Thr R=0.75R does not include the secondary resitance. The resistance of the inductor is .3R if you trust the DMM. Shorted leads were 0.1R and the actual read was 0.4R so I just subtracted it.
I Set R1 to yield the required voltage. I was lucky that I had a 3W resistor of the value in my box. I started with 1 ohm which yielded too low of a voltage, then piggybacked another one ohm ontop and the voltage was too high so I went between and used 0.75R and it came out just about right.
I Set R1 to yield the required voltage. I was lucky that I had a 3W resistor of the value in my box. I started with 1 ohm which yielded too low of a voltage, then piggybacked another one ohm ontop and the voltage was too high so I went between and used 0.75R and it came out just about right.
The AC mains is dangerous for inducing hum. Even if its near enough to the TT cables outside the box. Use steel plates for the sub box to enclose the phono preamp, even at the bottom. You can also mount the toroid perpendicularly if the height of the box allows.
The safest approach by my experience is 2 half width boxes, even one next to another on the rack looking like a nice full width combo. One receives the mains and has Tx, rectification, filter. A DC cable* goes to the main phono box that has the regs and Riaa preamp. The AC power all the way far from the side that TT input cables come in.
*Using XLR cable, shield connects the 2 chassis, the Tx & filter chassis is mains grounded.
** I use single chassis too, but I arrange across width, the mains are coming in as far aside as possible and an R-Core is tolerated. A toroid is offensive. Even with such measures always at least one channel will pick 5-10dB mains on FFT. Don't know if not if there was a steel sub box too. Me I don't mind a -90dB or -80dB single hum band even on my 95dB speakers, I know it will pick up probably when in the rack with the TT cables coming in near other mains feeds and equipment anyway. But FFT is your friend, just don't carve the box design in stone before you got all your parts and you are sure about the Riaa PCBs are dead quiet also, leave slack for changing your practices before final assembly. Low noise-high gain, is a bugger.
*Using XLR cable, shield connects the 2 chassis, the Tx & filter chassis is mains grounded.
** I use single chassis too, but I arrange across width, the mains are coming in as far aside as possible and an R-Core is tolerated. A toroid is offensive. Even with such measures always at least one channel will pick 5-10dB mains on FFT. Don't know if not if there was a steel sub box too. Me I don't mind a -90dB or -80dB single hum band even on my 95dB speakers, I know it will pick up probably when in the rack with the TT cables coming in near other mains feeds and equipment anyway. But FFT is your friend, just don't carve the box design in stone before you got all your parts and you are sure about the Riaa PCBs are dead quiet also, leave slack for changing your practices before final assembly. Low noise-high gain, is a bugger.
Attachments
Ok. Thanks for the picture. I have a little room to play to keep the AC more seperated from the RIAA. At some point I will build a second enclosure for the Tx and PS board. As you suggested, I want to get the circuit up and running first, learn from it and then move on to better optimization. Ultimatley I would like to have seperate tx and PS boards for each channel if this really does sound as good as it claims to be;-).
In the meantime I can make the internal steel enclosure large enough to give room to play and as a secondary precaution twist and shield the AC mains in "conduit". The IEC connection is already shielded so I just have to be mindful of the mains wiring itself and properly bonding the shields. The RCA in and out can be kept on the other side of the chassis to keep it as far from AC as possible.
In the meantime I can make the internal steel enclosure large enough to give room to play and as a secondary precaution twist and shield the AC mains in "conduit". The IEC connection is already shielded so I just have to be mindful of the mains wiring itself and properly bonding the shields. The RCA in and out can be kept on the other side of the chassis to keep it as far from AC as possible.
Yes works fine. Its somewhat smoother and bolder. Mainly it allowed very low field for using just one box medium size with 61dB gain in that.
Hi Salas
What do you mean by "90dB or -80dB single hum band" ?
In my recent evolution I got hum to be lower than riaa amp Shhhhh... And this noise can only be heard at full output without signal.
Just rearranged the riaa layout to minimize loop area... look at the pdf
It is better than ever but still sensible to the "opening the lid" effect.
I guess I now I am ready to go fullfilm again
BTW.... very nice build.... I guess this is for the DL103R right ?
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Say the LF noise is at -110dB to -100dB relative to 0dB=1VRMS output depending on gain and psu etc. and then you got a mains 50Hz or 60Hz hum band picked up by a field or a loop in the box or outside and that pokes at -90dB.
The lid must be always closed in a phono.
Yes that build is the test LowMc with C0G RIAA caps, the rest are generic and Russian parts. Its so smooth and dynamic you would not guess it can be made better. Yeah, you bet, we know it can.
The lid must be always closed in a phono.
Yes that build is the test LowMc with C0G RIAA caps, the rest are generic and Russian parts. Its so smooth and dynamic you would not guess it can be made better. Yeah, you bet, we know it can.
Salas,
Is there a particular Idss for Q7 that would be best? Same with Q6. I have hundreds of each. I hit the jack pot for LED's, and these type of fets. Just down the road from my house is BD Enterprise, a smaller version of Mouser. I bought the last of the sk170's from him. Either alot of people are building this phono riaa or there is another project going on at DIY audio. He claims to have had a run on them recently from this site.
Is there a particular Idss for Q7 that would be best? Same with Q6. I have hundreds of each. I hit the jack pot for LED's, and these type of fets. Just down the road from my house is BD Enterprise, a smaller version of Mouser. I bought the last of the sk170's from him. Either alot of people are building this phono riaa or there is another project going on at DIY audio. He claims to have had a run on them recently from this site.
Q7 is 2N5459, Q6 is BC550C in yours. 5-6mA for Q7 is OK for the LEDs.
Not many are building this, its the Pearl II and DCB1 Blue probably these days.
As I was not happy with the subjectively "thin" presentation, I went further and placed another gnd wire from the CCS leds to star GND, separating these from input GND.
Noticed gains in spaciousness as well as a more full presentation (lost the thin sound).
Is there any instrument that can measure magnetic fields... if there is not a commercial unit available, it should be easy to build right ?
My next mod will be to return to fullfilm shunt. Just found two 10u Audyn cap MKP that are much smaller than the obbligato so I guess it will reduce loop area.
Noticed gains in spaciousness as well as a more full presentation (lost the thin sound).
Is there any instrument that can measure magnetic fields... if there is not a commercial unit available, it should be easy to build right ?
My next mod will be to return to fullfilm shunt. Just found two 10u Audyn cap MKP that are much smaller than the obbligato so I guess it will reduce loop area.