Teddycap 3 - output voltage change

Mervyn

Have been considering buying a 2nd hand Teddycap 3 which has 2 x 24v outputs. The plan is to use it to initially power my Wins 7 Nexus server which can run up to 18v using one output. The 2nd output could then be used to power eg Young DAC also at 18v sometime in the future.
I believe you need to change only a resistor in the Teddycap to reduce this voltage. How straightforward is this for a complete electronics novice who can sort of solder ie me ?

Uzinusa

Contact Teddy Pardo, he's a very clever and helpful chap, and see if it's got variable resistors as my SuperTeddyReg boards have.  In which case, no soldering just adjust the output using a DVM.  I can help either way probably.

Andy

Uzinusa

Mervyn, did you PM me?  I'v been a bit busy of recent but will reply.

Andy

Mervyn

Great thanks Andy. Will contact Teddy Pardo as you suggest - hopefully adjustable !

Reply when you have time - no probs.

Thanks

Mervyn

 

Uzinusa

Yea, see what Teddy says but, as with the PFM STR GB, looking at his circuit i looks like he also uses a variable resistor (R3).  I think you need to know what R2 is as this will dictate the range of output voltage adjusted through R3.  See what the man says and let me know if you want a hand.  At most it's a simple resistor change.

Andy

That right Simon?

sq225917

If r3 is a 25k trim this should give you a range of about 8v adjustment without having to change any of the hard parts. Of course after the transformer there's a smoothing stage, with caps, resistors/inductors, you can add a couple of low ohm resistors in here, say 3 watt rated, 1-3 ohm to drop the voltage before it even hits the teddyreg itself.

Teddy will tell you.

By the way your Young will run on 24volts, the lowest rated part in the power supply is the 25v rated capacitor just after the plug on the inside of the pcb.

Mervyn

Teddy replied as follows :

"You can do that by reducing the value of R2 to around 40K, you will have to experiment a bit till you get the right value"

I assume you use R3 to adjust R2 if so how ?  Thanks

Uzinusa

Mervyn,

I seem to recall that Teddy produces 2 Voltage-ranges of the TeddyCap.  One is <20V and the other 20-30V.  He does this by changing a fixed resistor called R2.  We need to know which version you've got, and If R3 can go high enough to give 18V-22V (I know Simon says the Young is specced to 24V but I'd shy away from running it at that [for irrational reasons]).  

You'll not have a problem with a s/h TC3.  It should be either a quick twist of a small screwdriver in the variable resistor (R3), or at most increasing R2 to 40k followed by adjusting.  It's something a number of us can help with or guide you through.

Andy

Mervyn

Thanks for that Andy. The one I was looking at is 24v (from ex-Naim user) but it does not seem to be to difficult to tweak either way. ( very useful function of Teddycap ). I need 18v so as to power the server ( I think it cannot handle anynore than 20v)  and a future Young dac.

Mervyn

figlet108

Hi Mervyn,

I need to jump in here quick to tell you that somehow there must have been some confusion between us, as the Nexus won't work with anything above 13V.

The Nexus and the TFS are different things even though they both use a Xonar DAC. It's the TFS that's being driven by 18V.

The Nexus uses a picoPSU DC-DC board which has a safety cut-out at about 13V, so if you feed it more it won't necessarily damage anything, but it won't power up.

That's why Mark at Item Audio modified that Rapid PSU you have to output about 12.8V as he was also experimenting with the picoPSU boards in the PCs he was building.

I would also encourage you to try out a Teddycap before you commit cash as I wouldn't expect it to improve the sound much above what you have now. Correct me if I'm wrong someone, but I understood the main secret sauce in Teddy's designs to be in the regulation of the power supply. Since computers have a raft of regulators in them already at 12v, 5v, 3.3v and sometimes others to protect sensitive components like CPU, memory etc, having the supply perfectly pre-regulated at 12.8v or 18v or whatever only to be re-regulated at completely different levels makes no sense in theory (to me anyway).

I would still try it though as we all know theory and reality can often be very different.

Jason 

sq225917

Andy, it's not irrational, there's a low temp rated 25volt electrolytic just on the inside of the Young, under voltage strikes me as sensible. None of the power supplies I've made have been set at 24 volts all of them are a couple of volts under for that very reason.

Uzinusa

You're right Simon, there was some logic somewhere.  Cheers.

Mervyn

Hi Jason

Many thanks for that - I should have asked of course !

Mervyn