T3 stereo 300W amplifer board

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hifimediy

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Joined 2009
Hi all.
I got the PCB yesterday and it took me 2 hours to finish to solder work. Now here it is.
 

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Saturnus

Saturnus

Member
Joined 2005
Looks great hifimediy.

One comment though. I still don't understand why you (and other designers) place the output chip, and thereby the heatsink, on the component side of the PCB instead of the more natural bottom side so that it would be much easier to bolt onto a heatsink.
 
H

hifimediy

Member
Joined 2009
Saturnus said:
Looks great hifimediy.

One comment though. I still don't understand why you (and other designers) place the output chip, and thereby the heatsink, on the component side of the PCB instead of the more natural bottom side so that it would be much easier to bolt onto a heatsink.
Click to expand...

On the T3 mono version, we put output chip on the bottom side of pcb. That just depend on design.
 
A

alkasar

Member
Joined 2009
Hello,
so here it is :) excellent news.

tell us more
- i see 3 power terminals. Do I understand correctly that this board can be powered by AC dual voltage transformer or DC single voltage ?
- does it have external on/off control same as you have on T4 (PWR down connector) ?
- did you use the tripath output filter topology (like on T2) or the ST topology (like T3) ?
- have you already measured the board THD / IMD. How does it sound ? what is the gain setting on this board ?

Thanks
 
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T

trevmar

Member
Joined 2011
hifimediy said:
yes, we have some SMT parts for filter very close to the chip.
Click to expand...
When testing the new SURE TDA7498 board, I found their SMT ceramic caps for the output filter were the cause of excessive harmonic distortion, which cleared up when I replaced them with poly film. I know that it is customary to use ceramic SMT for the less critical components in the filter network, but is this really a good idea in an audiophile-quality product? Have you checked the harmonic distortion in the 1-20KHz region using both SMT and film capacitors?
.
 
Saturnus

Saturnus

Member
Joined 2005
trevmar said:
I know that it is customary to use ceramic SMT for the less critical components in the filter network, but is this really a good idea in an audiophile-quality product? Have you checked the harmonic distortion in the 1-20KHz region using both SMT and film capacitors?
.
Click to expand...

Maybe it's SMD poly caps? :D Ceramic caps certainly have no place in an audiophile product, especially not in the output filter.
 
nigelwright7557

nigelwright7557

Member
Joined 2008
murtonpikesystems.co.uk
trevmar said:
Looks like a nice, clean, board :)

I see a 680nF output cap, and two 100nF Zobel caps. Are they enough to critically damp the output inductor?
.
Click to expand...

There is uusally some residual carrier on the output.
This isnt a problem as the carrier frequency is way above what the speaker can reproduce.
My IRS2092 design has 10 volts carrier on the output. Adding to teh filter usually ends up with losing top end audio.
 
T

trevmar

Member
Joined 2011
nigelwright7557 said:
My IRS2092 design has 10 volts carrier on the output. Adding to the filter usually ends up with losing top end audio.
Click to expand...

Actually, I was looking at the output LCR values, and noting that with a 4 ohm load, a 680nf capacitor would give critical damping only with a total 11 uH inductor (two 5.5 uH coils) and a 58Khz cutoff frequency. Further, I noted that the two 100nF Zobel caps account for only about 1/13 of the effective total output cap value, which wouldn't seem to lead to very much Zobel damping :) A good filter design should ensure you don't end up losing top-end audio :)
.
 
J

jaistanley

Member
Joined 2005
This is good news.. I am still looking for a nice sounding amp for my stereo subs. Unfortunately they are 8 ohm. Can this be bridged into 8 ohms? I suspect not because of the topology.

I was previously looking at stereo T3 V1's but hopefully this will be just as good but cheaper because of the single power supply...

Jai
 
H

hifimediy

Member
Joined 2009
alkasar said:
Hello,
so here it is :) excellent news.

tell us more
- i see 3 power terminals. Do I understand correctly that this board can be powered by AC dual voltage transformer or DC single voltage ?
- does it have external on/off control same as you have on T4 (PWR down connector) ?
- did you use the tripath output filter topology (like on T2) or the ST topology (like T3) ?
- have you already measured the board THD / IMD. How does it sound ? what is the gain setting on this board ?

Thanks
Click to expand...
Hi Alain.
T3 V2 has similar PSU circuit as T4, so it accept AC/DC as you said. And It has Mute control port which will also power down the amplifier, also turn off the relays.
This board use ST's filter. There are some SMT component near the output chip, which is also according to the application notes. Beside, T3 mono version also use same sch, so no need to worry about the quality.
I think THD/IMD is similar to our other board, and I'm still working on the testing.
The gain is fixed to 25x(+28dB). The reason I didn't include the gain setting part in is it may be not good to the amplifier, what I'm doing now is make input circuit as simple as possible. And I can easily use a Volume controller to work with the amplifier.
 
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