If the second stage had nullor properties, there would not be any Miller effect in the first stage.
Hi carlmart !
... yes cacapity, the thing inside condensers...😀😉
I run complete (with all 20 transistors) SLNs / SUPRAs without servo (modified circuit from post #157), in a separate phono preamplifier in its own housing (together with my CX-Decoder ).
Furthermore in a preamplifier, the original Supra with unchanged circuit as in Elektor 7/8-1982. (the input capacity was even given as 280p, I have this Elektor edition)
I have the MM pickups Ortofon OM and Dual TKS236, with both there is no problem with the SUPRA.
In post #292 that was an attempt to see if the circuit works properly with just one pair of inputs. The simulation was OK, but the reality could have been different.
I also wanted to try out the servo and see if I could easily modify the PCBs which are already made.
The servo is IMO only really valid if you absolutely want to set up the circuit without an input and output capacitor. (which is done there)
@peranders
There are also some other topics / contributions to the SLN / SUPRA in the forum, in which the possibly problematic input capacity was mentioned.
Please read there.
For example, a connection capacity of 100-200pF is specified for various Audio Technica VM systems. This can easily be achieved with the player connection cable alone.
.asc file attached!
... yes cacapity, the thing inside condensers...😀😉
I run complete (with all 20 transistors) SLNs / SUPRAs without servo (modified circuit from post #157), in a separate phono preamplifier in its own housing (together with my CX-Decoder ).
Furthermore in a preamplifier, the original Supra with unchanged circuit as in Elektor 7/8-1982. (the input capacity was even given as 280p, I have this Elektor edition)
I have the MM pickups Ortofon OM and Dual TKS236, with both there is no problem with the SUPRA.
In post #292 that was an attempt to see if the circuit works properly with just one pair of inputs. The simulation was OK, but the reality could have been different.
I also wanted to try out the servo and see if I could easily modify the PCBs which are already made.
The servo is IMO only really valid if you absolutely want to set up the circuit without an input and output capacitor. (which is done there)
@peranders
There are also some other topics / contributions to the SLN / SUPRA in the forum, in which the possibly problematic input capacity was mentioned.
Please read there.
For example, a connection capacity of 100-200pF is specified for various Audio Technica VM systems. This can easily be achieved with the player connection cable alone.
.asc file attached!
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I tried different OpAmps lying around here as a DC servo.
From the "vintage parts box": ua741 (metal TO-39) and TBA 221.
Also OPA27 and now OP07. No significant differences in the result.
There are also OP177 and NE5534 that I could put in for a test.
...probably they are all vintage....🙄
I think in this application it makes no audible difference whether the related OPAmp is with FET or BJT.
From the "vintage parts box": ua741 (metal TO-39) and TBA 221.
Also OPA27 and now OP07. No significant differences in the result.
There are also OP177 and NE5534 that I could put in for a test.
...probably they are all vintage....🙄
I think in this application it makes no audible difference whether the related OPAmp is with FET or BJT.
You use FET opamp for servos so the output voltage error is small. Remember the large resistances needed for a long time constant will convert bipolar bias/offset current into definite voltage error in a servo application, or else you'll need a bulky expensive bipolar electrolytic just to keep the resistor smaller.
You are right about that but I chose to have cascodes which eliminates the extra capacitance.
Attachments
Quite a clever solution, I'd say 
! It also increases the input stages gain considerably.
Best regards!
! It also increases the input stages gain considerably.Best regards!
Actually, I don't like using an OpAmp as a DC servo in this case, I think it somehow contradicts this 1982 preamplifier concept, which originally only used BC550/560 transistors that were cheap and easy to get.
If I use OpAmps, I should use them for the MD preamp itself, which makes more sense.
IMO.
So I tried to do the whole thing with BC550/560 only, including DC servo.
The simulation works quite well. Now I have to build it soon to see if it really works.
Any opinions?
If I use OpAmps, I should use them for the MD preamp itself, which makes more sense.
IMO.
So I tried to do the whole thing with BC550/560 only, including DC servo.
The simulation works quite well. Now I have to build it soon to see if it really works.
Any opinions?
Attachments
Weren't T2 and T3 originally current sources rather than voltage followers? With voltage followers, the main amplifier is essentially a pair of differential pairs with folded cascodes. I wonder how much loop gain is left with this set-up.
The bias current of T12 and T13 seems rather unpredictable to me, as it depends on the matching between unequal devices. Why not add an extra diode and emitter resistors, making it a class-A servo amp?
The bias current of T12 and T13 seems rather unpredictable to me, as it depends on the matching between unequal devices. Why not add an extra diode and emitter resistors, making it a class-A servo amp?
Yes, I had already thought that the DC servo; -'discrete OpAmp'-, is not quite optimal in this way. It's a first test.
Additionally you have to consider different base currents at T4 and T5. Why not use FETs in these positions, if »discrete« is the primary goal?
Best regards!
Best regards!
Following your scheme, there is a simple active feedback RIAA, much better are two step, phase stable amplification with passive filter between. Discrete or OPAMP servo question in this your case mean nothing in quality of signal.
there's no low noise phono with such high impedance riaa network into a bipolar transistor base...
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BC550/560 are ideal for such as 1mA current in input line with maximum low noise and high transit frequency, On the output is for stable signal and good sound about 30mA need. In any case you are forced to combine the exit with BD139/140 for relevant results.
With 2SA970/2SC2240 is living easy, especially on drivers with higher voltage and direct usage without reductors.