ADCOM 5500 weak bass: possible reasons?

[zxzycorp]

I have the same bass response issue. Did you resolved it?

 

[bullittstang]

I have the same bass response issue. Did you resolved it?

See below from his previous reply. He replaced 11 capacitors and it fixed the issue.

Hi guys, just to give you an update. We replaced 8 large blue capacitors and 3 small capacitors in each channel, and the bass is back. The adcom turned out to be very capable amplifier in terms of bass control.

 

[zxzycorp]

After I did the re-cap as mentioned. It's sounds much better and very powerful. However, it sounds very metalized and sharp edged. good for string, a little harsh for the female voice handling on my mild B&W CM10.

 

[irext]

Sound like a signal path coupling cap was low in capacitance. Did you measure the values of the ones you replaced? Small value electrolytics are notorious for drying out. In signal paths it's best to use high grade Elna Cerafine caps (or similar) which are made specifically for audio coupling.

 

[phomchick]

Sound like a signal path coupling cap was low in capacitance. Did you measure the values of the ones you replaced? Small value electrolytics are notorious for drying out. In signal paths it's best to use high grade Elna Cerafine caps (or similar) which are made specifically for audio coupling.

In my case (and I suspect most cases) "no bass" problems are caused by the failure of the three electrolytic caps on the channel driver boards. Here are my measurements for the 47uF/50v cap (new and removed):

New part -
47.5 uF
ESR = 0.19 ohm
VLOSS = 0.77%


Old part -
30.9 uF
ESR = 140 ohms
VLOSS = 32%

 

[Mark Tillotson]

More cylinder full of gunk than electrolytic capacitor then!

 

[ticknpop]

Give the new caps a 100 hours at least of playing time to reduce the harsh edge

 

[Phloodpants]

Harshness in these amps may be caused by poorly matched input FETs. Try matching up new pairs per this article from Nelson Pass. You just need to match for Vgs.

PassDiy

 

[phomchick]

Here's the difference between a repaired channel and one yet to be fixed. (The spike at 70kHz is an artifact of the the measuring system).