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Naim Phono "E" Circuit?

flashgo

flashgo

DIY Practitioner
I'm trying to use a high output MC cartridge with a Naim Prefix "S" circuit, but there's just too much gain. I'd like to modify it to the lower gain "E" circuit. Does anyone have an "E" schematic that they could post? Or can I just increase the 220R inline with the 47uF feedback cap to 440R or so?

Thanks for any advice.
 
323.jpg


I also have a copy of the circuit diagram from a Naim source that has hand written annotations indicating that the following changes should be made to convert an 'S' or 'K' to an 'E':

R2 which is shown above as 3k3 but which is normally 4k3 in production should be changed to 9k1.

R15 changes from 15R to 56R.

Add a 15pF ceramic capacitor from base to collector of Q3.

I use a pair of 323K boards with the these changes with my Denon DL-110 with excellent results. I've also removed the on-board voltage regulators and supply the boards with 21.5v from local TPR2s. (to do this remove R26 and Q4 and link the emitter and collector pads in the Q4 position)


The notes also indicate that further gain reductions can be achieved by changing R13 (220R) as follows:

470R gives -6dB
1k0 gives -12dB

HTH

Malcolm

p.s. the circuit above is of a 323S, for a 323K R1 changes to 560R and C9 changes to 1nF.
 
I changed R13 to 500R for a Dynavector 10x5.
Sounds much better than standard gain but 1kOhm would have given more volume knob range.
 
While I'm about it, what's the current wisdom on MC cartridge loading? The Naim 323 circuit has 470R / 6n8, but I've seen much lower or even no capacitors here.
 
Typical MC resistance is a few ohms (say 5) so 6n8 gives a time constant of a bout 34ns, and a corner frequency of maybe 5MHz, so miles from having any effect in audio band.

MC inductance varies over a wide range depending on type; Hagerman suggests between 5uH and 5mH.

This mean there are potentially two different frequency scales to consider ( or a frequency and a damping factor). The L/R time constant depends on the load resistance, and for 500R (470 close enough for hand waving) would range between 10ns (5uH/500) and 10us (5mH/500), corresponding to 16MHz through 16KHz. So only for the highest inductance types (I guess high output ones) will the resistive loading roll off the treble.

The LC resonant frequency is given by 1/(2 pi sqrt( LC)) . Using the example range above for L and 6n8 for C, you frequencies ranging from 860KHz to 28kHz for the high inductance case.

The picture is further complicated by some MC designs having a massive ultrasonic resonance, which may want taming, while others are intrinsically flat.

I think the conclusion has got to be that each model needs its own loading, and that in many cases much bigger capacitances may be needed, up to as much as a uF in extreme cases.
 
Sorry to jump in on this thread but can anyone advise how to get the best out of my ESC Denon 103 ( para tip on saph cant) - you guys seem to know about this stuff.
I have an Avid sequel/SME V into 72/Hicap/110.
Les of Avondale kindly sent me a few resistors to play around with changing on the K boards but they seemed to make very little difference to me. I`m no techi and quite lost with some of your terminology , but I can use a soldering iron ! so if someone knows of any changes i could make to better this combo could you let me know.
Many many thanks
Fraser
 
Thanks, PD, your comments prompted me to look up the numbers for the Sumiko SHO cartridge that I'm using:
  • Type: high output moving coil
  • Output Voltage: 2.3 mV
  • Load Impedance: 47k ohms
  • Output Impedance: 160 ohms
  • Frequency Response: 20Hz - 40kHz
So I tried 1K / 6n8, and it's very balanced across both frequency and dynamics.

Thanks, Malcolm, the E mods worked out fine, although some of the values were different on my Prefix board than in the schematic you posted. I did the following:
  • R2 changed to 11K (R3 was already 100K instead of 82K, so the 11K gave a 10% divider instead of the original 3.8% divider)
  • R15 was already 75K, so left as is
  • Q3: Added 5.6pF silver-mica between base & collector underside of board (vs. 15pF recommended but this was all I had)
  • R13: 220R changed to 1K Caddock precision resistor
I think that's where I'll leave things. There's no going back to the modded Stageline N that I had used before this.
 
Hi, I am trying to do the opposite, convert a Stageline E to an S. I am trying to make it a better match for my Dynavector xx2. 0.28mv, 6 ohm impedence, wants better than 30 ohms load impedence. Unfortunatly the image link posted above is broken. Does anyone know where I could find the scematic?
 
fraserking said:
Sorry to jump in on this thread but can anyone advise how to get the best out of my ESC Denon 103 ( para tip on saph cant) - you guys seem to know about this stuff.
Fraser
Click to expand...

I also have a ESCO DL 103, with the Zu alloy body - probably the second best cartridge I've owned (I'm using my Decca London Gold at the moment) - I used my DL103 into both K and S boards and I couldn't hear any difference at all. I don't think it's particularly sensitive to loading.
 
Actually you can fiddle about with R15 to get a satisfactory level of gain.

Theoretically if R15 goes down from 56R then R2 can also come down from 9k1 a bit but I didn't bother.

I did that to match cards to the output of the Ortofon Kontrapunkt series which falls a bit High for S and a bit low for E.

The resistive and capacitive loading components can be changed to whatever the cartridge manufacturer recommends within reason.

I have 100R and 100pf form my Kontrapunkt. They recommend 50 to 100R and I found that C was best as low as it could go without creating hum and RFI issues.
 
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