Russ,
I followed the following advice you gave me, to match the Legato2 with the F5:
"Replacing R1-4 with 357R (.25 or .5W metal film) and R9-R16(CCS Rs) with 1K(.5W metal film) should yield much better results for you. Everything else can remain unchanged."
At first it sounded horrible. The FFT showed very deep clipping and distortion. I managed to reduce the distortion increasing a bit the positive rail of the legato. I set it at 16.5 V. I cannot go higher, both because my supply does not allow of that, and because I do not want to fry the opamp. The negative bias is around 13 V, and looks like it does not affect the distortion Additionally I had to set the reference voltages not at AVCC/2 (1.74 V) but around 1.45 V. Like this it sounds good, and there is no clipping even at 0db.
I am satisfied with the setting, I'd love to understand the reason behind this.
Thank and Happy Holiday,
Davide
I followed the following advice you gave me, to match the Legato2 with the F5:
"Replacing R1-4 with 357R (.25 or .5W metal film) and R9-R16(CCS Rs) with 1K(.5W metal film) should yield much better results for you. Everything else can remain unchanged."
At first it sounded horrible. The FFT showed very deep clipping and distortion. I managed to reduce the distortion increasing a bit the positive rail of the legato. I set it at 16.5 V. I cannot go higher, both because my supply does not allow of that, and because I do not want to fry the opamp. The negative bias is around 13 V, and looks like it does not affect the distortion Additionally I had to set the reference voltages not at AVCC/2 (1.74 V) but around 1.45 V. Like this it sounds good, and there is no clipping even at 0db.
I am satisfied with the setting, I'd love to understand the reason behind this.
Thank and Happy Holiday,
Davide
Another question: the burr-brown is a drop in replacement for the national, or I should change something else to experiment ?
D.
D.
Hi Davide,
Wow its been a while. Those values where meant as starting points. 🙂
Ok A couple notes. If it was clipping with 357R at R1-4 and 1K at R9-16 you have two choices. Reduce the negative rail to around 12 volts and leave the positive rail at 15-16V. Or, alternatively increase R9-16 to ~1.5K and use symmetrical rails.
I would also set the input bias voltage to 0V (or close). This gives the top half more headroom.
You could use any one of many dual opamps. Just make sure you are in compliance with the datasheet.
Cheers!
Russ
Wow its been a while. Those values where meant as starting points. 🙂
Ok A couple notes. If it was clipping with 357R at R1-4 and 1K at R9-16 you have two choices. Reduce the negative rail to around 12 volts and leave the positive rail at 15-16V. Or, alternatively increase R9-16 to ~1.5K and use symmetrical rails.
I would also set the input bias voltage to 0V (or close). This gives the top half more headroom.
You could use any one of many dual opamps. Just make sure you are in compliance with the datasheet.
Cheers!
Russ
Yes, I made few detours.
The FFT brought me to the first option, and I will probably stick with it.
Thanks,
D.
The FFT brought me to the first option, and I will probably stick with it.
Thanks,
D.
The key is to give keep the output bias at about 3 + ((V+ - 3) / 2) volts. 🙂
This gives the circuit headroom (which you will need since you want a large output swing) so it won't clip. You can simply adjust the negative rail until you reach a happy mid point.
Cheers!
Russ
This gives the circuit headroom (which you will need since you want a large output swing) so it won't clip. You can simply adjust the negative rail until you reach a happy mid point.
Cheers!
Russ
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I want to use my Legato 1.0.3 for my SE pcm1704, the standard I/V resistor is 150 ohms so I have to change for pcm1704 100 ohms, ok? if ok also I have to change the bottom resistors R20-R24 but due to the fact that I will use Legato as SE I only use the Hot & Gnd with Cold connected to Gnd I need to know wich resistors have I to change R1 & R3 or R2 & R4 also R20 & R23 or R21 & R24? Someone know if have I to change the 1nF & 15nF caps or how calculate the value neede to filter pcm1704?
Thanks for help
Felipe
Thanks for help
Felipe
If I remember correctly a statement from the "makers", paralleling more FETs increases the parasitic input capacitance, which might have a negative effect at some point.
Russ...
Has mentioned that he did already try more FETs in parallel, and that three turned out to be the magic number for best performance. It is easy to try more yourself, but could be a waste of time...
Has mentioned that he did already try more FETs in parallel, and that three turned out to be the magic number for best performance. It is easy to try more yourself, but could be a waste of time...
Yes, three FETs per channel and phase, like it is implemented in the Legato 3.1.
The three of them are already paralleled.
Not necessary but an option yes.
On my Legato 1 I did it like this
Be aware of orientation of the different FET's. The P version is 180 off the KL
On my Legato 1 I did it like this
Be aware of orientation of the different FET's. The P version is 180 off the KL
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