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HK 330A recap, bass overemphasis

mark_m

mark_m

AK Subscriber
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Hi. I'm going through an old Harman Kardon 330A which has been my shop receiver. It's typically sounded ok but fairly rolled off on both ends. Hearing a Three Thirty of my dad's made me think maybe my 330A could sound better. Since it's a small amp and not a very big project, I'm replacing all the electrolytics.

In the process, the sound has opened up a lot. But currently the bass is overemphasized to the point I need to turn it halfway down. I wondered if it might be because: I increased the size of two caps, one intentionally and one more or less inadvertently. I'm wondering if the inadvertent one might be the culprit. Here's the schematic.

I'll try to post a crop of this later on but if you look in the bottom right corner of page 10, the power supply, C914 (2200uF) was a pair of 1000 uF's which I replaced with a pair of 2200 uF's. I also replaced the 1000 uF speaker coupling caps with 2200 uF's.

I can imagine the coupling caps making such a tonal difference but I thought the other caps were just storage or filtering on the p.s. The overemphasis is on bass above the lowest frequencies, not just the very bottom...
 
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Yeah good suggestion and easy enough, just need to order them up... Any opinion about C914?
 
FWIW, when I was working on my Sansui 2000x I also did a simulation of the output circuit. It turned out that various parts of the circuit interacted and it would have been a mistake to change the value of some of the coupling and output caps. I would have said it could only improve things, but the sim showed it could have caused odd bumps in the low end of the response curve. Not that I couldn't have ironed out the issues with more changes, but my gut feel on just arbitrarily increasing the values was wrong.
 
The power supply caps are probably fine, though doubling the capacitance is a bit of a jump. I bet if you replace the coupling caps with their original value, it'll sound "right" again:yes:

The power supply caps wouldn't really affect the sound all too much, though at higher volumes it may be noticable.
 
Great information Conrad & 33, I'll replace the original ones, confirm that it's better, then if so order new of stock capacitance and maybe a couple in between to play with.

I'm going to back off on the p.s. cap too, I might go to 2800 instead of the specified 2200.

Thanks.
 
mark_m said:
I'm going to back off on the p.s. cap too, I might go to 2800 instead of the specified 2200.
Click to expand...

Maybe a good idea, checking the schematic it calls for 2200uF. Was the pair of 1000uF original, or were they replaced at some point?

I would guess they were in parallel, which means the values add, so two 1000uF was 2000uF (under what the schematic calls for), if they have to be replaced as a pair, rememeber that, so get something around 1200uF give or take a little. I could be reading it wrong, as i'm not familar with Hardon/Kardon layouts.

Schematics aren't always right, and production lines do "rolling changes" over the course of production, so it's a good idea to stick close to what actually came out of the unit.
 
There were two 1000uF's in parallel and they looked original, no sign of any work having ever been done on this amp. On the 330B schematic it explicitly shows the two caps in parallel. I don't know if there's any subtle difference between two in parallel and a single of equivalent value. I kind of assume it was based on what they had a million of to work with...
 
Put the original coupling caps back in and indeed it sounds more balanced. Am ordering some nice replacements for them just to complete the electrolytic update and will stay with original size. Some pics of the 330A innards. Nice little easy amp to work on.
330A_1.jpg

330A_2.jpg

330A_3.jpg

330A_4.jpg
 
I usually bump the filter caps by one catalog step. Not so much for circuit reasons, but because the larger snap lock caps always seem to come in near the low end of tolerance. Buying one step larger puts them back where the old ones probably started out, and if they come in at the high end, no problem there either. Nothing precise ever relied on the value of an electrolytic cap.
 
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