The high octane phono preamp

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Russellc

Member
Joined 2003
Paid Member
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2Bak

Member
Joined 2002
2bak.blogspot.dk
Modifications

I'm happy with my High Octane preamp.
But always nice to read suggestions for modifications.
I have noted these:

1.
C7, C107, change to 220uF and add 1K between SENSEV and C7, C107, as per post #314.
2.
R13, R113, change to 700K, as per post #317f.
R15, R115, change to 820R, as per post #317f.
3.
The Two Diodes LED Lift modification, as per post #334 and #338.
4.
Alternatively, replace the LED ref with a 2-pin 5V ref, as per post #330.

I would like to try 1 and 2, but perhaps also 3.

Hannes, could you please comment on these modifications.

Thank you,
Jan
 
noviygera

noviygera

Member
Joined 2009
Me too. I'm in the process of building this board and would like to know if there are tested and proven upgrades/mods that should be implemented. These need to be verified by people who tried them or measured the improvements.

I'm asking because I would rather do it the "updated" way (IF any) than to go back and re-solder/waste time. Hope this does not sound rude, just being rational.
thanks,
Herman
 
M

msdin

Member
Joined 2006
2Bak said:
I'm happy with my High Octane preamp.
But always nice to read suggestions for modifications.
I have noted these:

1.
C7, C107, change to 220uF and add 1K between SENSEV and C7, C107, as per post #314.
2.
R13, R113, change to 700K, as per post #317f.
R15, R115, change to 820R, as per post #317f.
3.
The Two Diodes LED Lift modification, as per post #334 and #338.
4.
Alternatively, replace the LED ref with a 2-pin 5V ref, as per post #330.

I would like to try 1 and 2, but perhaps also 3.

Hannes, could you please comment on these modifications.

Thank you,
Jan
Click to expand...

noviygera said:
Me too. I'm in the process of building this board and would like to know if there are tested and proven upgrades/mods that should be implemented. These need to be verified by people who tried them or measured the improvements.

I'm asking because I would rather do it the "updated" way (IF any) than to go back and re-solder/waste time. Hope this does not sound rude, just being rational.
thanks,
Herman
Click to expand...

I’ve built and modified it with the three modifications and can only say that it improved it, with the sound as a whole became more natural with vocals and instrument have a life like quality.

1.
C7, C107, change to 220uF and add 1K between SENSEV and C7, C107, as per post #314.

This modification improved the PSRR of the first transistor with a reduction in hum and I found it had a small effect on how it sounded.
As I did not have any real 2SC2547A I used a BC550C which was fair noisy, I found the bass was muddled and the treble had an etched quality.
The best transistor I try was a BC337-40 noise was lower and sound wise was very well balanced.

2.
R13, R113, change to 700K, as per post #317f.
R15, R115, change to 820R, as per post #317f.

The original riaa network was tested with an inverse riaa and a 20Hz -20kHz signal, with the output voltage read off a valve voltmeter and viewed on a scope.
I check the original riaa network using LTspice and this confirmed a very similar plot using the voltage values of the meter.

I made this change after listening to the preamp as I could hear the drop around 100Hz which had a dry sounded boxy.
The rising in the treble was also noticeable my first though was I hadn't set the input capacitance correctly for the Ortofon 2M Blue.

3.
The Two Diodes LED Lift modification, as per post #334 and #338.
4.
Alternatively, replace the LED ref with a 2-pin 5V ref, as per post #330.

Mods three and four achieve the same results.

This modifications came about with regards to the shunt psu when someone's preamp was oscillating and 'rjm' look into the problem.
The problem turn out to be the op-amp was not suitable for rail-to-rail operations, as it was marginal stable unless the components were carefully selected so rjm proposed lifting the reference voltage.

Sound wise you will have nothing to loss if you try all a three modifications.

This is just my thoughs sound wise the High Octane RIAA phonostage is very good.

Sharif.
 
M

Marra

Member
Joined 2009
Paid Member
I have just about finished my High Octane and have a couple of questions.

The p/s is at 47V and the output of the regulator is 42V which I believe is ok. If someone could confirm this I would be grateful.

The signal output is fluctuating all the time sometimes as high as 60mv. Is this simply because the output is not loaded by a preamp input or do I have a problem? TIA.
 
DIYBras

DIYBras

Member
Joined 2015
Bad offset...

DIYBras said:
Last Saturday I was researching a failure in a timer that I did recently, and the problem lay in the PCB. I "sanded" tracks around the suspect sector, and that solved the problem. And in the pre phono the problem was the same: some invisible residue left over from the corrosion time (I always clean the solder flow, but such cleaning is not the same as "sanding" the PCB).
.
Click to expand...
In my particular case, a dirt between some tracks made this problem (I'm used a DIY PCB).

But with the PCB kit, this is less likely, although excessive dirt or a microscopic solder bridge can play havoc with such low current input stage.

If not, a bad device can made this, and some "detective" work are needed (is easier when one channel works).

But first things first: make the atupi suggestion first (most time is this), even if needs to use 220R in the output.
 
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