[d-cee]

hi guys

I have a STEPS powering my PPAv2.

I didn't build this STEPS but it uses an LM317 regulator and an Amveco 70053 transformer (with 2 x 15v secondaries). It is currently set to output 24v. It's rated for 230v input but our power here in Australia is easily between 240-250v

I've noticed that the STEPS gets really hot, to the point where lately I've been running it with the lid off. The source of heat is the heatsink attached to the LM317.

I guess my question is, can I just increase the output voltage so that the voltage drop isn't so great... All the opamps I use in the PPAv2 - OPA627, OPA637, AD8610, AD744, AD829, LME49710) say they have a maximum voltage of +/- 18v (that's 36v right?)

So given that my transformer has 30v secondaries, can I just set its output to 30v so that there's little/no step down while staying within the safe limits for my amp?

Thanks in advance,

Dave

 

[FallenAngel]

Quote:

Originally Posted by d-cee /img/forum/go_quote.gif hi guys I have a STEPS powering my PPAv2. I didn't build this STEPS but it uses an LM317 regulator and an Amveco 70053 transformer (with 2 x 15v secondaries). It is currently set to output 24v. It's rated for 230v input but our power here in Australia is easily between 240-250v I've noticed that the STEPS gets really hot, to the point where lately I've been running it with the lid off. The source of heat is the heatsink attached to the LM317. I guess my question is, can I just increase the output voltage so that the voltage drop isn't so great... All the opamps I use in the PPAv2 - OPA627, OPA637, AD8610, AD744, AD829, LME49710) say they have a maximum voltage of +/- 18v (that's 36v right?) So given that my transformer has 30v secondaries, can I just set its output to 30v so that there's little/no step down while staying within the safe limits for my amp? Thanks in advance, Dave

The STEPS gets really got because you're dropping almost 16V through it, that's WAY too much. You can run it at 32V with enough room for regulation but the AD8610 is only rated for 26V, absolute maximum (where the chip fries) is 27V.

 

[d-cee]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif The STEPS gets really got because you're dropping almost 16V through it, that's WAY too much. You can run it at 32V with enough room for regulation but the AD8610 is only rated for 26V, absolute maximum (where the chip fries) is 27V.

ah you're right, I mis-read that was 37v on the AD8610 LOL I'm going to go through and double check the others...

i don't quite understand how it's dropping 16v???

30v > 24v is 6v (unless there's something i'm missing here)

and how am i supposed to get 32v from 2 x 15v??? (i'm really missing something here)

edit: the spec sheets for the AD744, AD829, OPA627 and OPA637 say ±18 V whereas the LME49710 just says 36v that's the same thing right?

 

[Beefy]

Quote:

Originally Posted by d-cee /img/forum/go_quote.gif 30v > 24v is 6v (unless there's something i'm missing here)

The transformer is putting out 30V AC. From memory, that becomes up to sqrt(2) * 30 = 42.4V when full-wave-rectified to DC. Definitely too high!

 

[d-cee]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif The transformer is putting out 30V AC. From memory, that becomes sqrt(2) * 30 = 42.4V when full-wave-rectified to DC. Definitely too high!

i see...

a lot of the above from FallenAngel makes much more sense now

so is 32v pretty good or can I push it higher? 33 or 34v perhaps?

 

[FallenAngel]

Quote:

Originally Posted by d-cee /img/forum/go_quote.gif i see... a lot of the above from FallenAngel makes much more sense now so is 32v pretty good or can I push it higher? 33 or 34v perhaps?

You can go higher than 32V, I doubt there is much benefit from it, up to about 36V should still be well regulated.

 

[d-cee]

Ah great, the turner maxes out at 28v. Min value is 22.6v.

I'll have a read of the STEPS page on Tangent's site, but what parts am I going to have to swap out to make this work?

 

[FallenAngel]

Quote:

Originally Posted by d-cee /img/forum/go_quote.gif Ah great, the turner maxes out at 28v. Min value is 22.6v. I'll have a read of the STEPS page on Tangent's site, but what parts am I going to have to swap out to make this work?

Personally I'd change the VSET trimpot to 1K, it will give you a much larger adjustment

 

[d-cee]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Personally I'd change the VSET trimpot to 1K, it will give you a much larger adjustment

Thanks for the suggestion!

I had a look at tangent's site and it seems R3 and R4 and what I would have changed.

Currently R3 is 120ohm, R4 is 2kohm. I guess that currently VSET is currently 500 ohm?

If I use a 1k trimpot will that give me more range up or down, and by roughly how much?

Thanks so much mate, you've been a real help =)

 

[FallenAngel]

Quote:

Originally Posted by d-cee /img/forum/go_quote.gif Thanks for the suggestion! I had a look at tangent's site and it seems R3 and R4 and what I would have changed. Currently R3 is 120ohm, R4 is 2kohm. I guess that currently VSET is currently 500 ohm? If I use a 1k trimpot will that give me more range up or down, and by roughly how much? Thanks so much mate, you've been a real help =)

The voltage out is ((R4 + VSET / R3) + 1) * 1.25.
So currently you have (( (2000 to 2500) / 120) + 1) * 1.25 = 22.08V to 27.29V
With a 1K VSET you'll have (( (2000 to 3000) / 120) + 1) * 1.25 = 22.08V to 32.5V

Maybe make that trimpot 2K for obscene capabilities?

 

[d-cee]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif The voltage out is ((R4 + VSET / R3) + 1) * 1.25. So currently you have (( (2000 to 2500) / 120) + 1) * 1.25 = 22.08V to 27.29V With a 1K VSET you'll have (( (2000 to 3000) / 120) + 1) * 1.25 = 22.08V to 32.5V Maybe make that trimpot 2K for obscene capabilities?

Great, THANKS!

That's just the information I needed.

Are there any downsides to using a large valued trimpot?

Edit: btw, have been running the STEPS at 28v and it's a bit cooler, but still warmer than I'd like. I did notice that the amp is now running a little warmer now. By increasing the output voltage does that mean that the bias measurements (eg. opamp and output transistors) have gone up too? I can only imagine that's where the extra heat is coming from...

 

[ruZZ.il]

Watch out not to go past the limit for the op-amps you're using. While the output of the STEPS will go through a diode or 2 on the way to them it's still a slim margin if you're pushing your steps to 26.5v+.

I had the same problem( thread here). I didn't have a good enough understanding of it all when I built my STEPS and used the 2x15v amveco shooting for 26v DC. With a drop of about 10v (after the diodes, caps, etc) Vreg was dissipating around 5 watts. After changing the trafo out for a 2x12 I got 26v with enough regulation margin, and 70% LESS heat.
Ultimately, this is what should be done. (Well, it's at-least what I did and its cool as.. well... its cool now

).

..In the meantime, sadly, I recommend you don't risk burning up the op-amps by over-voltage, and staying at around 26.5v max. Turn down the amps bias a bit to lower the current draw of the amp to take a load off the regulator in the STEPS. Try get an amveco 70062(25VA, about an amp at 26v) or 70052(15VA, about 0.6amps at 26v) to switch out your current one (its around 20$+shipping poopoo..)

The current specs of your amp are basically the sum of the bias currents plus about 50ma(?), then keep some margin..

.....if it's any consolation, I know how you feel

 

[d-cee]

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif Watch out not to go past the limit for the op-amps you're using. While the output of the STEPS will go through a diode or 2 on the way to them it's still a slim margin if you're pushing your steps to 26.5v+. I had the same problem( thread here). I didn't have a good enough understanding of it all when I built my STEPS and used the 2x15v amveco shooting for 26v DC. With a drop of about 10v (after the diodes, caps, etc) Vreg was dissipating around 5 watts. After changing the trafo out for a 2x12 I got 26v with enough regulation margin, and 70% LESS heat. Ultimately, this is what should be done. (Well, it's at-least what I did and its cool as.. well... its cool now ). ..In the meantime, sadly, I recommend you don't risk burning up the op-amps by over-voltage, and staying at around 26.5v max. Turn down the amps bias a bit to lower the current draw of the amp to take a load off the regulator in the STEPS. Try get an amveco 70062(25VA, about an amp at 26v) or 70052(15VA, about 0.6amps at 26v) to switch out your current one (its around 20$+shipping poopoo..) The current specs of your amp are basically the sum of the bias currents plus about 50ma(?), then keep some margin.. .....if it's any consolation, I know how you feel

thanks mate, appreciate the extra info. I'll keep that in mind.

since all the opamps i intend on using can go up to 36v (i don't like the sound of the AD8610 much) i'll try the cheaper option of replacing a trimpot and couple of resistors before splashing on a new transformer and shipping to australia!

 

[ruZZ.il]

well, if the amp can handle it, that's always an option

at-least you know the parameters now and can play freely. good luck and enjoy!

 

[d-cee]

yep got a 1k and 2k trimpot

decided to drop in the 2k trimpot and it goes from like 22 to 47v

anyway i've dialed the STEPS in so I get 34v at the opamp socket it's something like 35.5v coming out of the STEPS

MUCH cooler now, wow i can barely tell it's on (besides the big blue LED at the front

)

so, question hasn't been answered... i'll try again:




is there any downside from going with such a large value trimpot?

thanks everyone!