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Harman Kardon 430 - startup question

Darren James

Darren James

Active Member
Hello,

I just noticed that upon start up, the woofers move slowly in and out almost full range... a few times. then stop..
Not quickly... but 1 2 3 4 5 ..... done over maybe 5 seconds....

Everything sounds fine... I'm just wondering what is sneaking by or leaking into my speakers,,,,

Thoughts?
 
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I don't see any protect circuitry/relay in there, so some output from the power amps while they are settling is to be expected. If it bothers you, you could always turn the speakers off manually until the output settles (5 sec or so).
 
Ylli said:
I don't see any protect circuitry/relay in there, so some output from the power amps while they are settling is to be expected. If it bothers you, you could always turn the speakers off manually until the output settles (5 sec or so).
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That sounds to be a good plan Ylli.

But this is a popular brand , surely there must be something in there ... a capacitor to soak up some energy???

Remember am still learning.
 
This sort of thing is fairly common for amps and receivers of that vintage if they were not equipped with a protection relay. IIRC this unit has a bunch of fuses... I wouldn't worry about as long as its able to settle out. Does it do this with the volume down all the way?
 
atmasphere said:
This sort of thing is fairly common for amps and receivers of that vintage if they were not equipped with a protection relay. IIRC this unit has a bunch of fuses... I wouldn't worry about as long as its able to settle out. Does it do this with the volume down all the way?
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It does do it with volume down....
 
Raccoon1400 said:
The ones I've had have done it restored and unrestored.
I have a 730 I want to build a protection circuit into.
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It's not hurting anything. The 430 and 730 have a "soft start" circuit that prevents the "thump" at turn-on. The slow moving woofers is just a result of that "slow" charge and.... I put 3W 6.8k bleed resistors on the main filter caps to help keep the offset more "equal" at power-on, especially when you power it off, and back on soon after. One rail "drains" faster than the other causing the high DC offset. Note it's only the startup DC offset, not the "after it's been running" offset that is affected.
 
My 430 does it as well. Sometimes accompanied with a rather unsettling "hum", which has relegated it to the top of my re-cap list.

Is there any reason why H/K omitted putting in a simple protection relay? Wasn't this standard practice by the '70s?
 
FluxT said:
My 430 does it as well. Sometimes accompanied with a rather unsettling "hum", which has relegated it to the top of my re-cap list.

Is there any reason why H/K omitted putting in a simple protection relay? Wasn't this standard practice by the '70s?
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The whole point of the twin power setup was to improve sound/performance. If concerned about sound quality a protection relay would easily be in the crosshairs.

BTW the hum you describe might well be there even with new caps- depending on how the unit starts up. If the power amp is unbalanced the sawtooth on the power supply won't get cancelled so even with good filter caps the unit can still hum. But if you plan to keep the unit in service and the filter caps are original then they are overdue.
 
atmasphere said:
The whole point of the twin power setup was to improve sound/performance. If concerned about sound quality a protection relay would easily be in the crosshairs.
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How exactly would a protection relay degrade sound quality? Is it not just a simple circuit that mutes the amp for the first few seconds and then clicks off?

Good point on the filter caps, though. Those and the signal path caps are going to be my primary focus when I recap it. There’s just a wee bit too much hiss on empty inputs (bad transistor?) for my liking, and a very slight hum over headphones, which isn’t affected by the tone controls or volume knob. That’s for its own thread, though.
 
FluxT said:
How exactly would a protection relay degrade sound quality? Is it not just a simple circuit that mutes the amp for the first few seconds and then clicks off?
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Relays can fail and cause funny sonic issues if there is corrosion on the contacts. I used to see problems like that on receivers made at the same time, back when they were still in production. Its hard to imagine that 40 years on things would somehow be better. I see it as a good thing that there isn't a protection relay. It is adequately fused.

BTW If not mistaken there are some diodes in the input circuit, one feeding the collectors of the input stage, the other in the CCS that look like they play a role in the turn on thump. I don't see anything anywhere else in the receiver that would act like a turn-on thump limiter, but these diodes appear to prevent the front end from exacerbating the thump when the power supplies are coming up and when the feedback signal is thus wonky.
 
dlucy said:
Huh... I did not know that about the 430. Help me find where in the 430 schematic that soft start circuit is. I want to understand how it works.
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It's not pointed out, nor explained in the manual. But the "delay" is obvious before the music starts. Pioneer and others point it out and even explain how theirs works. I wish H/K manuals were better at things like this. Their manuals are a bit barren in some areas.
 
FluxT said:
How exactly would a protection relay degrade sound quality? Is it not just a simple circuit that mutes the amp for the first few seconds and then clicks off?

Good point on the filter caps, though. Those and the signal path caps are going to be my primary focus when I recap it. There’s just a wee bit too much hiss on empty inputs (bad transistor?) for my liking, and a very slight hum over headphones, which isn’t affected by the tone controls or volume knob. That’s for its own thread, though.
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The circuit isn't the problem. The points in the relays degrade over time. Especially when they are repeatedly kicking in and out under high loads. Some people seem to think they are high-current contactors. :rockon:
 
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