No-global-loop amplification

[rsavas]

My condolences to you Jeff and your family hearing of your loss.
Rick

 

[rhythmsandy]

ohh man thats sad would be very painful days. Hope your family recovers soon.

 

[jwilhelm]

Thanks for the condolences everyone! It's especially tough with all the Covid 19 restrictions in place. Can't get together with the family and friends.

 

[Cresnet]

My condolences to you Jeff, I am so sorry for your loss.

 

[jwilhelm]

Hi Jeff,

To answer the question about smps, the test was on a different amplifier, not the SimpelStark. I’m not changing the SimpelStark as it is a fully completed amplifier. Will most likely do this on the new version. I could send you the SMPS if you want to test them. Just need to check the voltage of them.

Thanks
Do

Do you have a spare power supply to test with? Is there any info available on them? I'm curious about dimensions, ect.

The AX3 uses a separate regulated low noise supply for the input board. It will likely remain conventional.

 

[rhythmsandy]

Jeff by the way have you tried using resistor at the output for the high speed opamp? Can you please let me know if the odnf gets stable?

 

[jwilhelm]

It's not that simple. There are resistors on the output of the op amps that need to match the gain of the amplifier. I'm going to try slugging it down a bit with a capacitor eventually.

 

[rhythmsandy]

which opamp are you using?

 

[jwilhelm]

We were experimenting with THS4082

 

[rhythmsandy]

then just have a look at the datasheet that its clearly mentioned that its output capacitance driving capability is 1pf not more than that for which they recommend using a 20ohm resistor in series on the min I would say just try with 51ohm resistors in there and see if its stable.

 

[jwilhelm]

There's already a 100 ohm resistor on the output.

 

[rhythmsandy]

did u try with opa2134?

 

[jwilhelm]

Yes, it works perfectly with an OPA2134, but doesn't have the bandwidth to operate through the whole audio range.

 

[rhythmsandy]

What's actually happening it's high bandwidth opamp right?

 

[jwilhelm]

The OPA2134 works great in the low and mid frequency ranges but it's slew rate isn't fast enough to do any error correction in the upper end of the audio range. The THS4082 has 10 times the slew rate but it just goes nuts and then heads for the positive rail, then overheats in operation.

 

[rhythmsandy]

which values of feedback caps have you tried?

 

[jwilhelm]

There are no feedback caps on the op amp itself. In the ODNF signal line from the output I've tried from 0 - 33pF, no difference.

 

[rhythmsandy]

that opamp is not stable even with 1pf of output cap. Hence they recommend to use resistor after the feedback loop but you are saying that there is no feedback loop for the opamp.

 

[thimios]

One source, two preamplifiers, two power amplifiers,two full range, two woofers. - YouTube
Silberstack drive a pair of salvaged Woofers, SX drive a pair of Fane 12-250TC.
Two separate preamplifiers are used for volume setting.

 

[rhythmsandy]

There are no feedback caps on the op amp itself. In the ODNF signal line from the output I've tried from 0 - 33pF, no difference.

any luck on the stability of the opamp?