Planning Phono Pre-amp upgrade

Hari Iyer

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After my successful stint of upgrading my tube amp components its now time for my phono pre-amp components upgrade. I am planning change of the following components type in the preamp

Resistors - Metal oxide to metal film (unbranded Chinese to Vishay)
Electrolytic capacitors - Keltron to Nichicon
Coupling capacitors - DEC to Russian PIO - military grade
RIAA capacitors - unbranded Chinese to Russian PIO - military grade
Supply Bypass capacitors - unbranded Chinese to probably Wima or some other brand.

What will not be changed
PCB - will take a new PCB but the ckt still remains the same.
Opamp - This will be the same LM4562
Dual JFET - Will use the same smd chip
BJT - will use the same transistors.

Approximate cost of modifications - Rs.3500/- to Rs.4000/-

Hoping to complete this activity in another month or two and will post feedback after that.

Thanks for looking.
 
After successful usage of this version of phono Preamplifier, I went for one more final upgrade. All discrete Resistors are replaced with thin film resistors, all filter caps are PIO. The opamp is LM4562. I did not add any additional power supply filtering in the preamplifier by adding a 100uF + 0.1uF bypass. There is an article written by Elan in the early 1980 the trick of using low PSU filtering and am following that approach.

In my LM317 & LM337 regulator has a primary filtering of 4700uF and after the regulator was a 220uF electrolytic. I retained the 4700uF filter but after the regulator have removed the 220uF electrolytic and replaced that with a 8uF + 68nF polypropylene type Capacitor. IME most people imagine lot of things in DIY about hum. I measured a much lower noise of 0.34mV with input short ( compared to a 12mV with higher PSU filter values).
The earlier opamp used was an AD827 and they seem to have more low end compared to LM4562. But again the LM4562 is fresh and will need 100+ hrs of break-in time to settle which means 2+ months.
 
Hari,

1) Listen to each parts change, to HEAR if it is better ,as......... it could also be worse.

2) At the output of the solid state regulators....to clean them up, you can TRY an L/C B+ filter add-on. Use a tiny Bourns RLB9012 hash choke, followed by a small uF film WIMA DC Link cap. Listen...... to that.

Jeff
 

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After 2+ hours of listening the module seem to open up after a stop of 1 hour Jeff. I am liking this sound more than the previous version chiefly because they are sounding very very neutral with no over emphasis or de- emphasis of any frequency. The sound stage is not overly sweet or shiny nor do they lack any critical mid-bass or low end. The mid- range is very clean and have a 3D holographic imaging at all sitting positions in my room and is fatigue free. The sound stage is very fatigue free wanting to listen more. They allow you to get immersed in the performance rather than getting lost in the technicalaties.
 
After 2+ hours of listening the module seem to open up after a stop of 1 hour Jeff. I am liking this sound more than the previous version chiefly because they are sounding very very neutral with no over emphasis or de- emphasis of any frequency. The sound stage is not overly sweet or shiny nor do they lack any critical mid-bass or low end. The mid- range is very clean and have a 3D holographic imaging at all sitting positions in my room and is fatigue free. The sound stage is very fatigue free wanting to listen more. They allow you to get immersed in the performance rather than getting lost in the technicalaties.
 
After much reading of Eric's article on LM317 filter capacitor i removed all the high value filter capacitors from my power supply board. 4700uf + 4700uf electrolytic gets replaced by 330uf + 330uf bipolar capacitors. Also I removed the 8uF + 68nF after the regulator and substitute with an RC combination of 150hms + 2kohms with c parallel to 2kohms with a value of 10 nF. Also added a 22nF supply decoupling capacitor next to the opamp.

Earlier after power off the voltage used to take almost a minute to be decay, now they decay within just 3 to 4 sec. This gives an indication of how fast is the charging/ discharging cycle time. This has given more depth, definition, realism and proper tonality to the preamplifier. The total current drawn will be around 10mA per channel and such low current requirements do not require high value filter capacitors. Higher filter capacitors make the sound stage dull, sterile and boring IME. Lower filter capacitors allow the powersupply to modulate and follow close to music signal and are more dynamic with less stored energy. The current required for the phono preamplifier is supplied by the transformer instead of the capacitor improving performance.
 
After successful working of my previous power supply capacitor mods, i have further reduced the value of the filter capacitors from 330uF to 250uF bipolar + 15uF MKP. Also added by-pass capacitor to the RIAA filter caps which is 100uF, Nichicon muse bi-polar with a 6uF MKP + 0.068uF MKP for further tightening the low-end. Have yet to connect and listen for any possible hum due to PSU filter modifications.
 
Day 2 usage of the modified power supply has no issues and everything works as intended. Previously was not using any cartridge loading capacitor as I was having only ceramic disc capacitors which could be noisy at that application. I could salvage a pair of 270pF tantalum capacitor from my vintage tape deck PCB and am using them for the cartridge loading with excellent results.
 
After my successful stint of upgrading my tube amp components its now time for my phono pre-amp components upgrade. I am planning change of the following components type in the preamp

Resistors - Metal oxide to metal film (unbranded Chinese to Vishay)
Electrolytic capacitors - Keltron to Nichicon
Coupling capacitors - DEC to Russian PIO - military grade
RIAA capacitors - unbranded Chinese to Russian PIO - military grade
Supply Bypass capacitors - unbranded Chinese to probably Wima or some other brand.

What will not be changed
PCB - will take a new PCB but the ckt still remains the same.
Opamp - This will be the same LM4562
Dual JFET - Will use the same smd chip
BJT - will use the same transistors.

Approximate cost of modifications - Rs.3500/- to Rs.4000/-

Hoping to complete this activity in another month or two and will post feedback after that.

Thanks for looking.
Hari, did I miss this? What brand/model of Phonopreamp are you upgrading?
 
Purchase the Audiolab 6000A Integrated Amplifier at a special offer price.
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