OK I will try again. Bear with me I am having problems posting. I probably have too many thumbs on this iPad keyboard. Let me start again. Fist, thanks for your quick response and that will be my prize for posting number 7000.
I measured "in circuit" all resistors. All are within spec except as follows. R10 measured 220K ohms versus 332K ohms. My Velleman DMM isn't too accurate at low Ohm measurements but Q1 and Q2 measure 0.5 ohms and Q3 and Q4 which disconnected measure 0.9 ohms.
Important note I will investigate is as stated is Q3 which has printing on the curved side. I see too it is a device I can test so I will give that a shot on my DMM.
I will take better photos and post shortly. And regarding this being and "odd fault", well you folks are starting to get to know me, my better half tells me that all the time.
I measured "in circuit" all resistors. All are within spec except as follows. R10 measured 220K ohms versus 332K ohms. My Velleman DMM isn't too accurate at low Ohm measurements but Q1 and Q2 measure 0.5 ohms and Q3 and Q4 which disconnected measure 0.9 ohms.
Important note I will investigate is as stated is Q3 which has printing on the curved side. I see too it is a device I can test so I will give that a shot on my DMM.
I will take better photos and post shortly. And regarding this being and "odd fault", well you folks are starting to get to know me, my better half tells me that all the time.
As a general rule you can't check resistors in circuit... there are interactions with other components, and even the meters own internal test voltage can influence in circuit measurement results.
R10 is probably the least critical part in there
100 ohm, 100meg... it would still work
A quick check would be to lift one end of R7 (10k) and power the amp up. Nothing should get hot and I would expect the bias or midpoint voltage to be very very low and there should also be no measurable voltage across any of those four very low value resistors.
R10 is probably the least critical part in there
100 ohm, 100meg... it would still work A quick check would be to lift one end of R7 (10k) and power the amp up. Nothing should get hot and I would expect the bias or midpoint voltage to be very very low and there should also be no measurable voltage across any of those four very low value resistors.
Umm, just a bit!
Anyway you can fix it now. Fingers crossed for no more resulting damage.
Alan
Update R3 and R4
So a quick update. The experiment of reducing the resistance of R15 to 2.2 ohms from the correct value of 2.2K ohms is complete. My suggestion is to not try it
Many thanks go to those early morning moderators who helped identify and resolve my error. I will report back when I finish testing but looks good so far. A note about the apparent durability of the parts selected for this design, they do appear pretty durable considering what I tried to do to them.
So a quick update. The experiment of reducing the resistance of R15 to 2.2 ohms from the correct value of 2.2K ohms is complete. My suggestion is to not try it
Many thanks go to those early morning moderators who helped identify and resolve my error. I will report back when I finish testing but looks good so far. A note about the apparent durability of the parts selected for this design, they do appear pretty durable considering what I tried to do to them.
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Update R3 and R4
Mooly and Alan1411:
Thank you for your help, rapid response, and for not hammering me with insults-although I may have deserved it. Because I see this string of exchanges is longer than some may want or have time to read I will summarize here.
Amp Camp Amp V1b (but would apply to other version that use R15 in the circuit). Boards and chassis purchased from diyaudio and parts from Digikey and a few others (for the specified transistors).
Symptom was overheating of R3 and R4, discolored R3, melted solder joint R3 and R4 disconnecting both as the heat reduced joint strength. Initial bias was able to be set to 10 volts. And oh yes, smoke emminating from solder joints after several minutes of warmup.
Cause was that value of R15 was wrong 2.2 Ohms instead of the schematic value of 2.2K Ohms. I made an error ordering parts and error when I checked value before installing. That missing little "k" in front of the ohm symbol on the DMM just didn't register in my head.
Initial sound testing is complete and at the present, I am thankful for both Mooly and Alan1411 taking the time to help.
Mooly and Alan1411:
Thank you for your help, rapid response, and for not hammering me with insults-although I may have deserved it. Because I see this string of exchanges is longer than some may want or have time to read I will summarize here.
Amp Camp Amp V1b (but would apply to other version that use R15 in the circuit). Boards and chassis purchased from diyaudio and parts from Digikey and a few others (for the specified transistors).
Symptom was overheating of R3 and R4, discolored R3, melted solder joint R3 and R4 disconnecting both as the heat reduced joint strength. Initial bias was able to be set to 10 volts. And oh yes, smoke emminating from solder joints after several minutes of warmup.
Cause was that value of R15 was wrong 2.2 Ohms instead of the schematic value of 2.2K Ohms. I made an error ordering parts and error when I checked value before installing. That missing little "k" in front of the ohm symbol on the DMM just didn't register in my head.
Initial sound testing is complete and at the present, I am thankful for both Mooly and Alan1411 taking the time to help.
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David G. Let me say your work looks great and others should take notice. My woes this am may have diverted attention away from your excellent work so let me say "Nice Work".
You're very welcome, and I'm sure I speak for Alan in saying that we are just very pleased you found the problem and that with a bit of luck it will all be performing correctly
And as for long exchanges... this one is tiny
nano metre sized.
I like the combo driving a pair of 2 Pi Towers that are about 95 db sensitive and are easy to drive.
Listen to jazz most of the time and other stuff mixed in from time to time. It generally isn't really loud but that's just my preference for listening. It'll go past the level of having a reasonable conversation if you want it to.
There are several other preamp options out there with gain that look interesting simply because others in this thread have stated a preference a preamp with gain for the ACA. Wayne's 2018 preamp looks interesting as does his Whammy headphone amp. If anyone has anything to share on those units please chime in.