Discrete Opamp Open Design

[Kindhornman]

Didn't even see that, just looked at the Sydney name, I should have caught the Harman, I do have an older Harman amp here, I won't spell Kardon right probably either. Damned English teachers, they never did show up for class.....

[wayne]

I have to say the HK stereo in my Benz is pretty nice I haven't felt the need to mess with it. The auto end sure appears to be good for them if the stock price is any indication.

[john curl]

I worked for HK-JBL too. Do you want me to expose what I found?

[bcarso]

Originally Posted by wayne

I have to say the HK stereo in my Benz is pretty nice I haven't felt the need to mess with it. The auto end sure appears to be good for them if the stock price is any indication.

The automotive biz has been the mainstay, although JBL Pro has been profitable.

It was joked about Gina Harman, Sid's daughter from a first marriage, that when she left heading up the Consumer Group to direct a non-profit foundation in NYC, that she was a good fit, having had lots of experience not making a profit.

The brands of course were used wherever it made sense in the Automotive Group, although they had nothing to do with the original businesses. In some ways Corporate would have considered shutting some of the originals down, but they needed to have brands to help sell car systems.

When Multimedia (under various names) started to make little powered speaker systems for Compaq and Dell, both the JBL and harman/kardon brands were deployed. It was remarked that regardless of whether the division made money (and it did, a little, for a while) the brand recognition was a considerable benefit --- many computer users had never heard of harman/kardon, although their parents and grandparents had.

[Kindhornman]

You too can share John, It seems to be dump on Harmon International day. I worked with them in the old Balboa Blvd. plant. They weren't terrible to work with all the time, but I sure learned my lessons about letting them see my work.

Steven

[staccatiss]

How about fully differential OPamp a la OPA1632 (aka THS4131)?

[homemodder]

Scott interesting circuit in post 135, something different to the usual seen to death circuits seen here. I did some simulating with it although I admit 15 min is not enough but Im a bit busy with other things. Maybe its the jfet models Im using or some other mistake but I dont get even near the distortion figures posted here by other members. At 20 Khz the only way I can get to close -100db is by increasing the vas current substancially to around double the figure. What does one call that cascode used in the vas, first time Ive seen such a setup with BJTs. Ive been using composite cascodes for the last 5 years with mosfets for vas when seeking very low THD and it seems to me your cascode does the same function. My sim though showed that the circuit actually performs better without it at 20Khz ?

Ill have a second go at it tonight if I can spare some time.

[scott wurcer]

Originally Posted by staccatiss

How about fully differential OPamp a la OPA1632 (aka THS4131)?

These are for low input impedance resistive feedback applications, if you scroll down the data sheet the high input impedance application requires a lot more stuff.

[scott wurcer]

Dick, this discussion of non-switching class B might be of interest.



margan : non switching class B

[bcarso]

Originally Posted by homemodder

Scott interesting circuit in post 135, something different to the usual seen to death circuits seen here. I did some simulating with it although I admit 15 min is not enough but Im a bit busy with other things. Maybe its the jfet models Im using or some other mistake but I dont get even near the distortion figures posted here by other members. At 20 Khz the only way I can get to close -100db is by increasing the vas current substancially to around double the figure. What does one call that cascode used in the vas, first time Ive seen such a setup with BJTs. Ive been using composite cascodes for the last 5 years with mosfets for vas when seeking very low THD and it seems to me your cascode does the same function. My sim though showed that the circuit actually performs better without it at 20Khz ?

Ill have a second go at it tonight if I can spare some time.

I see, open loop, about 136ppm, 2nd -81dBr, 3rd -80dBr, 1kHz, 14.5V out p-p, 200uV p-p in, with a perfect buffer, zero source impedance, R29 = 100 ohms. To make things settle more quickly I reduced C13 and C14 to 10nF from the suggested 100nF. Sims ran for 52ms with 1us steps.

Open loop d.c. gain shows as 123dB, -3dBr at 50Hz; phase is well-behaved at the canonical 90 degree shift to about 135 degrees at 22MHz, with C4 = 30pF as shown. The gain at that frequency is 9.2dB.

At 20kHz, 4mV p-p in, 14.5V p-p out, about 150ppm, again 2nd and 3rd dominating. Of course closed loop the higher loop gain for closed loop gains of a few will drastically reduce distortion, and at 1kHz especially.

Scott has of course warned us about the output buffer's contributions, so these results are rather idealized, but nonetheless interesting. And as usual perfect matching of the input devices is assumed.