Hi polyphaze
Despite my best attempts to match all transistors in the Phobos, I also had a DC offset in my output. 2V in one channel, 0.8V in other channel. As previously mentioned, I use transformer coupling, but with this offset I elected to put a cap in series with trafo to save it from DC current. But that's sort of cheating. So last week I finally did the job properly - got 100 ohm pots and wired them into the circuit across the emitter resistors in MAT02 front end. After adjustment I have got the offset down to a few mA. But - the offset is not steady - it wanders around quite a bit even after a few hours. But I am not worried about DC at this low level, and I have taken out the caps. Can't say I have heard any real improvement, but I feel better about myself for having done this.
After an extended stay at the work shop, the Lenco is back!! The motor bearings have been replaced, and a new teflon thrust pad put into main bearing. It runs beautifully. However it has been about 35 deg Celsius (95 deg F). the last few days and its damn hot outside and inside the house. I bi-amp my speakers, and dissipation from 4, 50 watt Class A amps is doing nothing to help the situation so I am not even able to turn on the system right now! What a drag, I am on holidays and not able to play records
Hi,
I like that simple, low parts count, but clever circuit
I wonder though why difficult to source PJFETs were used and NPNs in the first stage?
It should be easy to 'switch' to complementary transistors and reverse the supply rails.
In other threads about lownoise transistors the FZT/ZTX951 were mentioned as suitable for such input stages, and for N-channel JFETs there are a row of suitable and sourcable candidates.
Also one might think about running the JFETs a bit hotter.
After my experience suitable known JFETs sound better if they run on a couple of mA drain current.
Besides it'd allow to reduce the value of the 1k drain resistor, which is positive regarding bandwidth (bandwidth limiting RC-Lp of the R with the bipolar's C).
jauu
Calvin
I like that simple, low parts count, but clever circuit
I wonder though why difficult to source PJFETs were used and NPNs in the first stage?
It should be easy to 'switch' to complementary transistors and reverse the supply rails.
In other threads about lownoise transistors the FZT/ZTX951 were mentioned as suitable for such input stages, and for N-channel JFETs there are a row of suitable and sourcable candidates.
Also one might think about running the JFETs a bit hotter.
After my experience suitable known JFETs sound better if they run on a couple of mA drain current.
Besides it'd allow to reduce the value of the 1k drain resistor, which is positive regarding bandwidth (bandwidth limiting RC-Lp of the R with the bipolar's C).
jauu
Calvin
Hi Hazard..
To maintain near zero offset in this circuit, you need very tight voltage regulation. SLA batteries don't provide that as the voltage varies significantly over the discharge cycle.
On another subject, I visited SoundSmith not long ago to pickup a MI cartridge I had purchased, and was treated to a demo of their (very pricey) strain gauge system. I really liked it for reasons you have already articulated. I'm preparing a post to your SG thread with more details.
Happy New Year!
To maintain near zero offset in this circuit, you need very tight voltage regulation. SLA batteries don't provide that as the voltage varies significantly over the discharge cycle.
On another subject, I visited SoundSmith not long ago to pickup a MI cartridge I had purchased, and was treated to a demo of their (very pricey) strain gauge system. I really liked it for reasons you have already articulated. I'm preparing a post to your SG thread with more details.
Happy New Year!
Happy New Year to you too, Thomas. Get you point about regulated p-s. One day, maybe.... I have lots of projects to build and this is well down on my priority. I plan to retire in the next year or so so sometime around 2020 might be good.
Which Soundsmith did you get? And why did you feel a need to replace your last cartridge? Will you be running a low output model into the Phobos? I am very intrigued by these cartridges (I have enjoyed 4 different Grados over the years, also MI) but have not yet got a chance hear one. Would enjoy reading your impressions of the Soundsmith.
Regards, Paul
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Hi Guys,
Sad news, Hazard passed away 1 month ago, he and I have known each for 25 years and worked on many of these projects together.
I have inherited his phobos phono stage, I was very impressed with the sound from it in his system and was going to make one of my own using ssm2212.
Clearly I don't need to do that now but I have a question,,,,
On the board the inputs are marked R and T for both channels.
Can someone explain the meaning of those?
Which is positive in?
Thanks
Varle Hazard
Sad news, Hazard passed away 1 month ago, he and I have known each for 25 years and worked on many of these projects together.
I have inherited his phobos phono stage, I was very impressed with the sound from it in his system and was going to make one of my own using ssm2212.
Clearly I don't need to do that now but I have a question,,,,
On the board the inputs are marked R and T for both channels.
Can someone explain the meaning of those?
Which is positive in?
Thanks
Varle Hazard
Sad news indeed. I very much enjoyed working with Hazard on this project.
You probably have figured this out by now, but for the record T and R refer to the 'Tip' and 'Ring' of the 3.5mm audio jack that the board was designed for. Tip is positive.
Sorry for the extreme delay, I just haven't logged in to DIYA for that long.
Best Regards
You probably have figured this out by now, but for the record T and R refer to the 'Tip' and 'Ring' of the 3.5mm audio jack that the board was designed for. Tip is positive.
Sorry for the extreme delay, I just haven't logged in to DIYA for that long.
Best Regards
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