I finished PS board and it should looks like shown in attached pictures. I said should since I have an issue with that transformer. I bought Spitznagel 2x18V, 18VA SPF 1831818 model and with it I got +/-60V after rectifier/multiplier! That is far too much at least for 7924 which should have more then 40V on input. It's not damaged but cannot deliver -24V but -33V instead.
I'm wondering what kind of formula people in Spitznagel are using since my cheap multimeter measure 23.8VAC on secondary windings on no load. It is closer to peak then to RMS value. I tired to make measurement on some other Spitznagel trafo what I have and again, for 12VAC secondary I can measure 17.7VAC with the same multimeter.
Toroidal trafo used for dual channel pcb deliver 20VAC on no load and with that I got +/-44V after rectifier/multiplier.
Btw, I also tried another toroidal trafo with 16.3VAC on no load and got +/-37V after rectifier/multiplier.
So, I have to find i.e. 2x15VAC from Spitznagel or maybe 2x18VAC from other manufacturer (Block FL10/18, FL14/18, etc.).
I'm wondering what kind of formula people in Spitznagel are using since my cheap multimeter measure 23.8VAC on secondary windings on no load. It is closer to peak then to RMS value. I tired to make measurement on some other Spitznagel trafo what I have and again, for 12VAC secondary I can measure 17.7VAC with the same multimeter.
Toroidal trafo used for dual channel pcb deliver 20VAC on no load and with that I got +/-44V after rectifier/multiplier.
Btw, I also tried another toroidal trafo with 16.3VAC on no load and got +/-37V after rectifier/multiplier.
So, I have to find i.e. 2x15VAC from Spitznagel or maybe 2x18VAC from other manufacturer (Block FL10/18, FL14/18, etc.).
Attachments
what is the question?(Almost) all components arrived and I finalized PS section and upper channel from dual PCB. So far everything is ok except one minor mistake with hole diameter for 1K/2W resistors (R4, R5, R31, R32) which at least im my case should be 1mm.
I skipped ground loop breaker section in PS since I have it on another board. Mosfets for +/-33V really don't need any heatsinks, and for 78/79 regulators I used twice as shorter then listed in current BOM and that is more the enough.
You can see attached some of the first measurements (signal source is recorded CD not function generator).
Input transformer is 2x18V.
Unpopulated section of upper channel is intented for building of phase splitter as Koja requested.
Now I'm going to find somewhere P5 (50R) that I need to finalize lower channel on dual PCB
Are you wanting info on the two highlighted distortions?
Hi Andrew, no I just marked it to highlight that clipping area is nice (no oscillations, etc.) when preamp is overdriven (cca 4.5Vpp on input). As you can see on that measurement output swing is huge (over 45V). Am I correct here?
For me is mistery something what is marketed as 2x18VAC to provide almost 2x24VAC on no load.
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I think the high voltage is just the case of off load regulation. 18V at 500mA is probably 23V or so at no load which is 46V across both secondaries. Since this design draws nearly no current (<50mA I would guess) that will be a near no load condition for the transformer. This will be worse and worse with transformers with low VA ratings (higher percentage regulation) until the transformer power rating approaches the power consumed by the circuit.
You're right. Even with 300mA load there is minor voltage drop (cca 1.5V) what is far beyond 18VAC. In that case suggested 18VAC pcb transformers in the BOM list are not appropriate. I'll try to get one with 2x15VAC.
no, it will found in the spec sheet as 'regulation specs'
smaller trafos naturally need more
but the specs still varies
if the curcuit is unable produce a voltage drop, maybe look at higher wattage trafo with lower regulation
That was going to be my approach. I am also going to integrate this line amp with a Salas Folded Phono stage. I'm really looking forward to the results.
Have a great weekend
Matt
Only 4 single channel and 2 dual channel boards left. On dual board you have PS section for both channels.
Folks:
I've updated Prasimix' BOM v2.8 for the North American market. Digikey has been eliminated from this BOM because their stock availability and minimum purchase quantities were in many instances a problem. Allied Electronics can provide the transformers and some of the parts at a lower price than Mouser; green colored prices denote the less expensive supplier (not that you couldn't figure that out, but in the case of Mouser the lower price may require the purchase of a quantity in excess of the number required to build two channels and independent power supplies).
If you see any mistakes, please let us all know.
Regards,
Scott
I've updated Prasimix' BOM v2.8 for the North American market. Digikey has been eliminated from this BOM because their stock availability and minimum purchase quantities were in many instances a problem. Allied Electronics can provide the transformers and some of the parts at a lower price than Mouser; green colored prices denote the less expensive supplier (not that you couldn't figure that out, but in the case of Mouser the lower price may require the purchase of a quantity in excess of the number required to build two channels and independent power supplies).
If you see any mistakes, please let us all know.
Regards,
Scott
prasimix:
The boards have arrived -- thank you again!
To all:
I have placed an order for eight sets of V grade 2SK246 and 2SJ103 from the source that prasimix used and only need two sets (possibly four sets) for my build; these parts will likely take a month to arrive. I may also have an extra set of the through-hole boards (depending on a friend's interest). I make no promises regarding the 2SK246/2SJ103 sets, but if they were good enough for prasimix they ought to be good enough for me. Your cost is my cost plus shipping. If anyone is interested, please PM me (no need to hijack this thread).
Regards,
Scott
The boards have arrived -- thank you again!
To all:
I have placed an order for eight sets of V grade 2SK246 and 2SJ103 from the source that prasimix used and only need two sets (possibly four sets) for my build; these parts will likely take a month to arrive. I may also have an extra set of the through-hole boards (depending on a friend's interest). I make no promises regarding the 2SK246/2SJ103 sets, but if they were good enough for prasimix they ought to be good enough for me. Your cost is my cost plus shipping. If anyone is interested, please PM me (no need to hijack this thread).
Regards,
Scott
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