Wd88 Doa

[pre65]

Hi Paul-just remember

"he who never made a mistake-never did anything !"

I know when i built the Pre/Psu/Phono i had to read the instructions several times and check/double check EVERY connection and resistor value (by code and then DMM) and i still have a problem with Phono3s which Dr John has agreed to look at for me.

I'm sure you will be very pleased with the end result though.



Philip

[Primalsea]

Too true Phillip,

Last night I got the relay board working, It was due to another wiring error I made (I get some comfort in the fact that I normally find them eventually).

I tried it quickly this morning as I was up early but got a distorted sound and humming.

It was at that point I remembered that I had forgotten to solder the earth connection to the relay board!!

All being well once this is done all will be well and I can finally get rid of the standby SS amp out of my system.

[Primalsea]

Bonza! got the amp working and all is well. It sounded a bit harsh straight off but seems to be mellowing now.

However I do have a problem but I don't think its linked to the WD88 as something similar happened with my Kell84 as well.

Both of these are integrated but I have been using them with the Pre3 with the integrated volume up full.

For both of these I get a high pitched whistle which I originally put down to a duff valve. I guess now its interference.

Turning the volume down a bit on the integrated stopped it but I would rather modify the circuit for additional protection from interference unconditionally.

Whats recommended??????

[Richard]

Hi Paul,

Well done.

I too have had similar problems feeding into a power amp with volume control. The only reason I can see is that with a pot wired in the usual way, when it's at full volume the signal has no series resistance and is straight onto the input, a 1K resistor in this case. The amp isn't normally run (as an integrated) with the pot at this position so the problem may not usually arise.

Solution would be to increase the 1K stopper on the input, try 10K perhaps, or rewire the pot as per the shunt pot mod. Use a 39K or 47k series resistor before it (assuming 50K pot) and reconnect as per the faq article.

Rich

[A Stuart]

Originally Posted by Richard

...the signal has no series resistance ...to increase the 1K stopper on the input

As best I can see:

R21 (1k) is in series with the grid of the first valve which has near infinite resistance (other that at radio frequencies where the capacitance from the grid to other electrodes takes significant effect).

R22 (100k) to earth gives the input impedance.

I think .

Alastair

http://wduk.worldomain.net/acatalog/AmpKits.html - see "Design Article Part 2"

[Primalsea]

I've discovered that it's my CD player thats the whistle blower, I never expected that. I use a DAC but had the cd outputs connected to the preamp as well so I could switch between DAC and CD player for AB comparison.

I removed the interconnects between CDP and preamp and the noise went away.

The CD player is a Marantz CD94 and uses a 2 core mains lead so the earth floats at the same level as wheat ever its connected to via interconnects. I thought this helped with ground loops and the like.

So thats that fixed but I think I will still go for a belt and braces approach to RFI/EMI filtering on the mains and audio.

Its divide and conquer at the moment, now I can sort out the pops and clicks from when the heating & fridge turn on. However I have electrostatics at the moment and I understand that they often pop and click and there not much you can do about it.

I've sent communication to Dr john about the RFI filtering, hopefully he will get back soon after easter.

[Richard]

That's good Paul. Keep my comments in mind if it should surface again as, like I say, I've had similar.

Alistair, I think you've quoted me out-of-context

Originally Posted by Richard
...the signal has no series resistance ...to increase the 1K stopper on the input

I didn't say that. I said,

The only reason I can see is that with a pot wired in the usual way, when it's at full volume the signal has no series resistance and is straight onto the input, a 1K resistor in this case.

Rich