• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Nikko Beta II preamp issue

R

rfitts46

Active Member
Preamp powers up and allows signals in and out. One channel has lower audible volume along with intermittent noise.
Using oscope and signal generator was able to view output signals. These are very small signals so they looked similar.
Using DVM measuring VAC at outputs noted at lowest volume setting 0mV on good channel and 20mV on the channel exhibiting lower audible volume and noise.
Checked VDC at output for offset. Good channel 0mV the bad channel 50mV at power up dropping to 15mV.
Measuring DC offset at last Resistor R609 before reed relay 0mV. This would be the bad Left channel. After relay measure 20mV DC offset.
One might assume the Reed relay is inducing DC onto the output signal?
 

Attachments

Last edited:
Register to hide this ad
rfitts46 said:
Measuring DC offset at last Resistor R609 before reed relay 0mV. This would be the bad Left channel. After relay measure 20mV DC offset.
One might assume the Reed relay is inducing DC onto the output signal?
Click to expand...
Very unlikely it is the relay. Most likely would be bad coupling cap or amplifier input - much less likely would be bad resistor 68K to ground and no loading. Reverse connections to amplifier ad see if changes (assuming you are connected to an amp. ) if no amp, back to first two choices...
 
Wonder if this is the one I sold on eBay a week ago.
The measurement at relay makes no sense, and I doubt it’s the relay. Bypass it if you want to be sure.
I’d be replacing transistors.
 
Ivandezande
Sounds right if you shipped to NH.
I have a left channel oscope trace attached.
Top oscope trace shows the signal at base of Q501. Not pretty. The first xistor of the differential pair. Same symptom observed on either side of C501. Signal before R515 is good.
 

Attachments

  • 20230311_134336_copy_4080x3060.jpg
    20230311_134336_copy_4080x3060.jpg
    102.8 KB · Views: 17
Looks like the Dynaco ST120, which I had forgotten the outputs are capacitive coupled might have contributed to some of the noises.
Did end up resoldering the half dozen or so connections from the relay to the outputs for safe measure. I traced the signal through the left using the oscope and compared to the right. Looked great till after the relay. The signal would intermittently start wiggling.
Did go away after the resolder and have since tested using a Carver amp which was fine. Also have put the Dynaco back on it and other than some of the thump due to the amp no issues.
 
Well to be honest the issue showed back up. Put it back on bench and jumped the relay and both channels present in volume.
Decided to replace the unobtanium reed relay with Cota Technology's reed relay 8L02-12-01. It is in a molded IC construction and the pin layout is different. Flipped it upside down and used cut component leads to make the thru board connections and it is operating correctly.
 

Attachments

  • 20230808_182806_copy_2439x1395.jpg
    20230808_182806_copy_2439x1395.jpg
    98.6 KB · Views: 21
rfitts46 said:
Well to be honest the issue showed back up. Put it back on bench and jumped the relay and both channels present in volume.
Decided to replace the unobtanium reed relay with Cota Technology's reed relay 8L02-12-01. It is in a molded IC construction and the pin layout is different. Flipped it upside down and used cut component leads to make the thru board connections and it is operating correctly.
Click to expand...
:beerchug:

Nikko Beta II - Output Relay

Hello all, I recently was given (yay family!) a Nikko Beta II preamp with a channel dropping in and out. Searching the boards here led me to the speaker output relay and sure enough, if I lightly tap it with a plastic pen, etc. the amp works great for a while before cutting out again. More...
audiokarma.org
 
Question for you all. I picked up a Beta II the other day and have noticed a couple of issues. Initially audio dropped out on both channels. It was very graceful and then came back up in a few seconds. Then last night I started getting volume cuts on both channels intermittently as well as some distortion and a weird warbling sound on a 1kHz tone again it was affecting both channels intermittently but never at the same time. This morning is seems fine again.

Would this be caused by that relay? If so can you clean them like you would a more standard relay or is a swap my best bet?

Thanks!
 
RI HiFi Guy said:
Question for you all. I picked up a Beta II the other day and have noticed a couple of issues. Initially audio dropped out on both channels. It was very graceful and then came back up in a few seconds. Then last night I started getting volume cuts on both channels intermittently as well as some distortion and a weird warbling sound on a 1kHz tone again it was affecting both channels intermittently but never at the same time. This morning is seems fine again.

Would this be caused by that relay? If so can you clean them like you would a more standard relay or is a swap my best bet?

Thanks!
Click to expand...

I think disassembling would destroy it.
Tap on the relay with something non conductive when it acts up, if that fixes it there's your problem.
 
milo63 said:
I think disassembling would destroy it.
Tap on the relay with something non conductive when it acts up, if that fixes it there's your problem.
Click to expand...
I'd use a chop stick. I always pick up a few at my takeout.

I narrowed down a problem in an Onkyo preamp with a similar problem
 
I think it finally gave up last night after cutting a couple of times. I am going to take it apart tomorrow and see what it looks like. I had to futz with the Onkyo relays as well, and have replacements for those already.
 
You must log in or register to reply here.
Back
Top Bottom