[steve k]

That's a great idea. I'm curious to hear what the buffer does myself. I agree about the transparency. In my experience, the Class D amps are very sensitive to changing interconnects, power cords and even types of internal wiring.
steve

[earplay]

Maybe once my build is done we can do what Audiokarma (aptly) does for some gear and send it around to different people to try out w/ their own classdaudio amps and pres and report back (it's light and should easily fit in a Priority medium flat rate box).

I would be glad for an opportunity to hear the amp on tour. The reason being that, over the past three years, I bought several amps that were highly touted in the audio press and in forums, including tripaths and tubes. I no longer have any of those amps because my 25 year old Cary 807 surpassed them by far. In other words, I've misspent my meager audio budget, several times, and I do not want to repeat that unsound exercise.

[mjosef]

This thread has me thinking of trying the 600W module, mainly since its touted as stable into 2ohms, and my bass section is just under 4ohms. Plus I have found that there is no substitute for power when it comes to bass. I currently biamp, with a crossover point @ 320Hz.

[jtsnead]

I would be glad for an opportunity to hear the amp on tour. The reason being that, over the past three years, I bought several amps that were highly touted in the audio press and in forums, including tripaths and tubes. I no longer have any of those amps because my 25 year old Cary 807 surpassed them by far. In other words, I've misspent my meager audio budget, several times, and I do not want to repeat that unsound exercise.

See Niteshade post of "amplifier tour", they have one based on the ClassDamp design that they are sending out on tour

[srb]

When I asked Tom at Class D Audio to compare the TI amp to the IR amp as far as sound quality, the reply was:
 
"The 600W amp is the TI chip and sonic quality is not as good as our other amps with the IR chip. Our IR based amps are some of the finest sounding audio amplifiers on the market today. The TI rating of 600W is actually at 10% distortion, so our 250W X 2 4 ohm, 500W X 1 8 ohm is actually rated full power at 1% so actually are more powerful. Our IR based amps are more powerful than people think and all are surprised when they listen to them. The actual distortion levels of these amps through almost all of the power range is more like .006%.... very good!"

Steve

[jtwrace]

When I asked Tom at Class D Audio to compare the TI amp to the IR amp as far as sound quality, the reply was:
 
"The 600W amp is the TI chip and sonic quality is not as good as our other amps with the IR chip. Our IR based amps are some of the finest sounding audio amplifiers on the market today. The TI rating of 600W is actually at 10% distortion, so our 250W X 2 4 ohm, 500W X 1 8 ohm is actually rated full power at 1% so actually are more powerful. Our IR based amps are more powerful than people think and all are surprised when they listen to them. The actual distortion levels of these amps through almost all of the power range is more like .006%.... very good!"

Steve

Being an owner of both amps I'd agree with his statement.

[srb]

So it would seem the only reason one might choose the TI amp is to either drive a load of 2 ohms to 4 ohms in stereo mode or a 4 ohm load in bridged mode?
 
The description says "with a power stage designed to drive 2-Ω to 8-Ω speakers at up to 300 W per channel in stereo, or up to 600W bridged".
 
It doesn't mention the impedance range in bridged mode, but I would assume that it would be limited to 4 ohms in bridged mode, whereas the IR-based amps would be limited to 8 ohms in bridged mode?
 
Steve

[shadowlight]

This thread has me thinking of trying the 600W module, mainly since its touted as stable into 2ohms, and my bass section is just under 4ohms. Plus I have found that there is no substitute for power when it comes to bass. I currently biamp, with a crossover point @ 320Hz.

Martin,

Let me know if you want to borrow the 250x2 amp to try out.

[bprice2]

The Primary Election in Texas is over and my client won.  Now I get to move on to the really exciting stuff when my extra parts arrive...probably on Friday. 

Anyway, here's what I have so far and I'm looking forward to wiring this puppy up and hearing what it sounds like.

[Nick77]

Looks awesome, i think you will be impressed. Are you still running the single driver speaks? 

[ebag4]

The Primary Election in Texas is over and my client won.  Now I get to move on to the really exciting stuff when my extra parts arrive...probably on Friday. 

Anyway, here's what I have so far and I'm looking forward to wiring this puppy up and hearing what it sounds like.

I don't think you will be dissapointed.  I have about 90 hrs on my 120x2 and it is sounding sweet!

Best,
Ed

[bprice2]

Looks awesome, i think you will be impressed. Are you still running the single driver speaks? 

Yep, still have the Omega Bipoles and am really looking forward to what a little extra power might do.  Running them like I do, in bipole mode, will produce an 8 ohm load, which will double the 30 wpc I now have with the Sig 30.

I don't remember exactly what my system comprised of when last we spoke, but now it's a Bolder modified Squeezebox III into a Burson buffer, to a Mapletree pre, to the RWA Sig 30 and out to the Omegas.  I think with the buffer and the pre I'm going to have some latitude in setting this amp up to perform at its best...at least I hope so. 

[jtwrace]

So it would seem the only reason one might choose the TI amp is to either drive a load of 2 ohms to 4 ohms in stereo mode or a 4 ohm load in bridged mode?
 
The description says "with a power stage designed to drive 2-Ω to 8-Ω speakers at up to 300 W per channel in stereo, or up to 600W bridged".
 
It doesn't mention the impedance range in bridged mode, but I would assume that it would be limited to 4 ohms in bridged mode, whereas the IR-based amps would be limited to 8 ohms in bridged mode?
 
Steve

maybe this will help (from Tom)

The TI amp is a completely different configuration. The chip is actually 4 amps, so in stereo mode it’s actually 2 amps running in bridge mode, which actually quadruples the power rating from one amp, and when you put it into parallel bridged mode, it doubles again. The TI amp can run low loads from 2 ohm and up in stereo or bridged mode. The IR amps… other than our highest power one can also run 4 ohm in bridged mode with no problems. The power won’t double to 1000W at 4 ohm in bridged mode due to current limiting protection circuitry. The parts just aren’t made to run 1000W, but still very powerful.

[steve k]

I'm the one that originally mentioned the 3k input impedance in this thread. The measurements from which I derived that input impedance are on page 13, and I'm quite certain the input impedance of my amp is ~3k ohm. Also, as wushuliu stated, 3k is the value given in the spec sheet for the amp (also posted by me on page 13), and others on diyaudio have stated the input impedance is 3k. I would be very curious to see Tom's measurements demonstrating an input impedance of 45 k or to know if he's made changes to the amp since I ordered mine.

To clarify this, I asked Tom and he indicated he has modified the input impedance on his amps to be more compatible with more preamps on the market. It is indeed now 45K ohms. Here's a quote from Tom:

"I’ve modified the input impedance to 45K. Also lowered the gain. I’m trying to make them more compatible with all equipment. They’ve always worked with almost all preamps, but a few had had problems, so I make changes when necessary to always try to improve them. The sound quality has not changed, and it’s something most would never notice, unless of course they were one of the few that had a preamp mismatch."

steve

[gitarretyp]

Thank you for clarifying the impedance issue.

[poseidonsvoice]

To clarify this, I asked Tom and he indicated he has modified the input impedance on his amps to be more compatible with more preamps on the market. It is indeed now 45K ohms. Here's a quote from Tom:

"I’ve modified the input impedance to 45K. Also lowered the gain. I’m trying to make them more compatible with all equipment. They’ve always worked with almost all preamps, but a few had had problems, so I make changes when necessary to always try to improve them. The sound quality has not changed, and it’s something most would never notice, unless of course they were one of the few that had a preamp mismatch."

steve

Strong work. 45K will be far more compatible with nearly anything for that matter. Still, it would be nice to see the actual measurement as gitarretyp had noted. I'm glad that Tom is flexible with his amps. Perhaps he'll post this on his website when he has some time.

Anand.

[dewardh]

To clarify this, I asked Tom and he indicated he has modified the input impedance on his amps to be more compatible with more preamps on the market. It is indeed now 45K ohms.

I received my third 120x2 board just a couple days ago . . . its input is configured the same as the previous boards received.  Rin is 4k Ohms on all the boards.  It is not obvious how that could be significantly changed, since Rf/Rin determines overall gain, and Rf (100k in the 120x2 board) is constrained by the needs of the input integrator.  The obvious "solution" is to add a unity gain buffer (like the unity gain inverter used on channel 2 in bridge mode), and perhaps that will appear on a new board revision.  As of two or three days ago, however, the input impedance of boards delivered was not 45k Ohms.

Perhaps you can ask Tom exactly what he has changed?  The boards I have follow the IR reference amp almost exactly (although layout is different to accomodate the smds, and part numbers are changed, which makes circuit tracing more difficult).  If there is going to be new input circuitry it would be nice if it were documented . . .

I should note that the nominal gain of my boards is 24, and the equivalent IR reference amp has a Rin of 3.3k Ohms and a nominal gain of 30.

[pardales]

Anyone put a volume pot on theirs?

[steve k]

Perhaps you can ask Tom exactly what he has changed?  The boards I have follow the IR reference amp almost exactly (although layout is different to accomodate the smds, and part numbers are changed, which makes circuit tracing more difficult).  If there is going to be new input circuitry it would be nice if it were documented . . .

I should note that the nominal gain of my boards is 24, and the equivalent IR reference amp has a Rin of 3.3k Ohms and a nominal gain of 30.

I suggest you ask Tom this directly. He's very responsive to emails.
steve

[pumpkinman]

I'm very pleased with my amp so I'm going to build a case from scratch I will have help from the sheet metal shop




Since Pumpkins rule there will have to be some orange included in this project