Zen -> Cen -> Sen, evolution of a minimalistic IV Converter

similar to the current mirror the folded cascode allows to reference the output to 0V again, instead of the supply line.
In that it improves PSRR and omits with a coupling cap
Thanks! Yeah, I've always been concerned about that output coupling cap Jocko used.
So ... is there a quick-n-clean way to implement the folded cascode into the existing Jocko circuit w/o much fuss? Or is there another quick-n-clean way to get rid of the coupling cap w/o much fuss? I don't want to mess with the Jocko too much because it performs very well as is for my TDA1541(A). But I may be persuaded other wise if I could bodge in a tweak ;)
 
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If you have a proper signal generator and a scope, you can check the proper functioning of the IV circuit (version 18), on its own, as follows :

1. Connect the functions generator to the current input of SEN via a 1k resistor.
2. Connect func gen Gnd to R_iv Gnd (not power supply, which is floating).
3. Set the functions generator to output a DC offset of +1.65V, plus an AC sine signal of +/-1V, say 1kHz.
4. Measure voltage across R_iv.

You should be able to measure a 1kHz sine wave with an amplitude of (1mA*R_iv).
If that is the case the IV converter is functioning.


Patrick
Anyway to do this with a signal source where I cannot impose a DC offset (i.e. a Victor oscillator)?
Thanks,
Nic
 
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Sorry if this is a stupid question.

I’m wondering if the Sen could actually be used as a MC head amp?

Was this circuit not originally derived from an MC amp circuit?

I happen to come across a pair of Sen boards a few years back (V2.0&18.0) and bought them thinking I would use them in my DAC project.

However, I just resolved that DAC project with iv transformers that I am happy with.

I appear to have what I would need to populate the Sen…albeit the poly caps are .15 uf.

I have some 560k PRP resistors I could steal from another project…or just use some Dale R60 100k I have on hand (I think R1,R2 values are flexible?).

The question is…if its possible…how much gain would it provide?

I read through the original article and build manual a few times and cannot find any mention of gain.

For reference I’m after 20dB of gain.
 

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I was also wondering about the use of Sen for a MC head amp.

I just built an op-amp phono preamp for MM which does the RIAA eq. I had spare battery supplies in my Sen box which were originally for the servos before I moved the servos into the PC so I put the preamp in the box along with the Sen and used the spare batteries.

Since it’s already all in the same box and it ought to be easy to switch it in, I thought I might upgrade to a MC cartridge and use my existing Sen to get a nice quiet head amp. Also looking for 20dB.

I think it ought to be possible with an IV resistor 10x higher than the standard MC loading right? So maybe 500R to 1KR perhaps?

After looking at the prices of the MC cartridges I started to worry about making a mistake and burning one up by putting a DC offset on it.

So that’s the main question I had about it: is it going to be essential to decouple the MC cartridge or can it be DC coupled to the Sen input without any risk?
 
The simple answer is I have not tried and have no intention to.

The long answer is although the circuit is essentially the same as the Leach, he biased the BJTs much lower such that Zin is about 100R.
You can read this in his article.

The CEN IV has a Zin of about 15ohm or less. Not sure if it is ideal loading for your MC cartridge.
To get to around 100R, you need to use other JFET pair such as 2SK246/2SJ103.
But they are no longer as low noise as the 2SK170/2SJ74.


Patrick
 
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When I tried Sen with SMPS there wasn’t any mains hum, only switching noise. So I think the problem wasn’t magnetic coupling but that the isolation capacitance of the SMPS was too high. The isolation capacitance of those DC-DC converters is 10x lower than the JFET input capacitance. I think it has a good chance of working. The ripple and noise is quite high though so it might need to be cleaned up a bit perhaps. That isolation capacitance and the gate capacitance are the only ways the DAC current can differ from the current through the IV resistor right? It seems to me any junk from the DC-DC converter should end up down around the level of the harmonic distortion.
 
Min order quantity is 25 and lead time 78 days. It would be a £215 experiment.

I’m not in a hurry to do this but it’s still cheaper than replacing the 4 sets of batteries I have so I may try eventually.

I thought I could run them all off one set of batteries so I could still turn off the mains power inside the box which might help a bit.
 
I was looking at Farnell. I can order 4 from Mouser. I wanted sx12 which has a wider input voltage range more suitable for running from my batteries. That one is on back order so there will still be a wait.

£50.34 for 5 from Mouser including delivery. I have ordered and will have a go. I’m pretty busy though. It may take a while.
 
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