[justinm]

Thanks guys for the help. I will measure the resistance and try some out.

[rajesh]

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."

Thank you very much for the information. I found it particularly useful.

After discovering the missing lows, I had relegated my CDA254 to the attic. I've recently purchased a Tube preamp and Class AB SS power amp and a pair of electrostatic tower speakers. The electrostatic panels take over from 1.3Khz.

Your post has given me an idea. Since my preamp has two sets of outputs, I can bi-amp the speakers. I can use the Class AB SS to drive the woofers and drive the electrostatic panels with the CDA254. I can do the level matching of both the power amps by incorporating a resistor of appropriate value. But will this affect the sonics in anyway?

[rajesh]

As far as I remember, most of you guys have used Toroid trafos. Has anyone used an 'R' core? Are there some advantages of using R core which would be more expensive.

[wgscott]

My understanding is that there are more problems than just gain matching when using dissimilar amps for bi-amping.  Relative phase is most likely a big problem.

Did you ever manage to figure out why you were getting inferior bass?  Most people think Class D amps in general are better at bass than treble (and thus one sometimes hears of people who bi-amp with tube amps for treble and Class D for the bass and/or subs).

Since the transformer and power supply that is recommended with the kit is comparatively inexpensive (I would have to look but I think $100 for both), why not at least try that to see if it helps?

If the bass is problematic with the amp you currently have, do you trust the mid/treble?

The Vishay resistors themselves are claimed to be superior in sound to the pots provided in the kit (Tom suggested to me that you would have to have a golden ear to pick out the difference).

[krikor]

Your post has given me an idea. Since my preamp has two sets of outputs, I can bi-amp the speakers. I can use the Class AB SS to drive the woofers and drive the electrostatic panels with the CDA254. I can do the level matching of both the power amps by incorporating a resistor of appropriate value. But will this affect the sonics in anyway?

Not positive, but I believe the CDA amps do not have adjustable gain pots... they are preset to a fixed gain. Are you talking about changing a resistor on the board?

[rajesh]

Thank you wgscott for voicing your opinion. My only mistake I didn't order the whole kit and ordered only the amp and the Power supply from Tom as I suspected that there could be issue of safe handling of the heavy trafo and hence assumed that it can be sourced locally. Since toroids are not readily available and need to be custom ordered in Chennai, India, I have gone in for a EI core trafo of the voltage and capacity prescribed by Tom. I have a feeling that if I replace the EI trafo with a toroid or R core, things might improve. I have made inquiries on the costing and discovered that R core is more expensive than toroid. Hence I'm checking if any of those in AC have used a R core and if it would result anyway in better
sound.

My understanding is that there are more problems than just gain matching when using dissimilar amps for bi-amping.  Relative phase is most likely a big problem.

Did you ever manage to figure out why you were getting inferior bass?  Most people think Class D amps in general are better at bass than treble (and thus one sometimes hears of people who bi-amp with tube amps for treble and Class D for the bass and/or subs).

Since the transformer and power supply that is recommended with the kit is comparatively inexpensive (I would have to look but I think $100 for both), why not at least try that to see if it helps?

If the bass is problematic with the amp you currently have, do you trust the mid/treble?

The Vishay resistors themselves are claimed to be superior in sound to the pots provided in the kit (Tom suggested to me that you would have to have a golden ear to pick out the difference).

Not positive, but I believe the CDA amps do not have adjustable gain pots... they are preset to a fixed gain. Are you talking about changing a resistor on the board?

Yes, precisely; either on the Class D amp or the Class AB SS amp.

[soundnoob]

Rajesh: Why not get a SMPS from Connex?

[rajesh]

Rajesh: Why not get a SMPS from Connex?

Hi soundnoob, thanks for the suggestion but unfortunately, buying something from abroad sitting in India is quite cumbersome, complicated and also expensive. I discovered it hard way when I bought the Class D amp. So don't want to take the trouble once more.

[MarkSim]

Greetings, I've recently just ordered a couple of ClassDAudio amps, was wondering if my wiring plan is correct... The intention is to run each SDS board off a Connex 500R SMPS as monoblocks using the XLR balanced inputs, while retaining "flick of a switch (or two switches in this case)" capability to run as two stereo amps off the RCA inputs



At present, the case I'm planning to use is rather small and may not allow space for a 2nd XLR, so may forego the R channel XLR connection option. Would like to check with the more experienced folks here whether this is feasible or advisable?

Cheers all, and hello! <my first post 8-P>

[rarem]

Guys, I have a couple of questions; one on the potentiometers and the other on set up for XLR.

Potentiometers

The instructions say:

For the potentiometers included, the black wire goes to the center pin on the pot, and if holding the pot with pins facing up, and the pot shaft facing toward you and the pins of the pot facing up, the black wire goes to the right pot pin, the white to the center pin and the red to the left pin.

But how can the black wire go both to the center pin and to the right pot pin? I'm confused.

XLR Set up

The instructions say:

I already set up your amp for single ended input. The important thing to remember is… do not use the – on the input. Connect the + to + and the negative to G(ground). If you connect to -, it will damage the amp. For balanced input, just remove J1 and J2 jumpers completely. J1 and J2 have jumpers on pins 2 and 3… this is for single ended input. If you change the jumpers to pins 1 and 2, it will reverse the polarity…most situations this will probably not sound so good, so no need to mess with that.

Does this mean that for Balanced input I remove the jumpers and do connect + to +, - to -. and G to G?

[praedet]

^^^Ignore the wiring colors for the pot as he has sent out pots with various colors...

Read this

^^^Thanks!  Tom e-mailed me the following, apply it if you have the same color as me, or follow the picture above or the one after Tom's directions

"Thank you for pointing that out to me. I forget we just got in new wires and they’re different color than the last. Now, with the pot shaft facing toward you and the pins of the pot facing up, the black wire goes to the right pot pin, the white to the center pin, and the red to the left pin."



If you have little to no volume with an SDS, the pot is probably the problem...

[rarem]

Thanks Praedet, that's helpful.

Just need some direction on the balanced set up now. The amps are wonderful but he could do with a copyeditor for the instructions...

[poseidonsvoice]

Thanks Praedet, that's helpful.

Just need some direction on the balanced set up now. The amps are wonderful but he could do with a copyeditor for the instructions...

rarem,

Connect Pin 2 to "+" on the board. Connect Pin 3 to "-" on the board. Connect Pin 1 to "G" on the board.

Ideally Pin 1 should be connected to Chassis Ground, in order to maximize the benefits of balanced connections. Whether Tom has done that through the board by way of a solder mask directly to the mounting screw, I don't know. But that is the classical way of connecting Pin 1. I've seen several manufacturers who don't do that, so Pin 1 ends up being 'signal ground' instead  .

Best,
Anand.

[rarem]

Thanks Anand. I appreciate that, especially the tip on ground. Do I also need to remove the jumper, or not?

[poseidonsvoice]

Thanks Anand. I appreciate that, especially the tip on ground. Do I also need to remove the jumper, or not?

For balanced use only,yes you remove the jumper. If not you have to wire a DPDT switch so that pins 2 and 3 are attached together when using RCA inputs and not attached when using balanced. MarkSim has some nice diagrams earlier in this thread.

Anand

[wgscott]

Are there any known issues with connecting a subwoofer at speaker level with a Class D Audio amp?

I've heard, for example, Rel T-series don't play well with (at least some) Class D amps.

[krikor]

Are there any known issues with connecting a subwoofer at speaker level with a Class D Audio amp?

I've heard, for example, Rel T-series don't play well with (at least some) Class D amps.

Been wondering the same. Got conflicting responses of "Check with your amp manufacturer" and "Check with your speaker manufacturer" from those respective parties.

Particularly concerned about when running the SDS amps in balanced mode where the speaker outputs are floating (no common ground). I would like to use them at speaker level with an ACI Force subwoofer on each mono amp. These connect with a speaker level to line level adapter that has resistance built in.... but will this work with a floating speaker output without damaging the amp?

[WC]

Has anyone compared the sound of these amps to Virtue's Tripath based amps? Which did you like better?

Has anyone tried them with GR-Research N3S or N2X speakers? How is the sound?

[corndog71]

My SDS-258 drives my AV123 X-series speakers very well.  GR sells kits of them on the cheap.

[NeilT]

Has anyone compared the sound of these amps to Virtue's Tripath based amps? Which did you like better?

Has anyone tried them with GR-Research N3S or N2X speakers? How is the sound?

The SDS-470 sounds great with my GR-Research OB7's, very smooth, detailed and killer bass.
A surprisingly huge improvement over my previous amp.

Neil