[matt_garman]

Did you turn the amp on?  Not trying to insult you---this was the mistake I made!  There is a little rocker switch on one side of the amp; it kind of hangs under the board, so at least I missed it initially.

[CYoung234]

Did you turn the amp on?  Not trying to insult you---this was the mistake I made!  There is a little rocker switch on one side of the amp; it kind of hangs under the board, so at least I missed it initially.

LOL - no offense taken! It is good to always check the simple stuff first. Yes, it is turned on, and when the amp turns on, the yellow LEDs come on for a split second and then settle on BLUE solid. The YELLOW LEDs turn off completely. So, it appears that the amp powers up fine. We tested the PS before I hooked up the amp board, and the PS was supplying a solid +50V and -50V at the PS output to the board. The BLUE LEDs on the PS board are on solid as well. Later today of tomorrow I can take some photos with my meter to show what I see with the amp on. But before I do that, I will wire up the RCAs and test it as unbalanced, because I really think it is something simple with the input.

As a curiousity, has anybody else run an unbalanced preamp into this amp using the balanced XLRs, and, if so, what was your cable pinout?

[walkern]

One other potential culprit for no sound... the pots/attenuators work backwards from what I expected.  If you turn them clockwise to maximum, I would have expected that to turn the amp's gain all the way up... but it doesn't... it turns it all the way down.  If you turn them counterclockwise to the max, THAT turns the gain all the way up.  Just a thought.

Given that some balanced connectors us different pin configurations for what is hot, neutral and ground, I suspect you are correct that your XLR connections may be the stop gap.  Glad you got the amp up and running, and that all the LEDs are indicating proper functioning.  Fingers crossed that the single ended RCA connections work!

And SORRY RAY!  I did not realize you were blind.  My bad!

Neil

[CYoung234]

Okay, all is well. I set it up for RCA's and it is working fine. The gain pots needed to be adjusted slightly to center it, and the left and right channels were reversed because I wired it in a hurry - it is now correct. Sounds very good so far. More extended listening tomorrow, as I am out of time today.

[krikor]

2 Bi-amping is imposing to keep the pots (to allow for adjusting separately the level for lows and highs),.. therefore connect he 2 XLR symetrical (balanced) inputs in parallel..do yu know whether the position of each pot is modifying the input impedance or not? did anybody measure exactly which is the value of one channel's input impedance in balanced mode?(which will be divided by 2 when paralleled)

I've asked Tom this exact question about input impedance and he said the pots do not modify input impedance of the amp.  If I recall properly, the pots are located between the input stage/buffer and output amp. Input impedance is specified as 47k but I don't know if that is for both RCA and XLR. Might want to email Tom a question.

[CYoung234]

UPDATE AFTER SOME MORE EXTENSIVE LISTENING:

Some initial listening impressions, comparing the SDS-254 to a set of Bel Canto REF 1000M's:

The Bel Cantos may have a slightly better low end. It is very close though. UPDATE: THEY ARE ACTUALLY PRETTY EVEN HERE.

The ClassD has better mids; the Bel Cantos have some midrange suckout in my system, right in the male voice range. UPDATE: I MUCH PREFER THE CLASSD MIDS. THEY ARE SMOOTHER WITH A LOT LESS GRAIN, AND ARE NOT RECESSED THE WAY THE BEL CANTOS ARE.

The ClassD high end is a touch rolled off, but I actually like that. UPDATE: THIS ROLLOFF IS VERY SLIGHT. IT DOES NOT BOTHER ME AT ALL, AND THE HIGHS SPARKLE WHEN THEY NEED TO.

One thing that a lot of audio systems do that is not real is overemphasize upper mids and highs. The highs are there when they need to be with the ClassD, and are totally silent when there is no information there. I really like the silence of this amp - no hum, no nothing. It also runs very cool in my system, and my speakers are not efficient (84dB).

In terms of soundstage, right now it seems as if the Bel Cantos offer a slightly wider soundstage, but I have not listened enough yet to finalize this. The midrange suckout on the Bel Cantos is making it tough to assess the depth. UPDATE: WITH THE MATERIAL I WAS LISTENING TO THIS AFTERNOON, THE TWO SYSTEMS WERE PRETTY EVEN FOR WIDTH, AND THE CLASSD DID BETTER WITH SOUNDSTAGE FRONT TO BACK DEPTH.

So far, I do not find the ClassD to be fatiguing at all. I will need several weeks of listening to this in my system to finalize this. I also need to adjust the gain slightly, as I started out with it a little low (pots about 3.6K or so). I will end up putting fixed resistors in, likely either 3.3K or 2.2K. My preamp will be able to handle either I think, as right now, it it running at about 11 o'clock with the gain set where it is.

FINAL THOUGHTS. I SET THE GAIN UP FOR 2.2K AND IT IS JUST RIGHT. ALSO, THE MUSIC I USED THIS AFTERNOON IS ONE THAT I AM VERY FAMILIAR WITH; IN FACT, I HAVE PERFORMED WITH ABOUT A 1/4 OF THE PERFORMERS ON THIS DISC. CHICAGO SYMPHONY ORCHESTRA / LEONARD BERNSTEIN SHOSTAKOVICH SYM. 1 & 7, DG 1987

I HAVE TO SAY FOR A LOW COST PROJECT, THIS CLASSD AMP IS A KEEPER IN MY SYSTEM. ESPECIALLY CONSIDERING I DO NOT GET MUCH TIME TO EVEN LISTEN ANYMORE ANYHOW.

[guest1632]

UPDATE AFTER SOME MORE EXTENSIVE LISTENING:

Some initial listening impressions, comparing the SDS-254 to a set of Bel Canto REF 1000M's:

The Bel Cantos may have a slightly better low end. It is very close though. UPDATE: THEY ARE ACTUALLY PRETTY EVEN HERE.

The ClassD has better mids; the Bel Cantos have some midrange suckout in my system, right in the male voice range. UPDATE: I MUCH PREFER THE CLASSD MIDS. THEY ARE SMOOTHER WITH A LOT LESS GRAIN, AND ARE NOT RECESSED THE WAY THE BEL CANTOS ARE.

The ClassD high end is a touch rolled off, but I actually like that. UPDATE: THIS ROLLOFF IS VERY SLIGHT. IT DOES NOT BOTHER ME AT ALL, AND THE HIGHS SPARKLE WHEN THEY NEED TO.

One thing that a lot of audio systems do that is not real is overemphasize upper mids and highs. The highs are there when they need to be with the ClassD, and are totally silent when there is no information there. I really like the silence of this amp - no hum, no nothing. It also runs very cool in my system, and my speakers are not efficient (84dB).

In terms of soundstage, right now it seems as if the Bel Cantos offer a slightly wider soundstage, but I have not listened enough yet to finalize this. The midrange suckout on the Bel Cantos is making it tough to assess the depth. UPDATE: WITH THE MATERIAL I WAS LISTENING TO THIS AFTERNOON, THE TWO SYSTEMS WERE PRETTY EVEN FOR WIDTH, AND THE CLASSD DID BETTER WITH SOUNDSTAGE FRONT TO BACK DEPTH.

So far, I do not find the ClassD to be fatiguing at all. I will need several weeks of listening to this in my system to finalize this. I also need to adjust the gain slightly, as I started out with it a little low (pots about 3.6K or so). I will end up putting fixed resistors in, likely either 3.3K or 2.2K. My preamp will be able to handle either I think, as right now, it it running at about 11 o'clock with the gain set where it is.

FINAL THOUGHTS. I SET THE GAIN UP FOR 2.2K AND IT IS JUST RIGHT. ALSO, THE MUSIC I USED THIS AFTERNOON IS ONE THAT I AM VERY FAMILIAR WITH; IN FACT, I HAVE PERFORMED WITH ABOUT A 1/4 OF THE PERFORMERS ON THIS DISC. CHICAGO SYMPHONY ORCHESTRA / LEONARD BERNSTEIN SHOSTAKOVICH SYM. 1 & 7, DG 1987

I HAVE TO SAY FOR A LOW COST PROJECT, THIS CLASSD AMP IS A KEEPER IN MY SYSTEM. ESPECIALLY CONSIDERING I DO NOT GET MUCH TIME TO EVEN LISTEN ANYMORE ANYHOW.

Hi CYoung234,

Well, get those resistors, the 2.2 KOhm and remove the pots accordingly. What preamp are you using?

Hey Neil, no problem.

I don't have the moola at the moment to build one. A few years back I went through some hell building Greg Ball's SKA amp. This one however seems like it would be easier to build.

I was kinda thinking of getting the smaller version of this amp, since I am going to be switching my priorities to headphones. So I don't really need tons of power. So something like the 224S just might be the ticket to headphone bliss or with use of small speakers.

What do you guys think?

Ray Bronk

[CYoung234]

Ray,

Thanks for the advice. I put in some Vishay 1% metal film 2.2K 1/2W resistors, and the soundstage does open up, especially front to back. Very interesting. I sprang for a pair of the Vishay nude 2.2Ks ,and will try them out probably Friday to see if I can hear any difference. BTW, my preamp is an Audible Illusions Modulus 2D with Electro-Harmonix 6922's in it. It is a wonderful preamp, IMHO.

[enal]

My first post to say Hi. After reading through all 167pages of this post I decided to jump in and order a couple of the CDA1000 kits for a few projects I'm wanting to start.

I'm no audiophile like the majority of you, but know quality sound because of all my buddies that are!  This seems to be a good grouping of knowledge here with very minimal drama.

I took notes along the way from everyone elses experiences so hopefully I'll get it right the first round.  If anyone has any lessons learned I'd be glad to take those as well.

Thanks
Enal

[Nick77]

Good luck on the build, and welcome!

It has been noted that the IR boards sound a little sweeter than the TI units. Some of the higher power units are the Texas Instruments boards.

[mboxler]

+1

I guess my first suggestion would be to verify that the "high" gain on the CDA amps works for you.  Tom can lower the stock gain (32 - 33dB???) if that may be too high.

Mike 

[CYoung234]

Ray,

Thanks for the advice. I put in some Vishay 1% metal film 2.2K 1/2W resistors, and the soundstage does open up, especially front to back. Very interesting. I sprang for a pair of the Vishay nude 2.2Ks ,and will try them out probably Friday to see if I can hear any difference. BTW, my preamp is an Audible Illusions Modulus 2D with Electro-Harmonix 6922's in it. It is a wonderful preamp, IMHO.

Just an update to note that I put in the Vishay 2.2K "naked" resistors, and do not hear any difference. I will listen more, of course, but it looks like I just wasted $30 on them...

[Nick77]

Just an update to note that I put in the Vishay 2.2K "naked" resistors, and do not hear any difference. I will listen more, of course, but it looks like I just wasted $30 on them...

Their still perty to look at, of course hopefully you realize some sonic gains. They do need a little break-in from my experience using in other positions. I never tried the resistor swap as i like the adjustable gain, but that is the "cats meow" in resistors.

[CYoung234]

Their still perty to look at, of course hopefully you realize some sonic gains. They do need a little break-in from my experience using in other positions. I never tried the resistor swap as i like the adjustable gain, but that is the "cats meow" in resistors.

They may be the cat's meow in resistors, but in this amp, at least for me, they were pretty dead cats! I changed them back to the regular Vishay 1% metal film 2.2K's , and all is bliss again. THe amp has more air and dynamics with the regular old metal films. Maybe they need break in, but they are likely not going to get it at this point, as I am happy with what I am hearing.

[mjosef]

Well , with the hot summer temps. arrival over the last week, the sauna-like conditions in my NYC apt. has forced me to put my tube amp(power) on extended leave...after an extended leave of absence, my CDA254 build is back in play after a couple modifications, namely installation of an IEC socket and better input wiring...handling the mid/hi freq. above 250Hz.
I ordered a heatsink to attach to the fin-less one on the board, my p/s o/p voltage is slightly higher(+ 6vDC) than the max., causing the amp to run hotter than I would like.
The sound is adequate, clean and clear. Not as spectacular as my tube amps for sure.

[Zippy2000]

Hi all, new here so please be gentle 

I bought two CDA-1000 Kits a few months ago but only recently got the time to hook them up. Just as a test I measured the DC voltage output of the power supplies, and to my surprise they had an output of 95V instead of the expected 47V. When measuring the AC inputs on either side of the center tap I get around 67V which means the transformer has 33-34V secondaries. When measuring the center tap and one of the inputs on either side I get ~34V, which confirms the above.
According to the ClassDaudio website, the power supply should give me 1.41*33=47V DC output, so why is my output double at 95V? Am I doing something wrong?

The transformers are wired according to the 230V scheme as on Tom's website since I live in Europe.

[Zippy2000]

Hi all, new here so please be gentle 

I bought two CDA-1000 Kits a few months ago but only recently got the time to hook them up. Just as a test I measured the DC voltage output of the power supplies, and to my surprise they had an output of 95V instead of the expected 47V. When measuring the AC inputs on either side of the center tap I get around 67V which means the transformer has 33-34V secondaries. When measuring the center tap and one of the inputs on either side I get ~34V, which confirms the above.
According to the ClassDaudio website, the power supply should give me 1.41*33=47V DC output, so why is my output double at 95V? Am I doing something wrong?

The transformers are wired according to the 230V scheme as on Tom's website since I live in Europe.

Okay, Tom just got back to me. Apparently I had to measure ground and + or - to measure the correct voltage. My mistake...

[maxitonus]

Hello gentlemen,
My SDS470 amp,bought completed, has been (slightly) tweaked by: removing the wire which feeds the light located in the on/off switch,removing the asymetrical RCA inputs as well as the inverting switch allowing to choose between RCA and XLR.
I will also-in the near future- shorten the wires going to the pots by placing the pots at the RCA's holes location,then replace the short input wires by litz wire and the loudspeaker ones by pure silver (several 0.5mm dia),but the amp is working SO well that i hesitate to pursue tweaking it..Nota:I need to keep the pots since the sensitivity adjustment, with relation to the output level of my Weiss dac, modifies the balance and searching for a  good compromise allows to improve further,the position of my pots is about 50%)

A very important improvement has been to bi-wire my Duntech speakers and use for the medium/treble section:litz wire as follows: 8X0.28mm (+) 25X0;05mm which opened up the sound, more "air".Nota:The interconnects going from the dac directly to the amp should better be chosen without shield.
Such mods led to considerably improving the balance (tonal accuracy)and the subjective impression of quality delivered by the SDS470 which ,from "good" ,raised the level of "top level amp".(This is just my personal opinion..)

The reason for my coming today is i compared last saturday my SDS470 amp to an amp which is considered worldwide as equal to the cream's best, the DEVIALET amp.(price :12000 Euros)
For such comparison,i just had to remove the SDS and replace it by the Devialet,sole mod: adding a Neutrik XLR to RCA adaptor to the interconnects since the Devialet has only RCA inputs.

Conclusion: the 2 amps are in the same league as far as transparency and sound quality are concerned.
The SDS has been far from ridiculous and i even wonder whether some audiophiles could  always differentiate them in a blind test.
The very small differences of sound are : the Devialet is more "recessed" in the zone 2-4khz, giving him a more "neutral" sound,while the SDS pushes a little bit more forward this "presence zone", may be by 1 (or 1.5) dB(but i think this slight difference could be easily compensated if wished by the choice of interconnects or cables).
My interlocutor, who brought the Devialet at home for such test,has been voiceless since he was not anticipating such a small difference if taking into account the Devialet current worldwide aura..

However, i must emphasize that to obtain the best from an SDS amp,a lot of cable's optimizing is mandatory, INCLUDING the choice of the mains cable.

[Nick77]

  However, i must emphasize that to obtain the best from an SDS amp,a lot of cable's optimizing is mandatory, INCLUDING the choice of the mains cable.                                             

Thanks for the report, ive found the power cable makes a big difference also. Increasing the amps capacitance with better quality power caps increased dynamics and mico details considerably.
I first increased to 40k with great results, then bumped to 60k. The difference between 40-60 wasnt as significant but notable.

Might try better board power supply wiring also. Have fun!

[mboxler]

Thanks for the report, ive found the power cable makes a big difference also. Increasing the amps capacitance with better quality power caps increased dynamics and mico details considerably.
I first increased to 40k with great results, then bumped to 60k. The difference between 40-60 wasnt as significant but notable.

Might try better board power supply wiring also. Have fun!

What power cord did you settle on?  (you may have stated this earlier, but...).

Thanks, Mike