Cooksferry Posted August 30, 2009 Share Posted August 30, 2009 Carrying this over from another thread. I'm having some thoughts about replacing the AC convertor for my Dynavector P75 with a battery. The current wallwart converts to 12VDC, 500MA. To pick from Dynavectors website The P-75 mkII power supply runs at over 1/4MHz. It takes the low grade single voltage DC supply from the ac adapter and converts it to the dual high voltages required for true professional quality audio reproduction. The operating frequency is over 12 times higher than the top of the audio band and it incorporates super low noise wideband regulators in its output stage to give ultra low noise supply rails. The internal P-75 mkII power supply is totally self contained and stores many times the maximum possible energy requirements for the phono amplifiers. This means that the quality or size of the external ac adaptor is irrelevant. Increasing the capacity of the external supply will make no difference to the quality of the sound. The P75 requires at least 500MA at start up. I am thinking about replacing the wallwart with a small gel type motorcycle battery, 5 or 7ah which should give me plenty of playing time between charge up, my only concern is that such a battery might be too much for the phono stage, or will it only draw the amount of current it needs . My 2nd concern is that most motorcycle batteries when fully charged sit around 12.5V, will going over 12 V cause any harm? I know with my Meier Move headphone amp using a DC power convertor the maker stipulates not going over about 12.2v. As usual any help from the experts much appreciated. Link to comment Share on other sites More sharing options...
Beeman Posted August 30, 2009 Share Posted August 30, 2009 Sorry I am not qualified to comment on your specific teck questions but will put in a strong vote for battery power. My Sutherland phono amp uses 16 x d batteries (which I replaced yesterday after 9 months) and 50hz hum problems are gone. Also I am using a Altmann battery dac. The use of low noise battery supplies for the primary amplification phase just seems to work Link to comment Share on other sites More sharing options...
Electra Posted August 30, 2009 Share Posted August 30, 2009 Current draw is dependant on the resistance of the unit. If the unit was going to draw too much current for it to handle, it would do so on the wall wart, and probably kill said WW." Just make sure that its connected the correct way, and check the battery voltage to make sure its exactly what you think it is. 10 NiMH batteries will easily give you 12 volts also, so you could consider a box with 10 NiMH AA, C or D cells in it ( depending on how many Ah you want. if your max current draw is 500ma, then the 5ah battery will give you at least 10 hours ( although toward the end it may start to lose voltage ). Remember that 500ma is the max current draw, you need to figure out battery life with _average_ current draw. I would suggest that you investigate a bank of 10 NiMH batteries. Can fit inside a 2u case easily enough and will provide a heap of current capability if the demand is there, and easy to recharge. Link to comment Share on other sites More sharing options...
little blue penguin Posted August 30, 2009 Share Posted August 30, 2009 IME SLA type batteries have a terminal voltage closer to 13.75V when charged. However even that should not cause any problems for the PSU of the P75. Wall wart type transformers are notorious for being much higher in output voltage than stated. Link to comment Share on other sites More sharing options...
Shane Hanify Posted August 30, 2009 Share Posted August 30, 2009 Gidday Cooks, No, you shouldn't have a problem. Batteries can do high current on demand, and that claim of a 500mA min off a wallwart that only goes to 500 seems a bit odd. As for the excess voltage, that should also not be an issue. I've run the DAC off 2 6V batteries in series (13V) and a 12V low maH SLA that's putting out 13.2 - I've only just started running the little one now (2.4 maH one I borrowed) but instinct tells me it's far too small. I've found that most electronics - especially the good ones have a safety built in so you can over volt them to some degree. Be aware that SLA's require a dedicated (trickle) charger - you cannot use a normal car one. Cheers, Shane. Link to comment Share on other sites More sharing options...
Owen Y Posted August 30, 2009 Share Posted August 30, 2009 Personally, I would want to see a schematic of the PSU & the device itself. That way, you can assess the workable input voltage range, the regulator types & the load. You can see whether it may be beneficial/possible to bypass any SS regulator cct/s (thereby removing another poss source of PSU noise). Etc etc. For starters, you might check if the supplied plugpack is a Regulated 12Vdc or an unregulated type. I have a TT PSU that theoretically runs from a 12vdc wall plugpack, but I find that it runs better with ~16vdc supplied (less sag at startup, etc.). Can anyone show a DV P75 schematic? Link to comment Share on other sites More sharing options...
Owen Y Posted August 30, 2009 Share Posted August 30, 2009 OK... as Gary (I think) said, the P75 takes incoming 12vdc into a HF Switching type PSU cct & DV claim that they have implemented v good regulation & isolation of the cct from any PSU nasties. If true it may be that a batt supply will be of no improvement. So, it may pay not to spend a lot of money first up as a trial, but... It WOULD be interesting to find out if a DC batt supply makes any audible difference. A bit of over-voltage shouldn't hurt, judging by DV's rather loose suggestion to just go out & buy a 12vdc plugpack. Look forward to hearing! Link to comment Share on other sites More sharing options...
wrecker Posted August 30, 2009 Share Posted August 30, 2009 gidday Cooks have a go with the motor cycle battery. Just be mindfull of the polarity though. If you like the sound then invest in either a 12V SLA battery (heaps available for things like burglier arme etc from Jaycar etc) or a battery pack of rechargeble NiMh's. The stated start up of 500mA is not much and the running current is likely to be less than that. The only problem as I see any battery supplied gear is that the charger should be disconnected when listening. Give it a go!!!!!!!!!!! Link to comment Share on other sites More sharing options...
Cooksferry Posted August 30, 2009 Author Share Posted August 30, 2009 Owen Y;101354 wrote: OK... as Gary (I think) said, the P75 takes incoming 12vdc into a HF Switching type PSU cct & DV claim that they have implemented v good regulation & isolation of the cct from any PSU nasties. If true it may be that a batt supply will be of no improvement. So, it may pay not to spend a lot of money first up as a trial, but... It WOULD be interesting to find out if a DC batt supply makes any audible difference. A bit of over-voltage shouldn't hurt, judging by DV's rather loose suggestion to just go out & buy a 12vdc plugpack. Look forward to hearing! Yes, going by Dynavectors statement regarding power supplies not making any difference I could be flogging a dead horse but I'll make up a wire and tip and borrow a battery from work and give it a try in the next couple of weeks. From memory the supplied wallwart doesn't say anything about being regulated. Link to comment Share on other sites More sharing options...
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