[dwk]

I actually have a multi-amping project using a pair of sds-224 in flight as well. In my case, the xover will be done on the PC with output via a Steinberg MR816. I've stalled a bit as I was waiting for my connexelectronic SMPS to be delivered - my case is too small for 2 amp boards plus the standard xformer/PS setup. The smps took quite a while to be delivered, but it did eventually show up.
 Still a few things to be decided, particularly volume control. I have an MSB MVC which is a very slick remote-controlled 8-channel volume control which is the default plan, but the MR816 includes the ability to have the master fader control all output channels. This raises the possibility that I may be able to run direct balanced out from the MR816 into the sds-224 boards, and just use the dsp attenuation. The question is whether I can get the gain of the sds-224's down low enough that I don't need massive dsp attenuation. My gut instinct is that if I can keep it to a working range of no more than 10-15dB, then direct wiring and a balanced signal path should be a noticeable improvement over having the MSB in the loop, but maybe not - the MSB seems like a pretty good piece of kit.  It'll be a couple weeks before I'll be able to get the time to finish this up, unfortunately.

[wgscott]

I don't claim to understand what you are doing, but here is a guide to gain from Tom (posted earlier in this thread):

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:

 
560 Ohm = 31 dB

1K = 30 dB

2.2K = 27 dB

5.2K = 23 dB

6.2K = 18 dB

7.5K = 16 dB

It is a log relationship, so you should be able to extrapolate.

[corndog71]

Thanks for posting that.  I just happen to have some 1% 1K resistors laying around which I bet will sound better than those pots.

[wgscott]

Tom actually expressed some dismay about how people regard the pots.  He thinks it unlikely that you would get a sonic improvement, and believes, despite their superficial appearance and price-tag, are actually quite good.  I'm certainly curious, as I now have 4, which I set using a multimeter to 2.2 KΩ, but the slightest movement, and I am doomed.  Plus, I manage to screw up the solder connection on at least one every time I mess with the amp (which is still quite frequently).  Finally, all that spaghetti wire is kind of annoying. Right now I have them hanging out the top vents.  So replacing them with resistors, even if there is no sonic improvement, I think would be an advantage eventually.

Do you just jam them into molex connectors, or what?
Edit:  The answer is on page 108. (photo)

[bruson2]

I soldered my resistors on the underside of the SDS 258  board for a point to point connection.

The pots sound blurry, makes the amp sound ordinary. Soldering increases the clarity of sound and makes the amps seem like a bargain.

I'm sure it's something that can't be measured. Like when I measure my speakers FR with cheap block resistors and then substitute same value Mills the FR stays the same. Same with putting in some teflon caps. Mills and teflon caps no doubt improve the clarity of sound but I couldn't measure any difference. So I went with my ears.

Everything has limits.

[wgscott]

One of the benefits of this new amp is I can now tell when my tube is engaged on my pre-amp in my Nova.  However, the solid-state pre-amp sounds better than the circuit with the 6922 ElectoHarmonix $12 tube. 

Is there any 6922 tube that would be an ideal complement to the Class D amp?  I was thinking Amperex NOS, but worry about spending >$100 on this only to discover it is not an improvement...

[corndog71]

I can recommend a couple of places.

Ram Labs sells cream of the crop tubes at reasonable prices. 

http://www.tubeaudiostore.com/tubes.html

Tube Depot carries Genelex Gold Lion 6922 tubes for a bit more but still well under $100.
http://www.tubedepot.com/gl-e88cc.html

[wgscott]

Well, I just ordered 4 of the Vichy naked 2.2 K resistors, and they are on their way, so I am hoping I can figure out how to attach them.  Is it possible to re-use the Molex connectors?  I have no idea how to get them to let go of the wires.

[corndog71]

Well, I just ordered 4 of the Vichy naked 2.2 K resistors, and they are on their way, so I am hoping I can figure out how to attach them.  Is it possible to re-use the Molex connectors?  I have no idea how to get them to let go of the wires.

I just yanked the wires out.  Then using a needle-nose pliers I recrimped the connector to a solid core wire.  There might be a better way but it works for me.  Another option is to remove the molex connector from the board and just solder the resistors to the board.

[wgscott]

Thanks. I'll probably solder eventually, but I want to hear it first.

[Mmaxed]

Finally took the time to get the SDS254 I got from Wush hooked up.  Thanks Ainsley!

The SDS replaced a Yamaha M80.  Speakers are Zwaves from the big thread at AK.  Started with a CD in my cheap 5 disc player.  When the music first started I wasn't sure I liked what I was hearing.  So much more detail that my first reaction was that it would seem harsher, more fatiguing.  The Selenium drivers are not smooth to my ringing old ears.  The sound I am going for has to be smooth so as not set my ears off.  I detest harsh or bright.

Within less than 2 minutes I knew my initial impression was wrong, very wrong.  While the sound is definitely more detailed it is also much smoother and much more open.  Fills the room better at low volume while still being able to hear all the music.  Snare drum hits have more attack and detail yet somehow are smoother?? and easier on my picky ears.

Switched to some Marshall Tucker on the TT.  HOLY CRAP!!  The difference is amazing.  Guitar sounds like my son is in the room with his Taylor. 

Bottom line is I shoulda hooked this thing up much sooner. Thanks to everyone that has contributed so much to this thread as it is what got me to this amp.  Gotta go.  My typing finger is getting tired.     

[wgscott]

Fills the room better at low volume

That's exactly how I described it too. 

[guest1632]

Finally took the time to get the SDS254 I got from Wush hooked up.  Thanks Ainsley!

The SDS replaced a Yamaha M80.  Speakers are Zwaves from the big thread at AK.  Started with a CD in my cheap 5 disc player.  When the music first started I wasn't sure I liked what I was hearing.  So much more detail that my first reaction was that it would seem harsher, more fatiguing.  The Selenium drivers are not smooth to my ringing old ears.  The sound I am going for has to be smooth so as not set my ears off.  I detest harsh or bright.

Within less than 2 minutes I knew my initial impression was wrong, very wrong.  While the sound is definitely more detailed it is also much smoother and much more open.  Fills the room better at low volume while still being able to hear all the music.  Snare drum hits have more attack and detail yet somehow are smoother?? and easier on my picky ears.

Switched to some Marshall Tucker on the TT.  HOLY CRAP!!  The difference is amazing.  Guitar sounds like my son is in the room with his Taylor. 

Bottom line is I shoulda hooked this thing up much sooner. Thanks to everyone that has contributed so much to this thread as it is what got me to this amp.  Gotta go.  My typing finger is getting tired.     

What power supply configuration did you end up using? I was thinking about getting the SDS254, but haven't decided which supply config to get with it.

Ray Bronk

[Mmaxed]

What power supply configuration did you end up using? I was thinking about getting the SDS254, but haven't decided which supply config to get with it.

Ray Bronk

I got the amp from Wush on this forum.  It uses the SMPS500R power supply that I think came from Connexal??  If you check this therad around Page 110 I think you will find the info.

[mikeeastman]

I using a Dodd tube buffer with DR6H30 tube with my class d amp can anyone suggest what value resistors to use with this set up.

   Mike

[guest1632]

I using a Dodd tube buffer with DR6H30 tube with my class d amp can anyone suggest what value resistors to use with this set up.

   Mike

Hi Mike,

I'd suggest if you are using a buffer only, then I'd get the 1K value resistor. I think there was one value smaller which would give you slightly more gain, which you won't hear. The 1K gives you 30DB versus the smaller value which would give you 31DB. plus, I like to think that I am not running the ClassD amps at max.

Or, if you wish to get the amps to the "standard" 27DB, then get the 2.2K value resistor. Probably with a buffer would be better to get the 1K. If you watch movies and play the audio through the ClasssD amp, then that extra 4DB of gain will be handy.

Ray Bronk

[mikeeastman]

Thanks Ray. I only us the system for music. Will try out 1k and let you know.

  Mike

[wgscott]

I just bought 2.2 k Vichay naked resistors but haven't had a chance to stick them in yet.

Also, today's mail brought a learning IR on/off switch, which I can now use to turn the power off and on with the same button on the same remote that turns off/on my Nova.

http://www.simerec.com/zapper.htm

$50.  Doesn't seem to degrade the audio quality.

[wgscott]

I get a pair of popping noises (one per amp board) when I power this thing on.  Is that normal?  Is there a way to suppress this without impairing sound quality?

[TrungT]

^^^^^
If the amp ON before the pre may caused pop.
Specially with tube pre.