like this. That famous Acoustat coloration and the "too big to be a tweeter" sibilants - gone. I don't want to go all hyperbolic, but dang it's pretty close to perfect.

So combined with what I heard with the Final 1000i, I'm beginning to think the SDS-4 is *the* amp for stats. But of course I wonder if the other SDS boards are just as good with stats - or does the SDS-4 1 ohm stability have anything to do with it? Don't know, but curious.

The 60 Hz is not as bad in this room for whatever reason, but I have some ideas about the chassis wiring routing I will try soon. And whenever I have my laptop plugged into the wall I hear "crickets chirping" in the speakers, but not when running on battery, in all three rooms I've had the class D in so far. What's up with that?

raindance · « **Reply #1962 on:** 11 Sep 2010, 01:41 pm »

Quote from: hottuner on 11 Sep 2010, 01:34 pm

raindance, looking forward to your info on grounding.

OK I've got another WOW experience to report. last night I spent the evening setting up a pair of Acoustat 1+1's in my living room, running full range bringing a sub in to match. I spent a lot of the time dialing in the sub and room mode notch, got it sorted out pretty good, with a known decent amp. This morning I stuck the SDS-4 in and jaysus I never heard 1+1's sound like this. That famous Acoustat coloration and the "too big to be a tweeter" sibilants - gone. I don't want to go all hyperbolic, but dang it's pretty close to perfect.

So combined with what I heard with the Final 1000i, I'm beginning to think the SDS-4 is *the* amp for stats. But of course I wonder if the other SDS boards are just as good with stats - or does the SDS-4 1 ohm stability have anything to do with it? Don't know, but curious.

The 60 Hz is not as bad in this room for whatever reason, but I have some ideas about the chassis wiring routing I will try soon. And whenever I have my laptop plugged into the wall I hear "crickets chirping" in the speakers, but not when running on battery, in all three rooms I've had the class D in so far. What's up with that?

Please post pictures of your wiring scheme for me to review.

Crickets chirping are EMC/EMI from the crappy SMPS that the laptop runs on. I got so tired of this I bought a cheap device to give me an optical out:

It is a Behringer UCA202. Now I can use my computer with my DAC and the optical isolation gets rid of the crickets...

Let me help by viewing your grounding scheme as 60Hz hum really muddies bass, so without it you are in for a treat.

hottuner · « **Reply #1963 on:** 11 Sep 2010, 02:05 pm »

thanks for the offer to help, have a look at the pics in my gallery, if there isn't enough resolution I can post bigger files.

also thanks for the tip in killing the crickets (not the girl band, I like them)

Barry_NJ · « **Reply #1964 on:** 11 Sep 2010, 02:07 pm »

Thanks for the measurements raindance, your amp looks good!

Would someone please post the SDS board measurements, I'm not sure they're the same.

Thanks, Barry

raindance · « **Reply #1965 on:** 11 Sep 2010, 02:15 pm »

Quote from: hottuner on 11 Sep 2010, 02:05 pm

thanks for the offer to help, have a look at the pics in my gallery, if there isn't enough resolution I can post bigger files.

also thanks for the tip in killing the crickets (not the girl band, I like them)

OK, first observation - you have no grounding scheme. Second - you are trying to have the RCA connectors and XLR's connected to the board at the same time. You can't do this as the RCA input requires the "-" and ground to be shorted to make the input single ended. Usually you would add a switch to select between the two inputs, like B&K does. Are you driving the unit via the XLR input? If so, then you need to try dropping the shield at the amp end and let me know if the hum goes away. The shield does not carry signal in a balanced system, but can cause a ground loop.

jtwrace · « **Reply #1966 on:** 11 Sep 2010, 02:17 pm »

You can have the XLR and RCA inputs connected to the board at the same time you just can't use them at the same time.

raindance · « **Reply #1967 on:** 11 Sep 2010, 02:18 pm »

Quote from: jtwrace on 11 Sep 2010, 02:17 pm

You can have the XLR and RCA inputs connected to the board at the same time you just can't use them at the same time.

Explain how it stays balanced when you do this?

raindance · « **Reply #1968 on:** 11 Sep 2010, 02:24 pm »

OK, looked at the manual and - does not need to short to ground. I was wrong !!! So you can have both.

hottuner · « **Reply #1969 on:** 11 Sep 2010, 02:25 pm »

raindance I don't think the optical isolation of the Beringer thingy will fix the crickets in my case because they are chirping even using analog output from cd player to pre. It seems the nasties are being fed into the ac then back into the class D. But I was looking at your DAC (which looks quite good BTW, first time I'm seeing Keces), and found this, maybe this is what I kneed
http://www.audiocircle.com/index.php?topic=62587.0

appreciate your comments on grounding I'm posting this mid stream and not sure where it ends yet, but yes one of the things I was wondering was "grounding scheme".

raindance · « **Reply #1970 on:** 11 Sep 2010, 02:34 pm »

Keces makes good stuff. But an isolation transformer doesn't filter anything so it won't fix your issue. I'm going to add one of these to my amp to filter the AC:

It is an inlet filter made by Schurter and these work well. My reason for adding it is to stop the classd amp polluting the mains.

hottuner · « **Reply #1971 on:** 11 Sep 2010, 02:35 pm »

Oh and I'm using single ended only so far - on deck have a balanced pre to try to see what happens to hum then.

A few more notes about it: when I disconnect audio inputs (single ended) the hum gets pretty loud, then lift ground it goes back to not so bad. I have ground pin on IEC inlet grounded to chassis using one of the IEC mounting bolts.

The level of the hum is low, masked by music, but it's easy to hear with ear to speaker.

Was wondering if one of the stand offs was not reaching ground causing some kind of eddy, haven't tested that yet, and Tom suggested try flipping the xformer. Also thought I would then run power hook-up on chassis bottom and fly audio hook-ups closer to chassis top, and reduce audio trace lengths to as short as possible. If all else fails use coax for audio inputs.

But not sure how to implement a star ground scheme. Thanks again.

raindance · « **Reply #1972 on:** 11 Sep 2010, 02:39 pm »

First thing to try is take the 0V from the power supply and connect it to the chassis. Does that make a difference?

raindance · « **Reply #1973 on:** 11 Sep 2010, 02:46 pm »

I would also run shielded cable from input jacks to the board - bear in mind the SDS series is more sensitive to hum pickup with its 50K input impedance. But I'm not sure this is your problem as you have done a nice job of twisting the cables, which adds some shielding effect. I think its grounding.

hottuner · « **Reply #1974 on:** 11 Sep 2010, 02:47 pm »

Quote from: raindance on 11 Sep 2010, 02:34 pm

It is an inlet filter made by Schurter and these work well. My reason for adding it is to stop the classd amp polluting the mains.

Hummm (60Hz) looks like the 5120 is the ticket
http://www.schurterinc.com/en/New-Products/EMC-Products
where are you buying it?

raindance · « **Reply #1975 on:** 11 Sep 2010, 02:53 pm »

Mouser has 'em. But it will NOT cure 60Hz, just EMI/EMC issues such as your crickets. Only grounding and shielding can solve 60Hz issues.

raindance · « **Reply #1976 on:** 11 Sep 2010, 02:59 pm »

PS: filtering requires excellent grounding to be effective. In the case of the Schurter unit, it needs to be well grounded to the case and to the mains ground.

I'll also be experimenting with simple RC filters on the audio inputs on my amp to remove hash above 50KHz or so. This would not be audible, but it is ultrasonic stuff that can cause the amp to work harder and messes with harmonics.

hottuner · « **Reply #1977 on:** 11 Sep 2010, 03:02 pm »

Quote from: raindance on 11 Sep 2010, 02:39 pm

First thing to try is take the 0V from the power supply and connect it to the chassis. Does that make a difference?

OK want to make sure I understand - take one of the two ground taps off power supply board (I could use the empty one) and tie it to chassis?

raindance · « **Reply #1978 on:** 11 Sep 2010, 03:04 pm »

raindance · « **Reply #1979 on:** 11 Sep 2010, 03:05 pm »

If it helps, let me know & I'll put up a drawing that should help to revamp your grounding.