Class D Audio SDS-254

[senmurv76]

I'd like to hear from those who have used or heard the Class D Audio SDS-254. What are your general thoughts about this particular amp? Has anyone purchased the complete amp set as opposed to the kit? Does it include controls?

 

[jtwrace]

http://www.audiocircle.com/index.php?topic=76400.0

 

[esimms86]

wgscott, an active member of this forum, lists the amp among his audio setup.

 

Esau

 

[wgscott]

Here are some photos of my build.

 

Firedog just bought the completed amp. I'll let him fill in the details, but briefly, I think he likes the amp but shipping (overseas in his case) was the low point.

 

I built the kit. I bought a second SDS-254 board, and am now vertically bi-amping (passively, at the moment, but the ultimate goal is active).

 

I had never built any electronic kit before. The instructions are a bit sketchy in places, but Tom and the above-linked threat at AudioCircle are all willing to help (as am I).

 

This started out as a suggestion from 4est, and I decided to build it just to learn something, and I figured if it sounded better than the amp built into my Peachtree Nova, I would use it as my primary amp, and if not, use it to drive some outdoor speakers. I also liked the idea of saving some money (I was looking at Bel Canto and Rotel's Class D offerings). I wound up building a custom cabinet to match my Nova, so that put about $300 more on the price tag, and then I added another amp board, so I probably didn't save much money in the end, but I built it how I wanted it.

 

What do you mean by controls? It comes with two potentiometers to adjust the gain for each channel (I replaced with Vishay 2K2 naked resistors) and there is an input for an amp switch. You get to supply that kind of stuff. The boards are fully assembled, and wiring them up isn't really any harder than a model railroad.

 

It would help if you don't suck at soldering as much as I do.

 

If you mean remote control, you have to add that in yourself.

 

[senmurv76]

Thanks for the responses Gents. wgscott, your assembled amp looks nice! I do some soldering and hands-on work for a living so I don't mind getting the kit and putting the amp together! What I meant by the controls were the pots for volume/gain control. I also live outside the US and have contacted Class D for shipping costs to my destination.

 

 

[wgscott]

Yeah, it comes with two pots. They look kind of cheesy but Tom insists they are quite good. I played around with them and settled on a gain of about 27 dB, and put in some Vishay naked 2.2Kohm resistors. Per Tom (please note the wire color coding has changed):

 

"For those who wish to change the pots for fixed resistors, here are resistor values to produce required gain. Gain is listed in dB: To change gain potentiometer to a fixed resistor, you would connect a fixed resistor between the yellow and black wires on the gain controls (of course, remove the gain pots). Leave the red wire disconnected.

 

Use high quality 1% resistors: 1/2 watt is sufficient.

 

560 Ohm = 31 dB

 

1K = 30 dB

 

2.2K = 27 dB

 

5.2K = 23 dB

 

6.2K = 18 dB

 

7.5K = 16 dB

 

I hope this is of some help. Please feel free to post this on the forums if it will help others. On my personal systems here, I use the same pots that come with the kits."

 

[senmurv76]

So if I understand correctly you have a fixed volume level out of your amp? Can I ask why you decided on fixed resistors rather than using a pot and controling the volume?

 

I managed to look at some of the posts on audiocircle.com; you were talking about a log pot for natural volume control. Did you ever try it out?

 

Also, some posts mention using a Dodd buffer for better volume control. How would I benefit from using one (what is it anyways??)? Some where also talking about pre-amps.

 

I plan to hook up my MF V-DAC straight to the SDS-254 and then to the loudspeakers. I suppose you are doing the same (DAC -> Class D -> Speakers).

 

[wgscott]

I use a pre-amp (the one in the Nova) to control the volume, so it was just a question of finding the best gain setting. Really, the only reason I have the resistors is as a hedge against bumping the gain setting accidentally.

 

The pots aren't optimal volume controls, but I am sure you could replace it with a log one that controls both channels.

 

If you don't have or need a pre-amp, or have the need to switch between multiple devices for input, a passive buffer with a volume control is probably a good idea for impedance-matching. The Dodd buffer does this for you, and has a tube, which some people like. Some people go directly from DAC to amp with no problem. I just don't know enough about that to advise you.

 

[firedog]

You can see my posts at audiocircle.com

 

http://www.audiocircle.com/index.php?topic=76400.msg976400#msg976400

 

http://www.audiocircle.com/index.php?topic=76400.msg977310#msg977310

 

http://www.audiocircle.com/index.php?topic=76400.msg979919#msg979919

 

Try to read all three posts, as my reaction changes as I listen to the amp.

 

Bottom line:

 

1. Built amp is quite nice: looks okay, sounds very good. Outstanding value for the price. Bass response and dynamics are tremendous, mids are also great. High end is good, not outstanding.

 

I think you would have to spend a lot more to get similar performance and power elsewhere. My amp was less than $600 assembled for 250 WPC amp (500 WPC at 4 ohms). Probably if I spent $2000-$3000 or more I could get something with similar power and possibly slightly better sounding with a conventional audiophile amp. It sounds better than the power section of my MF X-150, as a comparison.

 

2. Try to listen to one of these before you buy. Or to another Class D amp. Sounded different than what I was used to. At first I thought it was a little lacking in very high end reproduction

(i.e. cymbals), but after I got used to it and did some comparison to a conventional amp, I realized that it isn't lacking in reproduction, just that it presents the sound differently - it has a much deeper soundstage than I was used to - and on some some recordings some instruments sound "farther away" . You may or may not like that.

 

3. I live in Israel. I was one of ClassD's very first complete amp customers. They had only sold amp boards (kits and parts)previously. The amp is heavy and was packed very amateurishly and as a result was damaged on arrival. I did manage to fix it without too much trouble and it works fine. None of the actual parts were damaged, just some of the connections inside the amp came loose and the case was slightly dented from underneath.

 

So DEMAND, and get in writing, that they will pack your amp properly. Tom at ClassD said he will learn his lesson about the packing, but if you want to buy one, demand that they:

 

Ensure that the amp can't move inside the box: either with hard styrofoam, or by packing the amp in big-bubble wrap, wrapped so thickly on all sides that it can't move inside the box. Also, it should have protection on all sides, and top and bottom. Double boxing would also help.

 

Feel free to refer to my experience if you wish. From stories I've heard, UPS and Fedex in the States routinely drop boxes 12-15 feet as part of their automated sorting and shipping process, so proper packing is a must.

 

Again, I've had it for about a month and am happy with my purchase in terms of SQ.

 

 

[wgscott]

If you buy the kit, it ships in a standard priority-mail cardboard box, which is fine. The transformer is drop-shipped. It weighs a lot, and my guess is that is what makes the fully assembled amp harder to pack properly.

 

I used frontpanelexpress.com to make the front and back plates. I made the color ClassDAudio logo myself. The font they use is Balhaus. It took me a long time to figure out how to make the engraving logo, so if you want what I have, just say so.

 

[senmurv76]

@firedog: I did come across your posts firedog. I live outside of the states and know no one who has a similar amp for me to listen to. I thought to myself the cost is not too high and there are pretty good reviews out there so it would be a nice experience to assemble my very first amp.

 

@wgscott: I have identified some nice AL enclosures locally. Alternatively I have seen some nice enclosures on ebay with volume control, on/off switch, power sockets, etc. which are reasonably priced. What I am not sure about is what size enclose I should go for. Tom sells 30cm by 30cm by 10cm enclosures; is the enclosure that you have made similar in size?

 

[Audio_ELF]

You may also want to check out the Hypex modules...

 

Slightly more DIY in that you need to work out your own configuration though.

 

Eloise

 

[wgscott]

Mine is slightly too small, really. Everything is tightly crammed in. I bought a box to move the transformer out, but haven't done that yet. Mine is 14" X 12" x 5" high, which is 35 X 30 X 13cm. (outside dimensions), so I don't recommend anything smaller than what Tom is using. I have 2 amp boards. The transformer is quite big.

 

[firedog]

Tom's enclosure is big enough if you have only one board; if you want 2 boards, you'd need something a little larger, I think.

 

[senmurv76]

Thanks guys .. For now I plan to stick to one board ..

 

[senmurv76]

Do any of you have any suggestion or advice in terms of a suitable pre-amp? Any particular brande/model that doesn't break the bank? I am asking this as I have never owned a dedicated pre-amp (I have always owned an integrated one).

 

Edit: by breaking the bank I mean under $500. I do not require switching.

 

[wgscott]

Build that Dodd passive tube buffer into the same box. The problem with a pre-amp and a digital source is that it is really an attenuator.

 

$150 kit: http://doddaudio.com/diy.aspx

 

The AudioCircle thread goes into this at great length.

 

[senmurv76]

 

If you buy the kit, it ships in a standard priority-mail cardboard box, which is fine. The transformer is drop-shipped. It weighs a lot, and my guess is that is what makes the fully assembled amp harder to pack properly. I used frontpanelexpress.com to make the front and back plates. I made the color ClassDAudio logo myself. The font they use is Balhaus. It took me a long time to figure out how to make the engraving logo, so if you want what I have, just say so.

 

Thanks for offering to share the logo - if you don't mind could you send me the file you used? I have access to a CNC so perhaps I can do the engraving that way.

 

For enclosure I went with this. Im hoping the finish will be nice!

 

My kit has been shipped. Hopefully I'll have it assembled in a month time.

 

[firedog]

How you set it up and how it sounds

 

[wgscott]

Here it is, as illustrator and hpgl (see link for zip file at the bottom of this post).

 

I used a program called Cenon (free software) to make the nested contours for the engraving template. There is a separate image for the letter D so it could be made in red instead of black.

 

Here is how the images should appear:

 

 

[wgscott]

Here is how it looks in color (the illustrator file). The black on my plate is black, not grey):

 

 

If memory serves, I think I had to trim the outside edge by 1 or 2 points on the hpgl templates in order to preserve the little gaps within the letters.

 

Here is the link for Cenon

 

[senmurv76]

Thanks man!

 

[senmurv76]

@wgscott: I finally managed to assemble my SDS-254 kit - all looks good except for a constant "hiss" of air that comes from my loudspeakers, regardless of whether there is any input connected to the RCA connectors that feed into my amp. I have used the stock pot and have sent them to around 2kOhm (1,999 Ohm to be precise); thats about 20% gain I suppose. The "hiss" is more or less constant over the 0-80% range of the pots, then slightly increase when I crank the pots from 80 to 100%. Tom suggested to disconnect the ground connector that I had in place between the amp board and the ground pin on my mains power socket. It made no difference. Since you put yours together, did you have such a problem? Attached are photos of the amp.

 

@firedog: does you amp hiss when there is no input into the amp?

 

[wgscott]

It shouldn't hiss. If you have your ear 1" away from the speaker, you can probably detect the amp is on, but apart from that, mine is rather silent. A loose ground wire can cause a buzz (presumably 60 Hz) which I discovered at one point during the assembly process. But it shouldn't hiss.

 

Judging by your photos, you put yours together better than I did.

 

What are these things I've circled in yellow? Try taking them out of the circuit and see if that makes any difference...

 

 

 

[firedog]

No, no hiss. Like WG, if I put my ear right up to a speaker I can tell it is on, but there's no hiss or what I would characterize as unwanted noise.

 

Did you check the "bridge" circuit? If it is engaged and the amp isn't wired up in bridge mode you will get hiss.

 

Attached is a picture of mine, maybe that will help.