ok a setup question:
im configuring the board for 2.1 operation, but something seems screwy in the instructions.
it states that out a and b are btl for the sub, and c and d are single ended for the stereo.
however, it says to set j19 to "diff" which is the jumper for inputs a and b (sub)
and if using single ended sub input ( i am) to set j4 to SE, but J4 is for channels c and d (single ended stereo channels).
surely this means a and b should be the stereo channels and c/d the BTL sub output?
if so, ive already pulled the soldered jumpers for channels c and d as per instructions, so im a bit stuck/confused.
im configuring the board for 2.1 operation, but something seems screwy in the instructions.
it states that out a and b are btl for the sub, and c and d are single ended for the stereo.
however, it says to set j19 to "diff" which is the jumper for inputs a and b (sub)
and if using single ended sub input ( i am) to set j4 to SE, but J4 is for channels c and d (single ended stereo channels).
surely this means a and b should be the stereo channels and c/d the BTL sub output?
if so, ive already pulled the soldered jumpers for channels c and d as per instructions, so im a bit stuck/confused.
thanks a lot for the clarification.
before powering it up again, could you advise the positions of j6 and j5 (the mode jumpers)
it states that j6 should be low and j5 should be high, but its not clear if these act together to set the overall amp mode, or if one jumper relates to each pair of channels, and if so, which channels.
if its the second case, will i risk breaking stuff if i power up with them the wrong way round?
reassuringly, its actually printed on the pcb that for 2.1 operation j6 should be low and j5 should be high.
before powering it up again, could you advise the positions of j6 and j5 (the mode jumpers)
it states that j6 should be low and j5 should be high, but its not clear if these act together to set the overall amp mode, or if one jumper relates to each pair of channels, and if so, which channels.
if its the second case, will i risk breaking stuff if i power up with them the wrong way round?
reassuringly, its actually printed on the pcb that for 2.1 operation j6 should be low and j5 should be high.
Whereas to me sounds just like the effects I get when adding transformers in-line with amp inputs, most especially classD ones. Which I put down to a decrease in common-mode noise interference. Transformers increase the apparent transparency of classD amps.
ok i think i see where the error is. on the schematic here:
http://www.ti.com/lit/df/slar129a/slar129a.pdf
j4 is shown as the input switcher for channels A and B
and j19 is shown for C and D
however on the PCB they are labelled as the opposite, and their physical locations on the board ( J4 is on the same side of the board as channels C/D, and J19 is on the A/B side) seem to confirm that the PCB is right.
http://www.ti.com/lit/df/slar129a/slar129a.pdf
j4 is shown as the input switcher for channels A and B
and j19 is shown for C and D
however on the PCB they are labelled as the opposite, and their physical locations on the board ( J4 is on the same side of the board as channels C/D, and J19 is on the A/B side) seem to confirm that the PCB is right.
So here’s my big question:
Since I’m a hi fi kind o’ guy I want to keep the distortion under 1%, let’s say 0.5%
And I got two of the boards so have one for each channel.
And probably 250w/ is more than plenty to drive my 2 woofers/ch.
So...do I get a 48v PSU and turn down the volume for these amps?
Or:
Get say a 36v PSU for each amp, and turn down the volume less?
Which gives me better specs?
Since I’m a hi fi kind o’ guy I want to keep the distortion under 1%, let’s say 0.5%
And I got two of the boards so have one for each channel.
And probably 250w/ is more than plenty to drive my 2 woofers/ch.
So...do I get a 48v PSU and turn down the volume for these amps?
Or:
Get say a 36v PSU for each amp, and turn down the volume less?
Which gives me better specs?
If I've understood the application note correctly, you'll need to make up that gain elsewhere, i.e. with an opamp just preceding.
Have a look on pages 17-18 of the EVM documentation, there's all the "DNP"s that are the PFFB implementation. You'd need to adjust the feedback network around the 5532 up front to make up the gain, but, as they say, that has a higher noise than the tpa3255 itself, so you're looking at further modifications, e.g. a lme49720 or the like.
Edit to add: I plan on implementing the PFFB, albeit not replacing the gain. Short-to-midterm, I'm in the same position as Variac and have way too much power/gain hanging around my system, so the reduction in gain from the PFFB is salutary to my overall SNR (it's simply made up by attenuating less). Long-term, I hope to implement a DAC myself, at which point I can design a "fancier" I/V-buffer that contains the extra gain (and buys me stability there).
Have a look on pages 17-18 of the EVM documentation, there's all the "DNP"s that are the PFFB implementation. You'd need to adjust the feedback network around the 5532 up front to make up the gain, but, as they say, that has a higher noise than the tpa3255 itself, so you're looking at further modifications, e.g. a lme49720 or the like.
Edit to add: I plan on implementing the PFFB, albeit not replacing the gain. Short-to-midterm, I'm in the same position as Variac and have way too much power/gain hanging around my system, so the reduction in gain from the PFFB is salutary to my overall SNR (it's simply made up by attenuating less). Long-term, I hope to implement a DAC myself, at which point I can design a "fancier" I/V-buffer that contains the extra gain (and buys me stability there).
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The amp should have a relatively constant gain, so the volume knob setting wouldn't change much with a supply voltage change. You will just hit clipping sooner with the lower voltage. Clipping sounds rather nasty on most class D amps. There are some "smart" systems that attempt to soft limit before clipping is reached, but most of them involve digital inputs.
I have not read the complete part data sheet, or the application note yet, so I don't know if this applies. I plan to use at least 48 volts even though my subwoofer will be on fire long before clipping is reached.
Agreed good doctor, we're definitely down in the smallest of inaudible details (I'd hope done for the fun/challenge of squeezing the last of performance). Just wanted 454casull to know what he's getting into. 
P.S. I'd probably pick the opa 2209 of any of the relatively inexpensive dual bjt-input opamps if I were replacing. But that's long getting neurotic.
P.S. I'd probably pick the opa 2209 of any of the relatively inexpensive dual bjt-input opamps if I were replacing. But that's long getting neurotic.
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ok. ive set up my boards in 2.1 successfully with all my space saving mods applied.
ive tested them and they work fine.. however im surprised by the lack of volume!
im using an old blackberry as my test source, running from the headphone output. ive also tested the bluetooth reciever board which will be built in eventually.
running from an 800w 51v smps, with the phone cranked to maximum, the volume from the speakers is decidedly underwhelming.
my test drivers ( a pair of old 6.5 inch car speakers, and a 600w sub which will be used in the final setup) hardly move.
id also note the little heatsink was barely warm after a few minutes of playing.
id assume this means that the phone has too low an output, however through the bluetooth board too?
i will actually be outputting from a minidsp in the final amp.. i assume that will provide sufficient signal without clipping, to run these amps up to a decent level?
ive tested them and they work fine.. however im surprised by the lack of volume!
im using an old blackberry as my test source, running from the headphone output. ive also tested the bluetooth reciever board which will be built in eventually.
running from an 800w 51v smps, with the phone cranked to maximum, the volume from the speakers is decidedly underwhelming.
my test drivers ( a pair of old 6.5 inch car speakers, and a 600w sub which will be used in the final setup) hardly move.
id also note the little heatsink was barely warm after a few minutes of playing.
id assume this means that the phone has too low an output, however through the bluetooth board too?
i will actually be outputting from a minidsp in the final amp.. i assume that will provide sufficient signal without clipping, to run these amps up to a decent level?
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My main issue is that I have to match the gain to 3 other 2ch amps for the Linkwitz active, multi-amp speakers. The other amps will prob all be the same to avoid this issue, but I didn't feel right using Class A amps for the bass. (or maybe I couldn't afford it, or dont want the heat here in the tropics, or maybe all of the above! )
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