My_Ref Fremen Edition RC - Build thread

[AndrewT]

Are you confirming you have measured 0.26Vdc (between signal Hot and Signal Return) before the DC blocking cap?
Where is that coming from?

 

[Marra]

Bob;restor values all seem ok and I've triple cleaned the boards and checked for solder links can't see any.
Some of the resistor values don't give an instant value but ramp up to the correct reading.

Andrew; yes its minus .26v which goes down and then back up again and once the relay clicks which isn't straight away I initially get 3.5v on the output and this then slowly drops in value.I havent left it powered up to see how low it gets as I did'nt want to burn anything out.

 

[AndrewT]

so you have 3.5Vdc on the output
where is the -0.26Vdc?

 

[Marra]

Across the input connectors before the input cap connects to the circuit.

 

[AndrewT]

if the DC blocking cap is not leaking then the input offset voltage cannot appear across the input.

You must have an error here. Somehow voltage is appearing across Sig to Sig G.
You must find how that is getting there.

 

[Marra]

Where to look is the question.

 

[AndrewT]

study the input with a microscope.
There must be something putting voltage on the RCA side of the DC blocking cap.
Is the input voltage zero when you add a dummy resistor to the RCA socket?
Is the input voltage also zero when you "short" the input socket?

Does the output voltage vary for any of these three conditions?

 

[Marra]

I am no doubt showing my ignorance here but what value dummy load would you recommend Andrew?

 

[AndrewT]

0r0 and 100r and 1k0 and 10k etc.

Get cheap RCA plugs and insert resistors to create your dummy test loads.

Mine are white plastic and easy to write on with sharpie (indelible pen).

 

[Marra]

Thanks Andrew I'll check that out and see what transpires.

 

[bcmbob]

Have you checked under C1 and C2? It will require un-soldering but that is a hidden area also.

 

[Marra]

The input offset is zero with the input shorted and various load resistors the output still reads 3.5v when the relay clicks in which is after a minute or when I start checking p/s voltages I don't posess a microscope but cannot see any thing untoward using a strong magnifying glass.

 

[AndrewT]

There must be a component or soldering error.
Check the output offset at the 318. That should also be the input offset at the 3886.
Check the value of every resistor while on PCB.
Some will give very odd (low) readings due to parallel paths. These may have to have one end lifted.

 

[Marra]

Thanks Andrew I'll check things tomorrow.

 

[ClaveFremen]

Hi Marra,

can you post pictures of your build so we can try to identify the problem?

 

[Marra]

I checked the voltages as Andrew suggested and at pin 6 of the 318 I have 0.027v but at the input of the 3886 I'm reading 0.070v this fluctuates slightly

Dario my camera is broken; won't charge for some reason but I will see if I can borrow a friends and post pics.

 

[Marra]

Forgot to say that these readings are to signal negative.

 

[atupi]

Since i've built MyRefFE i have installed R9-C10 group in the alternate position but today i changed to the original position indicated by Mauro and i must say i like it more.
Much music and i would more stereo image. (at least on the speakers that i have it temporary).

 

[ClaveFremen]

Dario my camera is broken; won't charge for some reason but I will see if I can borrow a friends and post pics.

This circuit has no need to be tuned to work, no trimmers or whatever.

If our build doesn't work we made an error:

• wrong component in the wrong place or incorrectly mounted
• bad solder joints
• active parts broken by static.

So I suggest to check first that all parts are mounted correctly and in the right position and reflow every suspect solder joint.

If regulators voltages are correct the usual suspects are R11, LM318 and/or LM3886.

A faulty PCB is unlikely since all boards passed electric test by the manifacturer.

 

[ClaveFremen]

Since i've built MyRefFE i have installed R9-C10 group in the alternate position but today i changed to the original position indicated by Mauro and i must say i like it more.
Much music and i would more stereo image. (at least on the speakers that i have it temporary).

Thanks for reporting

My impression was the opposite, we'll see what other builders will report.