[Vedder323]

Thanks all. Ill be forced to try analogue out right to the amp from my touch until i decide on a pre. As of now im leaning towards the dodd preamp, not the buffer.

[ptempel]

Not sure if it was talked about yet, but I found out that the input impedance of the CDA-254 amp is 7K ohms.  I asked this question to Tom since I'm currently building a Lighter Note attenuator from Uriah Dailey.  So for others planning to use this or another preamp/linestage/buffer with the great amp, there it is.

[corndog71]

7K ohms seems really low.  Are you sure you heard him right?  It should be a lot higher than that.

[dr_skoobie]

On the impedance issue, you can find this much earlier in this incredibly long thread :

"I’m sure there is some confusion on the impedance of the CDA series amps. They have gone through changes since out first design. Our first amps worked well with most preamps and input devices, but they did have very low input impedance, and some with tube preamps had problems. Since that time, we have made several changes to try to make them more compatible and able to match up well to all available input devices. We have used up to 45K, but now we have settled on 7.5K input impedance for the CDA series. This seems to match up very well with all available audio equipment so far, and keeps the input noise down to a minimum. The SDS amps have an input impedance of 45K in balanced mode, and about 42K in single ended mode. This seems to work great with these amps and the balanced input stage. For some time now, we haven’t heard of any problems matching our amps to other input devices."

Sorry I didn't note the original poster!

[srb]

The CDA series have (list) a 7K Ohm input impedance and the SDS series amplifiers have (list) a 47K Ohm input impedance.
 
Steve

[.Marcus.]

Did you ever try to run a bare wire between posts 2 and 3 instead of a resister?  I've never been convinced that a resister can be quieter than a wire jumper, but could be wrong!

Hi, i use a simple jumper on pin 2&3, for me it works.

Regards
Marcus

[Vedder323]

I'm very interested in your impressions of this amp driving your Gallo Reference 3. x speakers.
I've been debating one of these amps for some time now for my 3.5s.

What are you using now?

I'm using an Audio Alchemy DLC w/ PS3 > Audio Alchemy OM-150 w/ PSU150 &PSU150M.

I just bought the rest of the goods for my system... 

Ill be using Squeezebox Touch Analogue out > McCormack ALD-1 > Gallo SA amp + SDS470

Looking forward to the combo!

[Vedder323]

Amp just arrived! Ill be posting a full review shortly.

[Barry_NJ]

Amp just arrived! Ill be posting a full review shortly.

Excellent, really looking forward to this! Please try and pay attention to the sound of Cymbals, as this is where I find most class D amps seem to fall short.

[Vedder323]

I am going to take more time on this review than normal so give me a few days to come up with something substantial. I will say right off the bat that this new enclosure Toms team at class d is putting out really is top notch. Built like a tank and oozes quality.

The back panel is laid out with purpose and makes connections simple. So many companies skimp and cut corners where Tom has paid careful attention and this should be commended
 
As a preview to the sound:

Anyone jumping from tubes to the class d audio amps will feel like they have just came home from a long vacation. The overall sound leans a tad to the warm side but brings bass, speed and detail that my tube amp just couldnt pull off.

Bass is scary good and drives the Gallos like gods of thunder. I have never heard these speakers hit so low with such ease and authority. I am actually thinking about selling my sa amp, I doubt ill need it with this bad boy.

Mids are clean and accurate, nothing honky or smeared. Acoustic guitars pop and image really well in the deepest of mixes.

Treble and cymbals are crisp and natural. No squinting in agony from big symbol crashes even at triple digit decibels.

As you can see, this is gonna be a very positive review.

Good job Tom, thank god we have affordable audio that sounds like a million bucks.

[venteaufeu]

Hi

i am Marc , i live in france and i speak a little english

So i have one system with preampli Nelson Pass UGS and Magnepan 3.6
I have amplifier MC 402 and i would like to change with Classe D because i listen yesterday SDS470 and good good and good

So I hesite between classedaudio, wyred 4 sound sx 500 now 1000 and Hypex UcD700HG+HxR

It is complicated for me to make the difference between N-core, lists(classifies) T and other. Seen my English is just it is difficult for me to read quite your comments. Can help me PLEASE

best regards

Marc

[matt_garman]

An update on the overheating/static/hissing issues I've mentioned a couple times in the last few pages of this thread...

I drilled bigger holes for the standoffs, and also used a grinding bit to somewhat "countersink" the standoffs.  I also noticed that the screws that come with the standoffs are a bit too long, and (at least with my case) actually touch inside the standoff, leaving a little bit of play when you mount the board.  So I used some washers as a shim, ensuring that I could fully tighten the standoff screws.  Net result was that the amp's heatslugs now mate perfectly to the chassis.  I also put some thermal grease (made for CPU heatsinks) between the slugs and the chassis.

Now I can only duplicate the problem if I wrap the whole chassis in a couple fleece blankets.  Without the blankets, the whole chassis gets warm (but not hot) to the touch, but I don't have any audio problems.  I've only had it all worked out like this for less than a week, so time will tell to be sure.  But so far things look encouraging.

I got one of those infared laser thermometers and took some readings after forcing the hissing/overheat issue.  What I found was that the PCB itself was hottest, moreso on the right side than the left.  The PCB on the right side, near the output area was 150 degrees Celsius, but the left side was only 50 degrees Celsius.  I asked Tom about this, but all he said was "If you're using a laser type thermometer you will get this kind of reading."  I didn't want to bug him and ask for an elaboration... maybe someone on this thread can do that?  I know these laser infared heat guns aren't the most accurate, but shouldn't a 3x difference from one side to the other be indicative of something?

The only other quirk is the SMPS800R makes a slight humming/buzzing sound.  Generally it's quiet enough that it can only be heard when my ears are within about a foot of the unit.  But sometimes it's a bit louder and sometimes quieter.  I just asked Cristi about this over on the diyaudio forums.

I'm still immensely happy with the sound though.  I'm actually thinking about buying a second one! 

[Meicheng]

I think you'd have a rather long list of amps that overheat if you wrapped them in a couple of fleece blankets!  Not to mention potential fires and a host of other issues.

[matt_garman]

I think you'd have a rather long list of amps that overheat if you wrapped them in a couple of fleece blankets!  Not to mention potential fires and a host of other issues.

Agreed, I think that goes for a lot/most electronics in general. 

The fleece blankets came about because when I first noticed this problem, it took watching an entire movie to trigger the issue.  I didn't want to sit through the movie again while trying to debug this, so I used the blankets to speed up the heating.

Before the better mounting I just described, even after removing the blankets, the issue would persist.

But now, after the better mounting, once I remove the blankets, the issue goes away.

[siava1018]

What gauge wire runs between the power supply board and amp board?

[roymail]

Hey Matt, I'm curious about those who initially mounted their amps on boards or in wooden boxes.  I don't recall any heat related complaints.  Any thoughts?

Glad yours is working well. 

[matt_garman]

What gauge wire runs between the power supply board and amp board?

14 gauge.  In particular, Carol 14 AWG 3C SJOOW Power Cable.

[matt_garman]

Hey Matt, I'm curious about those who initially mounted their amps on boards or in wooden boxes.  I don't recall any heat related complaints.  Any thoughts?

Glad yours is working well. 

No thoughts of any significance.    Only wild guesses, such as:

• Perhaps all the wood enclosure guys had overall bigger enclosures (more breathing room and/or more ventilation)
• I don't recall anyone building an SDS-470 in a wood enclosure, seems those were all lower-power amp models
• Maybe the wood enclosure guys all happened to have easier to drive speakers (e.g. lower impedance and/or higher efficiency)
• Maybe those folks have an overall lower volume level (although I believe my listening levels are quite modest, but my room is huge)
• I am definitely in the minority for using a switch-mode power supply, and my crude measurements suggest my SMPS is less efficient than the linear PS (i.e. mine puts out more heat)

Again, that's just speculation.

[roymail]

Matt, me thinks you speculate correctly.  Good points that make sense to me.

Vedder323, what Class D Audio SDS model did you build?  Glad it's sounding so good.

[corndog71]

What gauge wire runs between the power supply board and amp board?

I use a solid core 16AWG wire.  I used the same kind of wire for the outputs.