[rajesh]

http://www.audiocircle.com/index.php?topic=18443.0

Or use the search function and type in "Felix".  There are many threads on them.

Thank you Jason. Appears to be a longish thread. Will read it at leisure. Subscribed to it.

[jtwrace]

Thank you Jason. Appears to be a longish thread. Will read it at leisure. Subscribed to it.

Welcome.  You can also do this http://www.audiocircle.com/index.php?topic=91208.0

[corndog71]

Firedog and Corndog71...

I notice on the pics of both your amps there are no gain pots... are these set for a fixed gain? It's hard to tell from the pics if you have a resistor in the molex connector where the pots usually attach.

Thanks... just wondering since I've got the SDS-450 on the way and I am planning to gain match it to my DAC/preamp.

I added the pots. 

[krikor]

Ooooh... Hover pots, I like them.    or are they antigravity pots

[firedog]

Okay, been listening to the SDS-470 pretty intensively today and it has about 75 hours of continuous play on it at this point. First, it seems to be working fine, so we can chalk all the previous problems up to "experience", and learn from it.

As far as sound, these are my impressions compared to using my MF-X150 integrated as the amp (I don't have a way to directly A/B it to anything else, but using the SDS as power amp with the MF as the pre is the only change I made to a system that I'm very used to):

1. Bass - very authoritative, controlled, with "slam"  - whatever you want to call it. Also sounds very warm and rounded - in a good way. Thumps when it should. Like the real thing. You can really hear/imagine a hit on a drum head, for instance.

2. Percussion. Very good and improved. Percussion seems very sharp and well defined  - no fuzzy edges.

3. Transients, Dynamics - micro and macro - very good. Overall my system sounds "faster" and seems to respond better to changes in the music. In general, there is a sense of "ease" in the sound, a little more like it is flowing from the speakers, and less like the the sound of the system "working".  This is especially apparent on big pieces like orchestras or big bands, but noticeable even on rock music and small ensembles.

4. Mids and up- Very Good. Voices, Horns and piano sound very lifelike. Better than what I expected. Listening to Keith Jarrett "The Koln Concert" as I write, and it really sounds like a piano.

5. Highs - Not sure here. At first I thought it was lacking a little in the upper highs. Most noticeable with cymbals. But I'm starting to change my opinion. It seems that on recordings where the cymbals are more prominent (like a jazz trio or quartet) they sound fine; on recordings where they aren't so prominent or hit with brushes, they seem slightly in the background, a little less clear, or less emphasized. This may mean that the amp is doing exactly what it  should, and my previous amp was emphasizing the cymbals slightly. Or it may mean the amp doesn't sustain cymbals quite as well or as long as it should. Not sure. I definitely don't hear any harshness, sibilance, or over done highs as some report with class D. (Later edit: more listening. I listened closely to several passages, one at a time, then switched cables to listen to the same passage with just the integrated amp. Seems like nothing is actually missing from cymbal reproduction, but for some reason I sometimes have the impression the cymbals just don't sound quite as loud with this amp. Odd.) Maybe the amp needed "breaking in" to sound its best. So my final conclusion is that the hi-end reproduction is very good, but cymbal reproduction is the only area in which I think the ClassD amp is only the equal to the MF amp and doesn't outshine it. (Another edit: see below, http://www.audiocircle.com/index.php?topic=76400.msg979919#msg979919, for later update about this).

Update: Now that I've had the amp for awhile, I'm very happy with the sound. The difference in the treble was more a difference in presentation and sound stage. My previous amp had a very up front presentation, this one has a deeper soundstage, so sometimes some instruments sound "far away" in comparison. See my other post here.

6. Sound stage- definitely deeper from back to front. More separation between instruments. Can hear each one more clearly. Again, especially apparent with large ensembles. The side to side sound stage is also wider, but this is harder to hear, as my small room is a limiting factor here.

Overall, I'm pretty happy with the purchase so far. Seems like I'm getting pretty much what I paid for. I think this amp produces sound well above its price point. And I still have plans to upgrade preamp and dac (or buy a DAC that doesn't need a pre) at some point, so that may improve the sound even more.

[NeilT]

Thanks for the great review firedog.
Glad to hear that you like it.

I am hoping to get my SDS-470 next week. 
I will be using it with an EE DAC and Dodd tube buffer.

Neil

[firedog]

Neil-

Be very interested to hear how you think your amp sounds with and without the buffer. Also where in the chain you think it sounds best.

Thinking of getting either one of the Chinese ones thats also a preamp or the new smaller Dodd Buffer (only one input).

[rarem]

Just got my SDS254. I'm very impressed by the product quality and the boards and transformer where all very well packed. I can't wait to try it but I'm going to take the build nice and slow.

I'd love some advice on adding suitable volume control. If I am using a single balanced input (from my Behringer ULtracurve DEQ2496) can I add a volume control directly to the SDS254 itself? The Ultracurve has selectable output of 12 or 22 dBu, and the output impedance is 100 ohms at 1kHz. I'd like something remote controllable and my budget is about $150 (no more initially!).

PS This thread has been super helpful, so thanks to all previous contributors.

[wgscott]

There might be a simple reason why you can't just use the potentiometers as a simple volume control, but if there isn't, and that is all you need, seems simple enough.  You might want to replace the linear one with a log one so it behaves conventionally, and maybe one that does both with a single knob.

Another option is the passive Dodd buffer everyone is talking about here and the other threads.

[rarem]

Thanks wgscott. I got a reply back from Tom, as ever not an effusive one, that confirms what you say.

"Yes, you can use the gain controls for volume."

Which makes sense to me.

However, I've noticed in this hobby that everything can seem simple, straightforward and logical, then I'll read a few forum posts and get confused.

For example just control the volume using some gain pots, no preamp needed, really minimal added components and more direct path = purest sound (the audiophile's dream).

But read some forum posts - no, things sound better with additional componentry (preamp or buffer), even though this adds much more (you'd think sound-destroying) circuitry in the audio path, or you need to look at all the impedances etc. It get's sooo confusing.

Think I'm going to try it cheap, pure and simple - gain pots only...Anyone tried it?

[wgscott]

I think the passive buffer, in addition to providing a convienient and potentially remote-controllable volume control, is that it does impedance matching from the input source.  Also, perhaps related, some have found particular gain settings on the amp to deliver optimal sound quality (i.e., dialed back to somewhere abound 28 dB of gain rather than 32).

The best thing to do is to try it both ways and see for yourself.

[wgscott]

One of my amp boards had to be repaired or replaced, but I am back up and running now for a few weeks, and all sounds good.  I think.  But being privy to every stupid thing I did along the way, I can see how there might be substantial room for improvement.  I wouldn't mind a bit of general advice and a reality check.

1.  My case is fairly tightly crammed, with 2 amp boards, a power supply board, and the transformer.  The wiring as a result looks a bit like a spaghetti bowl, and there is no real shielding, given that my case is wood with front and back aluminum panels only.  Would I benefit from moving the transformer and power supply board (or just the transformer itself) into a separate, shielded metal box?

2.  I chopped up a standard shielded 14-3 gauge power cable to use for wiring the power supply to the amp boards.  Should I do this differently?  Should I ground the shielding?

3.  Are solid-core wires better?

4.  I currently have a passive bi-amp configuration while I figure out whether or not to get an active crossover kit.  I am vertically bi-amping in the sense that I have a stereo amp board for each speaker.  Is this any better than horizontal bi-amping, given it is all coming from one power supply?

5.  In the current passive bi-amp configuration, I have one RCA input for left and one for right going into the box, and I split the left signal for one amp board, and I split the right signal for the other amp board.  Is this ok, or should I have some circuitry in there until/unless I replace it with an active crossover?

6.  Perhaps related to #5, if both amp boards are connected, I get two little pops when I turn on the power supply.  This originates within the amp, so if the pre-amp is disconnected, I still have the same issue.  If I disconnect either of the amp boards, there is no pop in the remaining one, so I assume it has to do with the two interacting at the level of the power supply.  Is this a cause for worry, and if so, what should I do about it?

7.  My inhibition to adding an active crossover is due to my inhibition to disconnecting the passive crossovers in my speakers.  Can any harm come from leaving both in place?

[firedog]

As I wrote in a previous post, I'm a new owner of an SDS-470. The only reservation I've had about the amp so far is that of cymbal reproduction - on many recordings it sounds fine, on others it sounds "recessed" or more in the background, compared to what I'm used to.

I wrote Blair at Nightshade audio about the possibility of matching one of his tube preamps with the SDS. I'm interested in a tube pre, and since Blair builds his own amps based on the ClassD boards, I thought he would be a good person to ask. As part of my email, I also described to him the "issue" I sometimes hear with cymbals. He had an interesting response to that part of my query:

"Class D Audio's amps have a panoramic sound stage, not a forward one. Portions of some recordings will sound more recessed as a result. It sounds like you're hearing the parameters of the amp's sound stage to me. "

That comment fits what I'm hearing - a different soundstage than what I'm used to, and that's why it's sometimes very noticeable to me.
Hopefully, I will get more used to the sound of the new amp, and won't notice that aspect anymore. After all, I want to enjoy listening to the music, and not notice the amp.

Update: Now that I've had the amp for awhile, I'm very happy with the sound. The difference in the treble was definitely more a difference in presentation and sound stage. My previous amp had a very up front presentation, this one has a deeper soundstage, so sometimes some instruments sound "far away" in comparison.

[roymail]

Does this sound right to everyone else?  Personally, when there is a cymbal crash that I'm used to hearing with my A/B mosfet amp, I'd expect to hear it regardless whether I'm using a Class D or any other amp.  Big cymbal crashes are exciting and ad realism to the orchestra.  Soft cymbals vs loud cymbals... I'm not sure about this? 

This is where the power supply really comes into play.  Gotta have that power in reserve.  I guess I'm not really getting this panorama sound thing.

I've kept up with this thread since the beginning, but I don't recall this being mentioned before.  Maybe I just missed it.  Other please jump in here.

[firedog]

Maybe I'm not explaining what I'm hearing well. I just listened to a Don Cherry (jazz quartet) album and the Neil Young "Live at Fillmore" album.
On both the cymbals sound fine - just like I'd expect. But on SOME albums, it seems like the cymbals are farther down in the mix, not quite as loud, or farther away than I'm used to. That's why I think what Blair said may be right - the presentation of this amp is different to what I'm used to, and therefore on some albums - those with significantly more depth in the soundstage - this amp recreates that and the cymbals sound different to me.

[roymail]

Maybe I'm not explaining what I'm hearing well. I just listened to a Don Cherry (jazz quartet) album and the Neil Young "Live at Fillmore" album.
On both the cymbals sound fine - just like I'd expect. But on SOME albums, it seems like the cymbals are farther down in the mix, not quite as loud, or farther away than I'm used to. That's why I think what Blair said may be right - the presentation of this amp is different to what I'm used to, and therefore on some albums - those with significantly more depth in the soundstage - this amp recreates that and the cymbals sound different to me.

OK, that's helpful and clears things up a bit.  I'm not doubting what you are hearing or what Blair is saying.  Others have repeatedly commented that the Class D amps do have a different sound, not the same as SS or tubes.  I can't comment further since I've never heard one.

Regardless, most seem to like what they hear with Class D.  Appreciate the explanation, firedog.

[jtsnead]

I feel with better imaging amps they do not push the sound
of cymbals out towards the speakers location ie:further away,
or behind the speakers.

It might be a more accurate representation of the "actual"
cymbal location in the sound field.

I know with these amps that I am getting great imaging
with better depth.

Also try different power cords, I just bought a PS Audio AC5
and it made a big difference. It did smooth out the upper treble
a bit.

JT

[justinm]

Built my SDS254 a few weeks ago and have been enjoying it for the most part. It replaced an old Adcom GFA 545II. I use a Melos SHA-1 Tube Headphone/Line stage for the pre-amp. I am hoping some one can tell me what size resistors in place of volume pots to use on amp board. I had gain issues with the Adcom and 1/4 turn was almost full volume? I have seen the chart but not sure what size resistor? My pre-amp specs are Line Gain 19 db, Input Impedance 100k Ohm, Out Impedance 0.5 volt. Thank for any help you can provide. 

[walkern]

Here are the resistor values listed a while back that will adjust the gain downward.  I've found the 5K resistor to be a nice starting place (cuts the gain down to 24 db or so)... but with a preamp with the amount of gain you have, you may find yourself liking even less gain in the amp.

"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."

[wgscott]

Built my SDS254 a few weeks ago and have been enjoying it for the most part. It replaced an old Adcom GFA 545II. I use a Melos SHA-1 Tube Headphone/Line stage for the pre-amp. I am hoping some one can tell me what size resistors in place of volume pots to use on amp board. I had gain issues with the Adcom and 1/4 turn was almost full volume? I have seen the chart but not sure what size resistor? My pre-amp specs are Line Gain 19 db, Input Impedance 100k Ohm, Out Impedance 0.5 volt. Thank for any help you can provide.

Adjust the gain pots to what you think is best (e.g., turn the volume up half-way before blood comes out your ears) and then measure the resistance with a multimeter.  Then go for the closest standard resistor value.  I bought 2.2K Vishay naked resistors, about $15 each.

Tom also says the pots are high quality and you shouldn't feel any need to replace them.  For me the main motive was to keep them from being accidentally changed.