[corndog71]

The power supply will have a huge effect on the end sound.  Gary Dodd recommended a bigger transformer than the ones that come in Tom's kit.  He also recommended for the best sound to power them with batteries.  When I get around to building one that's the route I'll take.  The cost isn't much different between transformer vs. battery builds.

[Barry_NJ]

Barry, just to be sure - while you were auditioning the amps, everything else in your system remained constant?

Don

Oh absolutely Don, same interconnects, same speaker cables, same power cord, the same everything.The only difference in the system during auditioning was the amplifier.

[nodiak]

Thanks Barry. It's good to hear of these comparisons. I enjoying the music from my cda, and don't hear any big problems or lack of abilities with it, but I haven't compared it to other amps yet. My big mistake in the amp search over last few years was in selling an AVA Omega III amp which would've been perfect to compare to everything else I tried.   

[topp]

I am new to the hole DIY amps and I ordered the CDA-254L Kit.  Now I need to order all the miscellaneous stuff to complete the amp.  One thing I noticed is that some people use the IEC inputs with filters in them.  What is the purpose of that and/or is it recommended?  Sorry is this is a pretty basic question.

Thanks,
Topp

[rjyap]

Anyone manage to contact Tom for the past few days? I received the SDS-4 kit but I had a problem with the left channel where there is cracking and distortion. Right channel is working fine and I like the ClassD amp sound signature compare to Jungson Class A amp. After further troubleshoot, I no longer getting any sound from the amp. I use a multimeter to check the power supply module and found out the power supply unit output is 98v. I believe the voltage is wrong. I check the transformer output and it is correct at 72v. Also when I turn off the main power, I can hear some noise from the speaker like the capacitor is discharging.

I'm thinking to build a 8 channel amp using 4 SDS-4 kit. As mention earlier, is the SMPS500R recommended compare to Transformer + power supply module? If I get SMPS500R, do I still need the power supply module (the board with rows of capacitor)? Also, which version should I get, the SMPS500R single rail or dual?

Thanks in advance.

[pelliott321]

I received back my CDA-254 from Tom.  He changed the gain and now it is a more usable amp.  It sounds pretty good, decent extensions either way.  It definitely is an in your face amp, very upfront but not very involving.  It does not suck you into the music like my other amps.  I would like to work on the PS.  What is the maximum capacitance I can add.   

[Nick77]

I am running 60kuf with no problems on the stock PS with Panasonic 10k TSHA caps, i think Wushiliu went even higher. I ran 40k for a while and bumped up to 60k with nice results, dont know if there is any benifit to going higher.

Digikey has these back in stock for a killer price.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P7492-ND

[waltsok]

I returned a cda224 for credit and purchased a sds254. No problem with the cda but with me not using a preamp exactly as raindance described. I changed out the supplied pots with PRP 2.2k ohm 1% resistors. I will try other resistors and will post if anything beneficial results.

I originally purchased the small power supply and changed caps to Panasonics 6800uf 63 volt so I couldn't return it. So I bought a 800va Antek transformer, changer the bridge rectifier to a 35 amp model and heavily heat sinked it for protection. Don't know if I had to do that but it works. I bypassed before the bridge with .1uf polypropylene caps and after the Panasonics too, and added all poly bypass poly caps following this link. http://www.tnt-audio.com/clinica/ssps2_e.html

I don't know if all this was necessary because I did not do it in stages, but I would certainly do it again. This amp has very deep base with control, reasonably good stage depth, lots of air around the musicians a sweet extended high, and it is quick. For me it's just wonderful and I would recommend it to all.

[Mass. Wine Guy]

Can someone please explain to me the concept of changing the gain of this amp? What is it about the stock unit that isn't so good?

[guest1632]

Can someone please explain to me the concept of changing the gain of this amp? What is it about the stock unit that isn't so good?

Hi, First of all, I don't know which model you have. From what I understand the units come with approximately 32DB of gain. Now, that's ok if you have a buffer, or passive Pre-amp  which has no gain. if you have the CD units, before you buy, you should ask tom to make it approximately 27DB of gain, which is about standard in the industry for amplifiers. Now if you have a SDS unit, it has a buffer built in, as well as providing a volume pot for each channel. At max the gain is
32DB. Rather than dial it down and guess if you have the gain set correctly, you can just sub these pots out for resistors of specific values. It appears that certain brands of resistors do make a difference in sound. If you are using a pre-amplifier, then you want to have at least the lower 27DB of gain, which means you need a 2.2 K-ohm  resistor.

This DB gain factor is from 0 at input to 27DB at output. I'll let the more technically minded give you a further explanation.

So to answer your question, as a summary, if you are using a buffer, then leave the gain at max 32DB. if you are using an active  pre-amplifier, SolidState or Tube, then you need to lower the gain to at least the standard 27DB. Hope this helps.

Now, some have lowered the gain anyway even though they had a buffer, and the sound improved.

Ray Bronk

[Mass. Wine Guy]

Uh, resistors? I thnk I remember what those are from my Vietnam War protest days.

I bought an SDS254 amp. From a photo of the finished amp in a chassis it didn't look like it had volume controls for each channel. I just don't understand the meaning and concept of gain. Isn't it all relative?

[waltsok]

Ha ha, I too was in that era of the Vietnam war.

 I probably misused the word gain in my post. I don't use a passive or active preamp but go directly from my cd player to the amp, so my speakers would not play loud enough for me. That is not a problem with the amp but my peculiar situation where a mismatch existed. Not so with the SDS254 where by using resistors or the supplied potentiometers you can adjust how loud the amp plays in relation to where the preamp volume level sounds best. It balances this using the input of the amp I believe.

[guest1632]

Uh, resistors? I thnk I remember what those are from my Vietnam War protest days.

I bought an SDS254 amp. From a photo of the finished amp in a chassis it didn't look like it had volume controls for each channel. I just don't understand the meaning and concept of gain. Isn't it all relative?

Hi, Well as far as relativity goes, yes, sorta. However, it does come with two separate for each channel volume pots. these can be used to raise and lower the gain of the amplifier. It really depends on your setup. If you are just going to your source item, like a CD/DVD Player, Well, you could use it directly. Personally, I think a preamp is in order. But that's my opinion. The preamp helps to balance out the source components electrically, so they will in theory sound there best.

As far as the gain issue goes, well like I said that depends on your setup. If you are not using an active component, then you might consider getting something like a TVC, which is a passive device. Well, this really needs to go in to another thread. Tell me your setup.

Ray Bronk

[Mass. Wine Guy]

Thanks, everyone. My system is pretty basic.

Arcam CD-72 player
Morrissey ELAD (active) preamp
Silverline Minuet speakers

When the ClassD arrives I'm going to install a Beresford TC-7520 DAC into the mix just to evaluate what it does.

[guest1632]

Thanks, everyone. My system is pretty basic.

Arcam CD-72 player
Morrissey ELAD (active) preamp
Silverline Minuet speakers

When the ClassD arrives I'm going to install a Beresford TC-7520 DAC into the mix just to evaluate what it does.

Then you might want to get some 2.2 K-ohm resistors and not use those pots at all. It would be 2 less holes in your case that you would have to punch. look further up this thread in which wires you use for the two resistors.

Ray Bronk

[srb]

It would be 2 less holes in your case that you would have to punch.

Ray, you would think that, but the majority of builds I have seen in this topic have left the pots and their signal-carrying wires coiled up in the case like antenna inductors.
 
Steve

[Mass. Wine Guy]

I'm afraid that I am totally inept when it comes to performing any kind of mechanical or electrical work. I'll just see how the unit fits in.

[guest1632]

I'm afraid that I am totally inept when it comes to performing any kind of mechanical or electrical work. I'll just see how the unit fits in.

Hi, Well, since this is a kit, and I'm not sure, but I think there is a bit of soldering to do. Not to bad though. you will have to mount the Transformer to the case, and mount the board to the case. If you don't know how to do this, then you will have to find someone locally to do the work for you. I myself have not had the chance to play with one.

Ray

[Mass. Wine Guy]

I bought the amp from someone on our own Trading Post.It's all built, in a chassis and ready to go.

[guest1632]

I bought the amp from someone on our own Trading Post.It's all built, in a chassis and ready to go.

Hi, That's cool. Ok, so if the two volume pots are not mounted, then I would just replace them with fixed resistors of 2.2 K-ohms. You have an active pre-amp, which has gain. From the read I read from the previous pages, fixed resistors do make a difference in sound. Happy listening.

Ray