Something I have failed to point out is that in SG cartridges the compliance is NOT controlled by the stylus assembly, but by the internal mounting and damping components used with the transducers, and by the transducers themselves.
The styli are completely interchangeable in the 450C2 and up, and have no bearing on the actual cartridge compliance.
The styli are completely interchangeable in the 450C2 and up, and have no bearing on the actual cartridge compliance.
Upcoming Version
The attached schematic is reflective of the direction I am pursuing.
It eliminates two of the 3 batteries, but fully implemented requires an additional -24V supply which provides power to the input stage cascode CCS which subtracts cathode current allowing the amplifier stage to run at higher current.
In addition I have switched to a cascode based hybrid mu-follower in the second stage.
There may be further revisions, and there will be a PCB, the details of which I will share here.
The non-optimum gain distribution remains, ideally most of the gain would be in the first stage, but because of my disdain for the 6DJ8 I am forced to use a higher mu second stage to get the target gain (and overshoot the mark a bit truth be said).
The 6CG7 is not ideal in the application either due to rather low transconductance and modest mu, but given the cartridge source impedance the dominant noise source when everything is working correctly should still be the cartridge itself.
There are a few things I need to check and fix in the PCB design before I get boards made. If there is sufficient interest I will post the pcb files here once I know they are OK.
The attached schematic is reflective of the direction I am pursuing.
It eliminates two of the 3 batteries, but fully implemented requires an additional -24V supply which provides power to the input stage cascode CCS which subtracts cathode current allowing the amplifier stage to run at higher current.
In addition I have switched to a cascode based hybrid mu-follower in the second stage.
There may be further revisions, and there will be a PCB, the details of which I will share here.
The non-optimum gain distribution remains, ideally most of the gain would be in the first stage, but because of my disdain for the 6DJ8 I am forced to use a higher mu second stage to get the target gain (and overshoot the mark a bit truth be said).
The 6CG7 is not ideal in the application either due to rather low transconductance and modest mu, but given the cartridge source impedance the dominant noise source when everything is working correctly should still be the cartridge itself.
There are a few things I need to check and fix in the PCB design before I get boards made. If there is sufficient interest I will post the pcb files here once I know they are OK.
Attachments
That's what we talked about, the values look good and that current source now should add only .7dB noise.
Yes, I was thinking about our discussion re current noise when I added that CCS. Will be very interested in your impressions when I finally get the next iteration built and tested. Planning to order the PCB in the next week once I am reasonably confident that I have not made a stupid mistake in the layout.
Jico Stylus
I was initially somewhat concerned by the very slightly looser fit on the cartridge body, but it actually seems to perform well.
I am struggling to decide whether or not it is in fact better than an NOS OEM, but I think I am heading that way.
In any event it is a viable and IMO reasonable choice.
Enjoying some very pleasant sounding tunes at the moment.
I was initially somewhat concerned by the very slightly looser fit on the cartridge body, but it actually seems to perform well.
I am struggling to decide whether or not it is in fact better than an NOS OEM, but I think I am heading that way.
In any event it is a viable and IMO reasonable choice.
Enjoying some very pleasant sounding tunes at the moment.
A good stereo microscope will tell you how good the once plentiful replacement stylus is on how the diamond was polished from the factory.
We sometimes focus on the tip profiles and forget about going the extra mile in polishing the contact area.
Soa Win ( of strain gauge/mc and FET fame ) was known to polish his work so much, that a long time reviewer commented that it made others " look like muddy baseball bats in comparison "
This would more than likely resuly in lower distortion ,less wear and better sound overall IMO
Regards
David
We sometimes focus on the tip profiles and forget about going the extra mile in polishing the contact area.
Soa Win ( of strain gauge/mc and FET fame ) was known to polish his work so much, that a long time reviewer commented that it made others " look like muddy baseball bats in comparison "
This would more than likely resuly in lower distortion ,less wear and better sound overall IMO
Regards
David
Thanks, Shooter!
Here are the complete schematics. There will be boms, and boards at some point.
In another major departure for me the power supply is solid state and uses no exotic or expensive components. It is however fully regulated. One card will power both channels and may be co-located or remote as preferred.
Here are the complete schematics. There will be boms, and boards at some point.
In another major departure for me the power supply is solid state and uses no exotic or expensive components. It is however fully regulated. One card will power both channels and may be co-located or remote as preferred.
Attachments
Strain Gauge Pre-Amp Board
To my considerable surprise 10 sets are spoken for at this time. Was not expecting this level of interest, so thank you! I probably should have set up a group buy thread, but I was expecting to just unload what I had on hand...
The first order is sold out, and the second order is booked for six sets so far, four additional sets are still available.
The sets will consist of a pair (2) of audio PCB and a single PSU PCB. If there is enough interest I will probably ask Edcor to make a power transformer for this design..
Here is the list:
First Round:
kevinkr 1 set
GTHICM 1 set
Shooter 2 sets
Atom666 1 set
Second Round:
Furface 1 set
Laiphroag 1 set
Ppap64 2 sets
raneypdx 2 set
Just so it is understood these will be sold at my cost, plus shipping and paypal fees..
More subscribers are welcome, please send me a PM if you are interested.
To my considerable surprise 10 sets are spoken for at this time. Was not expecting this level of interest, so thank you! I probably should have set up a group buy thread, but I was expecting to just unload what I had on hand...
The first order is sold out, and the second order is booked for six sets so far, four additional sets are still available.
The sets will consist of a pair (2) of audio PCB and a single PSU PCB. If there is enough interest I will probably ask Edcor to make a power transformer for this design..
Here is the list:
First Round:
kevinkr 1 set
GTHICM 1 set
Shooter 2 sets
Atom666 1 set
Second Round:
Furface 1 set
Laiphroag 1 set
Ppap64 2 sets
raneypdx 2 set
Just so it is understood these will be sold at my cost, plus shipping and paypal fees..
More subscribers are welcome, please send me a PM if you are interested.
HI Kevin,
As a rule I try to read most of your threads and so I came upon this one.
Due to Fathers Day activities I have not been a able to read this thread in its entirely so Im sorta jumping in here at the end and asking what may be a totally naive question.
Is the design/pcb board which is the subject of this thread applicable to other strain guage cartridges, in particular the Win Labs Strain Guage Cartridge?
I believe the element resistance of the Win Labs is in the neighborhood of 1K.
Thanks for all your efforts.
Curt
As a rule I try to read most of your threads and so I came upon this one.
Due to Fathers Day activities I have not been a able to read this thread in its entirely so Im sorta jumping in here at the end and asking what may be a totally naive question.
Is the design/pcb board which is the subject of this thread applicable to other strain guage cartridges, in particular the Win Labs Strain Guage Cartridge?
I believe the element resistance of the Win Labs is in the neighborhood of 1K.
Thanks for all your efforts.
Curt