[raindance]

Come on, someone please take the time to answer my questions from yesterday. I really appreciate your input.

[roymail]

You can't run either amp directly from a 100K volume control. The input impedance on the CDA amp is way too low to do this without significant loss and the SDS amp ends up sounding really thick and with almost no highs.

Your findings are not surprising.  The CDA amp has an input impedance of approx 7.5K which is very low.  That's why a buffered preamp is necessary for impedance matching like you said.  The CDA series amps are just not candidates for most common volume controls.  However, the SDS series amps, with their input impedance of 47K, should be fine with using 10K, 20K, 25K value attenuators.  I prefer the 20K Goldpoint/Elma stepped attenator, and would not anticipate any impedance matching problems with the SDS amps.

Regarding your earlier 2 questions, I recommend that you send a PM to Walkern.  He can answer those for you.

Hope his helps.

[roymail]

I just finished a stock CDA-245S kit and all i can say is I am most disappointed.  It is totally lifeless.  no freq extension either way. This is supposed to be 250watts and my 50watt glass amp beats it in every way.  whats going on? 

I think raindance is probably right about the impedance matching.  What preamp are you using?

[wushuliu]

Also, in my opinion, the CDA-254 is not a good candidate for driving with a tube preamp. I have tried a few options and it is just not practical as it loads the last tube stage too much. The SDS, on the other hand, is perfect for driving with a tube preamp. Also, the CDA-254 is dead quiet, whereas the SDS-254 is most certainly not due to the added gain stage. Once I try the buffered volume on the SDS, I'll post findings.

My aikido pre worked fine with the CDA-254. The input caps should be visible on the bottom of the board if you want to know the value. Last I knew they were 22uf for the CDA-254, but this may have changed. And do you need max gain?

[raindance]

Don't get me wrong, a tube pre will drive the CDA series, but the treble extension suffers and it loads the output tube heavily. I tried an SRPP specifically setup for a 7K load and it worked, but there was no air at the top end. With the LME74910 unity gain buffers, there is amazing extension top and bottom, but not enough gain when driven from my CD player or DAC.

This is not a coupling cap issue as the coupling cap governs the low frequency response.

[pelliott321]

My tube preamp has 200ohm output impedance I tried the amp with a SS preamp and it was no different and the same with feeding my dac directly into the D amp.  The DAC has extremly low output impedance. the Xformer measures 33.6 VAC and the PS measures 44.6VDC

 

[raindance]

My tube preamp has 200ohm output impedance I tried the amp with a SS preamp and it was no different and the same with feeding my dac directly into the D amp.  The DAC has extremly low output impedance. the Xformer measures 33.6 VAC and the PS measures 44.6VDC

What speakers are you using? And which tube pre, if you don't mind me asking.

[pelliott321]

Rebuilt Maggy IIIa's custom passive xover with 12ga coils and Solen /clarity caps.
Right now I am running bass panels with 150watt SS (db Systems) monoblocks and the mid/ribbons with a TAD-60 glass amp.  All is nicely balanced, confirmed with TrueRTA and a Behringer mic. Bass is supplemented with a pair of Janis W-1's running 40hz on down

The goal is to go four way active and using all new d amps.  I was hoping that these  class D audio kits would work.  The bass panels are 5 ohms, mids are 2.5 ohms and the ribbons are 2 ohms native.
for the active xover I was thinking the mini DSP 

[raindance]

Rebuilt Maggy IIIa's custom passive xover with 12ga coils and Solen /clarity caps.
Right now I am running bass panels with 150watt SS (db Systems) monoblocks and the mid/ribbons with a TAD-60 glass amp.  All is nicely balanced, confirmed with TrueRTA and a Behringer mic. Bass is supplemented with a pair of Janis W-1's running 40hz on down
The goal is to go four way active and using all new d amps.  I was hoping that these  class D audio kits would work.  The bass panels are 5 ohms, mids are 2.5 ohms and the ribbons are 2 ohms native.
for the active xover I was thinking the mini DSP

I'm not sure the D amps are going to do such low impedance loads. They are half bridge designs and on the high power models even 4 ohms is pushing it. There is a custom model I read about - the SDS-4 that might do it. The CDA series would probably need additional heatsinking.

You are also driving multiple amps from a single preamp with the passive setup, so the CDA series input impedance would stack up poorly in this mode. When you change to active, the preamp only needs to drive the crossover and the crossover has to be able to drive the 7.5K input on the class D's.

Before you dimiss the class D amp, try my suggestion of buffering its input with an LME49710 op amp for each channel configured as a non-inverting buffer. You might even be able to power this from the aux winding on your existing transformer. PM me if you need more help. I found the amps really sparkly but smooth and refined with this buffer up front. All it is really doing is making the amp a light load and simplifying the input impedance.

[pelliott321]

thanks for the reply and the help....sent you a e-mail

[steve k]

I'm running a similar system: Maggie IIIA's with modified outboard passive crossovers (Alpha core/sonicaps/jensens bypass). I'm biamping with a  ClassDAudio SDS 258 on the bass which runs around 400wpc/4 ohms and an SDS 224 on them mids/highs with no trouble at all. I run a tube preamp in front and get plenty of grip on the panels--clean, tight, punch bass, sweet mids and highs. I use a Dahlquist LP-1 crossover which is passive on the highs but adjustable on the lows. Very natural souding unit. Don't know that you need to go bridged monos to get what you want. I think they might have problems because each channel will be driving a 2 ohm load. Might be worth discussing with Tom at Class D though.
Best of luck,
steve

[steve k]

Forgot to mention--beautiful frames!!
steve

[nodiak]

Hope you get it figured out. Fwiw, my cda-254 runs a 12" 3 way, 4 ohm/90db with no problems. Lots of power, clarity and very clean strong bass. You should be able to get similar results imo.

[DougSmith]

Rebuilt Maggy IIIa's custom passive xover with 12ga coils and Solen /clarity caps.
Right now I am running bass panels with 150watt SS (db Systems) monoblocks and the mid/ribbons with a TAD-60 glass amp.  All is nicely balanced, confirmed with TrueRTA and a Behringer mic. Bass is supplemented with a pair of Janis W-1's running 40hz on down. The goal is to go four way active and using all new d amps.  I was hoping that these  class D audio kits would work.  The bass panels are 5 ohms, mids are 2.5 ohms and the ribbons are 2 ohms native.
for the active xover I was thinking the mini DSP

The TI-300/600 amps are stable down to 2 ohms, but the sound quality is probably not as good as the CDA/SDS amps that use the IR chips.  http://focus.ti.com/lit/ds/symlink/tas5630.pdf

[raindance]

Hope you get it figured out. Fwiw, my cda-254 runs a 12" 3 way, 4 ohm/90db with no problems. Lots of power, clarity and very clean strong bass. You should be able to get similar results imo.

BUT 4 ohms does not equal 2 ohms. If the ribbons are 2 ohms driven directly there is a problem. If you biamp using a passive X-over to the mids/highs that can offer a 4 ohm load to the amp, then you are in business.

I do not recommend running a half bridge amp into 2 ohms and DEFINITELY not a full bridge as it will see 1 ohm.

[pelliott321]

Andy adds a 1ohm resistor to the 2ohm ribbon bringing it to 3ohm in his active system.
I really appreciate everybody's comments and I realize I jumped too soon with the CDA.
So I am stuck with it, it will go on the shelf until I need the PS for some other project.

[waltsok]

 Thanks All But,

  I just hooked up my cda 224 and I have a mismatch with gain or impedance or something. It doesn't play as loud as my Audio Research or Forte ams. I am going directly from a JVC XLZ1050 into the amp using the variable outputs of the player. I have plenty of volume using either of the other two amps. I love the volume control of the JVC player can anyone advise me what to do?

PS The amp seems to sound fine. I beefed up the power supply to 6800uf like was suggested. And by the way the Hammond choke  193L, you spoke of made a big difference with the ClassD not as dramatic with the other amps. Thanks for the tips Wushuliu

[raindance]

Funny thing you just uncovered - I have mentioned this sensitivity thing before but no one else agrees - the CDA series amps need a preamp with a gain of 2 or 3 and the ability to drive a 7K load.

I have tried running an op amp buffer -> volume pot -> CDA amp and it sounds amazing, but I can't get much volume either.

[Barry_NJ]

Hmmm... I don't doubt what you are saying at all, but just to give perspective. When I hook up the CDA-254 I have for evaluation, it seems to have about 3db more gain than my Audio Alchemy OM150 which has 29dB of gain and a 40k Ohm input impedance. I use an Audio Alchemy DLC1 pre-amp with a 220 Ohm output impedance, which, IIRC, runs passive until it gets above unity-gain, and 90% of my listening is done somewhere between 20 to 30db below unity-gain.

[waltsok]

I think the difference is I'm not using a preamp at all. I'm going directly to the amp from the cd player. The player has variable outputs which I control from the remote, very handy. I quess the question is. Can I increase the gain in the amp? I don't think a passive amp will work for me but I don't know that much about this stuff. I can't turn my volume past 12 with the Audio Research amp or I'll blow out the drivers it's so loud. The Forte Amp also plays very loud but not as loud. The input sensitivity  on the tube amp is .55v and input impedance is 100k. I have no idea what those numbers mean. The speakers are quasi O-B 5 in drivers only from GR Research, pretty efficient, but I'm not using Dann'y crossover so mine can't compare, sound wise.   
 How can I up the volume? I got rid of my preamps because I could go direct to the amp and it sounded better than any pre I tried  Thanks