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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 1st Feb 2023, 9:38 am   #1
Calstock
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Default Vintage Akai AA-8030 Thump Thump Thump

Hi. I have an Akai AA-8030 circa 1974 (est). It has an intermittent but ongoing annoying problem where it produces a continuous THUMP THUMP THUMP noise at about 1 second intervals. (also crackles or thumps on turn on) I've disconnected the turntable and it has no other inputs; it happens on the radio & aux options as well, I only have the speakers on B channel (A uses headphone type speaker connection which I don't have), however the thumping doesn't come through on the headphones so assuming it to be related to the B speaker channel, but might be wrong.

Anybody got any ideas, is there typically a common cause?

I have tried dusting the internals with some air-in-a-can along with a bit of PCB cleaner/lube stuff into the pots & there is no crackling when I move them, but am VERY inexperienced in fixing PCBs & will take it to a techo if it's out of my comfort zone to fix.

Cheers
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Old 1st Feb 2023, 11:27 am   #2
Nickthedentist
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Default Re: Vintage Akai AA-8030 Thump Thump Thump

Hello and welcome!

Quote:
Originally Posted by Calstock View Post
I only have the speakers on B channel (A uses headphone type speaker connection which I don't have), however the thumping doesn't come through on the headphones so assuming it to be related to the B speaker channel, but might be wrong.
This arrangement sounds odd, but looking at online pics, you're absolutely right. On the back, there are outputs for two pairs of speakers, the "B" pair being via screw terminals and the "A" pair via 1/4" mono jacks. On the front, there's a standard stereo 1/4" headphone jack.

Normally, the speakers and headphones are fed by the same bit of the circuit, so it's puzzling why the symptoms are there on speakers but not headphones.

Can you get the fault to come and go by giving the receiver a (gentle) thump, or prod the PCB with an insulated pokey thing (e.g. a plastic pen)?
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Old 3rd Feb 2023, 2:29 pm   #3
Calstock
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Default Re: Vintage Akai AA-8030 Thump Thump Thump

Hi Nickthedentist.

I made a pair of speaker leads using two mono 1/4" headphone jacks, they work on speaker channel "A" but the thump thump thump continues on that channel as well. I can actually just hear it very faintly through the headphones when on headphone only, but full steam through the headphones when on speaker "A" or "B". (Another quirk with this AMP is that the headphones play when plugged in as do the speakers when selected on "A" or "B" channel). A few small thumps on the amp made no difference. Haven't tried lightly tapping the PCBs yet, will give that a go over the weekend.

The plot thickens
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Old 4th Feb 2023, 11:16 am   #4
hayerjoe
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Default Re: Vintage Akai AA-8030 Thump Thump Thump

Strangely a friend here in Hobart started reporting a thump thump thump from his Sanyo. Via email we went through a few options but he was convinced the amp was playing up. so he packed the whole thing up to bring to me. as it was in the car he thought he'd set up his backup system in the now gaping gap in his loungeroom, but the backup system started doing the same thing, finished up being his broadband router causing interference. moved the router and the problem went away. I wonder if Australian internet providers have updated firmware on their routers and the change is causing additional interference? seems like quite a coincidence that you're having a similar noise problem. try turning your router/WiFi off and let us know how you go
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Old 4th Feb 2023, 9:11 pm   #5
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Default Re: Vintage Akai AA-8030 Thump Thump Thump

I have an Akai 5200 amp from the same period (1974). It develped crackles and other sundry noises after around 20 years (it's not my main amp anymore). However I did give it a full service around 10 years ago and found that most of the crackles and pops were caused by noisy transistors of all things. They actually made a noise back through the speaker when tapped...and I thought it was only valves that went microphonic! I ended up changing all the transistors in the pre-amp and driver stages by carefully selected Mullard equivalents ....BC636, BC547/548 etc. and it's given trouble-free service ever since. I also carried out ESR checks on the electrolytics but found most of them to be perfectly OK.
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