Someone asked me how I fit the Jung-Didden regulators into this box...which led me to look at the phono section.
The two input transistors that Crown used, 2N3895A and PN4250A low Rb, the LM301A opamp is truly ancient. I hadn't seen this type of phono-pre, but only started seriously dabbling in phono pre and RIAA comp networks in the past decade or so!
SY isn't around to throw bricks at this Crown design. The compliance, in simulation, to the RIAA curve is very good. Will have to see if my actual living model is equal to the simulations.
The two input transistors that Crown used, 2N3895A and PN4250A low Rb, the LM301A opamp is truly ancient. I hadn't seen this type of phono-pre, but only started seriously dabbling in phono pre and RIAA comp networks in the past decade or so!
SY isn't around to throw bricks at this Crown design. The compliance, in simulation, to the RIAA curve is very good. Will have to see if my actual living model is equal to the simulations.
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Somewhere I think I have a tube of LM301s around. I never had an IC150, but have had a couple IC150As. The older 150 has a better reputation for SQ. The 150A, not so much. The 150A also uses an oddball Raytheon tracking regulator that tends to fail. Best to glue a small heatsink to them while they're still working. Always liked the panorama control!
It's a bit disappointing that Crown did not exploit one of the LM101 (milspec) / LM301 (commecrial grade) opamp's greatest features: EXTERNAL COMPENSATION. It gave board level circuit designers tons of flexibility. Application brief LB-4 discusses a few possibilities, and the datasheet discusses a few more.
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I fit the model into LTSpice without the compensation pins...there is 100pF from the inverting input to pin 1, and 1nF between output and pin 8.
Multisim has the complete model but I simplified for the purpose of using LTSpice.
Multisim has the complete model but I simplified for the purpose of using LTSpice.
I believe you got the schematic wrong. The 732K resistors connect to the emitters. I loved the 2N4250 transistor when it first came out. It was probably the best cheap low noise transistor available. It would run with microampere collector currents and still had good beta. Many transistors had severe beta loss at low currents.
Deane Jensen used the PN4250A as the 2nd amplifying stage ("VAS") of the JE-990 discrete opamp, and bragged about how good it was. But his design required a transistor that performed even better than the 2N4250 datasheet spec registered at JEDEC. So he ran a little mini-qual to find vendors who routinely beat the spec by enough margin to satisfy Deane Jensen. He found that Fairchild and National Semiconductor's PN4250As did. Both of them.
Nelson Pass also designed the 2N4250 into several of his Threshold products, including the NS10 preamp of 1978.
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Nelson Pass also designed the 2N4250 into several of his Threshold products, including the NS10 preamp of 1978.
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While we are nit-picking, the input transistors are the plastic PN4250 and TZ-81 not 2N3859A. The TZ-81 was by Sprague. I don't know where you would find a model for it. Probably use any decent low noise NPN.
Good to see that the collector bias currents are reasonably close to the noise optimum, not decades too high. Are the supplies +/- 15 V?
The Crown IC-150A schematic is still available here.
https://www.crownaudio.com/en-US/product_documents/ic-150a-owners-manual-ic-150aownersmanual-pdf
https://www.crownaudio.com/en-US/product_documents/ic-150a-owners-manual-ic-150aownersmanual-pdf
@rayfutrell -- tnx, my manual does not have the service bulletins. (I bought the unit with a DC300 a long time ago.)
post#15 attachment 1 seems to show RIAA conformance is ±0.1dB and I think that's extremely good. Congratulations!
Which is still damn good for the 1970's! That's better than plus-or-minus 2.5% in an era when 1% resistors were expensive and 5% capacitors were unavailable at any price.
To me, it appears that yellow crosses above 1% at the halfway point (on log axes!) between 100mV and 200mV.
antilog( (log10(0.1) + log10(0.2)) / 2 ) = 0.141 = 141mV.
antilog( (log10(0.1) + log10(0.2)) / 2 ) = 0.141 = 141mV.