Just got one of these and the noise levels are relatively high, its clearly audible from a few meters away with 85dB/1W/1M speakers. The original op amps are the 4580 as buffers and the 2060 for the filters, see partial schematic below. I have checked the power-supply to the op amps and its as clean as it gets with 7815/7915 regulators.
I am considering changing the 4580/2060 for the OPA165x Op Amps to get the noise levels down, any thoughts or other suggestions on this from anyone?
I am considering changing the 4580/2060 for the OPA165x Op Amps to get the noise levels down, any thoughts or other suggestions on this from anyone?
Seems my schematic is wrong, pulled it apart and there are only 4580's in there. I've tested/listened to it a bit on passiv filtered speakers and it sounds better than expected (it's only €110) and even though its not very resolved or 3D'ish and lacks a bit of low end punch it sounds clean, balanced and enjoyable enough for non critical listening.
I would not expect much from swapping op amps. NJM4580 is not that bad, but the circuitry around it is not what I call a low noise design.
I am using proper balanced signal in to the CX2310 but the amp I used for testing is not balanced but looking at the schematic it should be ok? That said it's way to noisy, if I had PA speakers it would be like listening to a waterfall. I will try another balanced preamp.
Do you know that will make a difference on the CX2310? I've done similar mods on other equipment but it has not in an any audible way changed the noise levels.
Yes, shorted or not. Just tried another balanced preamp and it's the same. This thing raises the noise floor with 20dB according to my 3rd gen focusrite and REW.
Its got a lot of high impedance stages, 50k pots etc - needs a redesign to lower the noise. Each 50k pot in series could be contributing upto about 30nV/√Hz.
For decent multistage filtering it pays to use low impedance design, keeping values more like 2k to 5k tops.
One trick you can use is to boost the signal going in and attenuate it on the output - so long as you don't hit headroom limits that will reduce the noise across the board.
For decent multistage filtering it pays to use low impedance design, keeping values more like 2k to 5k tops.
One trick you can use is to boost the signal going in and attenuate it on the output - so long as you don't hit headroom limits that will reduce the noise across the board.
I think Mark is correct but I changed the input op amp to the OPA1642 anyways as the unit was pulled apart and it was easy enough which lowered the noise floor somewhat, REW/Focusrite indicates around 12 dB lower. It's still noisy so the design is problematic.
I then changed the other op amps to a mix of OPA 1642 and 5532 (I run out of the 1642), also added a filter (22mH 0.5ohm) on the 78/79 supply and added 4x470uF/63V Nichi KW(M), 2 on each pcb for added local decoupling. Shorted all the dc blocking caps except for the final/output ones that I changed to Nichi BP Muse.
This did not change the noise floor but it now sounds pretty good, cleaner and more resolved.
I then changed the other op amps to a mix of OPA 1642 and 5532 (I run out of the 1642), also added a filter (22mH 0.5ohm) on the 78/79 supply and added 4x470uF/63V Nichi KW(M), 2 on each pcb for added local decoupling. Shorted all the dc blocking caps except for the final/output ones that I changed to Nichi BP Muse.
This did not change the noise floor but it now sounds pretty good, cleaner and more resolved.