I didn't show supply rails in a phono stage schematic posted here: http://www.diyaudio.com/forums/audio-sector/151938-phono-stage.html#post1928514
If I did, C4/C5 would be there, decoupling the rails. Suggested value is 100/25
If I did, C4/C5 would be there, decoupling the rails. Suggested value is 100/25
It all depends on your subsequent stages, if they have input caps or do not amplify DC, you may not need any coupling caps.
In case you decide to use them, 4.7uF is good overall value, and should be installed at the output.
As to the hum, there is probably something wrong with wiring, normally, the phono stage is quiet.
In case you decide to use them, 4.7uF is good overall value, and should be installed at the output.
As to the hum, there is probably something wrong with wiring, normally, the phono stage is quiet.
It all looks good. The offset will depend on second pair of chips (OPA637) and the hum is not caused by offset.
You may try connecting wire from TT to the common PS ground at C4/C5.
If nothing else helps you probably need a shielded enclosure, after all it's noise sensitive low signal circuit.
You may try connecting wire from TT to the common PS ground at C4/C5.
If nothing else helps you probably need a shielded enclosure, after all it's noise sensitive low signal circuit.
One problem I have noted...there seems to be some AC coming from the power supply, which I can't imagine is helping the situation...looks like ~50mV from the +ve rail, ~25mV from the -ve rail...
I have tried putting it in a metal case - didn't seem to help. I do notice that the amount of noise can be changed by moving the output IC's around...but not removed..
regards,
byron
I have tried putting it in a metal case - didn't seem to help. I do notice that the amount of noise can be changed by moving the output IC's around...but not removed..
regards,
byron
I changed to a different PS that measured NO AC and the hum has reduced very significantly...now I need to put it back in it's (aluminum) case and see what happens...I am still unconvinced that everything is good..I think I may re-do the signal wires with some shielded cat5 or something and see if that maybe helps sa well..
byron
byron
OPA627/637 works with ±4.5-18V. I'm using ±15V
I checked the AC and it's 0V in my circuit.
I checked the AC and it's 0V in my circuit.
Yeah, so I am not sure what's going on with that...anyway, I changed the power supply, and re-mounted the cartridge - I think that was what the problem was in the first place! I hooked it back up to the ARC and it was humming a lot too...so I remounted it, and voila - the phono stage is singing, and rather nicely too!
what a trial, but anyway...thanks again.
b
what a trial, but anyway...thanks again.
b
Peter,
I have a MM cartridge with an internal impedance of 660 ohms and an output of 3.6mV. Since the standard 75db gain won't work with the current output provided, and two nice resistors to make the gain 90db instead of 75db are cheaper than 2 nice step up transformers, I wondered if you might be able to provide the value for R2/3?
Thanks!
Chris
I have a MM cartridge with an internal impedance of 660 ohms and an output of 3.6mV. Since the standard 75db gain won't work with the current output provided, and two nice resistors to make the gain 90db instead of 75db are cheaper than 2 nice step up transformers, I wondered if you might be able to provide the value for R2/3?
Thanks!
Chris
I would normally use all nude Vishays in phono circuit, however one specific value, 330k, would be very expensive if ordered from Vishay (where pricing is proportinal to resistance and would be approx $30pc). So I combine Caddocks and Vishays and it works well.
From my experience with chip amps, Caddocks MK132 worked really well in shunt and feedback locations, actually much better than Vishays S102, for series applications though, Vishays are hard to beat.
All the locations are probably equally critical in this circuit, but if you want to experiment, I would first try with 3k3 series resistors.
From my experience with chip amps, Caddocks MK132 worked really well in shunt and feedback locations, actually much better than Vishays S102, for series applications though, Vishays are hard to beat.
All the locations are probably equally critical in this circuit, but if you want to experiment, I would first try with 3k3 series resistors.
Loading a Denon DL-304
Dear Peter,
Some time ago - long before this new model of yours - I bought a phono-pre from you. I use Cinemag transformers to amplify the signal from my Denon DL-304 moving coil pickup. This combination has served me well, but lately I have investigated a little into the loading of my Denon DL-304.
If I understand the schematics right, the loading resistor in your phono-pre is 47kohm. I have seen that someone recommend 100ohm for moving coils like this. Would this be a recommended and possible modification?
Thanks.
regards
Jan Ove from Norway
Dear Peter,
Some time ago - long before this new model of yours - I bought a phono-pre from you. I use Cinemag transformers to amplify the signal from my Denon DL-304 moving coil pickup. This combination has served me well, but lately I have investigated a little into the loading of my Denon DL-304.
If I understand the schematics right, the loading resistor in your phono-pre is 47kohm. I have seen that someone recommend 100ohm for moving coils like this. Would this be a recommended and possible modification?
Thanks.
regards
Jan Ove from Norway
resistive loading of step ups
Jan,
There are almost as many opinions about how to best load MC cartridges as there are MC cartridges.
Here's a link to a simple method of loading the secondary of your step-up. The math is pretty simple, but try plenty of values as certain ratios will cause ringing in your transformers.
K&K
Jan,
There are almost as many opinions about how to best load MC cartridges as there are MC cartridges.
Here's a link to a simple method of loading the secondary of your step-up. The math is pretty simple, but try plenty of values as certain ratios will cause ringing in your transformers.
K&K