I pulled this chip form some scrap electronics some time ago an now I need to build a small stereo amplifier so I thought I'd give this chip a go. I took a look at the datasheet and saw that when used in stereo, one of the inputs is an inverting input and the other channel is a non-inverting input. What difference is this going to make between the two channels? Is it even real stereo?
Here is the service manual HTTP 301 This page has been moved
Here is the service manual HTTP 301 This page has been moved
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Running the amp channels out of phase makes better use of the power supply in an unbridged configuration - just reverse the speaker connections to one of the outputs.
This chip isn't the usual type of opamp inside where a different circuit has to be used for inverting vs non-inverting. Rather it looks to be based on the Barrie Gilbert 'Active Feedback Amplifier'. You can learn more by looking at the DS for the AD830.
This chip isn't the usual type of opamp inside where a different circuit has to be used for inverting vs non-inverting. Rather it looks to be based on the Barrie Gilbert 'Active Feedback Amplifier'. You can learn more by looking at the DS for the AD830.
Thanks for the info, I appreciate it. I'll build this thing when I have time, meanwhile I'm going to modify the schematic a bit. The outputs in stereo have a bit of an odd connection method. Left and right speakers have their - terminals connected together, and then that common - terminal is grounded through a 1000uF cap. Can I just put 1000uF caps on the outputs, then connect speakers and then connect speaker - terminals to ground? Ya know, like the usual chip amp configuration. Also, I'm bypassing the output electros with .22 uF film caps.
You certainly can do that - I'm guessing they wanted to reduce cost and board space by using only one cap, figuring that the bass was out of phase so the 'virtual ground' would be held in place at low freqs by the relative balance of bass in the L and R channels. Going to two separate caps I'd up the value to at least 3300uF for decent bass. The voltage rating for these caps only needs to be 10V (around half the total supply).
What about using the same 1000uF output caps but using a bigger power reservoir capacitors, I could use two 16v caps that I have left over, one 10000uF and one 15000uF. I just don't know if I can find two 3300uf identical caps, as this amplifier will be built from parts bin leftovers. I do remember having a bunch of Rubycon MCZ 16V 1800uF capacitors that I have for motherboard repairs, so I can just throw those into the circuit.
Also, what about grounding the signal ground through a 10 ohm resistor? I read that someone who had a TDA1517 or 1519 amp did this to avoid ground loops.
Also, what about grounding the signal ground through a 10 ohm resistor? I read that someone who had a TDA1517 or 1519 amp did this to avoid ground loops.
Definitely throw all the spare caps you have onto the rails - can never have too much there. Use the 1800uF Rubys if you have nothing closer to 3300uF.
As for grounding its a system thing - without knowing details of the grounding of your source and any other components sharing the same ground plus details of the amp's power supply I won't make a comment
Best thing to do is try it and see.
As for grounding its a system thing - without knowing details of the grounding of your source and any other components sharing the same ground plus details of the amp's power supply I won't make a comment
Best thing to do is try it and see.That's what I was thinking. And would .22uF be enough bypass?
Thank you both for your help!
Hello again!
I finally got around to building it. I used a 10000uF power filter capacitor, bypassed by a 470nF film, 10V 3300uF Panasonic FC output capacitors, bypassed by 220nF film capacitors. For input coupling I used two 470nF film capacitors and a 220uF ripple rejection cap.
Using an ATX PSU to power it. It gives a high pitch whine through the speakers, but it's an SMPS, so that's typical. Test speakers are B&W DM310.
SQ can be best described with a simple three letter word: meh. Lacking bass and depth, not much detail and very "dry" sound, my beautiful B&Ws sound like computer speakers with this amplifier.
It does have a fair amount of power for a small IC, but sound really is sub par.
What to do now?
I finally got around to building it. I used a 10000uF power filter capacitor, bypassed by a 470nF film, 10V 3300uF Panasonic FC output capacitors, bypassed by 220nF film capacitors. For input coupling I used two 470nF film capacitors and a 220uF ripple rejection cap.
Using an ATX PSU to power it. It gives a high pitch whine through the speakers, but it's an SMPS, so that's typical. Test speakers are B&W DM310.
SQ can be best described with a simple three letter word: meh. Lacking bass and depth, not much detail and very "dry" sound, my beautiful B&Ws sound like computer speakers with this amplifier.
It does have a fair amount of power for a small IC, but sound really is sub par.
What to do now?
The switching PSU is putting too much hash on the rail - if you want better sound you'll need to filter this out. I've used LC (passive) filtering with good effect. Get some Sendust toroidal cores (the 20mm diameter size) and start winding....
You also probably are having problems with common-mode noise, this is much harder to fix. Try with a linear supply to see how it sounds.
You also probably are having problems with common-mode noise, this is much harder to fix. Try with a linear supply to see how it sounds.
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