Small size EI and Toroids with Gauss band i.e. external peripheral metal shield can be candidates for encasing with FSP. And even those, carefully judged for orientation and AC wires dressing. In a roomy box, because distance is your best friend vs stray magnetic field. Properly constructed R-Core rules for minimal stray field.
Today I found that not properly constructed R-Cores can indeed be very noisy.
I was rewiring the psu on my headphone preamp and decided to put the r-core inside the case..... Orientation was fundamental until I decided to replace the +Vdc lines with tightly twisted Cat5..... that killed the noise.
So, everything is important but TX orientation and special care on the wiring is a must.
I was rewiring the psu on my headphone preamp and decided to put the r-core inside the case..... Orientation was fundamental until I decided to replace the +Vdc lines with tightly twisted Cat5..... that killed the noise.
So, everything is important but TX orientation and special care on the wiring is a must.
Salas and all,
Coming back to this project once more with a couple of questions:
1. Is it possible to power both channels of this preamp using two regulators and ONE battery source? I'm thinking a 36V battery pack (3 x 12V).
2. I need the MC version, which on the schematics says it needs 38V... Can you please confirm that? I was under the impression that 24V would suffice for these chips.
3. If that's the case, is there a way to lower the input voltage? I suppose I can always use transformers for the MC, but I'd like to avoid that.
Thanks for any feedback.
Coming back to this project once more with a couple of questions:
1. Is it possible to power both channels of this preamp using two regulators and ONE battery source? I'm thinking a 36V battery pack (3 x 12V).
2. I need the MC version, which on the schematics says it needs 38V... Can you please confirm that? I was under the impression that 24V would suffice for these chips.
3. If that's the case, is there a way to lower the input voltage? I suppose I can always use transformers for the MC, but I'd like to avoid that.
Thanks for any feedback.
Moving coil loading question -
I use a 100R load at my polarity switch which is what my cartridge prefers.
Is there any need to retain the 47K resistor on the board?
Seems superfluous since it is swamped by the 100R - but I would appreciate your advice before I remove it. The 100R and polarity switch are about seven inches away from the board.
Thanks,
I use a 100R load at my polarity switch which is what my cartridge prefers.
Is there any need to retain the 47K resistor on the board?
Seems superfluous since it is swamped by the 100R - but I would appreciate your advice before I remove it. The 100R and polarity switch are about seven inches away from the board.
Thanks,
Almost everything of that current is crunched by the CCS and shunt operation to clean the dirty DC going in.
Its 200mA in total for two channels on two shunt regs. Directly from the rail two channels together draw 60-70mA
You can swap R1 47K for 100R if no DIP switch and several Rx are involved. R1 47K is a safeguard for always having reference to ground when DIP switching is installed and used, even in live conditions (but never when on high audio volume). Keeping the load resistor on board and near the input FETS that way, is also better for terminating the input coax nearer the receiving node end.
Thanks for the advice.
I will keep it there.
Finally getting the SALAS into my system and am very pleased. Still getting to know it but, so far, no disappointments.
Initial impressions; none to little if any signature sound of the amplification devices
One just cannot beat the sound of a well executed simple circuit.
Now to find an appropriate box! It is out in the open for the moment. No hum, but some 120 hz buzzing - rectifier noise?
Can't get over how quiet it is with a LOW output MC (Transfiguration Temper Supreme - my old friend).
THANKS!
I will keep it there.
Finally getting the SALAS into my system and am very pleased. Still getting to know it but, so far, no disappointments.
Initial impressions; none to little if any signature sound of the amplification devices
One just cannot beat the sound of a well executed simple circuit.
Now to find an appropriate box! It is out in the open for the moment. No hum, but some 120 hz buzzing - rectifier noise?
Can't get over how quiet it is with a LOW output MC (Transfiguration Temper Supreme - my old friend).
THANKS!
Hi Salas, I builded my balanced FSP, but something is going wrong.
Voltage regulators are ok at 35V, 57 dB gain with only one 369 version.
When I rise up the voltage with variac, the TP1 to TP2 voltage set to 3.4V when the regulated voltage is 22V , but go down to -0.8V at 35V.
At 22V the triplet and quartet leds are bright the same way.
At 35V the quartet is brighter.
The board sink about 100 mA, and the current across R2 is about 9mA.
What's wrong?
Voltage regulators are ok at 35V, 57 dB gain with only one 369 version.
When I rise up the voltage with variac, the TP1 to TP2 voltage set to 3.4V when the regulated voltage is 22V , but go down to -0.8V at 35V.
At 22V the triplet and quartet leds are bright the same way.
At 35V the quartet is brighter.
The board sink about 100 mA, and the current across R2 is about 9mA.
What's wrong?
Congratulations.
First impressions when good, usually remain good. 100Hz ripple I could not see on the rails (120Hz in USA) when scoping my unit. But scope it yourself too. If by some loop area sensitivity 120Hz from your FSP PSU or other nearby PSU manages to superimpose itself, on TT signal wires even, try to rearrange stuff while scoping the rail or the output (wherever you manage to see a little 120Hz interference on the scope). If it intrudes due to its out in the open, then a grounded case should solve it. If it really passes through the circuit as non ironed out PSU ripple, then harder passive pre-filtering or a capacitance multiplier should solve it. Post us pictures of the whole arrangement and more info on the particular raw PSU & wiring, maybe we can give a hand, if you will not be able to reject this nuisance even when boxed.
I wonder if anybody has used wooden box for their phono stage, and used some adhesive copper to line the box, for EMI shielding. A 20cm x 100cm roll is only £5 on Hong Kong eBay, enough to do a whole box easily. Would you imagine this to work well?
Here's a link to the kind of thing I mean:
Copper Foil Tape Shielding Sheet 200 x 1000mm Double-sided conductive adhesive | eBay
Here's a link to the kind of thing I mean:
Copper Foil Tape Shielding Sheet 200 x 1000mm Double-sided conductive adhesive | eBay
Hi, maybe nothing is wrong. As you go up with the variac, current division in the folded branches changes. This can initially give current to the FET branch, and allow TPs to rise, but the headroom is still low for AC. Since it does not react bad at 35V regulated, go there first. Allow 10V higher raw DC voltage in. Then use VR2X to lower 35V little by little until TP1-2 go to range again. Should home in before the 30V point. The LEDS shone as expected.
Should work well enough for creating a grounded shell. Its not that thick, but FSP is not to be placed in the same room with an RF transmitter either.
I use a wooden box (oak and mdf). tested the prints on a prototype mdf board before final boxing and had some problems with hum, i pointed the finger at the supposed sinner : my huge 2 X 300VA Torroids .
Experimented with location of the pcb relative to the toroids, no change......
There where more hum when holding my hand over the pcb than when moving the pcb directly over the toroid.
I then found out that the sinner was the metal (aluminum) cabinet under the prototype mdf board.
Lifting the board up 10cm above the metal removed all hum.
Good luck
P
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Hi Salas, thanks for reply, but the issue remains.
I tried 52V raw supply voltage, but nothing changed.
When I turn up the voltage, I read 7,7V across TP1-TP2(the quarted string leds voltage reference, I suppose), then at 22V the voltage become 3.4V, then go down again as far as -0.8V already at 25V and remains the same as far as 35V.
I measured some voltage with 35V regulate voltage psu;
TP1-GND = 8.4V
TP2-GND = 9.2V
across R13 = 24V
Can you help me? Thanks.
I tried 52V raw supply voltage, but nothing changed.
When I turn up the voltage, I read 7,7V across TP1-TP2(the quarted string leds voltage reference, I suppose), then at 22V the voltage become 3.4V, then go down again as far as -0.8V already at 25V and remains the same as far as 35V.
I measured some voltage with 35V regulate voltage psu;
TP1-GND = 8.4V
TP2-GND = 9.2V
across R13 = 24V
Can you help me? Thanks.