[john dozier]

Both amps use a special opamp designed for professional use by the head of Jensen Transformers. There are two versions, however, differing in common mode rejection. I do not know if they use the same version. I have "hot wired" mine, but I am running balanced and had the designer of my Anedio Dac reduce the output gain. As to whether there would be instability in running single ended, that is a Tom question. Regards John Dozier

[krikor]

I think it's time to move up. I have used a CDA-254 kit for 2 1/2 years, today I ordered the SDS-470 kit.  I would like to find a chassis for it that is different than the stock Class D chassis, I really don't like  IEC connectors, prefer PowerCon, and I prefer SpeakCon over binding post.

I used a couple Par-Metal cases to build my monos with PowerCon and SpeakOn connectors. Not sure if they are still selling since they had a fire, but I got mine through ebay since they were a bit cheaper that way (Antek/Par-Metal are under user name johnango). 

[maxitonus]

I just experienced a decisive improvement of the sound of my SDS470 amp,further to very simple mods:
The basic principle of mods is to reduce the parasitic capacitance of modulation cables, and replace the 4 loudspeaker internal wires by more transparent ones.The list of mods is:
1 Remove the RCA inputs with all their wires, and use only the XLR ones
2 Shorten drastically the wires going to the pots,by locating the pots at the holes made for the RCA inputs,then such wires have only about 4cm(separate them from proximity of other wires)
3 Separate the (+) wire from the (-) wire for each XLR input (5mm instead of sticked)
4 Replace the 4 speaker wires by: Mass(-)=2X rigid wires copper silver plated of 0,9mmdia   (+) 3Xwrapping wires copper silver plated of 0,6 or 0,5mmdia  + litz 8 strandX0,28mmdia

Time necessary=about 1 hour max cost=nothing
Result=dynamics further improved,definition &details further improved.

[bruson2]

Both amps use a special opamp designed for professional use by the head of Jensen Transformers. There are two versions, however, differing in common mode rejection. I do not know if they use the same version. I have "hot wired" mine, but I am running balanced and had the designer of my Anedio Dac reduce the output gain. As to whether there would be instability in running single ended, that is a Tom question. Regards John Dozier

Tom emailed back that eliminating the gain R is fine, but to replace it with a jumper wire. For my single ended input SDS amp.

Sounds much better, more relaxed, really reduced the negative feedback sound.

Very good for a free mod.
Of course I had to reduce the input to match the subs with 2 resistors. And there is a little bit more noise with my 95db speakers. 86db speakers probably won't hear the noise.

[sl_1800]

I recently purchased a SDS-470 kit and assembled it today but I have a problem and I hope someone here will have an idea as to what is wrong.  I built a CDA-254 2 years ago and a few other kits so I'm not brand new to the experience.  The two red LED's on the power supply board are light up and I measured +- 71VDC from the power supply board and also at the power input on the amp board.  The two LED's on the amp board are light indicating power "OFF".  When I switch the amp "ON" with the remote power switch nothing happens, the power "ON" LED's never turn on and the power "OFF" LED's remain light.  I also checked the amp board for proper connection at the remote power switch points and all appears ok.  Hope someone has run into this before.

[.Marcus.]

I'dont know the SDS470 Board. But at the border on the bottom side of the SDS254 is a small switch mounted which could be use to turn the board on / off without remote switch..
Is the switch also available on the SDS470 Board ? May be you could try to disconnect the remote and use the on board switch.

Did you connect anything to the board, may be there could be that the on board protection circuit raise..

Regards

[Nick77]

delete

[|Tch0rT|]

I recently stumbled across these kits and I have a few questions.

1) My front speakers are MartinLogan ElectroMotion ESL's that are 6ohm and dip down to 1.6ohms at 20khz (which I know is rarish for material to really get up there) and my rear speakers are MartinLogan Source that are 5ohm and just like my fronts dip down to 1.6ohms at 20khz. Is the CDA-254 module robust enough for impedance swings of ESL's?

2) Is the toroidal transformer in the CDA-1000 Kit enough to run three heavy duty power supplies, three CDA-254 modules and a CDA-258 module? My goal would be an all-in-one chassis for my 5.1 system.

Thanks!

[rarem]

I'm finally going to finish wiring up my SDS 254.

Would appreciate a quick bit of advice on the input wiring (mine came without PCB Phono Sockets).

There are three connections per input socket (+,-,G) but I only have two wires from my socket. Can you tell what goes where?

[sl_1800]

The center post from your phono socket goes to the "+" and the tag from your phono goes to the "G".

[rarem]

Thanks SL_1800, appreciate the super quick response! Presume it's the same for the right hand channel (i.e. I don't use the negative for that channel either)?

[krikor]

Thanks SL_1800, appreciate the super quick response! Presume it's the same for the right hand channel (i.e. I don't use the negative for that channel either)?

Negative is used for balanced sources. Make sure your on-board jumpers  are set for single-ended connections.

[rarem]

Great. Thanks Krikor! I wondered what the other connection was for. Much appreciated.

[sl_1800]

rarem,  how does it sound now?

[rarem]

sl_1800 - so I like it a lot! I was using a little T-Amp from AutoConstruire before. The T-Amp was also really nice little amp but it felt very underpowered because as soon as I remotely cranked up the volume it would max out and cut off. The ClassD on the other hand feels like it has acres of headroom.

I'd really like to thank all the major contributors to this forum. The great postings really enthused me and pushed me over the edge to trying the build. You know what? - it's really not that hard to do!

I feel like I need to tune it a bit though. At the moment it sounds pretty similar to the AutoConstruire Amp, though much more punchy, but that was running through digital room correction via an Ultracurve DEQ2496. If the Class D Amp sounds so good now prior to correction, I can't wait to see what it will sound like after!

There are a couple of issues that I think are probably down to build issues (all views or fix suggestions welcomed).

• Firstly, I am hearing the odd bit of distortion. I think this will be down to imperfect connections from the amp along to the speakers. For the initial setup, I made a number of intermediate connections for ease of testing.
• Secondly, I get the odd intereference 'crack' every now and again. The amp is not grounded yet and is in a plastic case. Could that be a cause?

[Spanglo]

Hi recently entered the DIY world, and for my first amp kit I chose a SDS-470.  I plan to use the amp to power two 4 ohm subs.  Unfortunately the amp is not working as intended, so I'm looking for some advice because I'm not sure how to go about troubleshooting the issue.

The amp is wired up correctly from what I can tell, lights are on, but it barely puts out any sound.  Currently I have only 1 sub connected using an unbalanced input.  I get the same weak output on either channel and with either gain pot.  Gain wired left to right - Black, White, Red when gain knob is pointed toward me and leads pointing down.

Perhaps the LFE output from my receiver is too low?  I have an older Harman Kardon AVR254.  Would something like this work as a signal booster: http://www.musiciansfriend.com/pro-audio/art-tube-mp-studio-mic-preamp to test that idea? 
 

Some blurry shots:

[Spanglo]

Update from my last post:

Per Tom's instructions, I jumpered the gain and got the same output as with the gain control, so I did have it wired correctly, but then I remembered my AVR's Sub level was set very low at -9db, so I maxed it out at +10db, and then I got good output with the amp gain maxed as well.  Still not as loud as I was expecting, but usable.

A couple odd things that I noticed: first, when I played the test tone from the AVR to set sub level, instead of the usual rumbling,low frequency pink noise, I got a high frequency sounding white noise.  Does anyone have an idea why the test tone wouldn't play normally through the amp? 

I also have 2 other powered subs I'm running from the same LFE output and the test tone comes through normally for them.  I swapped sub cables, tried the other input and output without success.

The second odd thing is that the weird sounding test tone comes through very loud with the gain maxed, but when I turn down the gain until I get a 80db reading, then the gain is too low to hear anything I play.  That's not the case with my other subs, where the test tone comes through normally, I set the 80db level, and then everything plays back at that level.  For some reason, the test tone is loud through amp, but anything I try to play is quiet unless I max the gain out.

Thanks,

[krikor]

Hi recently entered the DIY world, and for my first amp kit I chose a SDS-470.  I plan to use the amp to power two 4 ohm subs.  Unfortunately the amp is not working as intended, so I'm looking for some advice because I'm not sure how to go about troubleshooting the issue.

The amp is wired up correctly from what I can tell, lights are on, but it barely puts out any sound.  Currently I have only 1 sub connected using an unbalanced input.  I get the same weak output on either channel and with either gain pot.  Gain wired left to right - Black, White, Red when gain knob is pointed toward me and leads pointing down.

Perhaps the LFE output from my receiver is too low?  I have an older Harman Kardon AVR254.  Would something like this work as a signal booster: http://www.musiciansfriend.com/pro-audio/art-tube-mp-studio-mic-preamp to test that idea? 
 

Some blurry shots:

It looks like you have the amp board set up for balanced operation but are using an unbalanced source. You need jumpers J1 and J2 in place across pins 2 & 3 if i recall correctly.

[Nate Hansen]

A couple odd things that I noticed: first, when I played the test tone from the AVR to set sub level, instead of the usual rumbling,low frequency pink noise, I got a high frequency sounding white noise.  Does anyone have an idea why the test tone wouldn't play normally through the amp? 

I also have 2 other powered subs I'm running from the same LFE output and the test tone comes through normally for them.  I swapped sub cables, tried the other input and output without success.

Would those 2 other subs be types with plate amps that have a low pass filter? On the ones I've seen that filter isn't defeatable, only adjustable. Could be you're hearing the full range of pink noise through your sub on the Class D amp as opposed to a low pass filtered pink noise through the others. That will make the sound quite different.

If this isn't the case or your AVR is doing the filtering then carry on 

[Spanglo]

Would those 2 other subs be types with plate amps that have a low pass filter? On the ones I've seen that filter isn't defeatable, only adjustable. Could be you're hearing the full range of pink noise through your sub on the Class D amp as opposed to a low pass filtered pink noise through the others. That will make the sound quite different.

If this isn't the case or your AVR is doing the filtering then carry on 

Thanks for the response.

Yes, plate amps with the low pass disabled.  And I couldn't find an option on the AVR for any kind of pass filtering for the sub.

I got the same white noise and complete lack of low tone when I swapped the amp with a little tripath amp, and even when I tried a different sub with the tripath amp.  So I'm a bit perplexed why the DIY amps are not playing back the sub test tone normally.   

Kirkor - you've good eyes spotting the missing jumpers in those blurry pics.  Had taken the pic prior to installing the jumpers, so all good in that respect.

Movies and music sound good, so I don't think there's anything wrong with the amp, but it is disconcerting that there is still an issue with the test tone.  Tom suggested the issue is with the input signal from the AVR, which I would tend to agree since the swapping amps and drivers netted the same result - even though my other two subs play the tone correctly. 

Any suggestions on a good device that could "fix" the signal?