Zen preamp running very hot

supernet

Member
2001-12-12 1:45 am
Europe
I have built the zen line stage some days ago. Preamp is working, but I am worried about heat. I used one 60 VA transformer with 2 × 60 V secondaries. So when I turn on my preamp, the heatsinks get very hot. ( I can touch it for one second) Each heatsink has 16 K/W thermal disipation and for 750 ohm resistor I used two 1500 2W in parallel.

So could anybody tell me, it is OK that preamp produce so much heat, or I did something wrong?

Thank you for answer.
 
Whew! Getting hot in here.
The transformer Nelson suggested for the Bride of Zen was 30+30, not 60+60. If you series the two 60VAC windings the way it's shown in the schematic, you're going to get 120VAC, which will leave the regulator a pretty fierce job. No wonder you're on the warmish side.
Don't worry, all is not lost.
For the time being, unhook one winding of the secondary entirely. Run the preamp off of the remaining winding. (Measure all the voltages while you're at it, to make sure nothing got toasted.) Get enough parts for a second power supply--not the transformer, you've already got that, but another rectifier, bulk supply caps, and enough whatnots to contruct another regulator (and any replacements you may need for the circuit itself). That way you can have a separate power supply for each channel. Very high end stuff.

Grey
 

supernet

Member
2001-12-12 1:45 am
Europe
Sorry my mistake. The original plan for balanced zen line stage has got two transformes. Each one has two secondaries 30+30. So I used instead of two one transformer with 60+60, because the original plane has secondaries 30+30 in series.
So I get exactly +60V and -60V. The all voltages are fine, but Ihave never seen that one preamp get so hot. Maybe it is normal and I am only concerned that 16K /W heatsink have not enough disipation.
The amp is working, only problem is heat and too much gain.
I used for R15 430 ohm giving the gain 10dB and 10k input pot. But this gave too much gain for my Leach power amp.

Tkank you for any suggestion!
 
I would go back and make sure all the component values are correct. I don't have a heat problem with mine. I also don't have a problem overdriving the input on any amp I have hooked it to. Only being able to touch a sink for 1 sec. seems really hot. I'd be interested in knowing what the temperature is. You don't have access to a thermal probe or gun do you. I also use 430 ohm/r15 with a 10k pot though my transformer is 20 x 20 so my operating voltages are lower. I'm running at about + - 45volts dc. Maybe double check all wiring. Good luck:confused:

P.S. If your operating in un-bal to bal mode is one of the mosfets hotter than the other? If so did you ground the un-used input? The - input to ground.
 
Geoff's solution is easier and cheaper than mine, but unfortunately it sounds as though we were solving the wrong problem.
When you say you've used two 1.5k resistors to make a 750 ohm, this should lead to having eight 1.5k resistors under the Sources. If, by chance, you had only four (two per device) underneath the Sources, you'd be biasing the MOSFETs really hard, and they'd overheat. It would also effect the gain.

Grey
 

grataku

Member
2000-12-31 9:31 am
-
supernet,
the BOSOZ or BLS gets frickin' hot. See my posts under the thread 'more BOSOZ' for extensive exchange among the usual suspects on this site. With the standard heatsink you may as well get your baby back ribs spiced up and use the pre amp as a BBQ.
From my calcs the 750 ohm pair needs to dissipate about 2.75W and the top 750 ohm dissipates 1.2W . That is a lot of watts for those dinky metal film resistors.
Ahh so much fun! Sounds terrific though.
 
Hmmmmmmm, kind of reminds me of my BOZ preamp. The space allocated for the IRF 610 and TIP29 transistors and their heatsinks on the PCB as per Nelson's website is puny! As I've pointed out, I have to modify the PCB so that I can place these transistors upright with huge (relatively) heatsinks just to keep the temperatures down (a bit!).

With heatsink measurement (approx) 2.5 cm width, 2.5 cm height and 2 cm depth, I-shaped, the IRF610s are (still) cooking! The TIP29 required a heatsink of dimension (approx) 3cm width, 3cm height, 1cm depth, 5 fins running along the height of the heatsink just to keep relatively cool!

Thinking of adding a small, slow running fan soon........

But it does sound fabulous.....!
 
I always run transistors vertically so that the heatsink can get more air. Nelson makes commercial product that has to be shipped, and the mass of a heatsink can snap a transistor off during shipment.
If you have the option (and don't intend to move your equipment around a lot--guitar amps and such ought to go for reliability) stand the transistor up. Don't be afraid to mount the heatsink 'backwards,' i.e. with the fins pointing away from the body of the device. It will work just as well if not better...even if you think it looks funny. I have sometimes mounted two heatsinks on a single device by mounting them back-to-back and using a slightly longer screw. Works fine. Looks impressive with all those fins bristling from the device.

Grey