SX-9930 Idle Current Setting

According to the SM the Idle Current should be set at 50mV. My SX-9930 seems to run pretty hot at that setting. First is that the correct setting? And second, anyone try a lower setting to lower the temp and see what it sounds like? Any draw backs from running at around 30mV?

No problem as long as you don't cause or hear distortion. I'd try 40 mV.That's 20% less and should idle cooler.

The 9930 is the Black face version of the 939. PIONEER GOOFED when they calculated the total loads according to MTF. Set the Idle Current to 25mv which is correct. They also did this on the 1010. My 939 runs great, and COOL @ 25mv.

Thanks a lot. I knew I had read a thread somewhere about some of the Pioneer units SM being incorrect. I had dialed it down to 30mV which helped quite a bit, and it didn't seem to effect the sound, as a matter of fact I thought it sounded pretty good. I'll redo to 25mV. Cheers and Thanks Again

Hi, I was looking for some other information on SX9930 and found this thread.

If you look at the measurement points for idle current, they are at point 50 and 44 for one channel and 38 and 32 for other channel. On schematic these points are between two 0,5 resistors in series (R51 and R53, or R52 and R54). Measurement of 50 mV at points 50 and 44 (38 and 32) is sum of voltage drop on both resistors which means that on each resistor you have voltage drop of 25 mV (exactly half of voltage as both resistors are same). So I would say that 50 mV, as written in service manual, is correct voltage at given measurement points.

I set mine at 50 mV and my 9930 is not hot at all - just slightly warm. If your receiver is getting very hot, you might have some other problem.

There were some other threads with some other model where suggestion is that value in service manual is wrong - I suggest to look at schematic for this particular model and check again where are measurement points - between one resistor or two in series.

Best regards,

Ivo

On this thread I asked the question about 939 bias (which the 9930 for all intents and purposes) and got this explanation from Mark the Fixer. He explains how PIONEER goofed, and references a 1010 thread.

QUOTE by Mark The FIXER;

+ and - 80mA markings on the big schematic in the manual infer 40mA per channel, but the manual says 50mV at the test point.

edit- SAME error as that's in the SX-1010 manual - see this thread

Since there are four outputs PER CHANNEL, each transistor pair is 20 mA which is reasonable.

The voltage difference tho, ISN'T ADDITIVE (equipotential rule)- which is where they made their error.

THUS in my somewhat informed opinion it is reasonable to set to 20mV at the test points, which then multiplied by 4 sets of transistors results in the 80mA schematic notation.

If 50mA doesn't heat up badly, use it. The heat really comes on at higher amplifier power outputs and the slightly higher idle current will NOT make a significant difference in THOSE temperatures.

Click to expand...

Here's the post from the linked thread that explains WHY!
http://www.audiokarma.org/forums/showpost.php?p=5942374&postcount=7

Quote by Mark the FIXER;

I just realized my error!!

The schematic shows 100mA current, but that is for BOTH channels.

50mA per channel

which means 25mA per PAIR.

The measuring procedure is WRONG.

Pins 14 to 16 should show 25mV, which is more in line with other models.

Click to expand...

When I had my 939 @ 50mv, temps would reach 175*F when pushing the unit HARD (volume @ 2:00). After dropping the level to 20ma, temps would reach 120-125*F when pushed hard. Normal listening, I get NMT 105*F.

I have read these threads, and indeed either is wrong total current through both rails or value of 50 mV for adjustment per one channel.

I have checked with service manual for SX535 and values in schematic for rail current and idle current are correct.

Ivo