Sansui 9090DB Poppy Buzzy Bass

[degdug]

Hello! I have been playing my rebuilt 9090DB for about a month now. Yesterday I finally was able to turn it up to see how she sounds on a higher volume.

I did a full recap, replaced fusible resistors on the driver board, replaced some diodes, rebuilt the bridge rectifier, fixed the through holes on the Dolby Board, correct deoxit on the pots, DC offset, Bias, and some others. My Klipsch Cornwalls have had their crossovers rebuilt. I also fixed up the EQ.

The only problem I ran into during my rebuild is the trimmer pot on the driver board was put in and set to a setting which immediately took the receiver into protection. I had to put the original TR05,TR06 transistors back in. I currently believe this to be primary suspect.

The problem, video provided below, becomes more apparent at a higher volume. I've also noticed the receiver pops sometimes when turning on or off. I would love to have this receiver breathing well.

Please share the wisdom!

 

[mrk229]

I did a full recap, replaced fusible resistors on the driver board, replaced some diodes, rebuilt the bridge rectifier, fixed the through holes on the Dolby Board, correct deoxit on the pots, DC offset, Bias, and some others. My Klipsch Cornwalls have had their crossovers rebuilt. I also fixed up the EQ.

The only problem I ran into during my rebuild is the trimmer pot on the driver board was put in and set to a setting which immediately took the receiver into protection. I had to put the original TR05,TR06 transistors back in. I currently believe this to be primary suspect.

Can you expand a bit on the issue. And in what order things took place.

In the first paragraph you said you set offset and bias, but in the second paragraph you have a trimmer setting that takes you into protection. A bit contradictory.

Which trimmer, and how/why did it get set to a setting that took you into protection? Was this trimmer reset/checked after you swapped the original parts back in?

 

[degdug]

Can you expand a bit on the issue. And in what order things took place.

In the first paragraph you said you set offset and bias, but in the second paragraph you have a trimmer setting that takes you into protection. A bit contradictory.

Which trimmer, and how/why did it get set to a setting that took you into protection? Was this trimmer reset/checked after you swapped the original parts back in?

Thank you for your response. Towards the end of my rebuild, when installing the last components of my rebuild, VR03 and VR04 on the driver board, it went into protection. I found either TR05 and TR06 failed so I replaced both with the original transistor I took out. Because it is the original transistor, I am suspect of the issue being here.

After reinstalling the transistors and matching VR03 and VR04 to the resistance of the original trim pots, I was out of protection once again. It has not left protection since. Then I went through and dialed in the offset and bias, spot on to the specs in the manual. (I learned to match the resistance on the pots and not trust they are set to 50% because of this)

I have played the receiver under this configuration for a couple of weeks, but not at anything over 1/5 volume as it's just too loud for a casual day at the house.

I had friends over the other day and decided to push the amp. I had it at about 1/3 volume or greater when we started noticing the issue as heard in the recording.

To clear up the contradiction, I performed the offset and bias after I got it back out of protection. I wanted to disclose about the protection mode because my primary suspect are the old transistors that are still on the driver board.

 

[AE Bob]

What I hear in the OP video sounds like a defective woofer. He should try switching speakers left and right, and see if the issue stays in the same speaker. If so the woofer is damaged.

 

[degdug]

What I hear in the OP video sounds like a defective woofer. He should try switching speakers left and right, and see if the issue stays in the same speaker. If so the woofer is damaged.

Thanks for the response. Problem persists when swapping wires, and even when full left or full right. I have tried different speakers and problem remains. I am suspect of the power supply.

 

[mrk229]

Do you have a tone generator, oscilloscope and dummy loads? I think a visual look at things without putting your speakers in harms way may be the way to go.

Do you have another amp you can use with the 9090 pre-amp outputs to see (listen) if the pre-amp circuits are OK?