Recently, I DIY the Toccata Phono MKII preamp and found the amplificiation of the amp is far lower than expected. I am using Dynavector 17D3 MC phono and connect the Preamp to a headphone amplifier. I turn the volume to maximum and merely hear the music. I checked the voltages and found nothing adnormal. Attached the schematic with voltage shown. Please advise the possible cause of problem....many thanks.
Attachments
Try 2SK369. Still available, though maybe not for long. The K369 has the largest Yfs, and gain, of any of the low-noise Toshibas - and they sound excellent in the MC first-stage position. IMO, you can ignore the popular demand for the BL or V grade of these, and use the easy-to-find GR version. 4 to 7mA is plenty low noise for most cartridges, and gain and sound quality excellent.
You can get even more gain, and better sound, if you connect them up as shunt-cascode - search in the Analogue Source forum for Werner's OP637 RIAA amp, with K369 first stage. This circuit gives an idea of what that JFET can really do. You can use passive RIAA eq, followed by a valve in the second stage.
I found Werner's circuit.
http://www.diyaudio.com/forums/anal...ed-cascode-fet-opamp-mc-phono.html#post419559
Keep Q1 and all the parts to the LEFT of it. Throw out the op-amp.
Capacitor couple to the 6GK5 grid of the Toccata - you can delete the first stage Valve 5842.
This front end is lower noise, better sounding, and highly resistant to EMI and power line noise, compared to the original, IMHO.
http://www.diyaudio.com/forums/anal...ed-cascode-fet-opamp-mc-phono.html#post419559
Keep Q1 and all the parts to the LEFT of it. Throw out the op-amp.
Capacitor couple to the 6GK5 grid of the Toccata - you can delete the first stage Valve 5842.
This front end is lower noise, better sounding, and highly resistant to EMI and power line noise, compared to the original, IMHO.
Sad to say, the J201 will not respond to this change.
IT's because Idss of the J201 is 1mA max - this is the highest current it can deliver. Also, gfs is only 1mS, which means the gain in the first stage is only 10.
The input-eq noise is 6nV/(Hz^0.5) - not low enough for MC.
With a K369GR you get 40mS at 5mA, giving a gain of 400, and < 1nV/(Hz^0.5)
IT's because Idss of the J201 is 1mA max - this is the highest current it can deliver. Also, gfs is only 1mS, which means the gain in the first stage is only 10.
The input-eq noise is 6nV/(Hz^0.5) - not low enough for MC.
With a K369GR you get 40mS at 5mA, giving a gain of 400, and < 1nV/(Hz^0.5)
It is very likely! The output capacitor of 0,47uF requires the power amp (or line amp, of whatever the RIAA amp feeds into) must have input impedance 100K or more.
Solid state PAs have 20K input or even less, and need at least 2.2uF or more.
Yes, the Bass goes weak if the C value is too low.
Solid state PAs have 20K input or even less, and need at least 2.2uF or more.
Yes, the Bass goes weak if the C value is too low.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.