Hi - I have a Quad 33 where the balance is doing strange things. Symptoms;
I have checked RV5. The mechanical linkage is sound, the resistance of the pot is circa 1K Ohms, and in center setting about 500 Ohms either side. This grounding of the center of the pot is good as well.
I have swapped around the M12017 boards, left to right to confirm there is nothing wrong with either of them.
Should I be looking a be looking at potential issues around here?
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Any help or insight would be appreciated.
- With the Balance slide centered - The Right Channel is much brighter in the mid and treble, the left by comparison is dull
- With the Balance slide fully to the Right - The right level increases by about 70%, the left level decreases by about 20%, and remains dull
- With the Balance slide fully to the Left - The the left level increases by about 50-60% and the sound is not dull, the right level decreases by about 10-15%, and sound is dull
I have checked RV5. The mechanical linkage is sound, the resistance of the pot is circa 1K Ohms, and in center setting about 500 Ohms either side. This grounding of the center of the pot is good as well.
I have swapped around the M12017 boards, left to right to confirm there is nothing wrong with either of them.
Should I be looking a be looking at potential issues around here?
Any help or insight would be appreciated.
Never easy at a distance so...
Have you swapped the inputs to your power amp around to be 100% sure the problem really is in the preamp?
Speaker problem (for dull sound)?
If it is the Quad at fault then ideally you should be using a scope to look at what is going on. It is so much easier and so much more definite than guessing.
You could try linking pin 1 of both those boards together to force an identical signal to each channel.
You could also try linking pins 5 and 6 on each board to bypass the tone section and see if that proves anything.
Have you swapped the inputs to your power amp around to be 100% sure the problem really is in the preamp?
Speaker problem (for dull sound)?
If it is the Quad at fault then ideally you should be using a scope to look at what is going on. It is so much easier and so much more definite than guessing.
You could try linking pin 1 of both those boards together to force an identical signal to each channel.
You could also try linking pins 5 and 6 on each board to bypass the tone section and see if that proves anything.
Yes, positive it's the Quad 33 pre. Tested on two sets of power Amp, Nad C270 and Quad II monoblocks(2). Speakers are fine, confirmed bt using a McIntosh C26 preamp with the Nad power.
Checked all switches including Cancel, all good, making contact off and on all down their strips. Checked all pots, also operating as expected, Left & Right.
I wonder could a failed 100uF Electrolytic Cap, C5 or C6 cause this strange balance issue. No harm in replacing them.
Checked all switches including Cancel, all good, making contact off and on all down their strips. Checked all pots, also operating as expected, Left & Right.
I wonder could a failed 100uF Electrolytic Cap, C5 or C6 cause this strange balance issue. No harm in replacing them.
Its possible (and again a scope would show if the cap had failed) if the cap failed with a very high ESR (equivalent series resistance). If you suspect any electrolytic in the signal path you can just bridge them quickly to see if the issue clears. No need to unsolder the old one. Just dab one that is around the same size (or higher C) and see if the fault clears.
The balance knob on that pre changes the gain of the preamps. It is why the value is so low. Replace the 2 x 100uf caps
The actuator can break as well
The actuator can break as well
I replaced the two 100uF caps, no change, the issue persists.
I did a couple of test scenarios
I did a couple of test scenarios
- Short Pins 5 & 6 and mask off pin 7: Amp goes into oscillation
- Short Pins 5 & 6. and leave pin 7 connected: Problem persists
- Mask off Pins 5 & 6 and put a 4.7K resistor across them: Amp goes into oscillation
The oscillation is a bit unexpected... sorry about that.
I take it you haven't a scope as that would be the 'go to' of choice to see what is happening with this.
Did you try linking pin 1, the input of both boards to feed an identical signal to both final stages?
I take it you haven't a scope as that would be the 'go to' of choice to see what is happening with this.
Did you try linking pin 1, the input of both boards to feed an identical signal to both final stages?
I had anticipated the possibility fo oscillation, so was ready to power down quickly.
I'll bridge the two inputs at the pots tomorrow and test, but I think the fault is closer to the balance circuit given the symptoms.
I do have a scope, buried somewhere in the attic, might be time to dig it out!
I'll bridge the two inputs at the pots tomorrow and test, but I think the fault is closer to the balance circuit given the symptoms.
I do have a scope, buried somewhere in the attic, might be time to dig it out!
Please do 🙂 Scope and some test tones and slow frequency sweeps (use Audacity to make some files in seconds) and it will tell you so much.
No harm in changing the electrolytic caps on the L & R boards, but I have swapped the L & R boards and the left channel remains the problematic one. The main issue here is the balance doesn't function properly at all. I do think it's related to the Tone & Filter board
I'm go to look at the pins holding in the L & R boards as recommended by the Quad service supplement
This is the issue persists, I'll look at bypassing the filter-slope circuits(which consists of L1 & L2) and see.
I'm go to look at the pins holding in the L & R boards as recommended by the Quad service supplement
This is the issue persists, I'll look at bypassing the filter-slope circuits(which consists of L1 & L2) and see.
A simple continuity test proves that when the cancel button is pressed pin 4 from both the L & R go directly to the output DIN socket, so the Slope-10K-7K-5K section is not the issue.
I've bridged the Pin 1 on each of the Left & Right boards(by connecting the centre of RV1 & RV2 pots) and no difference on the balance behavour, albeit now in Mono as expected.
The balance is one thing but of more interest in a way is the problem of one channel being much brighter than the other.
This is where the scope comes into its own. If you have one then use it 🙂 Feed the preamp a mono signal and trace it through comparing channels.
I'm focusing on the balance issue first, any slight dullness in the left channel I'll tackle next. I've checked all resistors on the M12029, all within spec.
I wonder is there any merit in changing out all the 0.033uF caps on that M12029 board?
I wonder is there any merit in changing out all the 0.033uF caps on that M12029 board?
I wouldn't just swap them on a whim...
Try turning those pots to their extremes and see if the balance issue persists. If one of the 0.033uF was flaky then that might be a quick way of proving it. In other words if the perceived balance shifts as you turn the pots then something is amiss around there.
Try turning those pots to their extremes and see if the balance issue persists. If one of the 0.033uF was flaky then that might be a quick way of proving it. In other words if the perceived balance shifts as you turn the pots then something is amiss around there.
There is no merit whatsoever in changing those capacitors. They are not in circuit in the Cancel position, so you’ve already ruled them out.
Clean the pot. Don’t use WD40 or alcohol, use something that both cleans and lubricates. One very short squirt, then work it back and forth ten times.
Clean the pot. Don’t use WD40 or alcohol, use something that both cleans and lubricates. One very short squirt, then work it back and forth ten times.