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My other multimeter was faulty.
Everything is OK now. Working great and very stable.
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The way the layout has been made it looks like QP3/QP5 (QN3/QN5) are meant to be thermal coupled ?
Is that a correct assumption?
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The beta Placid's sounds very promising. I have been playing for a couple of hours and I can already say that Russ must a have done a very good job.
My first impression is that the new Placid dig deeper into the recording and has more resolution. Imaging and presentation of details is also improved.
I know that 2 hours of listening on a new component is a very short time to be able to tell something at all, but this also tells me that the new Placid's is on the right track.
Looking forward to hear from other beta Placid users and what you think.
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Originally Posted by: musicman  hmmm. can`t upload pic`s You can post pictures in one of two ways... When you are making a post, you check the "Attach files to this post?" checkbox under the editor window. This will bring you to an attachment screen after you Post. Secondly, you can attach pictures to an existing post by clicking the Attach button on your message in regular thread view. This will bring you to the same Attach file window.
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Originally Posted by: Brian Donegan Originally Posted by: miksi ...... Can we get schematic, perhaps? Yes. I need to generate it from CAD but can't do that at work. When I get home I will send it out to the BETA customers. pls
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My B-III with new Placid`s and Mundorf Caps. File Attachment(s):  b32.jpg (339kb) downloaded 35 time(s).You cannot view/download attachments. Try to login or register.
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Skipped the heatsinks and no longer problem with the temerature. Placid Hd feeding B-III measure 595mA and are shunting 60mA. The other Placid Hd is for the Exa usb board. Since the Exa draw only around 175mA there is no reason to be worried. I skipped the heatsinks here as well, becouse when not playing music the shunt measure over 100mA. With the old heatsinks it could be quite hot, but not anymore. musicman attached the following image(s): b3.jpg (220kb) downloaded 68 time(s).You cannot view/download attachments. Try to login or register.
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Originally Posted by: Russ White
This new PS can be very accurately set using a basic formula. No need to use the pot unless you want to.
Care to share how? I don't like pots. Originally Posted by: Russ White
Other parts that are changed are the power transistors which are now Darlington pairs in a CFP arrangement.
It is working quite well.
Indeed it looks so.
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Originally Posted by: musicman Skipped the heatsinks and no longer problem with the temerature. Placid Hd feeding B-III measure 595mA and are shunting 60mA. The other Placid Hd is for the Exa usb board. Since the Exa draw only around 175mA there is no reason to be worried. I skipped the heatsinks here as well, becouse when not playing music the shunt measure over 100mA. With the old heatsinks it could be quite hot, but not anymore. For future reference, it is better to simply put a 90degree bend in the transistor pins and mount them so the pins come up into the holes on the board. This keeps the trace length to a minimum. The way you have done it will also work, however.
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Originally Posted by: avr300 Originally Posted by: Russ White
This new PS can be very accurately set using a basic formula. No need to use the pot unless you want to.
Care to share how? I don't like pots. Originally Posted by: Russ White
Other parts that are changed are the power transistors which are now Darlington pairs in a CFP arrangement.
It is working quite well.
Indeed it looks so. And we got - oscillation!5v with less magnitude more distinctly @+-15v. It's audible, tweeters are hissing. For reference I just dropped in the old modded Placid (just dropped in, no other modifications were made). With that in place, absolutely no noise is heard. Attached are traces for both. avr300 attached the following image(s): beta5v.jpg (61kb) downloaded 38 time(s). beta15v.jpg (67kb) downloaded 45 time(s). old15v.jpg (63kb) downloaded 45 time(s).You cannot view/download attachments. Try to login or register.
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That can't be good. Mine hasn't arrived yet, but when it does I'll hook it up to the scope asap.
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No noise in my jbl horn speakers. Volume set to max with 2x600 powerful watts.
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Originally Posted by: Brian Donegan Originally Posted by: musicman Skipped the heatsinks and no longer problem with the temerature. Placid Hd feeding B-III measure 595mA and are shunting 60mA. The other Placid Hd is for the Exa usb board. Since the Exa draw only around 175mA there is no reason to be worried. I skipped the heatsinks here as well, becouse when not playing music the shunt measure over 100mA. With the old heatsinks it could be quite hot, but not anymore. For future reference, it is better to simply put a 90degree bend in the transistor pins and mount them so the pins come up into the holes on the board. This keeps the trace length to a minimum. The way you have done it will also work, however. Very smart solution Brian. I will fix it next time I open the dac
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avr300,
Are you using the 220pf caps?
Some things to try would be omitting or changing the value R8
Changing the comp cap (C5) value. Up to 10nf is fine.
Change or omit C3
I am using 220pf at C5 and my output has no sign of oscillation at all - but this is why we do betas. :)
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Yes, 220pf was in place when the plot was generated. Afterwards I completely removed C5, no difference.
Next up is to remove R8
Don't worry, I know it's beta - we'll eventually will end up having a great power supply.
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R8 removed, no difference.
Removing C3 causes massive oscillation. 300kHZ
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The other thing to try (though this will require a bit more work) - would be to add R-C filter from Ref 2 to the non-inverting input of the opamp. This will wuire the cutting of one trace, and soldering to the pin of the opamp.
I would try say 1K 47-220uf.
keep in mind - this will slow the startup time.
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First thing i would try is just a larger C3 - try 1nf
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This is QP4 base (with C5 removed, it's the same with C5 fitted). It's oscillating around 31kHz. avr300 attached the following image(s): beta15v-qp4base.jpg (98kb) downloaded 12 time(s).You cannot view/download attachments. Try to login or register.
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