Hi, I decided to start a new project with a bunch of spare parts I had. It's two 312 mic pres feeding a gssl buss compressor powered by a FiveFish PSU-2448 mk2 in a dual rack chassis. Since the 2448 can power four +-15V mic pres, I figured this would be a good candidate for this project. The gssl gets it's proper voltage and the two 312s also get their +-15V and the 48V phantom. So, the gssl works, the two 312s also work but, I'm using the fourth connection to power the bulbs in my VU meter and also a power bulb. The bulbs for the meter are two cm386 (14v) and the power jewel bulb is an AML-47 (6.3v). I'm using a couple resistors to knock down the voltage for the AML-47. Like I said the gssl worked fine on its own and so did the 312s. Now that everything is all wired up, the unit works fine for about 4 minutes and then there is a voltage drop on the +15V rail across the 312s and the gssl. It must be happening at the PSU. The heat sinks on PSU get very hot. To the point where you cant touch them. I'm assuming the bulbs are too much? Any ideas or should I just disconnect the bulbs?
Dual 312 mic pre feeding gssl project
- Thread starter orangerec
- Start date
Help Support GroupDIY Audio Forum:
Harpo
Well-known member
Your light bulbs draw more power than the GSSL and 312s together. Connect these in front of the Vregulators with voltage dropping resistor in between.
Assuming a 2x15VAC secondary, each CM386 needs a ((15V * SQRT(2) -0.6V)-14V)/0.08A=82.67ohm with at least 6.61V*0.08A=0.53W rating. Doubling up the power rating, you probably want a 82R/1W resistor in series for each CM386.
Same assumtion 2x15VAC secondary, each AML-47 needs a ((15V * SQRT(2) -0.6V)-6.3V)/0.15A=95.42ohm with at least 14.3V*0.15A=2.15W rating. Doubling up the power rating, you probably want a 100R/5W resistor for your AML-47. Use the other rail for this bulb to even out current demand.
Adapt formula with your transformer secondary voltages for these example values.
I'd probably use LEDs behind the meters and the power jewel for a lot less current and heat, but YMMV.
Assuming a 2x15VAC secondary, each CM386 needs a ((15V * SQRT(2) -0.6V)-14V)/0.08A=82.67ohm with at least 6.61V*0.08A=0.53W rating. Doubling up the power rating, you probably want a 82R/1W resistor in series for each CM386.
Same assumtion 2x15VAC secondary, each AML-47 needs a ((15V * SQRT(2) -0.6V)-6.3V)/0.15A=95.42ohm with at least 14.3V*0.15A=2.15W rating. Doubling up the power rating, you probably want a 100R/5W resistor for your AML-47. Use the other rail for this bulb to even out current demand.
Adapt formula with your transformer secondary voltages for these example values.
I'd probably use LEDs behind the meters and the power jewel for a lot less current and heat, but YMMV.
Thank you so much for the great and in depth info! You are totally right. I unplugged the bulbs and the unit worked great for an hour. The voltage regulators still get pretty hot, though. I'm assuming this is normal and their job. I'm going to wire up the LEDs as per your direction.
Cheers.
Cheers.
Harpo
Well-known member
Voltage differential between Vreg input and output times current demand of connected load generates the heat.
What is your transformers secondary voltages and VA rating?, what is your connected load current (without the light bulbs)?
Using the same transformer you maybe could share a little heat with a voltage dropping resistor in front of the Vregs. Just have an eye on Vregs dropout voltage.
What is your transformers secondary voltages and VA rating?, what is your connected load current (without the light bulbs)?
Using the same transformer you maybe could share a little heat with a voltage dropping resistor in front of the Vregs. Just have an eye on Vregs dropout voltage.
My secondary is 22VAC. Post rectifiers, I'm measuring +-27VDC at the power caps. Post voltage regulators, the 312s and the gssl are all reading +-16VDC at the proper points. The unit sounds and operates great. My only concern is the voltage regulators are really hot. I posted on Five Fish's forum, but haven't gotten a response.
27-16=11 volts to chew at a certain current,
if that current is say, 100 ma, you have 11 * ,1 = 1.1 watts of heat,
if you draw 200 ma, you double that and now we have a problem. 2.2 watts on a TO-220 means Heatsink Required. that heats wants a piece of Al about 1.5 inches by 3 inches if you want it to last forever,
how much surface area do you have on your heatsink?
if that current is say, 100 ma, you have 11 * ,1 = 1.1 watts of heat,
if you draw 200 ma, you double that and now we have a problem. 2.2 watts on a TO-220 means Heatsink Required. that heats wants a piece of Al about 1.5 inches by 3 inches if you want it to last forever,
how much surface area do you have on your heatsink?
Thanks for the reply. All three heatsinks are 1/2" x 3/4".
Update: the power transformer with the kit is a Avel Y236104. According to their website this is rated for 18-0-18 V. I measured the transformer disconnected from the PSU and it measured 22VAC as wired per directions (orange/red together). I'm assuming the higher measured voltage is due to no load (not connected to the circuit)?
What's strange is that Five Fish's site/forum says not to use a power transformer with a higher rating than 20-0-20V rating. I'm a bit perplexed.
Update: the power transformer with the kit is a Avel Y236104. According to their website this is rated for 18-0-18 V. I measured the transformer disconnected from the PSU and it measured 22VAC as wired per directions (orange/red together). I'm assuming the higher measured voltage is due to no load (not connected to the circuit)?
What's strange is that Five Fish's site/forum says not to use a power transformer with a higher rating than 20-0-20V rating. I'm a bit perplexed.
