I understand.
I got my other amp kit board and checked the pins on the back. Measured pin 1-2 1-3 and 2-3. They measured 0.6ohm on the 20k ohm setting. I did all the pots this way. Is that the wrong way to measure?
I got my other amp kit board and checked the pins on the back. Measured pin 1-2 1-3 and 2-3. They measured 0.6ohm on the 20k ohm setting. I did all the pots this way. Is that the wrong way to measure?
It sounds like you measured right, both pots should measure low resistance between all pins before power on
Can you check that the JEFTs (Q1, Q2) are in the right spot and are the right way round? They're tough to see in the pictures
Pair of monos ready.
The build was intresting and fun. Mostly. Chassis modification, although pretty minimal, was pain in the butt due to lack of proper tools and working areas, but i got there at the end.
With very limited listening so far i can already say that these sound amazing. Soundstage is wide, layered and has nice depth even in my cramped listening room. ACA min/max does a better job on that than my Lyngdorf TDAI 2170.
Very enjoyable.
Only gripe so far i have with the Mean Well rsp-75-24 powersupplys. Thay make annoying squeel for 20-30min while the amp is warming up. After that they are somewhat silent and don't annoy too much. Luckily no noise from the speakers.
Papa came up with a better powersupply, so i will upgrade those in the future.
The build was intresting and fun. Mostly. Chassis modification, although pretty minimal, was pain in the butt due to lack of proper tools and working areas, but i got there at the end.
With very limited listening so far i can already say that these sound amazing. Soundstage is wide, layered and has nice depth even in my cramped listening room. ACA min/max does a better job on that than my Lyngdorf TDAI 2170.
Very enjoyable.
Only gripe so far i have with the Mean Well rsp-75-24 powersupplys. Thay make annoying squeel for 20-30min while the amp is warming up. After that they are somewhat silent and don't annoy too much. Luckily no noise from the speakers.
Papa came up with a better powersupply, so i will upgrade those in the future.
Another finished MinMax. This was my first time building an amplifier and it was very fun. I also learned a lot.
I am new to this and I have a question: should I set the bias when the amp is connected to a source and to speakers? I also noticed that the bias current climbs significantly after the amp warms up. I imagine the way to do it would be with everything connected and with the amp fully warmed up?
Also I'm in Canada and it's very cold in the basement where I have the amp, and although after being fully warmed up the bias current climbs to 0.92A the heatsinks don't get burning hot, is 0.92A that fine for the components inside (voltage is 17.6V)? It's still very hot but I can still leave my hand on the heatsink without it burning. I made sure that my thermal grease is well applied and that I don't have too little or too much, so I'm pretty sure it dissipates heat correctly.
I'm not usually into speakers, and I have a bigger headphone collection, but oh my this little thing sounds goooood. Much clearer and natural than all the receivers I had been using with those speakers.
I am new to this and I have a question: should I set the bias when the amp is connected to a source and to speakers? I also noticed that the bias current climbs significantly after the amp warms up. I imagine the way to do it would be with everything connected and with the amp fully warmed up?
Also I'm in Canada and it's very cold in the basement where I have the amp, and although after being fully warmed up the bias current climbs to 0.92A the heatsinks don't get burning hot, is 0.92A that fine for the components inside (voltage is 17.6V)? It's still very hot but I can still leave my hand on the heatsink without it burning. I made sure that my thermal grease is well applied and that I don't have too little or too much, so I'm pretty sure it dissipates heat correctly.
I'm not usually into speakers, and I have a bigger headphone collection, but oh my this little thing sounds goooood. Much clearer and natural than all the receivers I had been using with those speakers.
No need to be connected to a source or a load when biasing. In the least, short the inputs so no noise is on the line. Most definitely don't want to be playing music or any other signal at the time.
Post #40: https://www.diyaudio.com/community/...it-for-aca-chassis.404975/page-2#post-7576286
Nelson B has his biased at 1.1A so you got some headroom there. Check on some of 6L6's build guides for the 1st Watt clones. He gives good criteria for biasing.
Reminds me, I need to get around to finishing mine.
Post #40: https://www.diyaudio.com/community/...it-for-aca-chassis.404975/page-2#post-7576286
Nelson B has his biased at 1.1A so you got some headroom there. Check on some of 6L6's build guides for the 1st Watt clones. He gives good criteria for biasing.
Reminds me, I need to get around to finishing mine.
Great job ismael!
If the basement has a stable temp year round then it sounds like you're okay. If it gets warmer the bias will continue to rise which could push it overtemp
I have since dialed this back to 850 mA. My initial bias was done on a cool evening and a few warm days proved it to be a bit much.
If the basement has a stable temp year round then it sounds like you're okay. If it gets warmer the bias will continue to rise which could push it overtemp
Ok thanks, all of that is good to know. Temp is stable for the winter, might recheck in a couple of months when it gets warmer again.
One other thing though, I am noticing when I measure DC voltage from my RCA inputs that although one input shows virtually 0mV, I measured as high as 300mV from the other RCA. Is that what DC offset is?
What usually can cause this? All my solder joints are clean except the negative one on my power connector, could that be it?
One other thing though, I am noticing when I measure DC voltage from my RCA inputs that although one input shows virtually 0mV, I measured as high as 300mV from the other RCA. Is that what DC offset is?
What usually can cause this? All my solder joints are clean except the negative one on my power connector, could that be it?
There is only one RCA input per channel so I assume that one channel is OK and the other channel is not OK.
Looking at your picture in post #206 I see all sorts of wires connected to the RCA inputs, and that does not appear correct.
See this post for wiring:https://www.diyaudio.com/community/...-retrofit-for-aca-chassis.404975/post-7503834
and https://www.diyaudio.com/community/attachments/minmax-chassis-wiring-rev0-png.1233033/
Looking at your picture in post #206 I see all sorts of wires connected to the RCA inputs, and that does not appear correct.
See this post for wiring:https://www.diyaudio.com/community/...-retrofit-for-aca-chassis.404975/post-7503834
and https://www.diyaudio.com/community/attachments/minmax-chassis-wiring-rev0-png.1233033/
Just to confirm, you are measuring from In+ to ground? The inputs are AC coupled through capacitor C1, so there isn't really a path for DC to flow through and I'm not sure the reading is giving meaningful information. My best bet is that you are seeing some residual charge on the input capacitor, in which case, nothing to be worried about. Try measuring with a source connected, and maybe check your source for DC on its output?
Post #206 looks okay to me, check against the wiring diagram in the first post of the thread. I have been keeping the info / attachments in the first post up to date so people always know where to look.
Technically that could be called DC offset but int he context of this amp and the manual as written, no. The DC offset is measured from test point Vo to ground. C2 is the AC coupling output capacitor, which is needed since this amp is a single supply. One side of C2 is connected between the MOSFETs and the other side goes to the positive output terminal. If we have no signal into the amp, we would expect 18 or so volts on the positive side of C2 since the two MOSFETs are conducting equally, this is the DC offset. We don't want to put 18 volts DC into a speaker since it would just get pushed to full excursion, stay there, then burn out. The capacitor blocks the DC voltage from going through it, while AC can still pass through. When a signal is applied, let's say that the positive side of C2 is now fluctuating between 17 volts and 19 volts with respect to ground. The output side of the capacitor will fluctuate between -1V and +1V. Test point Vo ("o" for offset) is connected to the positive side of C2. We target an offset value a little under half of the voltage rails so that the amp can output the largest AC signal without clipping.
Post #206 looks okay to me, check against the wiring diagram in the first post of the thread. I have been keeping the info / attachments in the first post up to date so people always know where to look.
Technically that could be called DC offset but int he context of this amp and the manual as written, no. The DC offset is measured from test point Vo to ground. C2 is the AC coupling output capacitor, which is needed since this amp is a single supply. One side of C2 is connected between the MOSFETs and the other side goes to the positive output terminal. If we have no signal into the amp, we would expect 18 or so volts on the positive side of C2 since the two MOSFETs are conducting equally, this is the DC offset. We don't want to put 18 volts DC into a speaker since it would just get pushed to full excursion, stay there, then burn out. The capacitor blocks the DC voltage from going through it, while AC can still pass through. When a signal is applied, let's say that the positive side of C2 is now fluctuating between 17 volts and 19 volts with respect to ground. The output side of the capacitor will fluctuate between -1V and +1V. Test point Vo ("o" for offset) is connected to the positive side of C2. We target an offset value a little under half of the voltage rails so that the amp can output the largest AC signal without clipping.
I did the wiring with the XLR plug installed as well, so there are indeed more wires in my picture. I followed the chassis wiring diagram from the MinMax store page and from the manual:
I'll check back when I'm home tomorrow to make sure I got it wired correctly, but I do not think this is the problem as I verified multiple times before turning it on for the first time. Thanks for the clue though, I'll report back.
I'll check back when I'm home tomorrow to make sure I got it wired correctly, but I do not think this is the problem as I verified multiple times before turning it on for the first time. Thanks for the clue though, I'll report back.
That might be it. There is not much if I measure from In+ to G and there is no DC in my source's outputs. Using speakers also doesn't make any unusual noise or big pop. Not really worried anymore.
And thanks for the explanation!
Nelson: I noticed that the wiring diagram requires crossed output wires to the binding posts because of the silkscreen on the ACA back panel for the binding posts. Any thought given to including small stickers in the next version of the kits to cover over and correct the polarity of the binding posts?
Hello. How do I bias the amp? Where should I be attaching my red leads? Everything powers on as it should, so what are the readings I should get at Vo and Vb? (Am assuming I connect black cable on my voltmeter to G on board.) Thanks!
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Basic biasing instructions are in the MiniMax manual, under Adjustment. The manual is downloadable from one of tge first posts on this thread.
Thanks Halauhula, it was right therfe under my nose. Separately, I was able to get both my P2 pots to zero out, but both P1s are stuck at ~64. If I turn the dial counterclockwise 8-10 times I can get it to drop maybe .1. What am I doing wrong? Thanks.
Yes and in fact the kits currently in the store have these stickers included. The pioneer kits did not come with stickers, so if anyone wants them, please message me and I'll send them in a envelope.
Maybe the wiper is staying on the resistive material rather than moving all the way to the metallic terminal. With this type of pot, at end of travel the screw disengages from the rotating wiper (see red arrow in pic below) so turning more doesn't move anything inside. Under 100 ohms is an okay place to start for first power before biasing, just check that turning it back the other way increases the measured resistance.