What have I done!?
After enjoying the wonderful sound of my ACA Mini for six months, I just discovered—by pure chance—that Q1 and Q2 on the right channel are installed the wrong way around. The markings on the PCB and the build guide are crystal clear, so I honestly have no idea how I managed to mess it up.
I powered it down immediately and will of course flip them as soon as I can (this time without a glass of red wine next to me). But I have two questions that I hope someone here might be able to answer:
After enjoying the wonderful sound of my ACA Mini for six months, I just discovered—by pure chance—that Q1 and Q2 on the right channel are installed the wrong way around. The markings on the PCB and the build guide are crystal clear, so I honestly have no idea how I managed to mess it up.
I powered it down immediately and will of course flip them as soon as I can (this time without a glass of red wine next to me). But I have two questions that I hope someone here might be able to answer:
- How on earth has it still sounded so good with the transistors partially installed backwards?
- Could Q1, Q2, or any other components have been damaged, considering it's been used almost daily?
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2SJ74 and 2SK170 are symmetrical. Since the drain and source are the outer pins 1 and 3, installing them "backwards" is not a worry.
1) See above.
2) No.
(I'm reasonably sure about this, but not certain. I still install them per the schematics, just in case. Also, not all JFETs are symmetrical.)
1) See above.
2) No.
(I'm reasonably sure about this, but not certain. I still install them per the schematics, just in case. Also, not all JFETs are symmetrical.)
Turns out Jfet are often symmetrical, and you’ve likely determined this is true for these parts! As it turns out, pin 2 being the Gate has saved the day.
😎
😎
Turns out I was really lucky to have flipped symmetrical components 🙂 Now I can calm down and re-solder them the right way—just for the sake of doing things properly.
Big thanks to both of you for your helpful replies!
Big thanks to both of you for your helpful replies!
It's an easy mistake. Don't beat yourself up too badly. Actually, red wine helps me stay calm... up to a point. 🙂
Nice base BTW.
Nice base BTW.
@WBS: It helps because you have the good stuff. 🙂
@Cederquist : Please be careful with the jfets if you want to resolder them. Or you can just remember their pinouts for the next time. 🙂
@Cederquist : Please be careful with the jfets if you want to resolder them. Or you can just remember their pinouts for the next time. 🙂
What the late and great Bob Pease told me...
"YOU are the SOURCE, and you are the DRAIN".
But not persistently at the same moment. Either you behave like the source, your partner becoming the drain, or else. .
Well, isn't that a fine example of Schrödingers Cat? Being in two mutually-exclusive states at the same time?
And of Heisenberg's Uncertainty Principle, that you can't look at it one way while if you look in a different way, it would have a totally different characterisc?
But not persistently at the same moment. Either you behave like the source, your partner becoming the drain, or else. .
Well, isn't that a fine example of Schrödingers Cat? Being in two mutually-exclusive states at the same time?
And of Heisenberg's Uncertainty Principle, that you can't look at it one way while if you look in a different way, it would have a totally different characterisc?
Pass DIY Addict
Joined 2000
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A few years back I sold a pair of Lowthers to someone in Berlin via Ebay. Something went wrong with the delivery (in fact I messed up the number). De buyer was not able to handle this, I found out his son did the trading. And that he was an old nucleair physicist. I was tempted to educate him on the day to day implications of Heisenberg. You can't trust me and at the same moment be in a fit.
Hey wait, can't we make it into a more universal theme applicable to listening to our audio concoctions?
Hey wait, can't we make it into a more universal theme applicable to listening to our audio concoctions?
I've been out of DIY audio for 2 years until yesterday when I built the ACA Mini in 3h45m. Had bought the kit in the interim to keep busy but didn't get around to it until yesterday. With little prep it went together fast. Set the VO to 11.5v and VB to .35. Runs a little hot to the touch but the 5 second touch rule is not broken. First tried on Triangle BRO2 at 89db sensitivity. Sounded OK so moved over to Reference 3A Grand Veena at 90db sensitivity. It's mainly a 6Ohm speaker. ACA Mini did ok with simple acoustic music but got a little confused with more complex music. Understandable. Right now, I prefer the jumper off with less 2nd harmonic, but inevitably I lean toward warmer sound. 3rd harmonic always engages me at first but it fades. Get the impression of more control with jumper off.
Kit was missing 1 header and one of the jacks when RCA inserted pushed out the internal wiring. Neither are a problem, although getting a tiny bit of hum in channel with bad RCA. Moving circuit to a box eventually so not a big deal.
Question: I'm getting a little audible distortion. Would cutting back the bias help?
The ACA Mini is between the F4 monoblocks. 🙂
Thank you Mr. Pass and everyone for this cool little kit! 👍
Kit was missing 1 header and one of the jacks when RCA inserted pushed out the internal wiring. Neither are a problem, although getting a tiny bit of hum in channel with bad RCA. Moving circuit to a box eventually so not a big deal.
Question: I'm getting a little audible distortion. Would cutting back the bias help?
The ACA Mini is between the F4 monoblocks. 🙂
Thank you Mr. Pass and everyone for this cool little kit! 👍
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The jumper position you have favours distorsions... but I find that suits the Mini very well, as it is intented with a specific choice of speaker family.
Indeed increasing the bias has positive effets on the sound but I found that 350mV or so was fine and going higher didn't bring big benefits... but increased the heat to a significant level.
Something that did audibly bring benefits and possibly in the direction of more control / firmness and more cleaness / less distorsions to my ears was adding the Murata coil to filter the SMPS (dead easy and plug in / out direct comparison possible "nearly on the fly") and further adding the bycaps I did.
Seach function is your friend, Birdbox offers a kit with all that in your country (low postage costs) plus sexy feet for 10 bucks...
Enjoy the Mini
Claude
Indeed increasing the bias has positive effets on the sound but I found that 350mV or so was fine and going higher didn't bring big benefits... but increased the heat to a significant level.
Something that did audibly bring benefits and possibly in the direction of more control / firmness and more cleaness / less distorsions to my ears was adding the Murata coil to filter the SMPS (dead easy and plug in / out direct comparison possible "nearly on the fly") and further adding the bycaps I did.
Seach function is your friend, Birdbox offers a kit with all that in your country (low postage costs) plus sexy feet for 10 bucks...
Enjoy the Mini
Claude
Hey folks... Been a lurker throughout my mini build but have a question (searched but didn't find a post in the myriad of conversations on this thread)...
I have the amp producing great sound as expected. When I power it off then come back the following day, I let it sit for awhile (30-45 minutes) to give the hamsters time to get it running. I'm finding that the bias does not seem to be permanent (I set it to 11.7V and .32VB based on an earlier comment by Senior Pass) in that the sound will fade in and out and never settles down. If I re-bias, everything is fantastic again for that session. Am I just impatient and need to let it run longer before use?
Many thanks to those keep the answers coming.
I have the amp producing great sound as expected. When I power it off then come back the following day, I let it sit for awhile (30-45 minutes) to give the hamsters time to get it running. I'm finding that the bias does not seem to be permanent (I set it to 11.7V and .32VB based on an earlier comment by Senior Pass) in that the sound will fade in and out and never settles down. If I re-bias, everything is fantastic again for that session. Am I just impatient and need to let it run longer before use?
Many thanks to those keep the answers coming.
