[Barry_NJ]

Wush can you give us some details, you replaced your gain pots with fixed naked Vishays?

Pics??

Nick, I too would like to see what Wushuliu has done, but in case you missed it, this started a few pages back...

http://www.audiocircle.com/index.php?topic=76400.msg852812#msg852812

[wushuliu]

Wush can you give us some details, you replaced your gain pots with fixed naked Vishays?

Pics??

[walkern]

Hey A.C... thanks for the feedback on the naked Vishays.  I've been playing with an assortment of resistors myself and have definitely noticed sonic differences.  Takmans sounded relaxed, smooth and warm. Tantalums (to my surprise) sounded dry, cool and a bit analytical.  Holcos were a dramatic step up in dynamics, clarity, articulation and speed, and also offered the widest soundstage and amazing bass extension and control.  Rikens have been my favorite so far.  Very even tonal balance (a tiny bit warm), excellent ambiance recovery, very 3D soundstage with excellent image focus, and almost as dynamic as the Holcos.  If you are using a tube preamp, the Holcos would give you a little 'solid state' character, and if you are using a solid state preamp the Rikens offer up a little tube character.  So now I'm thinking I've gotta try some naked Vishays and/or some of the top of the line Caddocks.  Are we having fun yet? 

[wushuliu]

I am for sure ! I agree with all the above. Yes, I was surprised by the tantalum sound as well. Definitely not warm and fuzzy. Personal favorite now are the Takman Metal. Perfect combination of metal clarity and carbon warmth. Just a pain to get because I have to go through Partsconnexion.

For some perspective I would also add that the biggest leap was losing the supplied gain pots.

Neil, now that you've mentioned Rikens... hmmmm...

[roymail]

How much do those resistors lessen or lower the output or volume?  Thanks!

[Barry_NJ]

How much do those resistors lessen or lower the output or volume?  Thanks!

It would depend on the value of the resistor. The higher the value, the more it will attenuate the volume. The potentiometer being replaced is nothing more than a variable resistor

[guest1632]

Hey A.C... thanks for the feedback on the naked Vishays.  I've been playing with an assortment of resistors myself and have definitely noticed sonic differences.  Takmans sounded relaxed, smooth and warm. Tantalums (to my surprise) sounded dry, cool and a bit analytical.  Holcos were a dramatic step up in dynamics, clarity, articulation and speed, and also offered the widest soundstage and amazing bass extension and control.  Rikens have been my favorite so far.  Very even tonal balance (a tiny bit warm), excellent ambiance recovery, very 3D soundstage with excellent image focus, and almost as dynamic as the Holcos.  If you are using a tube preamp, the Holcos would give you a little 'solid state' character, and if you are using a solid state preamp the Rikens offer up a little tube character.  So now I'm thinking I've gotta try some naked Vishays and/or some of the top of the line Caddocks.  Are we having fun yet? 

Very interesting. So what value and wattage of resistor did you settle on?

Are you running balanced or unbalanced?

Ray

[Nick77]

Very interesting. So what value and wattage of resistor did you settle on?
 

+1

[roymail]

What values are recommended for zero gain passives like the NP B1 or others?

That's why I was asking about resistors limiting the gain.

For those using active preamps, the resistor value would be greater to lower the output to balance with the pre.

[walkern]

10 Ohms gives you basically as much input sensitivity as you'd get if you left the volume controls in place, and cranked them all the way up.  I've been using values around 5K ohms, and that drops the input sensitivity by about 6 decibels (which works really well with my Pass DCB1).  I've tried 1/2 watt and 3/4 watt and even one 1 watt rated resistor and that doesn't seem to make any difference at all.  I guess I'd suggest using 1/2 watt resistors unless you can't find the impedance value you want at that rating, at which time I'd feel free to go up a bit.

[roymail]

10 Ohms gives you basically as much input sensitivity as you'd get if you left the volume controls in place, and cranked them all the way up.

Thanks Neil, that's what I needed to know... great find! 

[raindance]

Someone please explain to me the following:
1. Is the pot only used as a variable resistor in the SDS?
2. Why should I bother to use any resistor at all when I can use a piece of wire to get max gain?

I recently bought the SDS-254 to try in place of my CDA-254. The results were surprising: 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. When I buffer the volume control with a pair of LME74910 and feed the CDA-254 I get wonderfully extended highs. I haven't tried this with the SDS yet. But what this seems to reveal to me is that the amps have a fairly high input capacitance. This would explain the spread of opinions on the top end extension / roll off that I have seen on this discussion - it all depends on what you feed it with. So far I like the CDA-254 best.

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.

[raindance]

To expand on my post: I am trying to build an integrated using the ClassDaudio amp modules and using a diyclub.biz remote volume kit with input selection to feed it. Dead simple idea, but the 100K pot seems to be a deal breaker without adding additional circuitry.

[raindance]

And to expand just a tad more: The gain pots behave like volume controls in that they adjust between nothing and full gain. I don't see how a single resistor in a feedback loop can set the amp to "not amplify" when its value increases to 10K as it does with the pot used on the SDS.

[roymail]

To expand on my post: I am trying to build an integrated using the ClassDaudio amp modules and using a diyclub.biz remote volume kit with input selection to feed it. Dead simple idea, but the 100K pot seems to be a deal breaker without adding additional circuitry.

With an input impedance of 47K, I'd think a stepped attenuator of 10K or 20K should work well.

[pelliott321]

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? 

[Barry_NJ]

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? 

Wow, that's odd. I've got the CDA-254 that Bill built here for some auditioning, and I wouldn't call it lifeless at all. In my system there's more emphasis in the lower treble than with my Audio Alchemy OM150 amplifier, giving the impression of greater immediacy. But the sound-stage seems a bit larger over all, and I'd say it also sounds more dynamic, with greater difference in volume between soft and loud passages. I also notice no loss of extension at either of the frequency extremes.

The 'S' version you have does have less capacitance in the power supply, which could effect the sound. Why did you opt for the smaller power supply? There are discussions in this thread about he benefits of upgrading (adding capacitance to) the standard power supply, so I imagine that down-grading the PS, as you did, could have negative effects on the sound(?)

Regarding the out-put power, just to be clear, it's 250 wpc into 4 Ohms and only 125 wpc into 8 Ohms.

[Nick77]

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 Barry is certainly on to something concerning the PS, not only does the S model have the lower profile PS with less capactance but the kit comes with smaller transformer. I would contact Tom and see if its possible to get the L model.

[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?

"It is totally lifeless.  no freq extension either way."

I don't think using the smaller power supply would kill the performance of this amp, but the increased capacitance apparently steps up the dynamics.

There must be something else going on here.  Contact Tom, he may need to take a look at it or advise you in some way.

An amp that is "totally lifeless with no frequency extension" would not garner over 100 pages of interest.

[raindance]

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?

Disregard the stuff about the power supply. That is not the problem. The problem is, what I have been talking about all along, impedance matching. What are you driving the amp with? The only way to get frequency extension and liveliness out of the CDA series is with a low impedance driving source, such as a solid state preamp or solid state buffered volume control. PM me if you need help.

Later on, when you want more slam at high volume, just add some more caps to the power supply.