I have a few TI INA217 opamps,so thought I'd build myself a nice 8 ch.mic pre based on the published Ti Data sheet. I've already ordered the 2448 psu module from Five Fish Audio, but didn't buy the trafo from them. The FFA trafo is rated at 30VA, but I found two rated at 40VA & 50VA which seem suitable & the price difference too is just about 2 Euro! so I was wondering as to which one I should buy?. 40VA or the 50 VA. This seller doesn't have one in 30VA/24-0-24. So would 50 VA be an overkill, especially considering the high surge currents these toroidals would give on start-up!
The specs for the trafo is as follows; 230/24v-0-24v
The Original Ti Mic-pre circuit is fairly basic, so I'd like to include switchable Phantom power & peak LED indicator on all 8 ch. & a mains indicator on mine, hence my choice of this higher rated trafo!
Can someone kindly give me your thoughts or any advice on which one would be the ideal choice!
Thanks
The specs for the trafo is as follows; 230/24v-0-24v
The Original Ti Mic-pre circuit is fairly basic, so I'd like to include switchable Phantom power & peak LED indicator on all 8 ch. & a mains indicator on mine, hence my choice of this higher rated trafo!
Can someone kindly give me your thoughts or any advice on which one would be the ideal choice!
Thanks
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If you work out the total amount all the pre amps draw and the LED displays when all LEDs are on, add 25% and that will be enough.
Thanks JSE! Each INA217 draws 10mA on a +-15v supply = 80mA, LEDs are bit tricky,since theese come at different ratings.So lets take the worse case & add 9 x 30mA= 270 mA I'd certainly use resisitors to reduce the current draw!
Total current requirement 80+270=350mA + 25% =437.5mA
40VA = .833mA
50VA= 1.104mA
I could certainly choose either of these.....but I'm sure there must be just one reason to choose one over the other, Lol!
Total current requirement 80+270=350mA + 25% =437.5mA
40VA = .833mA
50VA= 1.104mA
I could certainly choose either of these.....but I'm sure there must be just one reason to choose one over the other, Lol!
I think that 24v 0v 24v is going to be a bit too high a voltage for your INA217preamps .... Your 24v 0v 24v is going to be about +/-35v DC then you are going to need to regulate the voltage down to +/-15v dc so you are going to be wasting a lot of power and generating a lot of heat in your regulators ....
I would suggest you get a 15v 0v 15v Transformer .....
There are a lot of PSU designs for preamps out there that use a Voltage tripler and regulator to get the 48v DC Phantom power voltage from 15v AC ....
Cheers
I would suggest you get a 15v 0v 15v Transformer .....
There are a lot of PSU designs for preamps out there that use a Voltage tripler and regulator to get the 48v DC Phantom power voltage from 15v AC ....
Cheers
So your saying that you are going to have +/-15v DC for the Instrumentation amps and +/-35v DC for some other circuitry ??
Yes, +/- 15v for the preamps & 48v for the phantom supply tapped from the same secondary windings. As I mentioned earlier, the FFA 2248 psu supply board does exactly that!
Would it make any significant difference if the secondary voltages are 24v-0-24v or 25v-0-25v? These voltges would be reduced to +/- 15v The reason I ask this 'cause I couldn't find any UK trafos with 24-0-24 but my regular supplier has one in 25-0-25v/50VA
Are there any advantages in using a single 0-230v as opposed to a 0-115v/0-115v trafo for a 230v mains?
Any advice? Thanks.
Are there any advantages in using a single 0-230v as opposed to a 0-115v/0-115v trafo for a 230v mains?
Any advice? Thanks.
The difference will be the Heat, that your regulators must dissipate.
25*1,4 - 1.2 = 33,8V (even more, because trannies use to have higher voltage at lower current, than specified)
Let's say 35V worst case, so 20V will be burned.
20V*437,5mA = almost 10Watts... That's a lot heat
So if you have large enough heat sink - go for 25V. 🙂
25*1,4 - 1.2 = 33,8V (even more, because trannies use to have higher voltage at lower current, than specified)
Let's say 35V worst case, so 20V will be burned.
20V*437,5mA = almost 10Watts... That's a lot heat
So if you have large enough heat sink - go for 25V. 🙂
Thanks Dimashek for your timely advice. Yes, you're right as Minion too had correctly warned me earlier. I realize now the perils of using higher voltages than required. As I've mentioned in my 1st post, this trafo will be supplying 8 INA217 mic pre-amps plus 48v phantom for the mics.
I just read a few posts on Five Fish forums, where many have been complaining of excessive heat especially in the LM317/LM337 regulators after using 20v-22v trafos! I can then use 15-0-15v trafo,but then the 48v phantom supply which is directly tapped from the same secondaries won't be 48v but a little less according to FF. However,this this will not be a problem.
So do you guys think a 18-0-18 trafo would be the best compromise? I also intend screwing the LMxxx heatsinks to the chassis as this will definitely help running the psu at lower temperatures.
As a matter of interest a.t.m I am using a 15-0-15v 12VA trafo which is then supplying 15-0-15v DC to a small guitar pre-amp without any heat issues.
I just read a few posts on Five Fish forums, where many have been complaining of excessive heat especially in the LM317/LM337 regulators after using 20v-22v trafos! I can then use 15-0-15v trafo,but then the 48v phantom supply which is directly tapped from the same secondaries won't be 48v but a little less according to FF. However,this this will not be a problem.
So do you guys think a 18-0-18 trafo would be the best compromise? I also intend screwing the LMxxx heatsinks to the chassis as this will definitely help running the psu at lower temperatures.
As a matter of interest a.t.m I am using a 15-0-15v 12VA trafo which is then supplying 15-0-15v DC to a small guitar pre-amp without any heat issues.
For heat dissipation you have to know voltage drop on the Reg AND current your device will consume.
What about additional small transformer with 48V secondary?
Or votage multiplier?
What about additional small transformer with 48V secondary?
Or votage multiplier?
Yes, good suggestion indeed....I'll check the availability of a small 24-0-24v preferably a toroidal trafo & report back. Would 100-200mA suffice?
max. current consuption for mic is 10mA, so 80mA for 8 channels. And 20% overhead
So, yes, 100mA will be OK
(mics usually draw only few mAmps, never saw 10mA part)
So, yes, 100mA will be OK
(mics usually draw only few mAmps, never saw 10mA part)
I just checked a few sellers in the UK & found that even a 0.15A/22-24V (150mA) toroid is nearly as expensive as the 50VA ones! So why not use a LM783 regulator in place of the LM317 as a direct swap? Does this require any component changes? The only drawback if any, is that it has a minimum 15mA current limit.
I've just checked with Ruel the owner of Five Fish studio & he advised that a 18v-0-18v trafo would be a good choice. He also agreed that mounting the regulators on to the chassis will considerably reduce the heat issue.This also will supply adequate voltage for the phantom if one is using the LM317T. He warned me that a 15-0-15 v trafo will not be sufficient for this, although will run much cooler.
My take:
1.Use a 15-0-15v trafo & use either a LM317HV (57v) or a LM783 (125v) as a trippler for 48v. However, LM317HV seem very hard get hold of these days!
2.Use a 18-0-18v trafo & use a LM317T to supply 48v
So can any of you experts out there please tell me which of these two would be the most efficient or foresee any issues with either of these?
Is LM783 as good as LM317?
My take:
1.Use a 15-0-15v trafo & use either a LM317HV (57v) or a LM783 (125v) as a trippler for 48v. However, LM317HV seem very hard get hold of these days!
2.Use a 18-0-18v trafo & use a LM317T to supply 48v
So can any of you experts out there please tell me which of these two would be the most efficient or foresee any issues with either of these?
Is LM783 as good as LM317?
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