The green (negative rail) led is weak. I replaced it, but it was OK, The resistor was reading 25k, I replaced it with a 20k and it got a little brighter. Another thought. All boards are on the same temporary chassis. I have not done anything to add an additional chassis ground to the phono boards, but they are connected to the input jack on the front panel.
PSU - is the Green LED dim?
on PSU 3 position terminal block. What is DC voltage from:
Blue to Yellow wire?
Yellow to Red wire?
What's going on with snubber positions? Do I see solder and/or sockets?
I see you're using a 12+12V transformer, not a 15+15V. That's going to result in a lower voltage than the 15V transformer.
My build is:
121.8 VAC on the wall socket.
25.1 VDC unloaded.
4R7 filter resistors in mine. I shipped 10R in the kits.
Loaded I get + 21.7 / - 22.1
Let's do some math.
My build unloaded we see 1.67x voltage. 15V secondaries x 1.67 = 25V Applying that factor.... 12v x 1.67 = 20V unloaded.
Similarly, about 1.46x loaded. 15V x 1.46 = 22V In your case I could expect 12V x 1.4ish 17V
But you're seeing more like 10V range.
What values are you using for filter resistors and bleeder resistors? These are values I shipped with kits:
Bleeders: R3-4 3k 1W
Filter: R5-8 10R 1W
on PSU 3 position terminal block. What is DC voltage from:
Blue to Yellow wire?
Yellow to Red wire?
What's going on with snubber positions? Do I see solder and/or sockets?
I see you're using a 12+12V transformer, not a 15+15V. That's going to result in a lower voltage than the 15V transformer.
My build is:
121.8 VAC on the wall socket.
25.1 VDC unloaded.
4R7 filter resistors in mine. I shipped 10R in the kits.
Loaded I get + 21.7 / - 22.1
Let's do some math.
My build unloaded we see 1.67x voltage. 15V secondaries x 1.67 = 25V Applying that factor.... 12v x 1.67 = 20V unloaded.
Similarly, about 1.46x loaded. 15V x 1.46 = 22V In your case I could expect 12V x 1.4ish 17V
But you're seeing more like 10V range.
What values are you using for filter resistors and bleeder resistors? These are values I shipped with kits:
Bleeders: R3-4 3k 1W
Filter: R5-8 10R 1W
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Does D3 light up on the phono boards? And what is the R26 resistor value on the phono boards?
Also, have you tried loading the PSU with only one phono board instead of 2?
What I'm wondering is if the 12V transformer is up to the task (maybe????) and/or if there is something on the board(s) that is amiss.
Also, have you tried loading the PSU with only one phono board instead of 2?
What I'm wondering is if the 12V transformer is up to the task (maybe????) and/or if there is something on the board(s) that is amiss.
neither D3 lights up. R26 on both board reads 10K, which is spec. I'll disconnect one board from the psu and see what happens. I did have one issue about a week ago, I installed Q6 backwards; I couldn't save it so I had to order a new one that came in yesterday; but everything seems ok now.
Wow, I just disconnected one phono board and got 18 vdc on the psu and the connected phono pcb.
Wow, I just disconnected one phono board and got 18 vdc on the psu and the connected phono pcb.
I think there’s two problems… something related to the improperly installed transistor, and an undersized transformer.
The math does not work out to get a 12v transformer to work with 7815/7915…
12*1.4=16.8
Minus two diode drops for rectification,
16.8 - (0.7+0.7) = 15.4
Minus at least .5v across the CRCRC
15.4 - 0.5 = 14.9v
As Tungsten mentions, the regulators need at least 2v greater input than output, so I’d say the raw DC supply needs to make no less than 17vdc under load.
Which shouldn't possible with a 12vac transformer in this circuit, unless the transformer has very poor load regulation.
Once the rest of the circuit is sorted you could change the regulators to 7812/7912, or get a 15v transformer.
The math does not work out to get a 12v transformer to work with 7815/7915…
12*1.4=16.8
Minus two diode drops for rectification,
16.8 - (0.7+0.7) = 15.4
Minus at least .5v across the CRCRC
15.4 - 0.5 = 14.9v
As Tungsten mentions, the regulators need at least 2v greater input than output, so I’d say the raw DC supply needs to make no less than 17vdc under load.
Which shouldn't possible with a 12vac transformer in this circuit, unless the transformer has very poor load regulation.
Once the rest of the circuit is sorted you could change the regulators to 7812/7912, or get a 15v transformer.
Wow, thanks for that Randy! Lovely explanation, now if I only knew what it all means
.Don't know if I was clear previously. D3 was in backward and is now working. With one board connected, the psu rails and the one pcb voltages are all at 18.
I just saw the remainder of this post. I used the components that were shipped without exception. I ordered the psu components from DigiKey as listed on the PSU BOM. No creativity.
As to snubber, I installed some caps that I had around and some resistor sockets with the idea of experimenting. However, I decided to postpone any experiments until everything was working properly. So I removed the caps. There is nothing in the snubber circuit.