Okay, DO NOT apply any input signal to the amp, then...
... wait until you fix it & trim it down first.
Ok I checked all 4 nodes for the conductive and it’s fine. I am just not seeing it, or I am not looking at the right places. The ground is good and both supplies are present but a little low due to the high bias current.
Is Q3 the correct type, inserted correctly?? R13&14 are the correct voltage divider resistors? Double check their values...
It is not working as a trimmer - it is just working at the moment as a discrete 2k ohm resistor.... that is why. The voltage drop across that 2k ohm resistor is too high => the bottom MOSFET transistor pair is conducting more than they should - hence the 1.25A bias
Remove the trimmer and check it (do full spin/turn check... I think 20 turns...), and monitor the smooth resistance change, concurrently with two ohm-metres (one will be increasing; the other will be decreasing the reading). The wipers might not be touching the carbon (plastic) substrate.... Bourns?? I had a case of dodgy trimpot in my Aleph J (!!). It was not Bourns... but some cheap crap.
I replaced all trim pots with discrete resistor values some 7-8 months ago.
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Just the input stage. It is not balanced / differential throughout.
It largely depends on what you consider a benefit. I used that pre-amp with my Aleph J, and I adored it. However, my rack is a bit embarrassing with some long cable runs that pass by mains wiring and routers and... and ... and... Plus, I like the idea of very low injected noise. I listen quietly in the mornings, and any hiss or hum bothers me.
It's not the "amp" that benefits in my situation, its simply that the amp receives a signal with less noise injected due to my sloppy wire management.
YMMV
An SE pre-amp is perfect. This is ALL really a matter of preference with (in my situation) one technical advantage to differential signaling. There are some minor measurable characteristics that will be different, but that does not mean that you will truly prefer one over the other. Sometimes I think I can hear the difference (other than injected noise) in the sound, but it is highly likely that it's just confirmation bias.
That's a long way of saying... If you a need or even just want a balanced signal into the back of your amplifier, then the IPSMD would be a good choice, IMO. The full differential signal will be used straight to the amplifier boards. You won't be "throwing away" the inverted signal. The IPSMD will even 'convert' the signal from your SE sources to balanced (if you like).
If you don't have long cable runs and/or if balanced is of no particular use to you or you really just have no interest in building a balanced pre-amp, then a single-ended pre amp is absolutely wonderful.
Very short version - The amplifier sounds absolutely wonderful no matter which input you use, but there can be some advantages to balanced that (IMO) have nothing to do with the actual sound 'quality' of the amplifier.
That's only one opinion, and every use case is different. I hope that helps.
Anyone now where to find a good replacement IEC socket power switch for the Deluxe 4U (27.5mm x 59mm). My fuse holder died when the Line side gave up the ghost and arced/melted down. The amp had been acting up and I noticed both boards went down at the same time. Checking, the PS voltages of -30v and +30V were fine, but then my IEC socket started arcing. Turns out the arcing was in the fuse holder on one side (L), so removal of said fuse resulted in the holder breaking because it was brittle/melted.
https://www.diyaudio.com/media/pdf/4u-300-e-back-panel-temporary-diagram.pdf
https://diyaudiostore.com/products/deluxe-chassis-back-panel-parts-kit
https://www.diyaudio.com/media/pdf/4u-300-e-back-panel-temporary-diagram.pdf
https://diyaudiostore.com/products/deluxe-chassis-back-panel-parts-kit
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Store page listing part number
From that page....
Schurter 4304.6090 IEC Power Entry Module
From Mouser
From that page....
Schurter 4304.6090 IEC Power Entry Module
From Mouser
good thing, while soldering wires to IEC, is to plug cable connector in
it'll add some mass to prevent too much heat and it'll secure alignment of IEC pins while plastic cools off
take care that - if using connector on end of mains cable, other end isn't plugged in mains
it'll add some mass to prevent too much heat and it'll secure alignment of IEC pins while plastic cools off
take care that - if using connector on end of mains cable, other end isn't plugged in mains
oh geez. I didn't see the link. Funny thing, I was on mouser digging... digging... digging... and just now arrived at the exact same power entry module and trying to determine if same! lolz.
Thanks so much for pointing out my ignorance Zen! As usual....
And thanks ItsAllInMyHead
Thanks so much for pointing out my ignorance Zen! As usual....
And thanks ItsAllInMyHead
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YES! I had my finger near there while investigating... and realized this POTENTIAL.
For anyone interested I found 4304.6088 with red illuminated switch! Its on the back of the power amp, but still... IMHO worth it!
https://canada.newark.com/schurter/4304-6088/power-entry-conn-plug-10a-panel/dp/23M1710
This is a great forum to ask question
You guys are very generous 🙂
I used to ask Zenmod via his mail
and I always get amazed by the detail and prompt reply
now I have started to post in the forum.. dont want to bother him
I have started with my DIY journey in Audio since 2023
I read a lot and collected lot of info to find a good project
Presently I have boards of Aleph J and ClaveFremen
MY Ref C LM3886 project...Iorn pre is in pipe line
So my latest question is what's the special with R-Core transformer which Fremen uses in his LM3886 project
which is 65w class AB...I asked him ..the answer I got was its Vgood ..but dint give a reason exactly
I have R-core availability here not much costlier than a toroid
Toroid I have read is not good option if mains supply has DC component and noise (which most probable here in India)
But R core some say has higher impedance and not do well in some cases ( I dint get this concept fully)
But heating will be less since they are wound on separate legs and no capacitive coupling and less stray flux and hum
with regard to Aleph J ,,,will R-core bring any advantage to a class A amp.. I am planning to do it in dual mono
Thanks
You guys are very generous 🙂
I used to ask Zenmod via his mail
and I always get amazed by the detail and prompt reply
now I have started to post in the forum.. dont want to bother him
I have started with my DIY journey in Audio since 2023
I read a lot and collected lot of info to find a good project
Presently I have boards of Aleph J and ClaveFremen
MY Ref C LM3886 project...Iorn pre is in pipe line
So my latest question is what's the special with R-Core transformer which Fremen uses in his LM3886 project
which is 65w class AB...I asked him ..the answer I got was its Vgood ..but dint give a reason exactly
I have R-core availability here not much costlier than a toroid
Toroid I have read is not good option if mains supply has DC component and noise (which most probable here in India)
But R core some say has higher impedance and not do well in some cases ( I dint get this concept fully)
But heating will be less since they are wound on separate legs and no capacitive coupling and less stray flux and hum
with regard to Aleph J ,,,will R-core bring any advantage to a class A amp.. I am planning to do it in dual mono
Thanks
it's simple as this: for A Class amp you need xformer made properly , so flux in core isn't too high, so no buzzesssssss
toroid, or R Core, who cares; I mean - it's more important that you get good one than which type it is. Though, for heavy load, I prefer Toroids
if you have option to order custom xformers, that would be best; just tell them that declared voltage must be at full load, and that it will be used for A Class amp, so you want them wound with lesser flux; proper winder will know everything from there
toroid, or R Core, who cares; I mean - it's more important that you get good one than which type it is. Though, for heavy load, I prefer Toroids
if you have option to order custom xformers, that would be best; just tell them that declared voltage must be at full load, and that it will be used for A Class amp, so you want them wound with lesser flux; proper winder will know everything from there
Finally got myself my first scope. What sort of AC ripple is acceptable on the PS output? My loaded output is reading 22VDC with about 50mV pp AC ripple. Bias I settled at ~480mA (with fans on 4U) where it sounded best to me. Not sure how to reproduce checking output distortion with just a scope - as exampled on the first pages of this thread.
Nice!!
Noise on the speaker output is what matters. Because the circuit will have some PSU noise rejection it’s going to be less than at the PSU output. If you can’t hear any hum, it’s good. 😎
You don't, because you’d need a distortion analyzer. The scope shots are essentially just a screen for the HP339A I used to make those tests.