I think I don't understand the jumper settings. I attached 4 resistors of 4 ohm between each output a,b,c,d and GND. On each input I put a 500mvp-p 1khz signal. Only over the resistor of output b I get ~2 times the input + 450khz switching. Both NE5532's have my input at pin 1 and 7. All voltages 15v, 12v, 3.3v are present.
Hi Boris,
Excellent job of soldering! Looks very clean and neat.
You did the W jumpers correctly. You are missing the input resistors A, B, C, D. Without these installed there is no audio signal going to the amp.
If you want PFFB enabled, use high quality metal thin film 0805 3.7kohm resistors here. If you do not want PFFB then use 0ohm jumpers.
With PFFB enabled you have 15dB gain only and amp maxes out at 75W into 8ohms. Without PFFB (0ohm jumper) you get 22dB gain and 150W max into 8ohms. But I would never use it above 125W for best sound quality.
The feedback resistors go where I concur led in red below.
For quadriphonic (4 ch SE out) you want the dip switches set like this:
This should work now if all your ancillary voltages are present.
Excellent job of soldering! Looks very clean and neat.
You did the W jumpers correctly. You are missing the input resistors A, B, C, D. Without these installed there is no audio signal going to the amp.
If you want PFFB enabled, use high quality metal thin film 0805 3.7kohm resistors here. If you do not want PFFB then use 0ohm jumpers.
With PFFB enabled you have 15dB gain only and amp maxes out at 75W into 8ohms. Without PFFB (0ohm jumper) you get 22dB gain and 150W max into 8ohms. But I would never use it above 125W for best sound quality.
The feedback resistors go where I concur led in red below.
For quadriphonic (4 ch SE out) you want the dip switches set like this:
This should work now if all your ancillary voltages are present.
As long as the output is 12v. I use the +12v from one of the 7812 regulators that’s turned on/off with the power enable. The BtSB I power from the “always on” 12v from the Meanwell AC/DC. @rhing had this done perfectly here: https://www.diyaudio.com/community/...ign-class-d-amp-with-pffb.372379/post-7397565
Note the two different connectors in the side of the SMPS.
Note the two different connectors in the side of the SMPS.
The suggested 12v to 15v dc/dc converter for the BTSB buffer wasn’t available when I built mine, but I saw a few others had same problem and just skipped it and ran 15v directly to it. So that’s why I need 15v for both the BTSB and the amp. It initially sounded like the VDR output was exactly for that purpose but then I saw no one was using it…so now I’m beginning to question whether I can or need to find another solution for running two 15v items off the SMPS630-SO.
I know I can buy the appropriate DC/DC converter from you, but then I can’t listen to the amp this weekend ;-)
I know I can buy the appropriate DC/DC converter from you, but then I can’t listen to the amp this weekend ;-)
Could I work around this by altering R105, R107, R115, R117 to 2k (for ~14db)? I would like to feed the amp directly from a DSP with an output of 2.8v-pp/1vrms.
With 2.83vpp or 1Vrms and 14 dB (5.0x) gain you have 5.0Vrms max output. Power is V^2/R or 25/8 or 3.13Wrms into 8ohms? Is that Ok for you? I don't think so since this is a 75W to 150W capable amp.
I have not checked what you mean to do by changing R115/117/105/107 but assume you are asking to change feedback values on input opamp? You will be deviating from Texas Instruments PFFB recommended network values, so the amp, may or may not work proerply with stability and correct behavior. But this is DIY, so yuo can always try.
I have not checked what you mean to do by changing R115/117/105/107 but assume you are asking to change feedback values on input opamp? You will be deviating from Texas Instruments PFFB recommended network values, so the amp, may or may not work proerply with stability and correct behavior. But this is DIY, so yuo can always try.
Thanks, I read in this PFFB document of TI the gain of the chip itself should be 15.93. As far as I know the opamp pre stage has no influence on the PFFB and thus can be adjusted (a bit). But I'd love to see someone confirm this as I cannot measure the results accurately. I'll give it a try.
The intrinsic gain of TPA3255 is 22dB without PFFB. Rin is 2.7k and Rfb=33k. If you follow the math, this makes the overall gain about 15dB.
Your Oscope shows 12.4v out and 8.4v in.
This is 20x@log(12.4/8.4)=3.4dB. Far from 15dB. I suspect you may have a solder bridge or missing some input or feedback resistors. I see some solder balls/blobs near R193 that could be shorting out. Please check board for shorts or other solder joint anomalies.
Did you assemble the board herself or buy it pre-assembled from me? This looks like your own self-assembled board because mine use Silmic II caps instead of red Wima box caps. Plus, you are missing the 2.7k resistors for all the 4 feedback resistors A/B/C/D.
Without those, the amp will not have 15dB gain per the PFFB document.
Use high quality metal thin film 0805 2.7k ohm resistors here.
Your Oscope shows 12.4v out and 8.4v in.
This is 20x@log(12.4/8.4)=3.4dB. Far from 15dB. I suspect you may have a solder bridge or missing some input or feedback resistors. I see some solder balls/blobs near R193 that could be shorting out. Please check board for shorts or other solder joint anomalies.
Did you assemble the board herself or buy it pre-assembled from me? This looks like your own self-assembled board because mine use Silmic II caps instead of red Wima box caps. Plus, you are missing the 2.7k resistors for all the 4 feedback resistors A/B/C/D.
Without those, the amp will not have 15dB gain per the PFFB document.
Use high quality metal thin film 0805 2.7k ohm resistors here.
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I still have a problem, I checked all resister values in the path, but I get a difference in gain, that is not frequency dependent.
Channel B and C are 10dB,
Channel A and D are ~7.3dB.
The voltage drops after resistor A and after resistor D (~50%), but not after resistor B and C (only ~5%) so that would imply something is drawing current, but I cannot find out what.
Green is input, blue is channel B, red channel A.
View attachment 1240973
Red channel C, blue channel D. (1khz)
Channel B and C are 10dB,
Channel A and D are ~7.3dB.
The voltage drops after resistor A and after resistor D (~50%), but not after resistor B and C (only ~5%) so that would imply something is drawing current, but I cannot find out what.
Green is input, blue is channel B, red channel A.
View attachment 1240973
Red channel C, blue channel D. (1khz)
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