IMHO, the filtering values are far too small for about 100mA output. I'd also replace plain diodes to ultrafast or shottky. Check the CCS current settings also. While the RMS value is 30mA per channel, the peak value can be a bit more (say 40mA), plus you should have spare 20mA for the regulator itself.
Real noise is very small if all works right.
Real noise is very small if all works right.
DMM can't tell much about the nature of the noise. Is it a little hum or hiss what you eventually hear?
Giea sou Nikos,
The noise on the phono output is definitely hum - a little higher in level than I would really like. I replaced the twisted pair wiring I usually use at the input and output with screened cable, but this didn't make much difference.
The line output noise is more a buzz, which is distracting at low levels. Again, I installed screened cable each side of the volume control, with little effect.
I wondered whether the filament supplies might be inducing the noise, but these are current regulated, so I suspect (perhaps naively) that these might not add much to the noise. I separated this wiring from the HT and ground wires anyway, but again little improvement.
Both channels have their own star ground, commoned to the chassis in the outboard PSU, with an additional 10R to chassis on each channel in the preamp box itself. I originally used your recommended separate wiring for sense and power on the outputs of the regulators, but after wondering whether noise was being induced in the (unscreened) sense lines, connected these together with no change.
This is one of the most frustrating problems I have come across - the SVP itself is actually sounding really good, apart from the noise!
Alex
Those are useful comments. I don't have space in the PSU box for any more polypropylene caps, but I could try adding another 100uF in electrolytics to see what happens.
Alex
In case the CCS level in the reg is not high enough it could pass ripple. Set at max around 80-100mA if you got the sinking since you need draw 60mA RMS as poty noted. Given the pre-filtering is good enough and the input to output is 10V-20V you should be safe from rail buzz and the heat on the CCS sink should stay under control. If you still got signal buzz after the currents are plenty then its a slim chance it comes from 100Hz on the rails. Should be some loop, either area or ground. Are the Tx & rectification located in the same box?
Thanks. I can see myself being forced to get a bigger box for my PSU so I can double up the transformers and increase the filtering. I have a full-size one for my RTP3, with fully dual mono supplies and still some space left over.
Alex
that 3mVac is an averaged ac measurement that is converted to sinewave equivalent.
I have found that a scope shows a peak to peak voltage of very approximately 3 times the Vac measurement reported by a DMM.
Ie. you have around 9mVpp of ripple on the supply.
If that is before the regulator, then that indicates good to very good smoothing.
If that is after the regulator, then I think there is something wrong with the regulator.
Salas mention drop out
you must check for this.
It cripples regulator performance.
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You can test your setup by just pulling out the mains plug of the device and listening to what will happen. The capacitors should support the B+ for some time and you will not have any 50/100Hz ripple source anymore.
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The message I am getting is to check the CCS current in the regulator, which may be too small. I will see if I can reduce the HT voltage coming out of the PSU for my RTP3 by 50V or so and connect that up - it has a much higher current capacity than the one I built for the SVP, and will give a bigger margin for experimentation.
Alex
OK, following your helpful suggestions, I tripled the capacitance after the choke and increased the shunt current in the regulator. The hum in the phono stage is gone altogether now, but a slight (but reduced) buzz remains from the line stage in one channel (which vanishes when I short the line output with the mute relay, so it's not cabling or the power amp).
I have swapped both line stage valves between channels, with no effect, so I surmise there must be something amiss with the wiring in that line stage, and I will chase this up.
Many thanks for your help!
Alex
I have swapped both line stage valves between channels, with no effect, so I surmise there must be something amiss with the wiring in that line stage, and I will chase this up.
Many thanks for your help!
Alex
congratsHi Fred,
No, the FVP5a/SVP is a very different design to the RTP3. It has half the valve count and is single-ended, instead of the differential RTP3. The phono stage is more similar to Thorsten Loesch's version of the Arthur Loesch preamp.
An externally hosted image should be here but it was not working when we last tested it.
Alex
Hi Alex,
Totally understood that RTP3 is a balance circuit and SVP is single-ended.
I did compare FVP5A to RTP3C. LOL, I just hope I could get some tip from you so that I can derive the SVP-2 from the RTP3D circuit
Sorry for the off-topic. Feel free to email me via the forum if you want to explore SVP-2.
Thanks!!
Totally understood that RTP3 is a balance circuit and SVP is single-ended.
I did compare FVP5A to RTP3C. LOL, I just hope I could get some tip from you so that I can derive the SVP-2 from the RTP3D circuit
Sorry for the off-topic. Feel free to email me via the forum if you want to explore SVP-2.
Thanks!!