After a disgusted failure with my attempted construction of a high quality phono stage from scratch I turned my attention, to much horror of the thing, to my Pro-Ject Phonobox II.
The Phonobox II is powered by 16v AC from a wall-wart tranny. Some audiophiles are appalled by this configuration so I thought I should for once address the "problem".
Opened up the unit and scanned around the PCB... found the two little chips (full of smoke). 79L15 & 78L15 IC regulators, which attempts to filter and smooth the half-wave AC from the single feed AC supply.
I carefully removed the two (yes only two!) diodes that divides the single phase AC current into two out-of-phase half-wave feeds. Also removed the AC input jack.
A nice cable was prepared and carefully soldered in place to feed the two regulators with < [+] [GRND] [-] > from the two 12v (-12v 0v +12v) batteries.
Wow! Am I surprised by the increase in sound quality! Look, the Phonobox II is actually a bloomin good RIAA pre-amp compared to pre-amps costing tenfold. (These days every pre-amp designer uses Op-Amps anyway... there is only a few left that has the guts to design a pre-amp using discreet components).
The sound-stage projected by the speakers suddenly has air and is almost tangible. My blasted hum is virtually gone and overall sound is inviting!
I am very pleased I took the plunge at converting the Phonobox. I wanted to do so for a long time but was scared. The tinkering with pre-amp building taught me one thing for sure - how a regulator looks and works! So there you go!
D
The Phonobox II is powered by 16v AC from a wall-wart tranny. Some audiophiles are appalled by this configuration so I thought I should for once address the "problem".
Opened up the unit and scanned around the PCB... found the two little chips (full of smoke). 79L15 & 78L15 IC regulators, which attempts to filter and smooth the half-wave AC from the single feed AC supply.
I carefully removed the two (yes only two!) diodes that divides the single phase AC current into two out-of-phase half-wave feeds. Also removed the AC input jack.
A nice cable was prepared and carefully soldered in place to feed the two regulators with < [+] [GRND] [-] > from the two 12v (-12v 0v +12v) batteries.
Wow! Am I surprised by the increase in sound quality! Look, the Phonobox II is actually a bloomin good RIAA pre-amp compared to pre-amps costing tenfold. (These days every pre-amp designer uses Op-Amps anyway... there is only a few left that has the guts to design a pre-amp using discreet components).
The sound-stage projected by the speakers suddenly has air and is almost tangible. My blasted hum is virtually gone and overall sound is inviting!
I am very pleased I took the plunge at converting the Phonobox. I wanted to do so for a long time but was scared. The tinkering with pre-amp building taught me one thing for sure - how a regulator looks and works! So there you go!
D
Attachments
Battery drawback?
Other then "green issues", dynamics for one imo/experience.
Different batteries also sound different btw...
In comparison to what reference are you calling this thing a "Super Audiophile Phono-Stage "?
It is not bad for the money in comparison to commercial options, better once some modifications are done to poor quality filter components and quite listenable but audiopile? Depends on what that means to the individual I guess.
Compares well to tenfold the price? What have you tried? For one the Clearaudio Smartphono craps all over it for say 3* the price. At ten times the price it is another ballgame all together and it is left far behind.
Other then "green issues", dynamics for one imo/experience.
Different batteries also sound different btw...
In comparison to what reference are you calling this thing a "Super Audiophile Phono-Stage "?
It is not bad for the money in comparison to commercial options, better once some modifications are done to poor quality filter components and quite listenable but audiopile? Depends on what that means to the individual I guess.
Compares well to tenfold the price? What have you tried? For one the Clearaudio Smartphono craps all over it for say 3* the price. At ten times the price it is another ballgame all together and it is left far behind.
GlidingDutchman said:
Ahh, the reason I ask is that I was considering purchasing a phonobox and then building a new power supply for it, But didn't want to take the battery powered route.
analog_sa said:
Batteries are a continual cost, something that will be a continual drain of my funds. These are funds that are short already, and I know these batteries are quite costly. I don't doubt that it doesn't sound way better than the stock psu, but I also believe that you could build a custom psu that would be much better as well.
-Justin
tubenut said:
Greetings G
Green issues?! Getting ready to move back to Europe? The only mass recycling in SA afaik is the result of theft.
I spent about five years listening to batteries: tube MC step-up and a 3-stage split passive opamp RIAA, each stage powered by a separate set of batteries.
Indeed different batteries sound surpisingly (or not) different. I liked a particular NiCd brand of around 300mA/h. When it became obsolete i never managed to find a suitable replacement. Acid batteries sound completely different of course.
These days i use ALW superregs in almost anything i build. They sound very good but not quite as good as batteries.
If one wants to compare batteries and mains supplies there is no better place IMO than a MC step-up.
This is what I actually did...
Beachwood face with 3mm green LED.
Rubber grommet from a Neutrik XLR plug and some Nylon braid.
DC connected!
D
Beachwood face with 3mm green LED.
An externally hosted image should be here but it was not working when we last tested it.
Rubber grommet from a Neutrik XLR plug and some Nylon braid.
An externally hosted image should be here but it was not working when we last tested it.
DC connected!
An externally hosted image should be here but it was not working when we last tested it.
D
GlidingDutchman said:
Hello All,
I realize the main topic is battery power, however..
I might possibly suggest to also replace the JRC2068/NJM2068 OpAmp with TI, NatSemi very low noise/faster? dual OpAmps.
(If I am reading the part correctly in the bottom photo; U4)
Possibly replace some of the ceramic caps with Poly/Styrene/Silvered Mica?
BC said:
Hello All,
I realize the main topic is battery power, however..
I might possibly suggest to also replace the JRC2068/NJM2068 OpAmp with TI, NatSemi very low noise/faster? dual OpAmps.
(If I am reading the part correctly in the bottom photo)
Possibly replace some of the ceramic caps with Poly/Styrene/Silvered Mica?
BC
It can surely be done... I just have to find the time and funds...
D
Onvinyl said:
It's not quite the "opposite". The superregs are very nice indeed and batteries vary to a surprising extent - one of the reasons i gave up on using them. Acids sound a bit slow and lacking PRAT; NiMH i used quite recently (5 years ago - from Nokia 5110 batteries in a 2SK170 MC step-up) and they were really not bad.
Hi analog_sa,
I second your sonic classification of lead acid batteries. NiMH are a lot better. But a superreg psu has the additional 'kick' -- and a very tiny bit of uneasiness. Mabye the open loop shunt regs I'm now using combine the best of both worlds -- but they are subjectivly so good I was too lazy to acutally check against NiMH's and superregs for now...
but to an extent it's all a matter of taste...
Rüdiger
I second your sonic classification of lead acid batteries. NiMH are a lot better. But a superreg psu has the additional 'kick' -- and a very tiny bit of uneasiness. Mabye the open loop shunt regs I'm now using combine the best of both worlds -- but they are subjectivly so good I was too lazy to acutally check against NiMH's and superregs for now...
but to an extent it's all a matter of taste...
Rüdiger
Glide, looking at the pics it seems you connected DC in the pads left by the diodes?
That means you are feeding 15V regulators 12V, this would not work properly and they would certainly be starved. It probably works though because for some bizarre reason project bypassed the regulator inputs to outputs with some resistors of a few hundred ohms though I know not why...
You may wish to remove the badly behaving starving regulators all together, or replace them with types that are at least 3V below your battery voltage, or up the battery voltage to at least 3V above the 15V regulators.
Or at least, remove the resistors and feed directly to the OP amp PSU pins through the pads left by the resistors. Leaving the regs out of circuit. This would loose the miserable small smoothing caps though.
Those teeny regulators starve the poor stage anyway, I replaced them with a little dexterity with TO220 versions and got rid of all the ceramics in the RIAA.
Rolling op amps can be fun and fustrating, like some cables and tubes.
@PK, no but since the advent of Croaky/ lill tubenutty I see a lot more batteries coming through my house before becoming landfill, there is guilt with that and our urban explosion just means that soon those dumps will be nearer some folks houses then ever, even in big old Africa!
That means you are feeding 15V regulators 12V, this would not work properly and they would certainly be starved. It probably works though because for some bizarre reason project bypassed the regulator inputs to outputs with some resistors of a few hundred ohms though I know not why...
You may wish to remove the badly behaving starving regulators all together, or replace them with types that are at least 3V below your battery voltage, or up the battery voltage to at least 3V above the 15V regulators.
Or at least, remove the resistors and feed directly to the OP amp PSU pins through the pads left by the resistors. Leaving the regs out of circuit. This would loose the miserable small smoothing caps though.
Those teeny regulators starve the poor stage anyway, I replaced them with a little dexterity with TO220 versions and got rid of all the ceramics in the RIAA.
Rolling op amps can be fun and fustrating, like some cables and tubes.
@PK, no but since the advent of Croaky/ lill tubenutty I see a lot more batteries coming through my house before becoming landfill, there is guilt with that and our urban explosion just means that soon those dumps will be nearer some folks houses then ever, even in big old Africa!
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