Truepath build questions HELP!!

[foreverzer0]

1. Q305- Transistor GP PNP SOT23
Q303- MOSFET N-sh SS 115 mA

* both of these transistors are in Bag 10 and they look identical. The marking on the chips are so tiny that I cannot telll which chip is a PNP and which is NPN. Please advise on how to identify these devices to place on the board.

2. We are buidling a 10A Amplifier, we accidentally solder 12K ohm for R106, R109, R206, and R209 - Is that ok?

3. Same with R100, and R200, R101 and R201, we used 47k ohm. Is that ok?
Will these values affect the quality of the amplifier?
[?]

[BddB]

Q305 (MMBT3906, PNP) has marking 7B* acc. to Philips datasheet.
* = p: made in Hong Kong.
* = t: made in Malaysia.

Manufact: Marking
SGS: 36
COMCHIP: -
GEN.SEM: 2A
TRANSYS: K3N, R2A
INFINEON: s2A
MICROSEMI: 2A
ZOWIE: 2A
ST: 36
VISHAY: 2A
FAIRCHILD: 2A
NATIONAL: 2A
PHILIPS: 7Bp, 7Bt
MCC: 2A
DIODES: K3N

I would use the correct values for the resistors.
/B

[thomaseliot]

On Q305 you would read "2A" and on Q303 "3A"

Tim (Audiophool) did following drawing with components in the kit:

http://picasaweb.google.com/zxeter/TruepathTestingPhotos/photo?authkey=VFRTDl1lDKM#5157820776076025810

[V-bro]

I posted them before too, but removed them to get space back on my free online photo album....
So now I posted it at DIYaudio.com....naughty me....
http://www.diyaudio.com/forums/attachment.php?s=&postid=1471962&stamp=1206993292

------X-max. can be several meters on any driver, too bad it can be done only once...------

[foreverzer0]

I think I got that now, thanks.

Now I want to ask, how do I attach everything between the FETs and the Heatsink, including the insulator and thermal pads/pastes. Do I buy extra for the regulator? Also, how is the heatsink and everything mounted? Last question is what size of screws/bolts are good fitments for these boards and insulators?

[foreverzer0]

There's some more build questions that I would really appreciate if they can be addressed, please. Here they are:

1. The supplied voltage that we are using for Truepath is +/- 35 V for VPP and VNN. Are the voltages coming from the voltage regulator similar to the the one shown from the instruction (10V and 5V)?

2. Our amplifier has 2 inputs and 2 outputs, but we will be using one input amplifier. How should we combine the channels into one? Do we just short either one of the inputs and outputs?

3. If I want to measure the frequency response of the Truepath, what is my expected result? Let's say I apply 1 V sinusoidal signal to the input, I will get 10V as my gain (since this is a 10Amp). When I vary the frequency, should I expect this to be a low pass, high pass...?

4. Does anybody know how to measure Total Harmonic Distortion (THD)?

5. If I want to measure noise, should I place the oscilloscope probe at the output node? Where is the best place to probe?

[BddB]

quote:<i]Originally posted by foreverzer0[/i]

There's some more build questions that I would really appreciate if they can be addressed, please. Here they are:

1. The supplied voltage that we are using for Truepath is +/- 35 V for VPP and VNN. Are the voltages coming from the voltage regulator similar to the the one shown from the instruction (10V and 5V)?

2. Our amplifier has 2 inputs and 2 outputs, but we will be using one input amplifier. How should we combine the channels into one? Do we just short either one of the inputs and outputs?

3. If I want to measure the frequency response of the Truepath, what is my expected result? Let's say I apply 1 V sinusoidal signal to the input, I will get 10V as my gain (since this is a 10Amp). When I vary the frequency, should I expect this to be a low pass, high pass...?

4. Does anybody know how to measure Total Harmonic Distortion (THD)?

5. If I want to measure noise, should I place the oscilloscope probe at the output node? Where is the best place to probe?



1. The VDD and VNN voltages do not need to be regulated. (Although, regulation does not worsen performance, most probably the opposite, but 35V is out of range to use LM317)
The analogue voltage (+5V) OTOH needs to be regulated and rock solid for best performance.
The same goes for 10V.

2. It seems that bridging the Truepath would solve the problem. This is not the normal usage for Truepath and not prepared for in the kit. But it can be done and you find the description in the datasheets. (TA3020.pdf, RB-TA3020.pdf and "Input stage" in BRBTA3020.pdf)
If just one channel is used, the [u]input</u> of the other channel should be shorted. I'm not quite sure if it's better to add a dummyload to that other channel or if this could be left open. Perhaps someone else on this forum have an experience?

3,4 & 5
Measuring performance on a switching amplifier is different compared to other amps.
You need to suppress the "out of band" artifacts, that for sure will degrade the measurements.

From TA3020-datasheet:
[u]Performance Measurements of a TA3020 Amplifier</u>
Tripath amplifiers operate by modulating the input signal with a high-frequency switching pattern. This signal is sent through a low-pass filter (external to the TA3020) that demodulates it to recover an amplified version of the audio input. The frequency of the switching pattern is spread spectrum and typically varies between 200kHz and 1.5MHz, which is well above the 20Hz #8211; 22kHz audio band. The pattern itself does not alter or distort the audio input signal but it does introduce some inaudible noise components.

The measurements of certain performance parameters, particularly those that have anything to do with noise, like THD+N, are significantly affected by the design of the low-pass filter used on the output of the TA3020 and also the bandwidth setting of the measurement instrument used. Unless the filter has a very sharp roll-off just past the audio band or the bandwidth of the measurement instrument ends there, some of the inaudible noise components introduced by the Tripath amplifier switching pattern will get integrated into the measurement, degrading it.

Tripath amplifiers do not require large multi-pole filters to achieve excellent performance in listening tests, usually a more critical factor than performance measurements. Though using a multi-pole filter may remove high-frequency noise and improve THD+N type measurements (when they are made with wide-bandwidth measuring equipment), these same filters can increase distortion due to inductor non-linearity. Multi-pole filters require relatively large inductors, and inductor non-linearity increases with inductor value.

Cheers
/B