[Jeff Guidry]

Howdy. I have a JMT built CMOY that uses the OPA2134PA with a single 9v battery. I would like to boost the voltage that I give it for better sound. Since I recently bought a META42 built by fyleow that came with an Elpac 24v DC power supply, I would like to replace the battery power and use the power supply for both amps.

However, I am not sure if this power supply would be too much juice for my CMOY. Can you give me some advice?

Also, concerning the META42....fyleow was forward thinking enough to socketize the OPA637 for this amp so I could roll the chips. I wanted to purchase either the AD843, AD845 or AD8610 to roll out to get a 'snappier' sound than the excessively laidback OPA637, but I was also concerned with giving these excessive voltage. Tangent's opamp roundup gives lots of info about how much is required to get good sound, but not on how much is too much. Can you help me with this as well?

 

[fiddler]

Try going to the opamp manufacturer's website and downloading their datasheets. They have info on how much voltage they can take.

 

[tangent]

Traditionally, op-amps have a high voltage limit of 30V (or +/-15V, if you prefer -- same thing) or better. Most current chips are like this. However, it's becoming more common to see chips with lower voltage tolerances. All of the chips you mention will run just fine from 24V; the lowest is the AD8610/20, which won't tolerate more than 26V.

The main risk is not the op-amp, but rather the power supply capacitors. To be safe, your power supply voltage should be under the caps' voltage tolerance, which will be printed on their side. If JMT used a 25V cap, you're golden; if the Elpac you have is the WM080, it's tightly regulated, so it will stay at 24V. I don't know about Elpac's other 24V supplies.

If your amp's PS caps have a lower tolerance than 25V, they're probably 16V. There are circumstances where you can risk a 24V supply with 16V caps and get away with it. Ideally, each PS cap in a Cmoy amp sees only half the power supply voltage, so in this ideal world, you could get away with a 32V power supply. In the real world, that amp probably uses a simple resistor-divider power splitter, which will become imbalanced easily, especially when you use low-impedance headphones. If you measure the amp under load from ground to each power rail, I expect that you won't find an even split. If the high side of the split exceeds your power supply caps' tolerance, you'll be cleaning black goo out of the innards of your amp in the near future.

 

[fyleow]

Just the clarify, the Elpac PSU is indeed the WM080 so the voltage will stay at 24V. I believe Tangent sells the AD8620 (or was it 8610) that is socketed and that should work fine. The buffers are also socketed on the board so if you would like to experiment with those you can as well.

If the power supply capacitors are not a problem the opamp should be able to handle the voltage. However I think that there is a limit with voltage, adding so much will only improve the sound to a certain degree and the rest will be wasted.

 

[Jeff Guidry]

Thanks for the informative replies guys.

Fyleow, I will be communicating with you further about this in PM. I think it makes more sense for me to use the PSU for the CMOY than wiring an extra 9v batt.