Bootstrap snubber is 330pF and 10R. The 220nF probably let too much current through - possibly a virtual short at 400kHz.
Hi guys, I'll re-check my ratings on the caps I'm using on the underside of the board, it's quite possible I have got the wrong parts.
Thank you for your prompt replies, I want to nail this update and then progress to the Cine-Mags (which I'm not entirely sure how to wire up), I'm guessing with PBTL I'm only going to use one Cine-Mag per board?
Thank you for your prompt replies, I want to nail this update and then progress to the Cine-Mags (which I'm not entirely sure how to wire up), I'm guessing with PBTL I'm only going to use one Cine-Mag per board?
Hi,
I bought this board for the anti-pop feature but... it doesn't work 😡
I still hear the noise when I turn my PC USB soundcard on/off. Any idea?
I bought this board for the anti-pop feature but... it doesn't work 😡
I still hear the noise when I turn my PC USB soundcard on/off. Any idea?
The "Anti-Pop" is for power-up/down the board so it doesn't work for external sources. To avoid this, the amp needs to be in shutdown first, then power-up/down your USB.
Doesn't seem that this board got a connector for shutdown functionality actually so rework is needed or you just power of the amp first.
try to ground the Ground of the signal to chassis.
for psu no grounding. Try that and see
I have 2 of these board stuffed together close each other in pbtl mode with 2 giant 4 amps traffo in one small case and no noise and pops at all. Dead silent and sounds spectacular...
Those smd parts near the input terminal are the anti pop circuit. I once avoid that and make direct connection to the TPA input let and it pops but after using the terminal pops gone...
Re: what is the proper way to ground the chassis, given that the PSU is in a separate box?
As I mentioned before, the whine/squeal (high-pitched noise) I was experiencing is fixed either by leaving the input ground open, or coupling it to the transformer center tap with a 1uF capacitor.
Also, Sharpi31 confirmed in a PM to me that he left the input ground open in his build with the Lundahl transformers.
My test speakers are pretty low in sensitivity. I did another test run on higher-sensitivity speakers, and noticed there is a hum (low-pitched noise) that scales with volume. (The hum is there on the low-sensitivity speakers too, just not as noticeable.)
I also put a 10k stepped attenuator in-between the RCA jacks and the transformer primaries. I used the same kind of attenuator (though 50k) on my Gmarsh Wiener build, and it has no hum at any volume. (But there I'm not using an input transformer, and the PSU is in the same case as the amp PCB, so I have a "true" earth... completely different build in other words.)
I suspect there's a ground loop in there somewhere, though I'm not sure where. I guess it could also be the transformers themselves picking up some noise---they don't have a fancy mu-metal shield case like more expensive transformers (Jensen, Lundahl, Cinemag).
My next steps are to experiment with wiring the transformers the way Sharpi31 did, i.e. per the Lundahl suggested application, with the RC circuit and transformer taps jumpered. I might also play with coupling signal ground to DC ground... or any other suggestions I get here!
As I mentioned before, the whine/squeal (high-pitched noise) I was experiencing is fixed either by leaving the input ground open, or coupling it to the transformer center tap with a 1uF capacitor.
Also, Sharpi31 confirmed in a PM to me that he left the input ground open in his build with the Lundahl transformers.
My test speakers are pretty low in sensitivity. I did another test run on higher-sensitivity speakers, and noticed there is a hum (low-pitched noise) that scales with volume. (The hum is there on the low-sensitivity speakers too, just not as noticeable.)
I also put a 10k stepped attenuator in-between the RCA jacks and the transformer primaries. I used the same kind of attenuator (though 50k) on my Gmarsh Wiener build, and it has no hum at any volume. (But there I'm not using an input transformer, and the PSU is in the same case as the amp PCB, so I have a "true" earth... completely different build in other words.)
I suspect there's a ground loop in there somewhere, though I'm not sure where. I guess it could also be the transformers themselves picking up some noise---they don't have a fancy mu-metal shield case like more expensive transformers (Jensen, Lundahl, Cinemag).
My next steps are to experiment with wiring the transformers the way Sharpi31 did, i.e. per the Lundahl suggested application, with the RC circuit and transformer taps jumpered. I might also play with coupling signal ground to DC ground... or any other suggestions I get here!
Thanks irribeo. I see a reference there to an LL-something transformer, so I assume you got that from a Lundahl application note. And to me it looks very similar to what Sharpi31 did with his LL1540s, but without the RC circuit (1nF + 22kR) between the amp-side signal inputs.
But where it differs from Sharpi's implementation is that the input signal ground is tied to chassis/earth, where Sharpi left input signal ground open. His argument is that the tpa3116 signal inputs have a 3V bias on them, and grounding the signal input might affect that. I don't have enough knowledge to argue that either way, so I defer to the expertise of the community. 🙂
As I've mentioned, I do know that a straight short between transformer center tap and input signal ground will cause the high-pitched squealing noise (in my case anyway; I'm using Edcors not Lundahls, but making the assumption that they are fundamentally the same).
Sharpi wired the LL's as in app noite for balanced symmetrical inputs, not really what you doing nor what he did. Also like he wrote and I said, he didn't leave gnd open, his standoffs are connected to gnd connection ampboard, no such thing on your dugs.
yJ build
Hi chaps, I have now managed to finish a couple of the mods on my PBTL mono boards.
They are now burning in with 18vdc per channel from three 6vdc SLA Batteries in series for each Monoblock.
I have set the gain at 20db with just R2 running a 5.6k Resistor, that keeps the hum down to sensible levels at idle
Maybe someone can advise me on the appropriate Input Coupling Capacitor values (currently got Wima 1.0uf)
Using Panasonic Oscons for main power caps
Finally figured out the Bootstrap Snubber values
My speakers are 100db and my Lowthers in them are 16ohm with Silver Voice Coils
I recently built a Transcendent Sound Masterpiece Preamp for the Pre-duty and I run a simple CD source
I am planning on ordering the Cine-Mags to use with these, I'm guessing the CMLI-15/5B Transformers are the correct ones to use?
Not too clued-up on how to wire the Cine's once they arrive, but maybe someone can advise me what to do.
Thanks to the members for the initiative to make me even consider using these pretty impressive little amps.
Hi chaps, I have now managed to finish a couple of the mods on my PBTL mono boards.
They are now burning in with 18vdc per channel from three 6vdc SLA Batteries in series for each Monoblock.
I have set the gain at 20db with just R2 running a 5.6k Resistor, that keeps the hum down to sensible levels at idle
Maybe someone can advise me on the appropriate Input Coupling Capacitor values (currently got Wima 1.0uf)
Using Panasonic Oscons for main power caps
Finally figured out the Bootstrap Snubber values
My speakers are 100db and my Lowthers in them are 16ohm with Silver Voice Coils
I recently built a Transcendent Sound Masterpiece Preamp for the Pre-duty and I run a simple CD source
I am planning on ordering the Cine-Mags to use with these, I'm guessing the CMLI-15/5B Transformers are the correct ones to use?
Not too clued-up on how to wire the Cine's once they arrive, but maybe someone can advise me what to do.
Thanks to the members for the initiative to make me even consider using these pretty impressive little amps.
I believe I am trying to do exactly what he did. The fundamental goal here is to use the balanced inputs of the tpa3116 chip. Doing unbalanced to balanced conversion, as well as DC-blocking and input isloation, is a typical application of 1:1 line-level transformers.
Now, am I doing it right? That's open to debate. 😕
When I said he left ground open, I was specifically referring to the input signal ground. Ultimately I guess all grounds are the same, so I think we're both right. But my point was that the connection on his amp board where the RCA ground typically goes he didn't explicitly connect it to anything... but yes, that input ground implicitly ties into the board ground, which in turn connects to the standoffs, which in turn connect to the chassis, which is tied to earth.
I am doing something similar, in that my input signal ground is "open", i.e., I didn't explicitly tie it to anything. But my DMM says the input ground is implicitly tied to the DC ground. I don't have a true earth in my chassis, since the PSU is in a separate box, so I'm guessing DC 0V will have to suffice for ground.
Anyway. I made some progress on the hum issue. That was by putting a jumper between pins 2 and 3 (CT and input NEG, respectively) on the primary side of the transformer. At least this fixed the hum on my low-sensitivity test speakers.
I took the rig to my other speakers, turned in on, hum still there. In this arrangement, I had the Astron power supply sitting on top of the amp chassis. Thinking maybe my jumpers came loose, I moved the PSU off the amp chassis so I could remove the amp's top cover. I checked my jumpers, they still looked good. I left the PSU off to the side, powered it back up, and the hum was gone. Wha?! So I put the Astron back on top of the amp chassis, and the hum came back.
So it appears the Astron SL-11R power supply leaks some kind of EMI? Also, just now I realized that the PSU itself has a very slight hum when powered on.
The natural question then is, was the hum fixed by the jumper or simply by moving the power supply? The answer is both. I just now pulled the jumper with the amp connected to the more sensitive speakers and the Astron moved away. Hum is back. Re-applying the jumper (and leaving the PSU aside) kills the hum.
I do get a weird noise (yet another kind of hum) in one speaker when the attenuator is all the way up, but I assume that's a problem with the attenuator... if I start using this amp in that manner, I'll just remove the attenuator outright.
So anyway, final config (for now😉) is like this:
Transformer Pri Pin 1 / input+ = RCA POS
Transformer Pri Pin 2 / CT = jumper to Pin 3
Transformer Pri Pin 3 / input- = RCA GND
Transformer Sec Pin 5 / output- = amp signal input-
Transformer Sec Pin 6 / CT = couple to amp signal input gnd via 1uF cap
Transformer Sec Pin 7 / output+ = amp signal input+
