[dewardh]

So given that the new amps have an input buffer built in, would it be superfluous to front end the input of the new class Ds with the Pass B1?

Yes.

[steve k]

Changing amplifier input impedance (or changing polarity) may well have changed "imaging" in your system.  It's hard to tell without knowing the details of your system, the comparison, and how you switched back and forth between the amps to do it.

All that seems to have changed *in the amplifier* is the addition of an input buffer . . . different systems will have different need for and different response to that, and different people will draw different conclusions as to what that means.  My system doesn't need an additional buffer, since my crossover's output buffers can drive the "original" board just fine, and I correct for polarity at the drivers.  Adding a buffer stage would accomplish nothing for me.  I'm glad it helped with your system . . . (did you set the "new" version for normal or inverted polarity?).

The only thing I changed due to the change in input impedance are the two caps in my DAhlquist crossover that set the high frequency cutoff. The cap value is based on the cutoff frequency, and the high/midrange amplifier's input impedance since it is passive. The bass cutoff is active.

You  may want to hear something first before determining  "the sound of the amplifier itself has not changed". That's a bit presumptious.
steve

[mjosef]

I’m not sure if it’s stated explicitly even in the IR Reference Design documentation . . . if it is I missed it.  It is shown in a block diagram (Fig 24, page 20) . . . look at the input and output “signal graphic”:

http://www.irf.com/technical-info/refdesigns/iraudamp7d.pdf

Thanks for posting the pdf link, hadn't seen that before.

[dewardh]

The only thing I changed due to the change in input impedance are the two caps in my DAhlquist crossover that set the high frequency cutoff. The cap value is based on the cutoff frequency, and the high/midrange amplifier's input impedance since it is passive. The bass cutoff is active.

So you potentially changed the frequency response and crossover point if the substitute caps didn't *precisely* match the changed input impedance (and had any effect elsewhere in the circuit).  Did you set the "new" amp to invert polarity like the "old" one does, or was that different as well?  How many times did you switch between amps while making this comparison?  Given all the other changes it's "a bit presumptious" to assume that any change you heard was do to functionally identical amplifiers sounding different.

You  may want to hear something first before determining  "the sound of the amplifier itself has not changed". That's a bit presumptious.

Are you suggesting that something in the amplifier has been changed in addition to adding an input buffer/phase inverter?  Do you have any documentation of that?  I'm sure many in addition to me would like to see a schematic of the new input stage, and especially any changes made in the amplifier itself . . .

[steve k]

Look, its a cheap amp that sounds good. I'm not going to debate the physics. I can't believe how critical some of you people are over a $175 amp! This guy is fixing boards screwed up by "modders" when they're clearly out of warranty and people are bitching about his webstie typos. Hey this isn't Wilson Audio, this is Cheap and Cheerful remember???

This was fun for awhile till all the experts came along and picked it to pieces. Tom told me tonight this is precisely why he doesn't get involved in forums.

I and my friends clearly hear a difference in the imaging of the Super D amp. Tom sent me one to verify this because he heard the difference and wanted some outside verifcation. 

That's all. I don't think I need to justify what Tom, myself and my friends heard to you. Be your own judge, but at least listen to it first.

[Mariusz]

Are you suggesting that something in the amplifier has been changed in addition to adding an input buffer/phase inverter?  Do you have any documentation of that?  I'm sure many in addition to me would like to see a schematic of the new input stage, and especially any changes made in the amplifier itself . . .

I am sure these questions can be directeded to designer/manufacturer himself avoiding plain speculations. 

And, ........ we all appreciate new offerings from the company but can we please stay on the topic that originated this thread!?
As far as the new product goes, Tom is more then welcome to introduce his new amp in "General Audio Industry News" or "Product Support Threads" and answer questions as needed. I am aware of the thread that has been already started in regards to new amp design, so this debate can be finished there or in less desirable place.

Cheers
Mariusz

[wushuliu]

This guy is fixing boards screwed up by "modders" when they're clearly out of warranty

That's a bummer. That's pretty lame for someone to send back a board after tinkering w/ it. That's definitely taking advantage.

I think it's time for a little humor break:






 

[dewardh]

That's a bummer. That's pretty lame for someone to send back a board after tinkering w/ it. That's definitely taking advantage.

Agree completely.  Once you put the soldering iron to it, it's yours.

As for the classDaudio amps . . . they are great . . . cheap and excellent.  If your source can handle the low input impedance get the "original" . . . it's "Cheap and Cheerful".  If you need a higher input impedance and volume control on the amp get the "new" version with an input buffer . . . it's not quite so "Cheap", but it's still "Cheerful".  It's the same amp (IRS2092), but the input buffer might make it sound better *with your system*.

[hasekisgod]

Look, its a cheap amp that sounds good. I'm not going to debate the physics. I can't believe how critical some of you people are over a $175 amp! This guy is fixing boards screwed up by "modders" when they're clearly out of warranty and people are bitching about his webstie typos. Hey this isn't Wilson Audio, this is Cheap and Cheerful remember???

This was fun for awhile till all the experts came along and picked it to pieces. Tom told me tonight this is precisely why he doesn't get involved in forums.

I and my friends clearly hear a difference in the imaging of the Super D amp. Tom sent me one to verify this because he heard the difference and wanted some outside verifcation. 

That's all. I don't think I need to justify what Tom, myself and my friends heard to you. Be your own judge, but at least listen to it first.

I dont think no one is picking it to pieces. He was just explaining the differences between them which I feel he is right. All the amps Tom makes are great, but with the new super people might be better with the buffer/gain adj. for there needs. The output can only putout what you feed it. In your system steve it must be working at its prime now with the added features where before with your other amp it wasnt because you said the soundstage is better now. So something must of been lacking on your system somewhere with matching with your other amp and pre. Matching is so important as you steve can see now with how your system sounds from now and before.

hope that makes sense im Czech so english is so so ha 

[roymail]

Blair Lamphear noted in an earlier post that the original amp (250/4, 125/8) worked quite well with a passive attenuator due to having high gain.

That being the case, why would someone need a buffer?  I'm just asking, not stirring the pot.  I'm still learning.

[srb]

That being the case, why would someone need a buffer?

I'm not sure under which circumstances one might need the better impedance matching of the input buffer, but because these amps seem to have higher gain (32) compared to most of the amps I've owned (26 - 29), the adjustable gain might be helpful because
 
1.  Your preamp has too much gain, so that the volume control has to be used within a very narrow range ?
 
2.  You have very high efficiency speakers, and reducing the gain reduces the background noise ?
 
Steve

[boone]

Greetings,

  I finished (I thought) my amp last week and hooked it up in my system.  I have a one system does all set up. I listen to music with computer and combo player as sources, watch DVD's, and watch TV using the same amps (active xo tri amp set up).  When I fired up the Class D amp which I have hooked up to drive my mid range drivers sound was great but... it really degrades the picture quality on my TV!  Today I'm going to pull it out, pop it open, and install a Felix power conditioner in the case.  Hope that will help.  Any other suggestions would be appreciated.
Almost forgot.. the amp is the 250x2-500x1 kit which I see is now called CDA-254S.

Sincerely
boone

[Mariusz]

I'm not sure under which circumstances one might need the better impedance matching of the input buffer, but because these amps seem to have higher gain (32) compared to most of the amps I've owned (26 - 29), adjustable gain might be helpful because
 
1.  Your preamp has too much gain, so that the volume control has to be used within a very narrow range?
 
2.  You have very high efficiency speakers, and reducing the gain reduces the background noise?
 
Steve

That is exactly my situation.
High efficient speakers etc.

One of the reasons I am STILL hoping to put my hands on one of those Nelson Pass buffers. 

P.S (to all)
we all enjoy constructive conversation/discussion but keep in mind that this is NOT "The Lab Circle" and most who found this kit interesting, love it because it's easy and cheap.
Over-building/over-complicating this project might take some fun away from this thread. It can also discourage some folks from trying out this very simple kit that isn't only simple but cheap and fun. 

Thanks
Mariusz

[roymail]

Am I correct that the amp comes with the 32db gain setting as default but Tom will change it to 26db upon request?  I think I read that somewhere on this thread.

If that's the case, it will work well for me since I use a Goldpoint/Elna stepped attenuator with no gain, of course.

[shadowlight]

Am I correct that the amp comes with the 32db gain setting as default but Tom will change it to 26db upon request?  I think I read that somewhere on this thread.

If that's the case, it will work well for me since I use a Goldpoint/Elna stepped attenuator with no gain, of course.

That is correct.  I had asked Tom to set my gain to 26db.  I believe on the superd you now have a switch to change the gain.

[jtwrace]

I believe on the superd you now have a switch to change the gain.

That is correct. 

It's very important to not forget if you email Tom with a specific gain that you request, he's more then happy to build the other amps with that spec'd gain. 

[wushuliu]

One of the reasons I am STILL hoping to put my hands on one of those Nelson Pass buffers. 

It's comin'! Had to twist some arms to get the seller to send the missing panels...

[srb]

I believe on the superd you now have a switch to change the gain.

The gain adjustment control on the Super D series are variable potentiometers with "conductive plastic element for ultra low noise".  However, the gain range is not mentioned, but "more specs coming soon" is.
 
I did notice on the Super D Series that the Product Description mentioned "Our Super D Series amps provide more life-like imaging and sound stage", for whatever technical reason.
 
Steve

[Mariusz]

It's comin'! Had to twist some arms to get the seller to send the missing panels...

Just say when Wush.

I have changed the idea about the encousure for my D-amp.
Do you or anyone else know a good source (link) for umbilical cord/plugs?

Cheers
Mariusz

[hasekisgod]

That is exactly my situation.
High efficient speakers etc.

One of the reasons I am STILL hoping to put my hands on one of those Nelson Pass buffers. 

P.S (to all)
we all enjoy constructive conversation/discussion but keep in mind that this is NOT "The Lab Circle" and most who found this kit interesting, love it because it's easy and cheap.
Over-building/over-complicating this project might take some fun away from this thread. It can also discourage some folks from trying out this very simple kit that isn't only simple but cheap and fun. 

Thanks
Mariusz

It is all people have to do when they order is first ask tom. If the person dont know what one to get ask him to call you and you can tell him what you have for a system and I bet he will be glade to set you up right. He did that for me and Im very happy. So it gets complicated with others are listening to what someone else has for a system and there are like five different ways to go. The good thing now he has a module for everyone's needs now.