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Harman Kardon 430 loud snap when switching off

Dom123

Dom123

Well-Known Member
Hi Everyone,

I bought a cheap HK430. Knobs are completely wrong & annoyingly the volume potentiometer has been replaced with a wrong value one (but additional resistors added) and so as a consequence the contour (loudness) doesn't work, even though the switch is working correctly.

Also changed all lights (dial, screen, stereo, & power on) as only one dial bulb was working ! Was pretty easy, so pleased about that. Installed LEDs in the dial screen & 8V incadescents elsewhere

The amps works well and seems to sound good. Bias is good. I intend to recap it but for the meantime I have dialed it to 20mV across an emitter resistor on each channel.

My concern is the very loud snap explosion when switching it off because I don't want to damage the tweeters on my speakers. It occurs on both channels, independant of volume. Switching on is quiet though, with no drama.

My intial thought is the snubber capacitor across the power switch must be defective but I can't see one.

Can anyone advise me if there is a snubber, or if there could be another thing to look at ?
Can I simply add one (X2 Safety cap) across the wires soldered to the switch ?

My other question is that on DBT the bulb (60W) is dimly lit all the time, whereas on most of my vintage amps the bulb tends to go fully out. Is this higher current draw related to the dual power supply configuration ?
 
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Hey Guys, any answers please ?

Also my HK430 is missing the 5 potentiometer knobs. I need to look for something appropriate, especially the size.
Can someone pls tell me the Dia × L of the original knobs ?
 
Dom123 said:
the very loud snap explosion when switching it off
Click to expand...
This could be a sign the main filter caps might need replacing.

To avoid the loud noise and protect your speakers, you can always turn off the speakers before turning off the receiver until you find the problem.
 
Yes I will try switching off with the mains to see if the switch is at fault or not. Otherwise a recap + new AC main filter caps is probably in order.

Itching to get working on this, but am away on vacation for the next 1.5 weeks.

I collect Sansui's normally - this is my first foray into HK. It will be interesting to see how the sound compares to my Sansui 2000 or 771.
 
Actually pretty good considering, 22mV and 27mV respectively. It's quiet switching on too, just a loud snap or pop noise when switching off. I can adjust the bias and it seems fairly stable, but I don't trust those ancient trimmer pots, so they will be changed at the same time as the recap.

Will also replaced all 2SC1345's for KSC1845, so including the diff pair.
 
Dom123 said:
Will also replaced all 2SC1345's for KSC1845, so including the diff pair.
Click to expand...

I used bc550cs. Different pin-out but closer to the originals. This isn't the problem though. Perhaps the soft start caps are leaky, and misbehave during shutdown, dunno.
 
It's not really muting the circuit or sound but delaying the full powered operation of the amplifier board. When the components start going bad, the delay will be shortened or disappear altogether allowing some snap, crackle, pop noise to come out of the speakers on startup. Possibly caused by stray DC voltage or voltage spikes before the boards components settle down and mellow out. Two of my rebuilt 630 Twins take around eight or nine seconds before the music comes out while another 630 which is all original takes between one and two seconds. This is another reason to keep the speakers turned off for several seconds on startup.
 
It seems to take about 5 secs for sound to come after switching on, no dramatics. I'm going to recap it when I back from vacation (Enjoying Greece, very hot still).

Recapping looks straight forward. An immediate concern is to replace the volume pot using a proper linear 100k one. I understand the pot should be a linear and not logarithmic one, as originally used. Any advice welcome here.

Then to restore at least some functionality to the contour (loudness), I understand i can use something like a 20-30k resistor wired from the loudness circuit to the wiper (middle) leg of the volume potentiometer. Is my understanding right ?

Finally, can anyone tell me the exact size of the vol/bass/balance/treble knobs Dia. X length?

Many thanks!
 
Great thanks! Need to look for something appropriate in place of the oversized monstrosities currently fitted.
Buying original ones will cost more than I paid for the receiver!
 
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