Harman Kardon A-402 Restoration

[jheu02]

And a little less zoomed...

As a side note, anyone have anything on the capacitor photo? I have a pair of these 0.39uF/100V film caps that I'm planning to use for the phono mod. I have both the 0.33 and 0.47 Panasonic ECQs if these don't sound good, but I have no other use for these and they would be the perfect 10x increase shown in the mod thread for a better RIAA curve. Can't find anything about them, but they test good on the DMM capacitance function.

 

[jheu02]

@dlucy

Do the phono boards you have redone include 270 ohm resistors attached on the trace side between the + terminal of the 100uF/10V caps and the emitters of the 2SA872s? Scat uploaded showing the connection in blue... if so, I take it they didn't affect the mods to the RIAA curve.

 

[dlucy]

The only resistors on the trace side were a pair of 5.6k (near the bottom of the card in the photo)

 

[jheu02]

Running changes or maybe service bulletin item as they look pretty original on mine.

 

[jheu02]

@dlucy
Another question Doug as I was replacing caps etc on the EQ board...

All board markings match the scat of the A-402 (except for that extra 270 ohm R on each underside). HOWEVER, R703/704 (input resistors) instead of being 220ohms, are ACTUALLY 2.2Kohm. I guess a factory mistake, as all the other photos I see of the 730 EQ, etc definitely show 220ohm. Replacing them with Dale RN60s.

 

[dlucy]

@dlucy
Another question Doug as I was replacing caps etc on the EQ board...

All board markings match the scat of the A-402 (except for that extra 270 ohm R on each underside). HOWEVER, R703/704 (input resistors) instead of being 220ohms, are ACTUALLY 2.2Kohm. I guess a factory mistake, as all the other photos I see of the 730 EQ, etc definitely show 220ohm. Replacing them with Dale RN60s.

The two units where I recorded the existing values on their way out were both 220, not 2.2K.

Hmmmm....

 

[jheu02]

Time to upload the photos of the Modded Phono EQ Board

Pre Work

Incorrect Input Resistors

Undocumented 270ohm Resistors on trace side

Post rebuild

Oblique showing mystery cap size

 

[dlucy]

Time to upload the photos of the Modded Phono EQ Board

well done!

 

[Soundork]

I was making up a parts list today, even though I don't have the amp yet. I thought about going up to 6800uF 50V caps for the mains. @jheu02 do you have the diameter and height (not so important).

@dlucy I was thinking the same thing about replacing the small signal transistors as well.

My advice to you would be against installing components with larger capacitance. By doing so, you will change the sound of the amp. For worse.

Having said that, you can experiment on your own and buy a set of 4700uF along. It would set you back $6-7 if that, but you would find out on your own and not by listening to someone on the Internet.

Best

Soundork.

 

[Soundork]

Time to upload the photos of the Modded Phono EQ Board

I have an A-402. I can look inside this weekend and take some pictures if you wish to get to the bottom of it (the undocumented changes that is).

Otherwise, looks very good.

Best

Soundork

 

[dlucy]

My advice to you would be against installing components with larger capacitance. By doing so, you will change the sound of the amp. For worse.

I hope what I've said in the past is not taken as "increasing the capacitance during recapping is good".

Increasing the capacitance on power-supplying caps is usually not a problem, just a question of how-far-to-go and will-it-really-make-a-difference.

Increasing the capacitance on signal-carrying caps, now that, in general, is asking for a change in audio performance. The inter-stage coupling caps are often a place to consider, but I wouldn't up the capacitance on any signal-carrying caps without some really good direction from others. Several others.

 

[leesonic]

My advice to you would be against installing components with larger capacitance. By doing so, you will change the sound of the amp. For worse.

Having said that, you can experiment on your own and buy a set of 4700uF along. It would set you back $6-7 if that, but you would find out on your own and not by listening to someone on the Internet.

Not true at all, insofar as power supply caps. Think about it. The caps are charged by the transformer via the bridge rectifier. When your amp amplifies a big peak in the music, a larger cap in the power supply will provide more peak current before draining too low. Small signal caps on the other hand, I wouldn't change them.

I don't listen to people on the Internet. I've been doing this **** for years. Most kids read comics, I read HiFi mags. Built my first amp before I was a teenager. Made a speaker driver from a pot pie dish and a paper cone, sounded crappy but proved how speakers work.

Nuff said.

 

[jheu02]

I have an A-402. I can look inside this weekend and take some pictures if you wish to get to the bottom of it (the undocumented changes that is).
Otherwise, looks very good.
Best
Soundork

Sure. The phono EQ board is very easy to remove. Thanks for the offer.

 

[jheu02]

Doug, do you open the pushbutton switches on the 730s you redo? Not really finding a way to get deoxit in, but not really sure I want to take each one apart.

 

[dlucy]

Doug, do you open the pushbutton switches on the 730s you redo? Not really finding a way to get deoxit in, but not really sure I want to take each one apart.

I make a very small hole with drill on the rear side of each switch, then spray Deoxit in there.

I tried opening them, but had less than success with that.

 

[Soundork]

Not true at all, insofar as power supply caps. Think about it. The caps are charged by the transformer via the bridge rectifier. When your amp amplifies a big peak in the music, a larger cap in the power supply will provide more peak current before draining too low. Small signal caps on the other hand, I wouldn't change them.

I don't listen to people on the Internet. I've been doing this **** for years. Most kids read comics, I read HiFi mags. Built my first amp before I was a teenager. Made a speaker driver from a pot pie dish and a paper cone, sounded crappy but proved how speakers work.

Nuff said.

It was a joke. It meant that you don't have to listen to what I said, also that's why I told the OP that it costs about $6 to verify my statements.

I don't have interest to argue with anyone about the piece of information I just passed along. As an engineer, I believe what the data shows me. The data says that if one were to increase the capacitance of the power capacitors in a HK330c from 6800uF to 12000uF, the sound would deteriorate. Experiment performed on two units with the same outcome. Seriously, I couldnt wait to put the old capacitors back in.

I admit, I did not expect this result either, it but this is what the data shows (from two units) and it is frustrating that off the top of my head I do not have a sound scientific explanation. It is even more frustrating that I do not have the time to pursue further, so take it with a salt of grain.

Best

Soundork

 

[leesonic]

It was a joke. It meant that you don't have to listen to what I said, also that's why I told the OP that it costs about $6 to verify my statements.

You need to put a smiley face then...

As Ringo Starr would say, peace and love Brother, peace and love.

 

[jheu02]

I make a very small hole with drill on the rear side of each switch, then spray Deoxit in there.

I tried opening them, but had less than success with that.

Thanks Doug.

@Soundork...

I'm just going by the SM for the A-402, which for the main filter caps states 4700uF/50V (+50%, -10%). This gives a range of 4230uF - 7050uF. Both 5600 and 6800uF fall nicely in the design range, but there's not many 5600uF caps that I liked. The 6800uF/63V Nichicon KWs have the added bonus of 12.5mm lead spacing, so no board modifications are necessary. BTW, purchasing both 6800 and 4700 caps would cost a bit more than $6 to verify your statement.

 

[jheu02]

A couple more boards are now done. Here's the Sub Rectifier Board.

The SM allowed for a +50% increase to the caps, so since I had a 3300uF/25V UPW cap on hand for a different project, I used it here. Also decided to bypass both caps on this board with 1uF/63V Kemet R82s, and use Dale RN60 series MF resistors.

Unrestored

Post Work

 

[jheu02]

Mode Control Board A This board contains the High/Low filters (Hinge) and the 2 caps are in the audio path leading to the Pre Out jacks. So, they got replaced by Nichicon UKL series (Low Leakage).

Pre

Post