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Brit01 11th August 2008 02:35 AM

What type of Relay for a power amp? Electro-mechanical?
2 Attachment(s)
I have purchased a power amp (Carver TFM-55) and it has been modified to some extent.

It has a faint hiss coming through the tweeters when gain is set at max with no source signal.

Now there are 2 relays that have been added at some point in it's 15 year history.


I see they are electro-mechanical relays. I read that these can be slow but they are suitable for high loads. (I'm not too knowledgeable about these).
photo attached.

Could these be the source of the hissing? Also are these the right kind of relays for this kind of equipment? Do I need to change them?

Look forward to your advice.


east electronics 11th August 2008 10:38 AM

you can
make a search for solid state relay if you want

AndrewT 11th August 2008 11:02 AM

Hi Brit,
when you disconnected the source did you insert a zero ohm (shorting) RCA plug into the amplifier input?

If not, then the hiss is probably due to the noise being generated by the high value of grounding resistor fitted to the input. This resistor sets Zin and is often in the range 20k to 100k. Rs should be less than 1k and preferably less than 100r. Shorting the input sets Rs=0r0 and shows best noise performance of the amplifier.
If the shorted input condition still hisses, it could be a high noise design or could be due to deterioration in components due to age and/or abuse.

Brit01 11th August 2008 01:08 PM


insert a zero ohm (shorting) RCA plug into the amplifier input
I did not do this. Is this an RCA plug which fits just onto the positive input or bridges the 2? I've never seen one of these before. Might be difficult to find here. What does it look like?


make a search for solid state relay if you want
Would a SS relay have any advantages over the current mechanical one?

ALSO: the hissing is amplified when I connect the pre amp CT-3. I had all the contacts cleaned and interconnect cable changed. The new cable did reduce the hissing somewhat.


AndrewT 11th August 2008 01:32 PM

build your own test RCA plug.
Short the input to ground with a very short copper link wire.

You can also make up non zero ohm input test plugs to mimic other source impedances. Buy some 1% metal film >=250mW resistors and solder them in.
100r, 1k0, 10k0 for starters.

Brit01 11th August 2008 02:14 PM

Hi AndreT,

Thks for the tip. Above are some links. Something along those lines??

Using the resistors between the input and ground.
I could use them to plug all of the inputs on the pre that are not in use? Is this the idea to help reduce unwanted noise and to investigate where the hiss is coming from?


east electronics 11th August 2008 02:27 PM

please remove
my answer that involves solid state relays to audio was just a teaser .....a joke to a rookie .....

there is no chance you use solid state relays in audio always will be electromechanical ....and except these types of relays there is no other available

also i dont see that relays will produce and hiss, you have to look somewere else

Brit01 11th August 2008 02:39 PM


it was just a teaser .....a joke to a rookie .....
Lol. Yes you've got a rookie on the thread. You gotta learn start somewhere:cool:


east electronics 11th August 2008 02:46 PM

please no hard feelings
it was mostly a joke

been there also ....nobody had good teachers about that you have to find out on your own ....talent ,luck, skills is involved ....also nobody was borned with that all of us has been a rookie sometimes

you are in the right place though experts are here

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