[oldguy]

Has anyone compared two identical battery powered headphone amps, one with new batteries, the other partially discharged?

My Grado RA1's performance begins to deteriorate long before the batteries run out.

I can feel a new amp coming on! Oh no, not that again. Help-help, somebody talk some sense into me! Either that or buy my Grado so I can get ANOTHER amp

 

[gaineso]

Try NiMH rechargeables. They stay fairly constant voltage right up to the end.

Your sig. I feel the same way everytime I'm out in the Low Frequency Boat. Got to have more power to get over 70.

 

[Hirsch]

Quote:

Originally posted by oldguy My Grado RA1's performance begins to deteriorate long before the batteries run out.

Hehe. Bad excuse to upgrade. Try the Plainview 9.6v NiMH rechargeable at thomas distributing. A search on rechargeable batteries should turn up some information. Basically this battery holds it's voltage pretty constant until the charge is almost gone. Using the RA-1, I got about 30 to 40 playing hours between charges, but that's a bit lower with the HPA-1 (20-30 hours).

I do not recommend an 8.4 volt NiMH (some go as low as 7.2 v). The RA-1 needs the extra voltage for optimum operation, IMO. The Plainview is the only 9.6 v NiMH I know about.

An alkaline battery slowly loses voltage over the life of the charge, which is what you're hearing.

 

[oldguy]

Thanks Hirsch, this is good information. I have had a look at the Plainview website and found the Nmh batteries. There is no mention of which type of charger to use and where to purchase one.

 

[puppyslugg]

Quote:

Originally posted by oldguy There is no mention of which type of charger to use and where to purchase one.

http://4cbradio.com/9v-nimh-batteries-chargers.htm

 

[Pepsione1]

Battery & Charger from Thomas Distributing

I usually charge mine for ten hours before use.

edit: hm... puppyslugg beat me to it because i made a fancy link. lol

 

[puppyslugg]

Quote:

Originally posted by Pepsione1 edit: hm... puppyslugg beat me to it because i made a fancy link. lol

If I knew how to do a 'fancy link'....probably not.

 

[oldguy]

Thanks for the help guys. I've ordered 2 NiMH batteries and charger, so we'll see how it goes.

BTW, does anyone know if the RA1 runs on 9v or 18v?

 

[Eagle_Driver]

Quote:

Originally posted by Hirsch Hehe. Bad excuse to upgrade. Try the Plainview 9.6v NiMH rechargeable at thomas distributing. A search on rechargeable batteries should turn up some information. Basically this battery holds it's voltage pretty constant until the charge is almost gone. Using the RA-1, I got about 30 to 40 playing hours between charges, but that's a bit lower with the HPA-1 (20-30 hours). I do not recommend an 8.4 volt NiMH (some go as low as 7.2 v). The RA-1 needs the extra voltage for optimum operation, IMO. The Plainview is the only 9.6 v NiMH I know about. An alkaline battery slowly loses voltage over the life of the charge, which is what you're hearing.

It all depends on the impedance of the headphones that you're planning to use with the RA-1. The Plainview 9.6V rechargeables are the batteries that I would use if that amp will be used mostly with high-impedance headphones, such as the Sennheiser HD 580 and HD 600 and the AKG K240M/K240DF. But if the main use of the Grado amp is to drive low-impedance, high-efficiency headphones such as Grados, then the alkalines -- especially the so-called "Ultra" types, such as the Duracell Ultra M3 -- are the better choice. (That's because the typical 9V alkaline is rated at 600mAh in capacity, versus less than 200mAh for rechargeable "9V"-size batteries, and NiMH batteries cannot sustain a current load much greater than the numerical current rating -- not to mention that NiMH's don't have anywhere as much stamina at low current draw as alkalines, as well as the fact that slow discharge due to nonuse isn't good for NiMH rechargeables.) But neither battery type is recommended if the Grado amp is used to drive low-impedance, low-efficiency headphones (such as the Sennheiser HD 495 and HD 570), due to the high current and high voltage requirement of such 'phones.

 

[Eagle_Driver]

Oh, I also found out why an 8.4V NiMH battery isn't recommended for the Grado amp:

Most commercially sold chargers at mass-market stores cannot properly charge those 8.4V batteries, as they output less than the 9.2V minimum voltage that's required to properly charge those 8.4V batteries - and the open-cell voltage of a fully charged 8.4V NiMH battery actually measures slightly higher than that of a fresh 9V alkaline battery (9.4V versus 9.2V). No wonder why most 9V-size chargers are crap; they can properly handle only the archaic 7.2V versions of those batteries.

And what about regular 9V alkalines? Well, an amp that's using them will sound no better overall than an identical amp that's using properly charged 8.4V NiMH batteries - and after just a few hours of use, the amp using regular 9V alkalines will actually sound almost as crappy as the identical amp using 7.2V NiMHs, due to the voltage loss during use with alkalines. Switching to a NiCd with the same voltage rating will improve the sound quality slightly, to roughly the level of an "Ultra" alkaline battery, though the overall stamina of the NiCd will be less; that's because NiCds have lower energy density but much greater current delivery capacity than NiMHs.

The truth is, an audiophile battery-powered amp will require both high voltage and high current. Unfortunately, 9V transistor-radio-sized batteries cannot provide both - at least not in their present form. The RatShack 8.4V/120mAh NiCd batteries come closest to what I'd consider an ideal 9V-size battery for Hi-Fi use (note that I haven't tried the Plainview 9.6V NiMH batteries yet).

 

[MadDog5145]

Does the difference in volts (7.3 vs 9.6) in the batteries affect the battery life? I am currently using a meta42 with my Beyer 770pro and I am not happy with the only 6-8 hour battery life.

 

[Hirsch]

Quote:

Originally posted by MadDog5145 Does the difference in volts (7.3 vs 9.6) in the batteries affect the battery life? I am currently using a meta42 with my Beyer 770pro and I am not happy with the only 6-8 hour battery life.

No, the life of the charge is determined by the amperage rating of the battery, not the voltage. The Plainview has a rating of 170 mah (a device rated at 170 ma will drain the battery in one hour). I've seen a Tysonic 9v at thomas-distributing that has a larger capacity in mah, but is only rated 8.4 v to the Plainview's 9.6 v. The Tysonic will last longer, but the Plainview will deliver a higher voltage.

 

[Eagle_Driver]

Quote:

Originally posted by Eagle_Driver The RatShack 8.4V/120mAh NiCd batteries come closest to what I'd consider an ideal 9V-size battery for Hi-Fi use (note that I haven't tried the Plainview 9.6V NiMH batteries yet).

This judgment of mine is based on charging the RadioSchwack NiCds for 12 hours on a first-generation Energizer ACCU NiCd/NiMH AA/AAA/9V charger, which outputs 9.8V into each battery at 15mA charging current. (12 hours is the correct charging time for those RadioSchwack batteries, based on my calculations.) But the current version of that charger cannot correctly charge the RatShack batteries because the output voltage of the newer Energizer charger is lower (at 9.0V with 16mA charging rate) than the open-cell voltage of those RatSchwack batteries (9.4V) - and that can cause damage to the charger and/or batteries. (For that matter, none of RadioSchwack's own chargers can properly handle their own 8.4V batteries.) The output charging voltage of a charger must be equal to or higher than the open-cell voltage of a battery for reliable results.

If you want a rough estimate of the open-cell voltage of a given rechargeable battery, multiply the battery's given (nominal) voltage rating by 1.125 (i.e. an 8.4V NiMH battery will produce an open-cell voltage of roughly 9.45V).

 

[Hirsch]

The Radio Shack 23-425 charger delivers 23 ma of charging current to a Plainview battery at 10.4 v. Open voltage of the charger is about 15.2 v for 9 v batteries. It looks like that charger is more than capable of handling the Plainviews, or just about anything else.