Sammy whine

[misterfish]

Hello again

Sorry to be a pain , but I don't seem to be able to find and definitive info on chokes and snoothing.

Should I be looking for a capacitor to put across either the input or output of the transformer and if so what sort of value should I be using.

Looking at the transformer the mains side is as I would expect with just two wires for the 220v ac. The output has 3 wires with only the outer two being used so I guess that this is a 12-0-12 output giving the 24 v [d between the two terminals.

Any further help or ideas would be really appreciated.

Thanks

Jeff

[logicprobe]

Not having a Sammy, I've never heard the whine... so I can't help much here.

I sure wouldn't put a capacitor across EITHER input or output of that AC transformer, though...
KaBOOM!

My guess... and purely a guess at this point... would be that a filter needs to be on the DC after rectification and regulation/filtering... OR... that it would need to be placed somewhere in the audio circuit.

Has anyone here ever done anything with this? Or have the volume controls made it acceptable for most people?

[Tulsa]

The volume controls have always worked well enough for me. I'm still of the opinion that it's a ground loop causing it. Radio Shack has a ground loop isolator for about $15. Just haven't been back to get one and try it yet.

[monaghj]

Hi, I have a Sammy - Savanna Park, and it had a whine. You can put a capacitor across the speakers. This works on the same principal as a cross over on a speaker. Ie a Tweeter has a capacitor on it to filter out all of the lows, and a sub has the same (usaully adjustable) to filter out all of the highs.

Here is a good article http://www.passivecrossovers.com/index.htm

If you scroll down through the article there are a couple of charts that show what compoents to buy... basically to get rid of the sammy squeal you want to build a low pass filter (passing only the lows).

The article reads.....For the 130-Hz low-pass filter, check the intersection of the 130-Hz and 4-ohm columns in Table 2. As you can see, you'll need a 200 pF capacitor for C2 and a 6.8 mH inductor for L2. .......

So much for the theory.....
Basically if you put a 200pf capacitor across the speaker wires the whine goes away.
You will need to do that for each of your speakers.

http://www.web-tronics.com/21cb200.html

[misterfish]

Once again guys - many thanks for the rapid replies.

Yes, the volume controls do make a lot of difference and if the truth be told the sound is perfectly acceptable. I suppose that compared to the Gurukun and the DDK it is a bit noisy.

Radio Shack - yes we used to have them in the UK trading under the Tandy name - brilliant stores with masses of components and even salespersons that were pleasant, knowledgable and willing to give advice. They went bust over here some time ago and the only real options where I live are mail order and even if you speak to a 'sales consultant' their technical knowledge is virually zilch.

But what I'll do next time I'm ordering some 'bits' from Maplin or Radiospares is include a slack handful of capacitors.

I'll now go and have a qick Camel and see if I can get another bonus round - it's a fairly stingy machine (even though set on 6) unlike the DDK that has just come up with left reel cherries a few times meaning another bonus is almost here.

Take care one and all.

Jeff

[arbycoffee]

Thank you monaghj

For the help

[Lddrizzt]

actually I think the whine is Japanese and it's saying "play me more, play me more!"

[monaghj]

Radio Shacks used to be good here too. They sold lots of parts. Then they thought they could compete with Best Buy and Circuit City with their home spun brands of Realistic, Tandy etc. It turns out they were simply brand spanking over top of techniques and Hitatchi so they stopped spending money in this area and just started retailing the unbranded product. They continued downhill until late where they are on this big add campaign "Got Questions, Radio Shack has answers". Their six dollar an hour sales force has few answers but it brings them closer to yester-year when they did have friendly knowlegable staff. I just heard that they were bought out but I am not sure who by ?

[DiskDevil]

The article reads.....For the 130-Hz low-pass filter, check the intersection of the 130-Hz and 4-ohm columns in Table 2. As you can see, you'll need a 200 pF capacitor for C2 and a 6.8 mH inductor for L2. .......

So much for the theory.....
Basically if you put a 200pf capacitor across the speaker wires the whine goes away.
You will need to do that for each of your speakers.

http://www.web-tronics.com/21cb200.html

Make sure, if you do this...use NON-POLARIZED capacitors or you will damage your speakers. NON-POLARIZED capacitors will NOT have a positive or negative side. They usually have one lead coming from each end.

[logicprobe]

Does the 200pf capacitor trick cause any loss to the rest of the audio response?
Or does that value somehow become the magic "notch filter" value for the frequency of the whine?
If I had a "Squeelin' Sammy" here I'd give it a shot. Since I don't, I guess I have to ask.

[monaghj]

I beg to differ about the polorized capacitor. Across a low resitance 4-16ohm speaker you have no neglegable DC charge n a 200pf capacitor that could cause any damage.

A 9v battery across a speaker will cause it to outwardly pop (or inwardly) which is a trick that speaker installers used to use when they used non-poliarized speaker wires.
If you kept that voltage on for a very long time (longer than a 9v might last) you might have a chance to heat up and burn out the coils.

To put this in perspective a fully charge 200pf capacitor would hold less than 10mv (.001 v) and as soon as its shorted across the speaker it would loose its charge. In the manner we are installing it it won't even get a chance to get charged and hold any kind of voltage.

However all this has made me think that if you install a polarized capacitor in the wrong direction you might not get any kind of noise dampening. Most capacitors have a +/- on them.

To answer logicprobes question, without the inductor you are not going to totally cut out your highs. You could back off from the 200pf to something smaller but your squeel would start coming back.

[DiskDevil]

Does the 200pf capacitor trick cause any loss to the rest of the audio response?
Or does that value somehow become the magic "notch filter" value for the frequency of the whine?
If I had a "Squeelin' Sammy" here I'd give it a shot. Since I don't, I guess I have to ask.

Basicly this capacitor mod creates a threshold that blocks all audible and in-audible sounds below the threshold value. So to answer your first question yes it would effect the speaker response, but only for the lower sound spectrum. If you select the proper capacitor value you would probably not notice anything, but the infamous whine would be gone.

[DiskDevil]

However all this has made me think that if you install a polarized capacitor in the wrong direction you might not get any kind of noise dampening. Most capacitors have a +/- on them.

Bingo!! That is why audio installers use non-polarized capacitors. It will work either way in the circuit, while a polarized capacitor will only work one way.