2. analog
  3. 1391397639

Optimal Phono Stage Output?

I recently traded in and up to a Jolida JD9 -- one of the originals from the Maryland factory. I'm still in the process of setting it up and wanted to check in and get some ideas.

The thing with the Jolida (and many of you probably already know this) is that there is a *ton* of gain on hand. I went trough several different settings only to arrive at using the low-outputs with the MM switch w/ 47kOhm switch engaged. So far, this seems to fit well with the AT120E/T cart I'm using.

The original version of the JD9 has trim pots that can be used to dial in the gain when using the low outputs. I pulled out my multimeter to balance the channels and got readings of 18Kohm and 12Kohm on L/R channels respectively. Using the pots, I balanced everything up - no problem.

It got me thinking though, what is the optimal output, what *should* the reading be? My integrated expects 47KOhm input, but I expect that the line level signal jumps all over the place. I suspect I should play a test tone through the preamp and then measure? Heck, I'm not even sure what these measurements actually mean... Please - set me straight! :)
martinman

Showing 2 responses by martinman

martinman's avatar
martinman OP
96 posts
 
Apologies in advance, I'm not a EE, so i'm not probably making a whole lot of sense. The measurements I provided was a signal to ground measurement for each low-output jack. So, 18Kohm for the left, and 12 for the right. I used the trim pots to bring these two values into alignment so the signal level was roughly equal. Twiddling the pots did raise / lower the volume. I'm trying to find the sweet spot and struggling to make some sense out of what I'm seeing.

For the MM cart i'm using, the output is 5.0mV -- which yields a 36dB optimal gain. Further settings 47kOhm inductance, and 200-300 capacitance. This all seems straight forward and I can translate this.

Reading through the interwebs, I looks like I should have the bank of 3 dip switches in the 'off' position so that it's set right around 35dB -- maybe that's where I should start. Currently I have switch 1 'up' -- this yields about 50dB -- and I'm attenuating the signal down using the trim pots.

Basically, I'm trying to find a starting point of the JD9 with my setup.
martinman's avatar
martinman OP
96 posts
 

1Khz test tone, measure the output in mV. Should be around 200mV.

Done deal. Sounds pretty good.

With a 5mV cart, I would not go this route again... It sounds good, but I think the sweet spot for this preamp is is a lower output cart. I'll get something else eventually, but for now i'm happy.

I might drop in some 5751 tubes to lower the gain a bit. I called Jolida and they said this was perfectly ok to do. Also, they said twiddling the switches on the back are ok while the preamp is on. Just lower volume on your power amp when doing so.
More to discover