Nice looking build @ItsAllInMyHead, please share the details of the white spacers that you used to mount Prasi CRC psu boards that has mounting holes not aligned with the perforated plate.
Thanks
Thanks
^ Thank you!
They're PCB spacers/feet.
https://www.amazon.com/gp/product/B0983368DX/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
They're PCB spacers/feet.
https://www.amazon.com/gp/product/B0983368DX/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Almost ready for liftoff.
It looks to me that you are short for some ground fast-on connectors at the PS output. Signal ground from the amplifier PCB should go to that middle ground connector, between two black wires. There are decoupling ground, loudspeaker ground and PE ground (through NTC or Ground Loop Breaker circuit) remaining.
^ Thank you as always! I am still debating direct soldering some of the connections and if so, on which end and/or under the board(s). The PSU boards will come up one more time before it's all buttoned up.
I have your GBR boards on the way. In the interim, I'll probably just put in a thermistor for each channel.
I had below in my build notes for connections / GND scheme. I'm sure it came from one of your previous posts, but for some reason, I forgot to note which one in my notes.
"GND connection points.
You need 3 – 4 depending on how is safety connection to chassis made. Signal ground connection is amplifier ground reference for input signal. Connect that to physically middle positioned gnd connection at the PS board. Loudspeaker gnd should be connected next to that gnd point, not at any other point down the gnd connectors array.
Decoupling gnd should be connected next, farthest as possible from former two connections. If you have prasi’s CRC boards, connectors marked as “IN-GND” are also allowed for this.
Safety grounding, probably through NTC resistor, if not connected otherwise, can be connected to any remaining gnd connector."
I have your GBR boards on the way. In the interim, I'll probably just put in a thermistor for each channel.
I had below in my build notes for connections / GND scheme. I'm sure it came from one of your previous posts, but for some reason, I forgot to note which one in my notes.
"GND connection points.
You need 3 – 4 depending on how is safety connection to chassis made. Signal ground connection is amplifier ground reference for input signal. Connect that to physically middle positioned gnd connection at the PS board. Loudspeaker gnd should be connected next to that gnd point, not at any other point down the gnd connectors array.
Decoupling gnd should be connected next, farthest as possible from former two connections. If you have prasi’s CRC boards, connectors marked as “IN-GND” are also allowed for this.
Safety grounding, probably through NTC resistor, if not connected otherwise, can be connected to any remaining gnd connector."
@ItsAllInMyHead here is what @tombo56 suggested during my build for your reference and I used same psu board but single as yours Prasi crc one.
Decoupling L
LS gnd L
Signal ground L
Safety ground
Signal ground R
LS ground R
Decoupling R
Decoupling L
LS gnd L
Signal ground L
Safety ground
Signal ground R
LS ground R
Decoupling R
Now I remember that I used these last year - https://www.amazon.com/gp/product/B0BKVCMWPK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1 but the big 8 cap psu board was not sturdy with these spacers which per reviews were meant for Arduino projects and/or wooden panels. How good are your stand-offs holding the psu board to the perforated plate?
^ Rock solid. M3 x 8 through the baseplate secured with a lock-nut.
I leave the bases and the boards loose while I wiggle them around to find a nice location. Once I lock them into place, they hold their location / position and have never budged. The standard screw provided works well to secure the boards to the mounts. I've used them in tons of projects. They've held up to my atypical bashing, moving, changing components around them with abandon.
Can't be certain, but since the ones I used are roughly 3/4" and the shortest you linked were roughly 1"... maybe the taller ones wiggle???
I leave the bases and the boards loose while I wiggle them around to find a nice location. Once I lock them into place, they hold their location / position and have never budged. The standard screw provided works well to secure the boards to the mounts. I've used them in tons of projects. They've held up to my atypical bashing, moving, changing components around them with abandon.
Can't be certain, but since the ones I used are roughly 3/4" and the shortest you linked were roughly 1"... maybe the taller ones wiggle???
I may have seen someone else do that... if I could only remember who...
I'm terrible. Since I have the attention span of a squirrel on crack, I read each thread at least a few times and take notes / make links to key posts. I have an MSWord doc for each project with little snippets of each thread and pictures I'd like to "honor with my interpretation".
@tombo56 -
Got my bits / taps. Mounted everything up.
I am biasing each channel. Back in post #56 you mentioned below -
From a dead start with cold heatsinks - Max voltage across R17 is 168mV on one channel and 188mV on the other. I don't remember reading, and I don't have any notes on any adjustments on the amplifier boards to allow for higher bias current. If I missed it, my apologies. Those results were achieved with the pots at the end of their travel. Devices are getting very slightly warm.
Any advice is appreciated. Output devices are from Profusion. Almost there. I won't button it up b/c I don't want to unmount the amp boards with it all tidied up until I know what I can do to get the bias up to target. Rails are rock steady at +- 19V5.
Thanks!
Got my bits / taps. Mounted everything up.
I am biasing each channel. Back in post #56 you mentioned below -
Everything is looking OK with one exception. My plan was to run 1A2 bias (or up to the 1A4 limit) b/c of my 4R speakers.
From a dead start with cold heatsinks - Max voltage across R17 is 168mV on one channel and 188mV on the other. I don't remember reading, and I don't have any notes on any adjustments on the amplifier boards to allow for higher bias current. If I missed it, my apologies. Those results were achieved with the pots at the end of their travel. Devices are getting very slightly warm.
Any advice is appreciated. Output devices are from Profusion. Almost there. I won't button it up b/c I don't want to unmount the amp boards with it all tidied up until I know what I can do to get the bias up to target. Rails are rock steady at +- 19V5.
Thanks!
IAIMH,
Measure the voltage at the opamp legs or resistors R7 and R8 end towards opamp. (Pin7 P-supply, Pin4 N-supply)
Be careful not to slip with DMM probe and short adjacent legs.
If your supply is 19V5, R7 and R8 need to drop 2V to keep the little critter happy. I measured 350R to work perfectly. If you don’t have a 350R, use two resistors in series or the next higher value in your stash.
As for the bias adjustment range, I won’t be able to help there. Mine biased up to 1A no prob, left it there because my speakers are an easy 8R load.
Measure the voltage at the opamp legs or resistors R7 and R8 end towards opamp. (Pin7 P-supply, Pin4 N-supply)
Be careful not to slip with DMM probe and short adjacent legs.
If your supply is 19V5, R7 and R8 need to drop 2V to keep the little critter happy. I measured 350R to work perfectly. If you don’t have a 350R, use two resistors in series or the next higher value in your stash.
As for the bias adjustment range, I won’t be able to help there. Mine biased up to 1A no prob, left it there because my speakers are an easy 8R load.
Measured values are suspiciously close to usual minimum bias voltages.
Pots are at the end of their travel, but which end? I guess, at the naturally assumed CW end, and that is minimum bias position. Adjust trimmers with CCW rotation and bias should increase.
Well, I have to laugh. Also, I am very happy that you limited the bias. Otherwise... some things may have gone up in smoke.
I made a complete hash of things...
It would have helped tremendously if I had been measuring across R17 instead of R12. No excuses, but I looked at one of my blank boards as a reference for the position to attach my probes, since I can't see very well. I just peeked at the board. Then I said to myself, attach to the 2nd resistor in from the end. I attached the probes to the 2nd resistor in from the end on my populated boards. Totally ignored that the first position isn't stuffed. SHEESH!
Sorry to waste your time. Biased up perfectly. My max on each side is actually ~318mV on one side and ~366mV on the other. I've set it to 315 cold, and it's cooking a bit now to see where it settles.
If my ballpark math works... Later, I should measure ~23W (voltage limited) into 8R and ~20W (current limited) into 4R => 10W into 2R.
That's more than sufficient for what I need.
Should have some tunes playing later today.
Thank you again for your patience and all the help! As much as I try to document everything and be as careful as possible...
It happens, I was once measuring some spectacular numbers while probes were disconnected.
Eh, what time is now in Minnesota? Shouldn’t you be taking your beauty sleep?
Anyway, you will get some 15 W max to 8Ω and some 25 W to 4Ω in class AB.
Bias can be increased further by reducing R10 value.
Eh, what time is now in Minnesota? Shouldn’t you be taking your beauty sleep?
Anyway, you will get some 15 W max to 8Ω and some 25 W to 4Ω in class AB.
Bias can be increased further by reducing R10 value.
^ LOL! I guess it happens.
I forgot to take into account the voltage losses for the output transistors etc. So, only about 15.5Vp from 19V5 rails.
I also forgot to double the available current through the output pair for Class A/B ... So roughly 2A5 available.
Still learning...
It's 0410 in Minnesota. My best time to focus is in the mornings when it's quiet. Also... all the beauty sleep in the world won't do me much good.
Tidying everything up now. Test speakers in a little while.
I forgot to take into account the voltage losses for the output transistors etc. So, only about 15.5Vp from 19V5 rails.
I also forgot to double the available current through the output pair for Class A/B ... So roughly 2A5 available.
Still learning...
It's 0410 in Minnesota. My best time to focus is in the mornings when it's quiet. Also... all the beauty sleep in the world won't do me much good.
Tidying everything up now. Test speakers in a little while.
Making beautiful music on the test speakers. Full day ahead, but I may have some time to do a few measurements. I'll let it settle in then check it out on some other speakers and use something other than my phone as a source.
There's one annoying error, but I'll put it out of my mind.
There's one annoying error, but I'll put it out of my mind.