HPS 4.0 phono stage

[Ultima Thule]

Don't know if I see wrong but the input on ML JC-1DC are the emitters on Q5 and Q6, the schematic is visually misleading for the eyes at a quick glance.

[syn08]

Originally Posted by Ultima Thule

Don't know if I see wrong but the input on ML JC-1DC are the emitters on Q5 and Q6, the schematic is visually misleading for the eyes at a quick glance.

Sorry, my bad. Q7 and Q8 are in fact the same current mirrors as in the Hiraga schematic. In fact, the two preamps are pretty much identical, signal path wise.

BTW, it seems like in this particular case, capacitors (electrolytics!) in the signal path are acceptable. I can't stop recalling how one of the contributors around expressed his disgust for my HPS 1.0 having a a film cap in the input stage signal path

P.S. The ML preamp is just another piece of ancient technology. Those transistors were considered "low noise" about 40 years ago. That's the reason why it can afford running at low Ic, Rbb is so large that it masks any current noise contribution. Such a preamp will fail the noise test with any modern 10ohm low output cartridge.

[Joachim Gerhard]

John Curl himself recommends that circuit not any more. See his Blowtorch thread.

[Lumba Ogir]

syn08,
grounded base is not a suitable topology for MM, where the input impedance needs to be set externally, by listening as the only way, the values can be up to 100kOhm.
An increased bias current improves almost all parameters of interest, in all topologies, like noise. In practice, compromise is always necessary, not forgetting the annoying thermal-dependent DC offset in grounded base, for instance.

- Non degenerated common emitter and common base have exactly the same input impedance (Beta/gm) and transconductance gain (gm).

That´s not a factual assertion. The equations are easily accessible.

[syn08]

Originally Posted by Lumba Ogir

syn08,
grounded base is not a suitable topology for MM, where the input impedance needs to be set externally, by listening as the only way, the values can be up to 100kOhm.

Set aside MM is off topic here, that's nonsense anyway. Manufacturer are specifying the optimal load for MM. Of course, some GEB members can make some good coin by helping ignorant user in optimizing their sound using the "critical listening" method.

The common base and common emitter nondegenerated transconductances are identical. The common base input impedance is lower (my bad) and that's the real reason why you can't use high currents in the Hiraga stage. The input impedance is 1/gm. If this is to be set for 100 ohm, this would require a maximum collector current of 250uA. At this current level, you don't need special low noise devices, you can use any medium power double diffused bipolar from your junkbox, with the same crappy results.

[Lumba Ogir]

Michael,
your presence lends positive supportive energy and confidence. This thread is heavily polluted by misconceptions, maybe you could contribute to clarification.

[Lumba Ogir]

syn08,

The common base input impedance is lower (my bad) and that's the real reason why you can't use high currents in the Hiraga stage. The input impedance is 1/gm. If this is to be set for 100 ohm, this would require a maximum collector current of 250uA. At this current level, you don't need special low noise devices, you can use any medium power double diffused bipolar from your junkbox, with the same crappy results.

These are not factual assertions. Please study the equations comprehensively and try again.

[syn08]

Originally Posted by Lumba Ogir

These are not factual assertions. Please study the equations comprehensively and try again.

I did. It is entirely correct. As usual, your blank statements have zero factual value.

[john curl]

Where do you think that I LEARNED about the problems with MC loading? The JC-1, AC-DC, of course. It did not sound as good as it should have. WHY?

[Joachim Gerhard]

In case you use a low impedance cardridge the input impedance can be much lower then 100 Ohms without harm. I use a Lyra Titan with an impedance of 5.5 Ohm and inductance of less then 0.5uH. It certainly works well into the MPP that has an input resistance of 25 Ohms in case i shunt the current mirrors with caps. I run the input transistors on 3.5mA each. Output transresistance at that point is 50mS for the MAT02.
A bit higher in the MAT03. Consider also that no current is "burned" in a shunt resistor but everything flows into the input transistors. With a high impedance design shunted with 100 Ohms you loose around 5.5% of current (with the Titan). Hardly much but maybe audible compared with say a 47 kOhm load just because the sound is not as load. Douglas Self claims that a volume change of 0.3dB is just audible.
I have not finished my survey into cardtridge loading but i will try to calculate the volume differences too. For a Denon DL 103 with 40 Ohms and more inductance a loading too low will roll of the treble because the inductance with interact with the low input impedance. I also learned from Malkolm Hawksford that after they decided on the input impedance of the Essex Equalizer they found out that samples sounded very different. Although they always used the same value resistor they found that different makes and brands sounded very different especially when they put the needle in the groove and listened to the mechanical and electrical noise. I think they settled on a tantalum resistor. Call me biased or stupid i trust that man and can hear it myself. Has anybody a scientific explanation to persuade Syn08 into listening to various makes of resistors ? i do not think so.