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Empress Tape Delay current draw

Billy Idle

Member
Messages
579
Builder says 280mA at 9 volts. But they don"t specify how many mA it will draw at 18 volts. 560 or 280 ?
 

iaresee

Member
Messages
3,841
This is a digital pedal. Doubling the voltage is not something you should do ad hoc. The manual says it's operating range is 9VDC - 12VDC. What are you hoping to gain running it outside of that range?
 

Whereishumhum

Member
Messages
322
It can go 18v but there is no point, to me, mine sounds the same at 9v and 18v

I guess technically at 18v it would draw 560ma
 

stinkfoot

Member
Messages
6,138
We had a discussion about this just a couple of days ago: https://www.thegearpage.net/board/index.php?threads/1520628

Basically, in theory the current draw will be doubled too (so 560mA @ 18vDC). In practice, though, it will be somewhere between 280 and 560mA, as the load the pedal places on the supply (its internal resistance, if you may) might not be 100% the same at the higher voltage.

140mA would be the answer for a power supply - at twice the voltage, half the current is needed to do the same job. But the pedal is a power consumer, rather than supply, so the rules are different.
 

iaresee

Member
Messages
3,841

stringman340

Member
Messages
471
When I wrote Empress sometime ago, they said there is nothing to gain when running at 18v, and 9-12 volt is recommended - but also mentioned that they designed it to work with PP2's outlets 5 or 6 with the DIP switch away. This is how I've been running it prior to adding a 4X4 to the board. Now it runs off a 12v/400mA outlet. Both power scenarios have turned out identical sounds/performance.
 

empress_effects

Double Platinum Member
Messages
330
Hi guys,

iaresee let me know there was some confusion about running the tape delay at 18V.

First, tldr: Current consumption on the tape delay doesn't increase when you increase the voltage from 9V to 18V. Headroom doesn't increase either, so you can just run your pedal at 9V or 12V, or run it at 18V. It's not going to make an audible difference. Unless you use Monster cables.

Okay, here's the reason: we use at LM2937 for voltage regulation. Here's the datasheet: http://www.ti.com/lit/gpn/lm2937

The total current that the pedal consumes is the current that the LM2937 supplies to the rest of the circuit (which stays pretty constant) plus the current that the LM2937 uses to keep the voltage stable (this is called the LM2937's quiescent current). If you check out page 8 on the datasheet, you'll see figure 5, which is Quiescent Current vs. Input Voltage. You'll notice that quiescent current actually drops with increased voltage.

So, when people think doubling the voltage means a doubling the current, they are modeling the circuit as a simple resistor. In general, the current vs voltage function can look like anything (especially if you throw in some magnetic hysteresis!) , and the power input looks nothing like a resistor.

Please let me know if you have any questions. There's a lot more I don't know than do know though, so I might not have the answers!

Steve.
 




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