Offtopic sorry. After this posting, we have to get back to the ACA mini 🙂
@hpro I am sorry, but I know what I am writing here. I also clearly understand what you mean, I know this tax free import cost limit. But digikey.ch is like a Swiss Shop, Prices in local currency including tax. The goods are delivered from US. You find in the shopping card this text:
Translation: Import-Fee and Tax is payed by Digi-Key
I ordered goods for more than 65 CHF
Yes I know, have ordered there as well. I was talking about the regular rules which usually apply.
And you supplied the proof of it. with the attached Picture.. Translation: Import-Fee and Tax is paid by Digi-Key
This also counts for Farnell and other distributors.. but if they do not pay that cost, then you will be the first one to open your Wallet wider and pay Import Fee and Tax.
Have nice weekend and greetings from Bern
And you supplied the proof of it. with the attached Picture.. Translation: Import-Fee and Tax is paid by Digi-Key
This also counts for Farnell and other distributors.. but if they do not pay that cost, then you will be the first one to open your Wallet wider and pay Import Fee and Tax.
Have nice weekend and greetings from Bern
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Back to the ACA Mini:
Franz
- I reduced VB to 0.28VDC to reduce the heat a little bit
- @Nelson Pass: I prefer the sound WITH jumper
Franz
Right off, I'd like to thank Nelson for his generosity, and again to KevinHeem for facilitating the group buy. I've been building audio gear for 20+ years, but this is my first solid state - and my first Pass - amp, so I'm quite excited to hear first hand what all the fuss is about.
The build was straightforward, and, though a bit fiddly at first, fairly simple to bias. After confirming no DC offset on the outputs (one can't be too careful), I inserted it into my second system and played some music.
Without doing any critical listening, it was immediately clear that one channel was significantly lower in volume than the other. It was fairly late so I shut everything down for the night.
Digging into it again, my VO/VB readings are 11.56/.299 and 11.47/.306 for R and L channels respectively. These measurements, and the ones below, were taken after roughly 1.5 hours of operation and with no connections on input or output.
Voltage readings (R / L) across each resistor are as follows:
R1 - 0 / 0 (no connection)
R2 - 11.64 / 11.64
R3 - 11.63 / 11.63
R4 - .367 / .371
R5 - .191 / .269 (!)
R6 - 0 / 0
R7 - 0 / 0 (n/c)
R8 - .298 / .299
R9 - .299 / .301
R10 - .130 / .133
R11 - 0 / 0 (no jumper)
To my inexperienced eye, the only thing that jumps out at me is the variance between the R5 readings. Given that everything else checks out, is it reasonable to suspect R5?
Can anyone suggest where else to look and/or what to try next? Thank you!
The build was straightforward, and, though a bit fiddly at first, fairly simple to bias. After confirming no DC offset on the outputs (one can't be too careful), I inserted it into my second system and played some music.
Without doing any critical listening, it was immediately clear that one channel was significantly lower in volume than the other. It was fairly late so I shut everything down for the night.
Digging into it again, my VO/VB readings are 11.56/.299 and 11.47/.306 for R and L channels respectively. These measurements, and the ones below, were taken after roughly 1.5 hours of operation and with no connections on input or output.
Voltage readings (R / L) across each resistor are as follows:
R1 - 0 / 0 (no connection)
R2 - 11.64 / 11.64
R3 - 11.63 / 11.63
R4 - .367 / .371
R5 - .191 / .269 (!)
R6 - 0 / 0
R7 - 0 / 0 (n/c)
R8 - .298 / .299
R9 - .299 / .301
R10 - .130 / .133
R11 - 0 / 0 (no jumper)
To my inexperienced eye, the only thing that jumps out at me is the variance between the R5 readings. Given that everything else checks out, is it reasonable to suspect R5?
Can anyone suggest where else to look and/or what to try next? Thank you!
Which channel has "significantly lower volume"?
We were looking at your photo on the other thread and couldn't tell if the pin 3 of QR2 is seated properly.
We were looking at your photo on the other thread and couldn't tell if the pin 3 of QR2 is seated properly.
The left channel is barely audible, but there is signal - unless it’s crosstalk, which I doubt.
The JFETs are socketed, so I can swap them between channels.
However, from your comment, a closer look reveals that the drain pins of all four MOSFETS have less solder flowed through to the topside of the board than the others. I was letting the iron linger a little less than I typically do, given the scarcity of the devices, but I’ll get solder all the way through the holes just in case.
I’ll swap JFETs first, one pair at a time (matched quad) as that’s easy, and reflow if that doesn’t bear fruit. In any case I’ll report back with results.
Swapping JFETs and reflowing solder on all for MOSFETs had no effect.
Just for grins I checked voltages across both R1, and got fairly consistent (I.e. not wildly different) readings with a stereo 1KHz signal, though it was a challenge to get a solid reading on either channel for some reason.
Just for grins I checked voltages across both R1, and got fairly consistent (I.e. not wildly different) readings with a stereo 1KHz signal, though it was a challenge to get a solid reading on either channel for some reason.
Sadly, I don’t have a signal generator; I was playing a YouTube video that was nothing but a 1KHz tone - essentially a simple check that the input jacks and R1 were sound (no pun intended). The resistors measure better than .5%.
It's alive! Well...more like "it's built". Haven't turned it on yet.
REW has a signal generator and is a free program. I use a DAC to amplifiers for testing. Probably not the best solution but it does seem to work
Thanks for the suggestion - I’ve used REW for speaker measurements in the past, if I recall.
Curious what heatsink (or MOSFET) temps you guys are getting after VO and VB are set. I'm at ~30C on the devices and ~52C at the top of the heatsinks with VO = 11.49 and VB = .337. Thanks.
I'm almost done building mine so I can't comment on the temp. But if you are concerned then dial that Vb down a bit. In Papa's original article he says a Vb of .30 is easier on the parts with virtually no difference in sound quality from a hotter bias. Maybe worth trying?
Yeah I brought it down to .31 and temps are virtually the same. I'm not concerned per-se, just curious if my temps are within acceptable range. I know Papa's temp scale, but don't know if this amp is designed with that in mind.
It could take a short while for the temp to adjust down. How long did you wait to meausre? I'm curious as I'll be dealing with this stuff shortly. Thanks.