Hi Marcel and Mark
After something of a search (because manufacturers only quote vn in the outline spec) there is a current op-amp that has similar performance that the 5534A. The OPA1692 is a dual opamp with vn = 4.2nV/rootHz at 1kHz and in = 0.39pA/rootHz. What is more significant for RIAA performance is that the 1/f knee is much lower in frequency than the 5532A.
The OPA1692 doubles the vn and in at not much more than 1Hz, as compared with 10Hz for the NE5534A
After something of a search (because manufacturers only quote vn in the outline spec) there is a current op-amp that has similar performance that the 5534A. The OPA1692 is a dual opamp with vn = 4.2nV/rootHz at 1kHz and in = 0.39pA/rootHz. What is more significant for RIAA performance is that the 1/f knee is much lower in frequency than the 5532A.
The OPA1692 doubles the vn and in at not much more than 1Hz, as compared with 10Hz for the NE5534A
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But what preamp do you want to assemble with that OPA?
That would be a completely different project, that I do not think is what this thread is about.
I am exploring other options outside this thread for RIAA preamps.
Is there a model for the OPA1692 anywhere?
One preamp I will assemble too is the one published in Audio Electronics, modifying an Adcom preamp. The original Adcom's RIAA was based on one on the LT1115 data, and the AE mod replaced the LT1115 for and AD745.
I did simulate that preamp, also replacing the very expensive AD1745 for an also FET-input from LT: LT1792. The simulation shows very good results.
My idea is to use a socket, and then listen with the LT1115 and the LT1792.
Also will be assembling a Luxman 5C50 RIAA clone, discrete, with dual FET input.
And I also wanted to have an SLN available to listen to.
Hopefully that should be a useful comparison. The ones I do not prefer I should sell. But I expect things to be a real tie.
That would be a completely different project, that I do not think is what this thread is about.
I am exploring other options outside this thread for RIAA preamps.
Is there a model for the OPA1692 anywhere?
One preamp I will assemble too is the one published in Audio Electronics, modifying an Adcom preamp. The original Adcom's RIAA was based on one on the LT1115 data, and the AE mod replaced the LT1115 for and AD745.
I did simulate that preamp, also replacing the very expensive AD1745 for an also FET-input from LT: LT1792. The simulation shows very good results.
My idea is to use a socket, and then listen with the LT1115 and the LT1792.
Also will be assembling a Luxman 5C50 RIAA clone, discrete, with dual FET input.
And I also wanted to have an SLN available to listen to.
Hopefully that should be a useful comparison. The ones I do not prefer I should sell. But I expect things to be a real tie.
They could still be coming from legit overstock some of them. Because they went EOL recently. But you never know.
It is quite simle to find C550/560 on first class service:
Bc560 - Iskalni niz | Elektronske komponente. Distributer in spletna trgovina – Transfer Multisort Elektronik
They are safe and good.
Bc560 - Iskalni niz | Elektronske komponente. Distributer in spletna trgovina – Transfer Multisort Elektronik
They are safe and good.
I appreciate that. But the BC550C/BC560C is obsolete. As time goes by the chance of buying ones that are not fakes becomes vanishingly small.
Try the TI website. You'll find it easy enough.
Be careful in general about models. Particularly regarding noise mechanisms. As an example the LM4562 is quite accurate, but the OPA2134 as a flat vn spectrum (no 1/f), and I seem to recall omits current noise.
Who knows whether or not transistor models include noise sources - it depends on whether the manufacturer has even measured them.
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I've been scammed three or four times, most recently on JFETs from a legit Japanese source. That is UKP100 I won't get back.
Even c3675, a 900V, 100mA transistor that was used in late model TV's that used CRT's. At the time of this scam, recently obsolete. I used those in an electrostatic headphone amp I was building, and every darned one blew with massive collateral damage. I found they were fake and broke down at 550V. Who would have thought it was worth someone's while faking a such a transistor?
I've also been scammed on recently obsolete power transistors.
I've learnt the hard way that "recently obsolete" = open day for the semiconductor scammers.
How do you know they were fake? An electrostatic speaker is a nonlinear capacitor and the voltage on its plates can go much higher than the supply voltage.
These are made by CDIL (Continental Devices India Ltd). They seem to be a legitimate manufacturer, and have a product line comprising, from what I can see, 50% current products and 50% obsolete, which they remanufacture.
They are not stocked by the major component suppliers, such as Mouser, Digikey, RS, Farnell etc.
I can't say how accurate the remanufactured semiconductors are as compared to the originals (BC560C etc were Fairchild, before OnSemi took them over three years ago, and have since been "rationalizing" the product line IOW obsoleting anything of utility to the audio industry)
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Because I am a professional electronics designer, and among an exceptionally well equipped lab, I have a Tektronix 576 semiconductor curve tracer.
I had recently asked about CDIL an Indian member here and he told me that they are not enjoying a great reputation especially for consistency of spec in their small transistors line. He specifically mentioned their BC560C hfe is all over the place. But since they are cheap to buy many and match I would rather be more worried about their noise and Ft adherence to spec or not.
Collector and base shot noise depends solely on the collector and base current, so as long as hFE is close to reality, they should also be OK. Base resistance thermal noise and 1/f noise are a different matter altogether.
OK, let's go back to using these 2SA/2SC pair on the SLN.
What things could or should be changed/adjusted to better tune it to an MM cartridge?
Someone had mentioned the LTP current. To how much should be it be adjusted?
Increasing the power supply voltage seems to reduce THD, but is it worth it?
Should the output transistor pair be the same 2SA/2SC?
What about using a DC servo or not? If we don't, a large feedback cap should be used, and an output cap too.
What things could or should be changed/adjusted to better tune it to an MM cartridge?
Someone had mentioned the LTP current. To how much should be it be adjusted?
Increasing the power supply voltage seems to reduce THD, but is it worth it?
Should the output transistor pair be the same 2SA/2SC?
What about using a DC servo or not? If we don't, a large feedback cap should be used, and an output cap too.
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Theoretically, the noise optimum should be around 70 uA tail current when you use a single NPN and a single PNP differential pair, otherwise 70 uA/n per pair when using n NPN and n PNP pairs. I would recommend that value if and only if it results in an acceptable loop gain, so in good RIAA conformity and not too much distortion. Otherwise as close as you can go without degrading the RIAA conformity and distortion too much. The noise optimum is broad, so using a somewhat higher current will not do that much damage; you have to exceed 430 uA per pair (at hFE = 400 and assuming a single NPN and a single PNP pair) before the base shot noise starts to dominate over input termination resistor noise.
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Assuming that you have only one NPN pair and one PNP pair:
The noise should improve when you use 180 kohm tail resistors instead, but only slightly and the distortion and RIAA conformity may get worse.
Assuming four pairs each:
The noise should improve when you use 820 kohm tail resistors instead, but the distortion and RIAA conformity may get worse. You may have to find some compromise value.
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