I am in the process of re-vitalizing my LP playback equipment.
From eons ago I have an SME III arm and an Entre MC-1 moving coil cartridge.
I have recently picked up an AR turntable, so all I needed was a phono stage.
Not so easy!
There are many on the markets, some at silly prices, so recently I picked up a Creek OBH-15 for cheap, and gave it a quick test.
Wow - this thing is a bit noisy, quoted SNR is 75dB on moving coil input - I don't know about that, out of the box the noise envelope on the scope was about 2mV RMS. If that is 75dB down, we must be talking @11V output RMS! My unit's SNR was about 62dB by my calculation (@ 2.5V rms).
So I opened it up, replaced all signal pass-through caps from electrolytic to polystyrene, coupled all smoothing caps with more polystyrene, used copper tape to make a housing for the MC input stage, disconnected the MM section & the switch.
After this the noise envelope improved to 1.2mV RMS ( 4.5dB better).
Then I just hooked up two 9V batteries together and tested it again.
Noise level now is 0.7mV RMS (about 2mV peak to peak) another 4.5dB !
But that is not all, the nature of noise changed from a harsh background to a mild, even handed hash.
I am going to use cheap mobile phone batteries ( at £5 for five) and fit them inside the box, there is room in there, I just need to figure out an easy way to charge them up. a 900mA/h battery should run the circuit for about 25 hours.
I have not even heard it yet, I had to sort out the noise first.
Any ideas as how to go further ?
From eons ago I have an SME III arm and an Entre MC-1 moving coil cartridge.
I have recently picked up an AR turntable, so all I needed was a phono stage.
Not so easy!
There are many on the markets, some at silly prices, so recently I picked up a Creek OBH-15 for cheap, and gave it a quick test.
Wow - this thing is a bit noisy, quoted SNR is 75dB on moving coil input - I don't know about that, out of the box the noise envelope on the scope was about 2mV RMS. If that is 75dB down, we must be talking @11V output RMS! My unit's SNR was about 62dB by my calculation (@ 2.5V rms).
So I opened it up, replaced all signal pass-through caps from electrolytic to polystyrene, coupled all smoothing caps with more polystyrene, used copper tape to make a housing for the MC input stage, disconnected the MM section & the switch.
After this the noise envelope improved to 1.2mV RMS ( 4.5dB better).
Then I just hooked up two 9V batteries together and tested it again.
Noise level now is 0.7mV RMS (about 2mV peak to peak) another 4.5dB !
But that is not all, the nature of noise changed from a harsh background to a mild, even handed hash.
I am going to use cheap mobile phone batteries ( at £5 for five) and fit them inside the box, there is room in there, I just need to figure out an easy way to charge them up. a 900mA/h battery should run the circuit for about 25 hours.
I have not even heard it yet, I had to sort out the noise first.
Any ideas as how to go further ?
Your noise floor is now probably lower than the surface noise of even the quietest LP.
Sit back and just listen.
Sit back and just listen.
i have a not-so-hifi TT with m55e cart and a diy phonostage(vsps), i had to connect ground of my setup to earth ground to make noise lower. my equip don't have earth ground nor has a 3-prong outlet so im not worried of ground loop due to earthing one unit.
are there schematics anywhere?
By a closer look to the PCB - go to
http://audiomusic-hifi.ru/wp-content/uploads/2010/03/OBH15-open-La1.jpg
and the specifications - go to
http://web.archive.org/web/20120810012921/http://www.creekaudio.com/products/obh15mk2.php
it seems to be a completly other topology than follow mentioned under
http://www.diyaudio.com/forums/analogue-source/151527-how-convert-creek-obh-8-mc-cartridges-3.html
Who knows more ?
By a closer look to the PCB - go to
http://audiomusic-hifi.ru/wp-content/uploads/2010/03/OBH15-open-La1.jpg
and the specifications - go to
http://web.archive.org/web/20120810012921/http://www.creekaudio.com/products/obh15mk2.php
it seems to be a completly other topology than follow mentioned under
http://www.diyaudio.com/forums/analogue-source/151527-how-convert-creek-obh-8-mc-cartridges-3.html
Who knows more ?
Well done so far! 🙂
I would suggest you use SLAs rather than mobile phone batteries as SLAs will have a much lower Zout (which is a good thing, in a PS). And chargers are readily available for SLAs.
What DC voltage do you need to feed the OBH-15?
Andy
I didn't think anybody was following this thread any longer.
at any rate,
Yes the device works, the batteries hold a decent charge for few days of listening and charge up quickly (a few hours).
BTW - Creek were kind enough to provide the circuit diagram - complete with modifications to convert to MC input, however when I asked if I was allowed to post them here, I was told no! so if anyone needs it privately, email me, and you can have it on the promise that you will not post it to internet.
The noise level did improve with batteries, but I am not sure if the sound did.
But changing signal caps to high grade Nichicon's did improve things a bit.
Over all it was a success, and I do use it from time to time.
My greatest success was to fit the batteries, the charging circuit and the toggle switch ( on - off - charge ), three LED's ( on - charging - full ) into the same enclosure!
at any rate,
Yes the device works, the batteries hold a decent charge for few days of listening and charge up quickly (a few hours).
BTW - Creek were kind enough to provide the circuit diagram - complete with modifications to convert to MC input, however when I asked if I was allowed to post them here, I was told no! so if anyone needs it privately, email me, and you can have it on the promise that you will not post it to internet.
The noise level did improve with batteries, but I am not sure if the sound did.
But changing signal caps to high grade Nichicon's did improve things a bit.
Over all it was a success, and I do use it from time to time.
My greatest success was to fit the batteries, the charging circuit and the toggle switch ( on - off - charge ), three LED's ( on - charging - full ) into the same enclosure!