Rod Elliot P06 Riaa problem

[gchrist]

I was just thinking at work that I have used the P05 project as my power supply. I have used a standard transformer with dual secondaries. I have connected the transformers as 15-0-15. But I have not connected the transformers common point to chassis ground. I have connected this point only to the GND point on the powersupply pcb.

Maybe this effects the riaa board.

I cannot understand why the C5 capacitor will not let the AC music signal go through it and stops!

I will search again today and let you know of my findings.

Regards
George

 

[gchrist]

Unfortunately I have not been able to solve my problem. Since I am not an experienced electrician and I have not received more feedback from the forum I have only one choice. I will shelf this project and try to build another riaa stage.


I would like to thank all of you that responded to my messages in this forum.

Regards
George

 

[Eva]

A crazy capacitor should not be enough to make you abandon the project ...

 

[tschrama]

Did you try the forum of Rod Elliot? I would be a shame to give up now... I am sure it is just a simple problem you have overlooked..

Maybe it is your ground connection.. you shouldn't leave the preamp floating, connect the gnd to the powersupply ground..

Don't give up, goodluck,
Thijs

 

[peranders]

If youn have bought a pcb from Rod I think it would be quite easy to succeed, just put the right parts in the right place. A photo of your amp might help.

 

[gchrist]

Yes guys I have posted this problem on Rod's forum but I did not get any replies that solved my problem.

I have connected the ground to my power supply ground also.

How can I find out if my signal is shorted to ground somewhere?

How can I measure the DC offset reaching c5 cap. This capacitor is blocking the DC voltage at the output.

I will try to send a picture in the next few days. I do not own a digital camera. I will need to borrow one.

Thank you all
George

 

[masfe]

Could you explain how did you made your power supply and how did you conected it to the riia circuit?

 

[gchrist]

For the power supply I have constructed Rod Elliott's P05 project. I have bought the pcb from Rod Elliott.
I have used one toroidal transformer with two secondary windings.
I have connected together the end of the first winding with the starting of the second wiring. This center tap has been connected to the PCB where it states "GND".
I have also connected this center tab to chassis ground which is then connected to the ground of the power inlet.

The other two wires from the tranformer have been connected to the ps pcb where it states AC.

The ps pcb gives me a +,- and gnd output connections. I have the same connections on the riaa board. I have connected the same symbols together.

Now on the signal side:

The center of the input RCA goes to the riaa input L and R designations. The ground from the RCA sockets goes to the relative L or R ground designations. The ground wire from the TT goes to the chassis ground.

I have measured the voltage I get from the ps. I get +-14.8volts. This voltage is applied on the correct IC pins.


Hope the above help.

George

 

[peranders]

This project is rather easy to troubleshoot so if you take a few pictures if think we solve this. You have four possible problems:

1 Not right values of parts

2 Opamps turned 180 degress.

3 wrong wiring

4 Bad soldering

Can't think of anything more if you have +-14-15 volts DC.

 

[gchrist]

Peranders,

I have checked again and again all parts. I have checked them also from digikeys invoice because the caps have special markings. All resistors are ok.

I have checked the opamps and I beleive them to be correct. If they where 180 degr. turned then wouldn't they be destroyed on power up? I do get a signal from pin 1 and 7!

I have checked the wiring many times.

The underside of the pcb is very clean. If I poke around I beleive that I will make more damage then good.

I do not understand why I loose the signal at the very end. It passes through the riaa stage but not over c5. Where can it be going?

It must be very simple but eludes me.

I will try to post some pictures.

Thanks
George

 

[peranders]

Do you have plus 14 volts at pin 8 and -14 volts at pin 4 of the opams?

Do you have DC out at the outputs of each opamp of max 3-5 mV? Do you have almost 0 mV at pin, 2, 3, 5, 6?

Is C5 really 1 uF and nothing else? Is R9 really 100 k?

I think a picture will clear up your placement of parts.

If you have 1% metal film with red and brown at the end, you haven't got that wrong?

Only 12 kohms can't be read wrong!

You haven't missed red, brown and orange which can be very near in colour?

 

[tschrama]

Maybe even better, post a schematic with the Vdc values you measure and were the signal (AC) is lost.. I'm sure Rod won't mind... to debug it this way..

Thijs

 

[gchrist]

Guys I found the problem. I disconnected the ground connections at the riaa output going to the preamp and everything is working ok. I will try to find out why this is happening.

Thank you all for your replies.

Very soon I will post pictures of all my project:

AKSA 55W
BOSOZ
ESP P05+P06
SCANSPEAK REFERENCE MONITOR

Best regards to all
George