Harman Kardon 450 Bass Problems

[Logchop]

Hi everyone,

Recently got a new to me Harman Kardon HK 450 that works pretty well except for problems with the bass. It essentially has no bass response at all, and turning the bass up does nothing but give a big pop at about 80% of max. This unit did get pretty beat up in shipping thanks to FedEx which my tech was nice enough to fix, so I'm concerned that there may be damage to the bass pot itself. My tech has said that the problem is likely due to damage to the pot and that he doesn't have a replacement part for that. When opening it up, it looks like what appears to be all the resistors in line with the pot have been taken out. I attached a pic of this (top middle of pic). At this point, I'm thinking I should replace the resistors after finding a parts list but I'm wondering if it's worth it to replace the bass pot at the same time. Any ideas? And if I should replace the pot, does anyone have any good replacements? I believe it's a 100k ohm pot. I've been looking around online and all of the pots seem to have very short shafts that don't look like they'd work right for the unit.

Thank you

 

[analogwisdom]

I'm sorry I can't help you with the problem, but I did look and saw that the board is empty in those spots in the service manual.

 

[painttoad]

My tech has said that the problem is likely due to damage to the pot

but did he take it out and measure it?.

no sense looking for a pot unless you KNOW that is the problem.

 

[Logchop]

I'm sorry I can't help you with the problem, but I did look and saw that the board is empty in those spots in the service manual.

This is helpful, points me more towards the pot. I wonder why the HK engineers would design a labeled board like that not meant for components...hmmm. Now to find a pot that will work for the unit.

but did he take it out and measure it?.

no sense looking for a pot unless you KNOW that is the problem.

He didn't as far as I know, but I'll do that myself soon and report back. Any suggestions on 100k ohm pots that will fit in the unit assuming that is the problem?

 

[painttoad]

Any suggestions on 100k ohm pots that will fit in the unit assuming that is the problem?

no clue. there are soooo many parameters to potentiometers, it's a daunting task to find one.

if you can find the same style and length of shaft , you can often attach it to the inner face and extend the legs to the pcb.

i hope that you do not have a damaged pot.

be careful removing it. they like to fold over a couple legs TIGHT and it's difficult to unbend without snapping it off.

it's also best to measure it with an old analog meter so you can see how smooth it tracks but that's not entirely necessary.

i've never measured a pot in circuit so i am unsure of how accurate it would be.

I wonder why the HK engineers would design a labeled board like that not meant for components...hmmm

same board for multiple models.

 

[Logchop]

Thank you for all the help @painttoad . I'll try to measure it in circuit first just to see, didn't think of that. It seems they didn't make these HKs very easy to disassemble and access necessary components. Space inside is very cramped, especially behind the faceplate and under the dial lights right where the pot is of course. Finding the appropriate shaft length for the pot seems to be the problem, I've been able to find the correct style but not the correct length so far. Will keep looking and update here as I go. Thanks again

 

[Logchop]

Update: Opened up the 450 and realized there would be no way to effectively measure the pot in circuit given how tucked away it is. Took a look at getting the pot off the board and realized how much of a chore that would be, so decided I was probably just going to give up on it. The board itself is not easy to take out and would require restringing of the tuner pulley system and removing various wires. I decided to resolder all the legs for the pot and a couple of the transistors in line with the pot as a last ditch effort and was pleasantly surprised that the bass is now present and sounds great! Still get a pop when pushing the bass past about 90% of max, but honestly this thing puts out such full and rich bass at the standard halfway point that I'll never need to push it up much. Very pleasantly surprised with how good this HK sounds, I can't say for sure yet but it may beat out the Marantz, Sansui, and Tandberg units I have. I may be converted to a Harman Kardon guy!