if you require 28Vdc from the Salas Style Regulator, you may find that 25Vac is too low. 30Vac is certainly enough for worst case conditions.
But that CCS mosFET may require an enormous heatsink to survive worst case conditions with 30Vac fed from highest mains voltage. Notice I said "survive". That is not the same as work and regulate properly.
I describe "survive" as: the circuit returns to normal operation and works to full undamaged specification after the worst case event is completed.
But that CCS mosFET may require an enormous heatsink to survive worst case conditions with 30Vac fed from highest mains voltage. Notice I said "survive". That is not the same as work and regulate properly.
I describe "survive" as: the circuit returns to normal operation and works to full undamaged specification after the worst case event is completed.
If you will play an LP record you will realize that with the recommended Simplistic NJFET Riaa gains the sound levels of a an average CD recording are near if just a bit louder for the same volume pot position due to the way the dynamics on a record are cut. Hitting over 0dB often. I did those tests early in the design stage. High output levels if needed for other reason, like a low overall gain system, would need to resort to a loop feedback design with opamp second stage to keep THD low, or to add a X3 stage to this one's output.
What Pieter means is that he will use a passive Line - here a TVC or autoformer and dealing with the same signal voltages like a CDP delivers. So we need a 20dB more gain.
@Salas
If I understand you correct you mean when designing the phono stage with that +20dB, allover 66 ~ 72dB, you shozld do this like you described?
@Salas
If I understand you correct you mean when designing the phono stage with that +20dB, allover 66 ~ 72dB, you shozld do this like you described?
He should add a basic (OpAmp?) line gain stage after the Riaa to pot passively drive a 0dbV+ amp then. If he will drive with 5mV 50dB using this phono circuit only, it will overload with THD noticeably.
But he makes transformers, why not wind +6dB & +12dB taps? Sowter has autoformer pots with +6dB extra taps for instance. That way he can avoid an active line boost. 5mV on the 37dB MM circuit + 12dB =1415mV. Although he may end up using up to the +6dB. Records are louder many times.
*No, that thing does not have to do with overall design of this one, was talking of other possible circuits.
But he makes transformers, why not wind +6dB & +12dB taps? Sowter has autoformer pots with +6dB extra taps for instance. That way he can avoid an active line boost. 5mV on the 37dB MM circuit + 12dB =1415mV. Although he may end up using up to the +6dB. Records are louder many times.
*No, that thing does not have to do with overall design of this one, was talking of other possible circuits.
Salas,
Thanks for your input.
I understand that the 5mV / 50dB will, as I already expected, lead to maybe intolerable THD.
Yes I could make +6dB or even +12dB taps (realize however that this requires double or four times the number of windings, requiring a totally different design for my autoformer, compromising other important parameters at the same time!) but these things do not come for free. Step up ratios alter impedance relationships between source and load squared in a negative way, that's why I don't like that in inductive volume controls where a main advantage is that load impedances are transformed "down" at attenuated volume settings in order to get better driving ability for the next stage - very good "passive" preamps in other words; a 12dB step up would make the source impedance close to 1k (I don't believe the specified output impedance of the source follower output - it will be closer to 60 ohms instead of 30 ohms as the transconductance of that stage will not reach the max 22 mS of a 2SK170).
There should be more elegant ways to squeeze up the gain and preserve low output impedance, but preferably not with an op amp
; a discrete op amp topology like the output of the Pearl Two is a better option maybe, but that one runs on bipolar power supplies Or maybe an additional 2SK170 stage cascaded to the first output stage, before the output follower; could something like this being designed direct coupled with the available power supply? With reference to the circuit of post 417, could the output stage (2SK170 with 6k8 drain resistor - source follower) be replaced by two cascaded 2SK170 stages - source follower to reach the overall 50 dB gain? Higher power supply voltage required to do this?
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The digital sources have a maximum output level. CDP for instance is usually around 2.2Vac.
Vinyl does not have a maximum. The output voltage depends on the speed that you move the generator.
For 5cm/s the output of an MM is usually in the range 2mVac to 7mVac.
But that is NOT the maximum.
Maximum could be 10dB, or 20dB, or more above that 5cm/s, typical speed, chosen for sensitivity comparisons in the specifications. 25cm/s is common in high energy recordings and I believe that nearly 40cm/s is possible.
What if you drop the cart carrier accidentally, or the cart jumps a track, or jumps over a boulder in the track.
Vinyl does not have a maximum. The output voltage depends on the speed that you move the generator.
For 5cm/s the output of an MM is usually in the range 2mVac to 7mVac.
But that is NOT the maximum.
Maximum could be 10dB, or 20dB, or more above that 5cm/s, typical speed, chosen for sensitivity comparisons in the specifications. 25cm/s is common in high energy recordings and I believe that nearly 40cm/s is possible.
What if you drop the cart carrier accidentally, or the cart jumps a track, or jumps over a boulder in the track.
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In order to play my LP collection I think 5mV is not a bad starting point.
When there eventually is a recording with a high mean level it can be adjusted by attenuating the volume; on the other hand total gain of the phono preamp should be enough to cope with the majority of recordings, and I'd like the output signal of the phono preamp to be comparable with the signal of my internet radio and CDP.
When there eventually is a recording with a high mean level it can be adjusted by attenuating the volume; on the other hand total gain of the phono preamp should be enough to cope with the majority of recordings, and I'd like the output signal of the phono preamp to be comparable with the signal of my internet radio and CDP.
I did that and I did not like it. You may try, but the overload is going to onset in the first stage partially too, especially at the treble.
Pieter,
you are not listening.
The maximum digital level is ~2.2Vac.
After adding a +50dB RIAA stage the MM cart output maximum level is ~25cm/s * 1V/cm/s * 300 (~+50dB) ~=7.5Vac
It is not an extra gain stage to bring up the vinyl source to match the CDP output that you need.
It is extra attenuation for recordings that for you are a bit loud. I think you will find that a +50dB RIAA stage combined with a MM cart that outputs ~5mVac @ 5cm/s will generally give more SPL that an equivalent CD recording feeding direct into your pre-amp/buffer.
you are not listening.
The maximum digital level is ~2.2Vac.
After adding a +50dB RIAA stage the MM cart output maximum level is ~25cm/s * 1V/cm/s * 300 (~+50dB) ~=7.5Vac
It is not an extra gain stage to bring up the vinyl source to match the CDP output that you need.
It is extra attenuation for recordings that for you are a bit loud. I think you will find that a +50dB RIAA stage combined with a MM cart that outputs ~5mVac @ 5cm/s will generally give more SPL that an equivalent CD recording feeding direct into your pre-amp/buffer.
Andrew,
I do listen
.Still I think a 50 dB gain preamp is the way to go and reach the level of digital sources.
We have a turntable here with two cartridges: AT440MLA and Grado Gold (4 and 5 mV resp. 5cm/1kHz).
Preamp is a Cambridge 640P; this one has a gain of 39 dB at its MM input.
When we listen through the AT cartridge the output level at 1kH/5cm is 4 x 89 (39dB) = 356 mV.
When we switch from LP to CD we have to turn down the volume 10-12 dB on average to match volumes; indeed there are LP's with higher recording levels and then the difference is smaller, but once more, on average (the majority of LP's) the difference is around 10 dB.
Therefore I think that a 50 dB gain preamp will bring levels pretty close together.
As I wrote originally if there is no line gain stage that usually has dB to spare, it can be needy in a passive pot situation directly to a 1VRMS amp or more. Unfortunately I don't recommend modding the gain stages in this kind of phono directly, but to add gain after. Maybe change the output buffer to some 3X scheme of choice with good Zo.
About the 30 Ohm spec of its standard buffer you are right, for BL should be ~60-70 Ohm. Looks like I had noted max spec for V type Fets that I had measured in a special build. Its an inadequate note. Should read ''under 100 Ohm with average IDSS JFETS''.
About the 30 Ohm spec of its standard buffer you are right, for BL should be ~60-70 Ohm. Looks like I had noted max spec for V type Fets that I had measured in a special build. Its an inadequate note. Should read ''under 100 Ohm with average IDSS JFETS''.
Found a bad joint - problem solved
In trying to find my problem I changed the transformer to 25Vac. This is giving me 40V into the LM317, which is only just warm dropping to 38.3V. The IRFs are bolted to the case and are cool. Now I'm getting a steady 28V out from the shunt.
Now to build another then connect to the RIAA circuits.
In trying to find my problem I changed the transformer to 25Vac. This is giving me 40V into the LM317, which is only just warm dropping to 38.3V. The IRFs are bolted to the case and are cool. Now I'm getting a steady 28V out from the shunt.
Now to build another then connect to the RIAA circuits.
Yes, a LM317 does not feel happy with some 1V of voltage drop; it has a 1.25V reference so ....
I wondered how you get 40V DC out of a 25VAC transformer (25 x 1.4 minus diode drop...), or maybe you have a high power transformer which does not have to deliver its current?