It really depends on the turntable. I have seen the RCA connectors fully isolated and joined to ground inside the turntable. It's usually not major surgery to change them to isolated, as this is usually done near the chassis ground near the rear. Again, this is highly dependent on the turntable you have.
Try measuring the continuity between RCA shells.
If they are, or you can make them isolated, then just hook them up to the Retro.
Hi All,
Been thinking of purchasing the low z Retro for my low output moving coil. The grounds on my turntable RCA outs are not connected so I guess that would work well. I need a way to control volume though. I happen to have an 8 channel PGA2310 based volume control but it is not balanced. Would this be usable?
The Joshua Tree is out of stock. Any plans to make more available?
Been thinking of purchasing the low z Retro for my low output moving coil. The grounds on my turntable RCA outs are not connected so I guess that would work well. I need a way to control volume though. I happen to have an 8 channel PGA2310 based volume control but it is not balanced. Would this be usable?
The Joshua Tree is out of stock. Any plans to make more available?
My questions are all targeting the Low-Z version.
What’s the overall system gain as supplied by the parts included in the standard kit? How is the gain calculated?
What’s the best approach to increase gain? Looking at the schematic, this seems to be accomplished by either lowering the value of R2 and/or R13. What trade-offs are involved in the different approaches?
Thanks!
What’s the overall system gain as supplied by the parts included in the standard kit? How is the gain calculated?
What’s the best approach to increase gain? Looking at the schematic, this seems to be accomplished by either lowering the value of R2 and/or R13. What trade-offs are involved in the different approaches?
Thanks!
My Ortofon cartridge outputs 0.45 mV. I found that the low-Z module's default gain setting was nowhere near sufficient. I therefore adjusted the gain, using the Edison as opposed to the Tesla approach: i.e., tinkering rather than a super-awesome calculation.
As I understand it, the best approach is to get most of the gain in the first stage, say, two-thirds or more of the desired additional gain. That leaves the second stage to perform the remaining gain increase. This ensures that you are leaving dynamic headroom for the hard-working second stage, and that the second stage will not be amplifying a signal with a less-than-ideal S/N ratio.
So much for theory. In practice, I found that I got better results by reversing the gain adjustments. If R2 (which sets gain for the first stage) is more than halved in value, the sound will start to hiss and spit. I have therefore reduced its value by about a quarter, and more than halved the value of R13.
My settings at this time are:
R2 = 720R
R13 = 480R
I am sorry I missed this question! The very best adjustment to make on the low-z retro to get more gain is to first replace R18/R19 with jumpers (0R) - the gain increase after changing that will depend on the output impedance of your cartridge (overall gain will always be effected by that parameter with this circuit) - in my setup I got about 12db increase (measured) by going from 100R to 0R. Only after doing that would I adjust other resistors. Because of all the variables involved - the Edison approach is sometimes the best. 
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I am sorry I missed this question! The very best adjustment to make on the low-z retro to get more gain is to first replace R18/R19 with jumpers (0R) - the gain increase after changing that will depend on the output impedance of your cartridge (overall gain will always be effected by that parameter with this circuit) - in my setup I got about 12db increase (measured) by going from 100R to 0R. Only after doing that would I adjust other resistors. Because of all the variables involved - the Edison approach is sometimes the best.
Thanks, Russ.
I am going to make that adjustment.
I should probably mention that I'm driving my power amps directly from the Twisted Pair modules. I don't have a line amp.
Thanks M Knight and Russ for your replies. They are very helpful.
I have planned to jump R18/R19 all along. Trouble is the Lyra Clavis DC cartridge I have currently mounted is rated at 2.5mv output therefor needs quite high gain to operate properly. I have other low output MC cartridges that output as high as 0.6mv. I guess I'll need to try the Edison approach. If I cannot find a good compromise that works for all cartridges I'll need to find a reasonable way to change the system gain of the RIAA stage without too much pain.
I have planned to jump R18/R19 all along. Trouble is the Lyra Clavis DC cartridge I have currently mounted is rated at 2.5mv output therefor needs quite high gain to operate properly. I have other low output MC cartridges that output as high as 0.6mv. I guess I'll need to try the Edison approach. If I cannot find a good compromise that works for all cartridges I'll need to find a reasonable way to change the system gain of the RIAA stage without too much pain.
Shunting R18 and R19 makes a large difference. I was expecting that because 12dB is large. What I wasn't expecting is that I now have noticeable 100 Hz hum. When the cables from the cart are disconnected, the hum ceases. I suspect that the OPA1632 chips are oscillating.
Considering putting 22.1R resistors in the R18 and R19 positions. Also considering bypassing the OPA1632 chips as per the datasheet, using 10uF tantalum and 0.1uF ceramic caps.
Considering putting 22.1R resistors in the R18 and R19 positions. Also considering bypassing the OPA1632 chips as per the datasheet, using 10uF tantalum and 0.1uF ceramic caps.
The Clavis' internal impedance is only 2R so I am eager to find out the answers to the same questions too.
Hi all,
my experience on LOW Z: shorting R18 and R19 will result the circuit not working, I have a DC of about 10-14 volts on the output!
I tryed to increase them to 3.3 ohm, nothing to do... I found that on this position, to let the circuit work properly, a minimum of 10 ohm resitors should be installed.
I guess with R18 and R19 shorthed and my cartridge of about 2ohm or even using a resistor at its place, the first IC is oscillating...
I'd like to ask Russ if there is any countermeasures I can apply to let R18 and R19 shorted without troubles...
Thanks very much,
GM
my experience on LOW Z: shorting R18 and R19 will result the circuit not working, I have a DC of about 10-14 volts on the output!
I tryed to increase them to 3.3 ohm, nothing to do... I found that on this position, to let the circuit work properly, a minimum of 10 ohm resitors should be installed.
I guess with R18 and R19 shorthed and my cartridge of about 2ohm or even using a resistor at its place, the first IC is oscillating...
I'd like to ask Russ if there is any countermeasures I can apply to let R18 and R19 shorted without troubles...
Thanks very much,
GM