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Comparing battery-powered phono pre-amps, from RS ($$) to ASR ($$$$) ... and beyond!
- Thread starter D-500 Flogger
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I am going to keep the original form factor/metal box, I like the size and the metal provides good shielding. Gold plated RCA jacks are also in the pipeline.
Spent some time listing and checking components. Plus checking resistor color codes against the schematic 3D posted, and learning which way they go.
Transistors
4x 2SC1740 -- replace with low noise version, possible replacement of something even better?
Caps upgrade low values to red wima caps e.g. 50v/1uf/0.015uf/47pf (c3,c4,c9,c12) the rest high audio grade electrolytic (c13/c10/c5/c6)
c11 16/470uf or 25/470uf (power cap)
c13/c10 16/10uf
c2/c1 50/1uf
c5/c6 25/47uf
C3/C4 0.015uf use red wima caps
C7/C8 0.0047uf (maybe leave these alone due to space restrictions, as C9/C12 upgraded will take up a fair bit of space)
C9/C12 47PF use red wima caps
Resistors upgrade to tight tolerance metal film
R1/R2 56K
R3/R4 1K
R5/R6 460 ohm
R7/R8 22OK
R9/R10 120K
R11/R12 460K
R13/R14 2.2K
R15/R16 16K
R17/R18 12K
Some progress there, comments welcome.
Spent some time listing and checking components. Plus checking resistor color codes against the schematic 3D posted, and learning which way they go.
Transistors
4x 2SC1740 -- replace with low noise version, possible replacement of something even better?
Caps upgrade low values to red wima caps e.g. 50v/1uf/0.015uf/47pf (c3,c4,c9,c12) the rest high audio grade electrolytic (c13/c10/c5/c6)
c11 16/470uf or 25/470uf (power cap)
c13/c10 16/10uf
c2/c1 50/1uf
c5/c6 25/47uf
C3/C4 0.015uf use red wima caps
C7/C8 0.0047uf (maybe leave these alone due to space restrictions, as C9/C12 upgraded will take up a fair bit of space)
C9/C12 47PF use red wima caps
Resistors upgrade to tight tolerance metal film
R1/R2 56K
R3/R4 1K
R5/R6 460 ohm
R7/R8 22OK
R9/R10 120K
R11/R12 460K
R13/R14 2.2K
R15/R16 16K
R17/R18 12K
Some progress there, comments welcome.
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Here's a likely replacement for the C1740 transistors, (BC237B) datasheet seems very close to the original.
BC237B PBFREE Central Semiconductor | Mouser Australia
Here is the datasheet for the original C1740 transistor:
BC237B PBFREE Central Semiconductor | Mouser Australia
Here is the datasheet for the original C1740 transistor:
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Hi Derek92994,
Even though my primary focus at the moment is assembling/re-capping/debugging my personal electronics lab, I made a recent TT purchase that is stoking the fires to ensure that at some point down the road I have the best preamp I can brew up. I still firmly believe that hotrodding this little battery-powered phono preamp is the best place to begin...even if I end up building a battery-powered version of J!m's phono preamp, I at least will get to understand that circuit from the inside out.
Anyway, in order for the following post to make sense, you may have to read this post twice -- 1st time just to assemble the big picture, and the 2nd time for comprehension. (Disclaimer: I'm a audio enthusiast, NOT an expert, compounded by the fact that I'm not a professional tech writer.)
With that disclaimer out of the way, let's see what I was able to collect since I last posted in this thread.
****
First things first -- I acted on my threat to amass 10,000 ufd worth of capacitance -- here's the listing:
Thanks to the free shipping, it really was $6.75 (+ 8% tax) to the door. {~ 0.73 apiece)
Because buying Panasonic caps on ebay can be iffy, the first thing I did when I received them was to check the top & bottom of the 10 caps to ascertain if they were counterfeit or not:
Both top & bottom covers matched the anti-counterfeit capacitor marking document -- whew.
If you are curious as to how massive the 10000 uf @ 10Vdc cap bank is, this gives the reader a good idea. (EDIT: As you can see, it isn't that massive, especially at the 10v storage level...but as Lee has noted we have a certain 'hyperbole quota' to maintain in this forum. :0)
Note: Since I'm giving myself permission to work with a larger case, my implementation would be to remove the stock 100uf cap at C11, install the 1000uf cap in it's place...and then connect the remaining 9000uf capacitance (configured as a small cap bank just off board) in parallel to where the 9V battery connection is made to the circuit board.
And of course create the 3rd file in the before/after series then see if I can discern any difference.
In terms of power mods, that would be step #1 for me. According to the gurus, a 'DC lab power supply' is the ultimate feed -- supposedly a good lab supply that is highly regulated has an even lower impedance than a typical 9V battery. (I know, we've already just added a 100x worth of capacitance over the original 'as sold' value.)
But I'm willing to try anything, so step #2 will be to connect *this* to the phono preamp in place of the 9V battery & see if I can hear the difference. (Working correctly, there should be negligible AC ripple/noise superimposed on top of the 9Vdc output:
(Note: For completeness, you would actually hook this up first with the original 100uF cap in place, do the before & after, then upgrade to the 10,000uf cap bank for local decoupling & create a 4th file.-- at this point I think that all the inner details & dynamic 'slam' possible with this phono preamp board will have been made available. :0)
****
Please allow me to switch to the before & after audio files you uploaded into dropbox. Good news - I finally had a chance to fix my old (forgotten) dropbox password, and I managed to actually download your files straight into my computer as you recommended:
Like you said, this allows me to avoid any dropbox playback compression business.
OK, so here's my current (temporary) predicament. Right now, audio-wise, I am firmly stuck in a low-resolution environment. Eventually with the right headphone amp & high-resolution cans I will have a decent chance of hearing any audible differences the old-school way.
But we may have a high-tech way out of this predicament, by using a software program to run a DIFFerence function between 2 audio files:
FWIW, here's the link to the actual website: (Also, be sure to read the AES paper that's attached to the end of this post.)
In the lower right hand corner it mentions "Different kinds of op amps, transistors, or...(vacuum tubes). To this I would add power supply mods.
I haven't had a chance to download/install/try to run your 2 files through this -- yet. But I am going to. Maybe you will beat me to it? :0)
****
OK, so where am I going to go from here?
1) The first scenario is that I change all the carbon film to metal film. Don't hear any difference. Then I improve the quality of all the caps, leaving the ones in the signal path at the same/close as possible capacitance value as designed. (So I don't throw off the RIAA curve freq. response, as well as where the bass frequencies roll off. (Of course C11 is part of the power supply, so I *will* change both the quality AND the quantity of capacitance in this spot. Still don't hear any difference. Finally, I find a modern, low-noise transistor to replace the 'out of production' obsolete original.
Still don't hear any difference. At this point I'm going to stop & try to figure out if my main system doesn't have enough resolution to allow me to hear the difference. I am also going to not purchase Doug Self's book titled "Electronics for vinyl."
And go focus instead on the CD player & see if I can make any money over there.
2) The second scenario is that when I switch to metal film resistors from the original carbon film units I hear a distinct lowering of background hiss. (Lower noise floor.) I then change out the old sloppy, flabby caps for newer, better stuff, and the sound is cleaner/more natural/less smeary as a result. (ie: The right voltage at the wrong time = the wrong voltage. (!) Finally, I find some new, low-noise transistors where the other curves on the data sheets match, and install those too. And this time I can hear the difference, but it's subtle.
IF this scenario happens to me, then I will have no choice but to spring for this book by Mr. Doug Self:
Here's the link to this book's web page:
...and after reading this book, hopefully by this time I will also be a high-functioning SPICE novice, and I can simulate the hot-rodded Rat's Hack phono preamp, and see if anything further can be done...or do I need to man up & build a copy of the phono preamp circuit that J!m has built?
****
Apologies for the length, but at least you know over in Oz that over here in the finger lakes region of NY I haven't lost interest/forgotten about this little phono preamp.
And anything we happen to learn way, way down here in the microvolt area of amplification now can (& will) help us down the road later when we are trying to tease out the last little bits of inner detail from the rest of our audio system signal path...
Happy Hunting!
3D
Even though my primary focus at the moment is assembling/re-capping/debugging my personal electronics lab, I made a recent TT purchase that is stoking the fires to ensure that at some point down the road I have the best preamp I can brew up. I still firmly believe that hotrodding this little battery-powered phono preamp is the best place to begin...even if I end up building a battery-powered version of J!m's phono preamp, I at least will get to understand that circuit from the inside out.
Anyway, in order for the following post to make sense, you may have to read this post twice -- 1st time just to assemble the big picture, and the 2nd time for comprehension. (Disclaimer: I'm a audio enthusiast, NOT an expert, compounded by the fact that I'm not a professional tech writer.)
With that disclaimer out of the way, let's see what I was able to collect since I last posted in this thread.
****
First things first -- I acted on my threat to amass 10,000 ufd worth of capacitance -- here's the listing:
Thanks to the free shipping, it really was $6.75 (+ 8% tax) to the door. {~ 0.73 apiece)
Because buying Panasonic caps on ebay can be iffy, the first thing I did when I received them was to check the top & bottom of the 10 caps to ascertain if they were counterfeit or not:
Both top & bottom covers matched the anti-counterfeit capacitor marking document -- whew.
If you are curious as to how massive the 10000 uf @ 10Vdc cap bank is, this gives the reader a good idea. (EDIT: As you can see, it isn't that massive, especially at the 10v storage level...but as Lee has noted we have a certain 'hyperbole quota' to maintain in this forum. :0)
Note: Since I'm giving myself permission to work with a larger case, my implementation would be to remove the stock 100uf cap at C11, install the 1000uf cap in it's place...and then connect the remaining 9000uf capacitance (configured as a small cap bank just off board) in parallel to where the 9V battery connection is made to the circuit board.
And of course create the 3rd file in the before/after series then see if I can discern any difference.
In terms of power mods, that would be step #1 for me. According to the gurus, a 'DC lab power supply' is the ultimate feed -- supposedly a good lab supply that is highly regulated has an even lower impedance than a typical 9V battery. (I know, we've already just added a 100x worth of capacitance over the original 'as sold' value.)
But I'm willing to try anything, so step #2 will be to connect *this* to the phono preamp in place of the 9V battery & see if I can hear the difference. (Working correctly, there should be negligible AC ripple/noise superimposed on top of the 9Vdc output:
(Note: For completeness, you would actually hook this up first with the original 100uF cap in place, do the before & after, then upgrade to the 10,000uf cap bank for local decoupling & create a 4th file.-- at this point I think that all the inner details & dynamic 'slam' possible with this phono preamp board will have been made available. :0)
****
Please allow me to switch to the before & after audio files you uploaded into dropbox. Good news - I finally had a chance to fix my old (forgotten) dropbox password, and I managed to actually download your files straight into my computer as you recommended:
Like you said, this allows me to avoid any dropbox playback compression business.
OK, so here's my current (temporary) predicament. Right now, audio-wise, I am firmly stuck in a low-resolution environment. Eventually with the right headphone amp & high-resolution cans I will have a decent chance of hearing any audible differences the old-school way.
But we may have a high-tech way out of this predicament, by using a software program to run a DIFFerence function between 2 audio files:
FWIW, here's the link to the actual website: (Also, be sure to read the AES paper that's attached to the end of this post.)
In the lower right hand corner it mentions "Different kinds of op amps, transistors, or...(vacuum tubes). To this I would add power supply mods.
I haven't had a chance to download/install/try to run your 2 files through this -- yet. But I am going to. Maybe you will beat me to it? :0)
****
OK, so where am I going to go from here?
1) The first scenario is that I change all the carbon film to metal film. Don't hear any difference. Then I improve the quality of all the caps, leaving the ones in the signal path at the same/close as possible capacitance value as designed. (So I don't throw off the RIAA curve freq. response, as well as where the bass frequencies roll off. (Of course C11 is part of the power supply, so I *will* change both the quality AND the quantity of capacitance in this spot. Still don't hear any difference. Finally, I find a modern, low-noise transistor to replace the 'out of production' obsolete original.
Still don't hear any difference. At this point I'm going to stop & try to figure out if my main system doesn't have enough resolution to allow me to hear the difference. I am also going to not purchase Doug Self's book titled "Electronics for vinyl."
And go focus instead on the CD player & see if I can make any money over there.
2) The second scenario is that when I switch to metal film resistors from the original carbon film units I hear a distinct lowering of background hiss. (Lower noise floor.) I then change out the old sloppy, flabby caps for newer, better stuff, and the sound is cleaner/more natural/less smeary as a result. (ie: The right voltage at the wrong time = the wrong voltage. (!) Finally, I find some new, low-noise transistors where the other curves on the data sheets match, and install those too. And this time I can hear the difference, but it's subtle.
IF this scenario happens to me, then I will have no choice but to spring for this book by Mr. Doug Self:
Here's the link to this book's web page:
...and after reading this book, hopefully by this time I will also be a high-functioning SPICE novice, and I can simulate the hot-rodded Rat's Hack phono preamp, and see if anything further can be done...or do I need to man up & build a copy of the phono preamp circuit that J!m has built?
****
Apologies for the length, but at least you know over in Oz that over here in the finger lakes region of NY I haven't lost interest/forgotten about this little phono preamp.
And anything we happen to learn way, way down here in the microvolt area of amplification now can (& will) help us down the road later when we are trying to tease out the last little bits of inner detail from the rest of our audio system signal path...
Happy Hunting!
3D
Last edited:
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Hi 3D, parts are on order, using 470uf cap for storage. Its good to know that the 1000uf is still manageable. You will have a powerbank with that many caps.
All resistors and caps are being replaced with the tightest tolerance possible along with replacement transistors. Only exception is the 2x 50v/1uf capacitors which will be 5% and there was a pair of resistors that I could only get 2%, all the rest will be 1%. The remaining electrolytics will be 20% audio grade nichicons.
Its great how far you plan to take the experiments and testing. I heard a slight difference between the two audio files using akg reference headphones. Maybe even more difference will be observed with the higher quality parts. I will also test with 2 individual upgraded units, 1 channel per preamp.
All resistors and caps are being replaced with the tightest tolerance possible along with replacement transistors. Only exception is the 2x 50v/1uf capacitors which will be 5% and there was a pair of resistors that I could only get 2%, all the rest will be 1%. The remaining electrolytics will be 20% audio grade nichicons.
Its great how far you plan to take the experiments and testing. I heard a slight difference between the two audio files using akg reference headphones. Maybe even more difference will be observed with the higher quality parts. I will also test with 2 individual upgraded units, 1 channel per preamp.
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Got it, yes. Did about 10 hours work on it. Had to bypass a few tracks due to losing the solder pad. There were challenges due to capacitor size, managed to squeeze them in. The nichicon muse caps would not fit into the connector holes, the legs on them were too thick. I resorted to putting in separate legs and mounting the caps horizontally, not ideal and looks messy but it works, and thats all that matters.
Those BC237B replacement transistors have the wrong pinout, fuck! Had to put the C1740’s back in.
First test run the left channel was dead, tested Q1 which had an abnormally high value, took it out and tested out of circuit, no issues. Found C5 and C6 almost shorting, trimmed the legs to fix. Put Q1 back in, tested ok. tested for continuity and shorts all over the board. Now Im listening and it sounds sweet. Will record that same track used last time for comparison and share soon. No pics of soldering side of board, its a war zone
Rca input/output replaced with gold plated type.
Cap/Resistor make and type used:
Koa Speer Resistors mostly 1%
Wima MKP, FKP 2.5%
Cornell Dubilier CDE Grey Film (For the 50v/1uf 5% Cap, couldnt find Wimas in this value)
Elna Silmic 2’s (Electrolytic)
Nichicon UES and UKZ (Electrolytic)
Stocked up on 50v/1uf Nichicon Muse BP green caps, just for shits and giggles, these come in handy, forever running out of them.
By the way, used sil pads are handy to protect the board from the jaw clamps.
Those BC237B replacement transistors have the wrong pinout, fuck! Had to put the C1740’s back in.
First test run the left channel was dead, tested Q1 which had an abnormally high value, took it out and tested out of circuit, no issues. Found C5 and C6 almost shorting, trimmed the legs to fix. Put Q1 back in, tested ok. tested for continuity and shorts all over the board. Now Im listening and it sounds sweet. Will record that same track used last time for comparison and share soon. No pics of soldering side of board, its a war zone
Rca input/output replaced with gold plated type.
Cap/Resistor make and type used:
Koa Speer Resistors mostly 1%
Wima MKP, FKP 2.5%
Cornell Dubilier CDE Grey Film (For the 50v/1uf 5% Cap, couldnt find Wimas in this value)
Elna Silmic 2’s (Electrolytic)
Nichicon UES and UKZ (Electrolytic)
Stocked up on 50v/1uf Nichicon Muse BP green caps, just for shits and giggles, these come in handy, forever running out of them.
By the way, used sil pads are handy to protect the board from the jaw clamps.
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- Joined
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Audio file of Old Caps:
https://www.dropbox.com/s/yz0103gg9xsgy2i/Rat Shack Stock Caps.wav?dl=0
Audio file of Upgraded Caps 2:
https://www.dropbox.com/s/1bjs0ii67ckkxql/Rat Shack Resistor - Cap Upgrades 2.wav?dl=0
Not sure if I hear a huge difference, maybe changing the transistors will have more of an influence. Certainly can't go wrong tightening cap and resistor tolerances, good practice for the next run
https://www.dropbox.com/s/yz0103gg9xsgy2i/Rat Shack Stock Caps.wav?dl=0
Audio file of Upgraded Caps 2:
https://www.dropbox.com/s/1bjs0ii67ckkxql/Rat Shack Resistor - Cap Upgrades 2.wav?dl=0
Not sure if I hear a huge difference, maybe changing the transistors will have more of an influence. Certainly can't go wrong tightening cap and resistor tolerances, good practice for the next run
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Write your 2 transistor pin outs down on paper. Bend the leads on the new ones to match the old.
When using a pin vise to enlarge holes, always start on the copper side. Use very gentle pressure as a copper burr is usually created. Reverse direction a little, cock the bit so the sharp flute cuts the burr off, continue. Don't twist the pad off the board due to the burr! Small bits are available in equally small indexes.
Muse caps are usually physically larger than Fine Gold "FG" counterparts.
Have fun, I enjoy watching your experimentation!
When using a pin vise to enlarge holes, always start on the copper side. Use very gentle pressure as a copper burr is usually created. Reverse direction a little, cock the bit so the sharp flute cuts the burr off, continue. Don't twist the pad off the board due to the burr! Small bits are available in equally small indexes.
Muse caps are usually physically larger than Fine Gold "FG" counterparts.
Have fun, I enjoy watching your experimentation!
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