This time I bought a completed unit as the price was hard to beat. It was only AUS$200 delivered to my door from this mob.
https://www.aliexpress.com/item/100....order_list.order_list_main.42.78501802uvooKN
You can get just the boards as well from AliExpress but I couldn't build one for less than the fully assembled unit.
https://www.aliexpress.com/item/100...031666010!sea!AU!0&curPageLogUid=5gTpG4Ymc6LC
https://www.aliexpress.com/item/100....order_list.order_list_main.42.78501802uvooKN
You can get just the boards as well from AliExpress but I couldn't build one for less than the fully assembled unit.
https://www.aliexpress.com/item/100...031666010!sea!AU!0&curPageLogUid=5gTpG4Ymc6LC
Hi, A couple of months ago I read & took up a recommendation to upgrade the op-amp in my unit. The op-amp I ordered was a OPA244PA. It arrived the other day, slotted it in & checked the voltage & it was about 1/2 the 24 VDC that the unit was set for & I need to run my Pass B1-Korg.
Can anyone recommend an upgrade Op-amp that will not have this affect.
Cheers
Can anyone recommend an upgrade Op-amp that will not have this affect.
Cheers
TL072 I think. If you need a couple i can put them in the mail for postage.
Compare quiecent current to see if the OPA draws significantly more current per amplifier(2x in one package) another option is that the frequency compensation is not right. Another is that the output of the OPA cannot swing high enough to force the BD140 transistor into cut-off.
The last option is plausible. Looking at the available schematic, we see that Q105 has 330R between base emitter, and the OPA is connected to that node with 680R resistor. So if the opa cannot approach + supply within ~2V it cannot "close" Q105 and it will continue supplying current to Q104 Bellow => output goes low.
You can test this hypothesis by changing the resistor R114 to 1K or 1K2.
Edit I just read the OPA datasheet, scratch the output stage hypothesis, you are replacing a 3Mhz FET input opamp with a 400Khz bipolar jobbie, that is bound to give issues, its likely oscillation or latch-up.
Cheers,
V4LVE
Compare quiecent current to see if the OPA draws significantly more current per amplifier(2x in one package) another option is that the frequency compensation is not right. Another is that the output of the OPA cannot swing high enough to force the BD140 transistor into cut-off.
The last option is plausible. Looking at the available schematic, we see that Q105 has 330R between base emitter, and the OPA is connected to that node with 680R resistor. So if the opa cannot approach + supply within ~2V it cannot "close" Q105 and it will continue supplying current to Q104 Bellow => output goes low.
You can test this hypothesis by changing the resistor R114 to 1K or 1K2.
Edit I just read the OPA datasheet, scratch the output stage hypothesis, you are replacing a 3Mhz FET input opamp with a 400Khz bipolar jobbie, that is bound to give issues, its likely oscillation or latch-up.
Cheers,
V4LVE
Attachments
Any recall on how long the TLE2072 takes to fully "come on song"? I've got 24 hours on one in this PSU and it improves the sense of detail and separation a bit on my DAC, but so far seems to do so through tilting the frequency curve up a bit rather than through lower noise and greater dimensionality -- and it loses soundstage depth and some naturalness compared to the TL072. So wondering if it just needs a good bit more hours or if I just prefer the TL072 here.
Hey guys, help needed. I got one of these to power a Pocket Class A amp (xrk971 design). I needed to resolder for 120VAC operation and adjust the potentiometer for 16.4VDC output. However, when I use it, I get a very pronounced medium-high pitch noise. It is finite - less sensitive headphones diminish the noise. I did at first plug the output in backwards on the amp and roasted the input caps on the amp, which I fixed. It works with batteries with no noise, but the PSU has the noise. Any possible troubleshooting steps?
"Resolder for 120VAC," what do you mean? The transformer determines whether it takes 120VAC, 240VAC or other. You should have a transformer rated for 120VAC input and probably 21-23VAC output and feed that into the PCB's voltage input.
You didn't say what sort of current (amps) you need to run this amplifier properly.
For higher voltage (as you need) and higher current you should be looking at post 328 (page 17).
Thanks @brucew268. Re: resolder, I meant the jumpers provided on the board. The 240VAC jumper was soldered to set up the xfmr in 240VAC mode so I desoldered that and soldered the jumpers for 120VAC mode.
Re: current, I haven't measured it myself but others with similarly appointed amps have gotten ~50mA which seems to be within the unmodified range for this PSU (unless I did something spectacularly wrong with my understanding of how the calcs work in which case I'll head down to the market to look for crow).
Would drawing excess current cause an oscillation problem?
Re: current, I haven't measured it myself but others with similarly appointed amps have gotten ~50mA which seems to be within the unmodified range for this PSU (unless I did something spectacularly wrong with my understanding of how the calcs work in which case I'll head down to the market to look for crow).
Would drawing excess current cause an oscillation problem?
Sounds like you bought a prebuilt PSU in a case rather than just a Studer900 PCB and building the PSU. OK, no prob. If the transformer is underpowered it could have problems doing 16.4VDC and act rather weirdly, though 50mA is nothing. So, still not sure what the VAC of the transformer secondaries (transformer output) are.
Sorry, yeah, should've clarified it was a pre-built. Out of the box, it was set for 18VDC operation which I was able to lower down to 16.4VDC with just the pot. I need to re-open the case and see which version of the xfmr I have... I can also poke around to see if I can find the outputs of the transformer on the board for measuring purposes though I'm not super confident in my safety precautions when dealing with live 120VAC. Also, there is a component that seems to be thermally potted to the case and I don't have anything that would be a suitable replacement for that potting compound should I pull it off to access the underside of the PCB.
Looking at one of the circuit diagrams posted earlier in this thread, it seems there are some output caps. Is it possible I fried the direction one when I plugged my headphone amp in backward? Is it possible a spike caused by frying the caps on my amp have caused a feedback which fried the cap on the PSU?
Sorry, no idea. I'd think the danger to the amp was greater than to the PSU from connecting them backwards. If this was sold as a finished 18VDC supply, I'd hope the transformer and circuit config were up to it, though it should be printed on the side of the transformer what its input and output are. If the jumpers for 120 vs 230VAC were done wrong/not done and it was plugged in, that could fry things.