ampex 440 problem

[thinktank2]

I'm trying to fix one of my channels on my 1/4inch 2 track 440b.
Tried to post a message at the ampex list, but with no luck. One of the
channels is really noisey when I plug into the headphone jack. All connections to the module are disconnected excluding the power source from the supply. Still some sort of crackling noise. The unit is in ready/repro mode and when I turn up the left pot, that's when the noise is happening. Switched out repro card with bottom working unit, but no different. I've changed the electo caps on the cards, but that's it. Just realized there is a sprague atom at the back of the connector boards. Should this be replaced? Or maybe the pot is bad.

Thanks,
Nate

 

[thinktank2]

Anybody know how to post a thread at the ampex recordist site?

 

[guitarmaker]

Sure sounds like a bad pot. If turning the pot makes the nloise change I'd try replacing it.

post to: [email protected] for the ampex list. It can take a while for the post to appear.

Steve

 

[Butterylicious]

I've seen plenty of scratchy pots, but seldom do they cause a constant crackling that cannot be momentarily stopped by a thump on the knob. Often crackling is a bad connection somewhere. Bust out the magnifying glass and check all your solder joints from the previous cap job.

Crackling can also be a symptom of a dieing transistor. Does the crackling get louder when you increase the level? If yes, the issue is most likely in the front end and it won't break the bank to change out Q1, Q2, Q3, & Q4.

If you have an o-scope handy, look at the noise on the output, then start probing your way backwards through the transistor stages, probably increasing your sensitivity along the way until the noise disappears. Change that transistor and maybe it's neighboring caps just for giggles.

 

[fazeka]

[quote author="thinktank2"]Anybody know how to post a thread at the ampex recordist site?[/quote]

There's no thread to post to as there's no forum. You have to subscribe to the mailing list (old skool). The digest gets emailed to you and you post via email. People reply accordingly.

 

[soundguy]

hi nate-

the cap on the back of the cage could be bad but I think youd see lots of savage effects before you started to hear crackling too, is the meter working ok? One place where I had problems was actually with the plugin EQ cards, was about the last place I looked after tearing the machine down. Make sure your parts on there are good and make sure the contacts on the cards are clean. I put a ton of effort into making my 440 hifi, one thing I did was change the in/out pots with a wire wound ten turn pot, if you change the pot I would pretty much reccomnd not going in that direction and keeping a carbon in there unless you want to change the sound of the deck quite a bit- which you may find preferable, but the wirewound cleaned things up a bit too much for my taste. Im going to mix one project and then assume I'll put a carbon back in there...

why are you plugging into the headphone jack in the first place? Are you plugging headphones in there or using it as a line level output or something? Not sure what that jack wants to drive. Are you able to repeat the noise through the regular line level output? If its just isolated to the headphone jack Id investigate what kind of load that output was designed to drive and see if you are closely matching it. If its not dirt on a pot or a connector, Id start thinking down that road.

dave

 

[thinktank2]

Thanks for the help. I'll go ahead and take a look at it more closely this weekend. As far as the pots, I'll go ahead and replace those. Dave, do you know what those values are for the two front pots? If they are old, I want to make sure to get the values correct. I'll go through and make sure all the contacts are cleaned.

One other thing that I notice is that the vu meter lights go from dim to bright and back and forth. Could that be something to do with the power supply? It's not a drastic difference, but it happens. When it dim's out,
the noise doesn't seem to be affected by it though.

I'll take another listen this weekend and listen through my board to make
sure it's not just the headphone jack. Seems like there is something else wrong here. This tape machine has got to be 30 or 40 years old I would guess. Thanks again,

Nate

 

[fazeka]

[quote author="thinktank2"]This tape machine has got to be 30 or 40 years old I would guess.[/quote]

You are correct. IIRC, the 440B started life around '69, I think. 440Cs came on the scene a few years later.