Technics SU-V9 adjusment procedure questions

clear on the CD and Phono, havent adjusted yet, i think it must be underbiased since no heat ( trimmers were put at minimum).... might take time to heat up . DC offset is best at zero that means left channel droppping to 05 .4mv was better than the right at 1.3mv

The problem is only the left channel is working with PHONO, was sure when i checked the phono was showing continuity, hope there hasnt been any transistor blow out in the short, or maybe opamp ? or adapter or dry joint at best i hope, most liklely is i had to repair a trace but was sure it was fine,


As for bias maybe run a bit to get warm, turn off then power up wait about 10 and do adjustment or wait 1min if already warm
 
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hello. Bias should move if you adjust the trimpots regardless of the time from power On. Let me check the service manual.

Are you measuring across the emitter resistors, from emitter to emitter? resistance should be 0.44 ohm (2x 0.22 ohm) (perhaps your DMM is not accurate at that value, but should show less than 1 ohm)

What's the voltage across both resistors ?( across 0.44 ohm, not across one 0.22 ohm) It should react to the bias trimpots.
 
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Hello Fernando
Thank you, i shall look later.
My meter has 200, 2000, 1K 10K 200K 20M and 200M, which would be best to use 200 or 200M. Its not very good with low ohm is a cheap one, i got new leads yesterday for it
 
The lowest scale to measure small resistors. 200 ohm.

Where are you measuring bias ? I can't locate the test points in the service manual.
 
BE CAREFUL. TRYING TO ADJUST BIAS IS ONE OF THE REASONS PEOPLE BURN THEIR AMPLIFIERS. (plenty of threads at AK)
 
Yes, i careful, i set the trimpots at almost zero ohm (minimum), amp runs but doest not warm up much, i expect since low bias. I measured where i marked the old trimpot and ohms 170ohm - not safe to go to that

200, it should show up then i got 0.6om on the trimmers

the diagram in the servivce manual shows the location

bias adjust points.jpg

Phono postion for 1mv ( no boost in volume on left channel) , but is fine on 2.5mv postion. I checked solder, seems fine, hope the teeth in the selector is not broken in that position, might have to check what is in the path of 1mv on the left
 
OK, so you are measuring across just one 0.22 ohm resistor. You can measure across 2 resistors (across 0.44 ohm) , the voltage reading will be doubled, so better accuracy.

The manual is asking for 1mV across 0.22 ohm, that's 4.54 mA, quite low bias current. (if it were my amp I'd go higher, to 12 or 15mA, but I can't advice that on the Internet without a deeper knowledge of the amplifier)

Try to get 2mV across 0.44ohm , measuring across the ends of those double ceramic resistors. Set your meter to DC, the lowest scale (I think it will be 200mV)

Please check the resistors are fine, measure resistance before checking the bias. If just one resistor is open, current won't flow.
 
I’d expect 20mV or so in new class A

I will fire up a factory condition V9 and measure it’s bias

It’s not uncommon for them to mess up manual printing. 1mv is near on class B point

They pulled this stunt on the V5505/707 bias points too.... they after 20 min are 25-35mV... can set at 1mv after 1min then check after 10min then 20min - what does it come back as?
 
OK, so you are measuring across just one 0.22 ohm resistor. You can measure across 2 resistors (across 0.44 ohm) , the voltage reading will be doubled, so better accuracy.

The manual is asking for 1mV across 0.22 ohm, that's 4.54 mA, quite low bias current. (if it were my amp I'd go higher, to 12 or 15mA, but I can't advice that on the Internet without a deeper knowledge of the amplifier)

Try to get 2mV across 0.44ohm , measuring across the ends of those double ceramic resistors. Set your meter to DC, the lowest scale (I think it will be 200mV)

Please check the resistors are fine, measure resistance before checking the bias. If just one resistor is open, current won't flow.

Hi Fernando,
Yes, is rather low the bias. Do I do this with power on or turning the trimmer in a clockwise direction> Both resistors will be better with my meter. its good say higher values example 82ohm ( 82.1) risistor, but lower values it is not as good unless i measure directly from the DMM not using leads

I’d expect 20mV or so in new class A

I will fire up a factory condition V9 and measure it’s bias

It’s not uncommon for them to mess up manual printing. 1mv is near on class B point

They pulled this stunt on the V5505/707 bias points too.... they after 20 min are 25-35mV... can set at 1mv after 1min then check after 10min then 20min - what does it come back as?

Hi Baily
Yes is rather low bias, all the other amps i have in new class A V8 (40mv) and V8X (23mv) are high.

I measued the trimpot the old one where i marked it 170ohm pin1 (near transformer) and middle pin 2.

Be interesting to see what see what the bias is actually with the V9, takes a long run to get much heat, never hot on the heatsink - this V9 - german one she has be under repair in germany before, so chance they set its bias as per the manual

V909 would be like the V707 etc more like the V8X bias

see if i can get, it to 1mv, - might need to just move the trimmers at 00.6 ohm up to 10ohm to get some reading
 
measuring the resistors

A and B left channel ( -ve probe on B)

00.8 ohm

D and C right channel ( -ve probe on D)
00.5 ohm

trimmers - pin 1/2 00.5 / 00.4

resistors both A to C
1316 ohm but rising


? thoughts turn up trimmers a tiny bit before adjustment?
 
I'd measure from the external pins on the double resistors, so you measure 2 resistors in series (not from point A to C, just measure each double resistor at the external pins) . Just to be sure one of them is not open, and to have more accurate readings.

Measure just the leads and substract from the total resistance.

Anyway, less than 1 ohm looks fine for a regular DMM.
 
It was a quite a good cheap DDM in the day, some review on it branded Dick Smith *re branded Uni-Trend UT33D, it did well in resistance and dc, against other cheap models in the test

each resistor A B and 3rd pin means i measure A and 3rd pin of one and D and 3rd pin of the other. They have 2 resistors within, the short would have passed their way.

checking each resistor ( not measuring the center pin)

i get 00.7ohm for each of them

new leads i got , give better a better result to the trimmers
pin 1 and 2

00.1 and 00.2 ohm.
 
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That's perfect, around 0.5 ohm ( resistance should be 0.44 ohm)

Try to measure voltage on those points when adjusting bias. Try to see if it goes to 5 or 10mV.
 
pretty close to 0.5ohm them - least they are not shorted

With the amp on? or off? to measure voltage, or just multimeter voltage and dc 200mv setting on the same pins (no middle one)

trimmers are basically at their lowest 0 ohm
 
Fernando,
it took a bit of time listened to 11 tracks of a cd to give it a chance 20+ mins ( no heat on heatsink) but noticed with the trimpots have to turn them a bit since at zero, i got it exactly 5.0mv, really great the multi turn trimpots :D nice to work with

Baily, what is the V9 balance was it around 20mv?
 
Well, 5mA across 0.44ohm is 11mA.

I'd adjust to something between 20 and 40mA (both are very safe values, not high) that's something between 9 and 18 mV across 0.44 ohm (the external pins, not the middle pin ). And monitor for 30 minutes and readjust. Until it stays steady.

We could " guess" the manual has a typo and says 1mV instead of 10mV. That would make 45mA bias current, it makes sense. It would be 20mV across the double resistor.
 
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I connected the leads to monitor and turned on DMM and amp. ( with previous day) i set around 20mins or so to 5.0mv

Anyway, around 2 mins 2.7mv , 5.0mv at 5mins, then it kept risng 5.4 etc. I cam back maybe another 5 minutes later and heard clicking sound in the amplifer so i turned it off :confused:

Would expect it to be 10mv.

model under V9 SU-V7 10mins 2mv !o_O
technics su-v7.jpg
 
If in doubt, adjust as per service manual, and keep monitoring how it raises and stabilizes, But don't wait to heat up the amp. If the manual says after 1 minutes, do it after 1 minute. The bias has a rising curve, that for sure is part of the procedure.

Clicking sound from the amplifier shouldn't be related to bias current, that's another problem. Bias is just a very small current flowing at the output transistors, it's nothing compared to playing music at loud levels near full power, so you won't damage the amp if bias is a bit on the high side. Just monitor it, and make sure if you are measuring across 0.22ohm or across 0.44ohm, because values are double, or half, and so the bias current flowing.
 
left channel, was good went to 1.1mv in a about a minute

right channel, not sure started low, may have turn it up a bit more, but i had it at 1.2mv at about 1 min currently 5mins - later 18mv, see what is at 10min
 
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