Having difficulty measuring kenwood receiver output

[Mike Mag]

I wish I could figure out what is not going correctly
I have a 35WPC Kenwood receiver I am trying to measure output
I feel I have everything connected correctly but the DM says the RX is 1WPC (2.783V) and the scope says 60WPC (21.8V) (DM is true RMS reading)
I know both are wrong
but I can not figure out why this it is so weird today
I have measured other amps and receivers in the past without a problem but this Kenwood is confusing me
why are neither readouts reasonable

anyone experience this before ?

 

[painttoad]

are your scope probes and scope set to x10?

that would describe the almost 10x discrepancy, i could pass the rest between inaccuracies between the meters i guess.

 

[Buck Rogers]

At 21.8 volts across 8 ohms is 59.405 watts.

DMM's are not usually used across the audio spectrum, We use an AC VTVM or audio voltmeter.

 

[Mike Mag]

are your scope probes and scope set to x10?

that would describe the almost 10x discrepancy, i could pass the rest between inaccuracies between the meters i guess.

I thought it was set to X1 but it wasn't ! Now the scope and meter basically agree.
next issue is why is the receiver clipping so soon
TY

 

[whoaru99]

DMM can be fine as long as it can measure the frequency(ies) being sent through the amp. Some have wide enough bandwidth, some don't.

 

[whoaru99]

I thought it was set to X1 but it wasn't ! Now the scope and meter basically agree.
next issue is why is the receiver clipping so soon
TY

Clipping?

I'm not see any obvious sign on the scope, Do you have some other way you're identifying clipping?

 

[Mike Mag]

Clipping?

I'm not see any obvious sign on the scope, Do you have some other way you're identifying clipping?

That is just before clipping
It is clipping only on the bottom though
Flat as a table

 

[Dave1027]

Both channels?

 

[tadawson]

Read the power supply rails to the final - it sounds like the low side has a problem and is running low.

 

[sregor]

Model? Is it cap coupled? thinking clipping asymmetry could be caused by center voltage problem.

 

[Mike Mag]

Both channels?

Yes

 

[Mike Mag]

Read the power supply rails to the final - it sounds like the low side has a problem and is running low.

They measure down to 36 when volume is turned up. That is a reduction of less than10%

 

[Mike Mag]

Model? Is it cap coupled? thinking clipping asymmetry could be caused by center voltage problem.

Model KR-4010, they call it a DC receiver
SM https://www.google.com/url?sa=t&sou...8QFnoECD0QAQ&usg=AOvVaw3VyDAlvE_rBnpvWvbEUulQ

 

[tarior]

It's clipping the bottoms of the waves on both channels at ~3VRMS output into eight ohms? What frequency? What happens when you go to lower frequencies?
You're not trying to measure output while on DBT are you?

 

[Dave1027]

Read the voltages on the emitters of the regulator transistors.

Q13 should be +22 volts
Q14 should be -22 volts.

 

[whoaru99]

You're not trying to measure output while on DBT are you?

That's a great question.

 

[Mike Mag]

It's clipping the bottoms of the waves on both channels at ~3VRMS output into eight ohms? What frequency? What happens when you go to lower frequencies?
You're not trying to measure output while on DBT are you?

no DBT while testing
I tired both 100Hz and 1kHz

 

[Mike Mag]

Read the voltages on the emitters of the regulator transistors.

Q13 should be +22 volts
Q14 should be -22 volts.

+23 and -23

 

[Mike Mag]

I am trying to go backwards in debugging to when the clipping starts but when I try to check the input to the STK modules my scope is giving weird results. can anyone tell me what I am doing wrong? scope is at pins 0 and 1. scope does not even know the frequency (1KHz)

 

[llwhtt]

Do you have scope ground connected to Pin 0? If so that's your problem.

Craig