[StanRex]

I've just realized that I didn't know how much current a ppav2 draws.

I checked other amp sites and found the mosfet max needed a supply capable of delivering at least 1A. I hope a PPA doesn' t draw as much because I'm unable to find any wallwart exceeding 750mA output at 24V AC (in fact I've only found two 24AC wallwarts, one outputting 750mA max, the other 500mA).

So I'm just wondering if one of you know if those would be enough for all kind of ppas, or only those using less current consuming opamps, or even if they wouldn't be enough for any kind of ppa

thanks in advance

ps : I've already checked tangent's site multiple times but have been unable to find indications of the ppa current draw

 

[MisterX]

Assuming the 500mA adapter is regulated, it has plenty of output current capacity for a PPA2.

Edit: Remember the Elpac WM080 suggested in the parts list only outputs .33 amps.

 

[FallenAngel]

You can (and SHOULD) measure it to make sure your build works properly.

The current draw of the amp will be the sum of the current draws of the opamps (check datasheet of the opamps of what they should use - Iq), plus whatever you set your opamp Class-A bias at and how much you bias your buffers at.

STEP 8 - setting buffer bias.

So if you're using OPA627 which draws 6mA, you bias it into Class-A with 1mA, and set your buffers to 25mA each, you're looking at ((6 + 1) x 3) + (25 x 3) + a few mA for LED and such (device mismatch tollerence) so it should be a total of about 100mA.

 

[StanRex]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif You can (and SHOULD) measure it to make sure your build works properly. The current draw of the amp will be the sum of the current draws of the opamps (check datasheet of the opamps of what they should use - Iq), plus whatever you set your opamp Class-A bias at and how much you bias your buffers at. STEP 8 - setting buffer bias. So if you're using OPA627 which draws 6mA, you bias it into Class-A with 1mA, and set your buffers to 25mA each, you're looking at ((6 + 1) x 3) + (25 x 3) + a few mA for LED and such (device mismatch tollerence) so it should be a total of about 100mA.

Ok, so I'd be good with both wallwarts. Great to know. Thanks to both of you for your answers.

Just wondering though, why does the Mosfet Max draws so much current compared to the PPA? is it because of the fact it uses tubes?

edit : oh and the whole idea is to fit the PPA and a TREAD in the same box and use an external unregulated 24VAC wallwart

if I understood properly there shouldn t be emi issues since the transformer is out of the box and the tread should take care of the regulation

 

[FallenAngel]

Like I said, add the current draw of each.

MOSFETs are biased to 110mA per channel (as in Mosfet MAX or M^3)! The BJT (as in regular MAX or PPAv2) are usually set at 25-30mA, see the difference.

Tubes draw 150mA I think in the MAX, most opamps draw under 10mA.

 

[StanRex]

Mmmm, just a quick question concerning CRD, because I'm not totally sure I understood

it's useless if the amp is not battery powered right? I can just use rled and be done with it?

thanks in advance

btw, living in France, I'm going to get *$^f^ù* on shipping costs ^^ (ordered yesterday from tangent, and the digikey, mouser and farnell orders are ready to go)

I expect to end up @ +- 300 €, everything included

 

[tangent]

"Useless" is a little strong. A CRD does its job quite well no matter what the supply. It just doesn't justify its cost when the supply voltage doesn't change.

 

[StanRex]

Ok, thank you Tangent

 

[StanRex]

Mmm I have a quick question regarding power

I'd like to have the TREAD (fed by an AC wallwart) + PPA in a single hammond 1455T1601 case to avoid having X thousand boxes of components near my pc

I was thinking of using a single switch to power on/off both the PPA and the TREAD.

I recall reading in this thread that there was a risk to fry the regulator and damage the TREAD when powering off either the PPA or the TREAD first (cant remember exactly which one) so you had to do it in a precise order

I was wondering if there was also a risk to damage components when using a single switch to power on/off both the TREAD and the PPA at the same time.

If yes, I'll modify my order to use two boxes, one for the TREAD and one for the PPA

thanks in advance

 

[tangent]

There's less risk of problems here with the TREAD than the STEPS, due to the smaller filtering cap. But if you don't mind burning ~10 mA to keep the TREAD running, the simplest and most reliable is to put the power switch between the TREAD and the PPA. The power supply stays running all the time, but draws very little power, and it's always up and ready to go.

The only other thing is to avoid excessive rail capacitance in the PPA. See the docs.

 

[StanRex]

Ok, I'm going to go with that solution.

And maybe add an additionnal switch for the power supply at the back of the case if I ever feel the need to switch it off separately

thanks for your answer Tangent

 

[tangent]

Rather than a switch on the incoming line, I'd just use a connector for the wall supply, so you can unplug the cable. Say, for going on vacation. Anything more convenient is just going to cause confusion about which switch to use when, later on when you forget why the amp has two switches.

 

[StanRex]

That's indeed a better though solution ^^ I must be really tired for imagining such an impractical solution ^^

I'll go with only one switch, thank you once more tangent for your advices!

 

[steinba]

Does anyone have an up to date BOM for the PPAv2 from mouser, digikey or maybe even Elfa?

(BTW: I have the opamps and C1's as well as the Alps pots)

 

[StanRex]

damnit, I ve just checked the availability of opa627 and 637 at mouser and they re out of stock. I'll still have other opamps to play with, but still... missing those sucks!

I ve checked farnell and digikey and they dont have them. Do you know where I might be able to find a few 627 and 637 (in a store that ships internationnaly if possible ^^) ?

PS : i have a bom, but it s not totally up to date, as I ve just found, and it sources parts from digikey,mouser and farnell