HI and DR504 clone

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HI and DR504 clone

Postby snailspacejase on Sat Jul 01, 2017 8:55 pm

Hi Guys

This is my first post here and I'm going to be cheeky and ask for some help.
I have recently built a Hiwatt DR504 clone and it is perfect except for a noise issue.
I have eliminated the various stages of the preamp by bypassing each, and the noise remains. I have also tried a known good preamp valve in each position.
I am getting to the stage where the only components I have not eliminated from my tests are the filter caps, and of course they are expensive just to change on a hunch.
If I could be so bold as to ask you to take a listen and see if this is something you recognise, I would be very grateful.

https://soundcloud.com/jason-mills-34/d ... se/s-Nrf2l
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Re: HI and DR504 clone

Postby ep1966 on Tue Aug 08, 2017 2:29 pm

Well never heard a filter cap sound like that. If you have a single tracer of some kind you should be able to at least find the stage where the noise is getting in the signal. Just be sure the tracer can block the high voltage. Did you use all new components? Kinda sounds like a noisy component. Know it sure help me find a old carbon comp 10k that drove me nuts for a while.
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Re: HI and DR504 clone

Postby Vortexion on Tue Aug 08, 2017 3:27 pm

I've heard that sound before.

If the noise is present even with the Master Volume control fully down (this, of course, is assuming that the MV ground leg is making perfect contact with ground), then the source of the noise must lie somewhere from the MV onward - i.e. the phase-splitter, driver, output stage and/or PSU circuitry.

It could well be coming from a dodgy PSU, filter or coupling cap (even brand new components can be bad off the shelf) - but it could equally be coming from an iffy solder joint. Dry solder joints behave like little semiconductors, their imperfect contact producing oscillating/squealing noises. They can also pick up RF interference and frequency-shift it into an audible noise.

Yes, I know... your soldering skills are magnificent! :wink: ...but check all of your joints again. Contrary to popular wisdom, a bad solder joint doesn't always LOOK bad to the eye: it can look lovely and shiny but be bad underneath. With the amp switched on and the MV turned down, try the old chopstick-tapping/prodding thing on all the joints in the amp sections I've mentioned above. If you find that prodding a certain solder joint makes the noise worse or better, you'll have found your culprit.
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Re: HI and DR504 clone

Postby ep1966 on Wed Aug 09, 2017 3:42 am

Well Mr Vortexion I agree had the perfect example on the bench today. I was working on a Sundown A50 that had a major hum and wound squeal like crazy if you hit the gain boost. Found the problem on solder joint on the ground of the gain control resolder the joint and check the other grounds and the amp is working as it should.
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