DIY Super Simple Preamp

[renga435]

Finally done with my SSP. Had few issues got support from Sachin during the setup. Initial impression - The sound quality improved a lot.Yet to do detailed audition.

Thanks to Sachin for providing the kit and supporting me during the setup. Also thanks to Murali sir for boosting my confidence in doing this setup and guiding me to integrate with Norge 2060.Currently I have kept the SSP separate. Plannning to integrate with 2060 soon.

 

[duncan]

Guys!

Finally got my SSP fully built and running. Sound quality "was" awesome (with zero noise/hum even at full volume using the norge as the power-amp) until I added the source selector. It kind of gives an irritatingly awful hum at a very high note. For the Source Selector, I used 6 of the pins by adjusting the silver plate but I use just four sources as described below:

Position1 : Off
Position2 : AUX
Position3 : PC/Pi
Position4 : DVD
Position5 : TV
Position6 : Off

Now although I may select off position on position 1 or 6, the SSP remains on outputting signal.

If I remove all sources now, and move the Selector from 1 - 6 positions( of which, now non are connected to any source), on positions 1 & 6 (off positions- not connected to any relay) there is no noise; but on the relay connected channels, theres a lot of noise.

Guessing the relays are causing this. But need inputs from you guys. FM Sachin too tried a lot to diagnose the problem...

Below are some pics.

Thanks... Hoping to sort this out early.

Oh one more thing, without the source selector sound is crisp and with no input there is zero noise even at full volume.

 

[omishra]

What is voltage supplied to source selector?
Also where that shield of wires connected? If not used then can connect it to one end, at RCA and at SSP end. Also report back with connection after source and playing music too. I am suspecting open input.
Some more pics of PS, SSP and volume control expected.

 

[duncan]

Dear Sir

SS supply voltage is 18v. Shield already connected to one end at RCA and for SSP directly to the -ve input.

While playing music hum is nearly inaudible but during the gap when tracks are changed its clearly audible only on higher volumes beyond 50%.

 

[sarith]

With all due respect, I would like to point out that the soldering is bad. I guess there is a need to change the 2 core shield to a better one. It's also better to use good wires to connect volume pot and selector. Use shielded wire if possible to source selector, vol pot and both input and output (rca) connectors. Rather than using locally available thin ribbon wire, it's better to use little more thick wire (better gauge) for dc connection

 

[faizal]

1)connect the shield to ground
2)make sure that ground is common for source selector and SSP
3)supply wire for Source selector is running down side of SSP,change the position of supply wire as it may induce some noise
4)shift the output wires of SSP from the vicinity of transformer
5)reduce the length of ribbon wire(shielded wire is best for low magnitude signal paths) to volume control
6)there is some chance of shortening between shield and core,so check the continuity

the above check points are as per priority,first three are very very important
I think the above steps of troubleshooting can rectify u r problem with SSP n Source selector

 

[omishra]

I can see there is ground loop as chassis is not isolated from RCA metal shell. Thus all grounds have connection within metal chassis. Same time ground wires are running separately too. Try to connect signal ground separately but isolated from chassis.
See second picture how I isolated ground from source RCA to b1 buffer(your case is SSP board).
http://www.hifivision.com/diy/21036-pass-b1-153.html#post573666

Metal case need to connected earth ground, then connect ground isolator between PS ground and mains ground. Wait I will post picture.

 

[duncan]

With all due respect, I would like to point out that the soldering is bad. I guess there is a need to change the 2 core shield to a better one. It's also better to use good wires to connect volume pot and selector. Use shielded wire if possible to source selector, vol pot and both input and output (rca) connectors. Rather than using locally available thin ribbon wire, it's better to use little more thick wire (better gauge) for dc connection

Hi Sarith, I'm a total newbie in electronics and this was the first time i actually held the soldering iron in my hand.... LOL my hands were actually shaking...:lol:

Thanks anyways... will take help from a friend to rewire...

 

[duncan]

1)connect the shield to ground
2)make sure that ground is common for source selector and SSP
3)supply wire for Source selector is running down side of SSP,change the position of supply wire as it may induce some noise
4)shift the output wires of SSP from the vicinity of transformer
5)reduce the length of ribbon wire(shielded wire is best for low magnitude signal paths) to volume control
6)there is some chance of shortening between shield and core,so check the continuity

the above check points are as per priority,first three are very very important
I think the above steps of troubleshooting can rectify u r problem with SSP n Source selector

Thanks Faizal. Will try implementing your suggestions. Just that i'm a newbie to this field and will take time to get neat and understand different factors...

 

[duncan]

I can see there is ground loop as chassis is not isolated from RCA metal shell. Thus all grounds have connection within metal chassis. Same time ground wires are running separately too. Try to connect signal ground separately but isolated from chassis.

Sir, How do I isolate? can you tell me the description so that i can ask a local electrical store if they have it. or can i use simple insulation tape? I know it will make it untidy. HELP!!!

 

[sarith]

Sir, How do I isolate? can you tell me the description so that i can ask a local electrical store if they have it. or can i use simple insulation tape? I know it will make it untidy. HELP!!!

The question is shot towards omishra but I'm taking the liberty to comment on this matter. This image is borrowed from the link posted by omishra in his post #351 in this very thread.

Look closely and you can see that the ground connector of the rca sockets are isolated using black and red coloured 'washers'

http://imagizer.imageshack.us/a/img35/9194/gjmh.jpg

 

[reubensm]

Whenever I work with shielded cabling, I always ensure that the shield is grounded at both ends, see that you've gounded only at one end. Also I never leave the cabinet to take care of grounding. I run separate ground wires wherever required (even seperate grounds for the input and output socket wiring).

Are you able to recognize what kind of hum it is? Does it sound like a deep hum (what you hear when some fans or transformers) or is it a kind of shrill hum. When you touch earthing, etc, is there any drop or increase?

If the hum is deep and from the powersupply, you may require additional filtering.

 

[duncan]

Whenever I work with shielded cabling, I always ensure that the shield is grounded at both ends, see that you've gounded only at one end. Also I never leave the cabinet to take care of grounding. I run separate ground wires wherever required (even seperate grounds for the input and output socket wiring).

Are you able to recognize what kind of hum it is? Does it sound like a deep hum (what you hear when some fans or transformers) or is it a kind of shrill hum. When you touch earthing, etc, is there any drop or increase?

If the hum is deep and from the powersupply, you may require additional filtering.

The hum is like a high freq mosquito repellent...

 

[sachu888]

I agree with Om. It seems to be a ground loop.

Regards
Sachin

 

[omishra]

Look closely and you can see that the ground connector of the rca sockets are isolated using black and red coloured 'washers'

http://imagizer.imageshack.us/a/img35/9194/gjmh.jpg

Those are not simple washers! these come along RCA connectors and has some edge which keeps RCA metal body in centre of hole separated from chassis.

 

[sarith]

Those are not simple washers! these come along RCA connectors and has some edge which keeps RCA metal body in centre of hole separated from chassis.

I know those are not simple washers and comes along with RCA connectors. I normally use them. But Duncan said he is a newbie when it comes to diy. That's why I mentioned the word in inverted commas so as to make him understand. Been doing electronics from the late 90's

 

[omishra]

I know those are not simple washers and comes along with RCA connectors. I normally use them. But Duncan said he is a newbie when it comes to diy. That's why I mentioned the word in inverted commas so as to make him understand. Been doing electronics from the late 90's

I mentioned that for OP because he may buy some washers and use pair of it for each RCA. Then still threads of RCA body can contact chassis. no objection for your explanation. Cheers.

 

[duncan]

Those are not simple washers! these come along RCA connectors and has some edge which keeps RCA metal body in centre of hole separated from chassis.

Sir, Can you please suggest what are these called? and if any Indian online DIY site offers them for sale....

 

[omishra]

It does not come separately.
Either you make one yourself. Buy proper mica washers packet of 100 from hardware stores with 6.5mm hole diameter. Its used by mixer repair men to fix gap of blade shaft. Use one from either side and fill some Teflon tape on threads to avoid contact with metal chassis.

You have to buy good RCA connectors if you feel okay.
Its on kiransales.com -> 78-80Rs each.
So you have to drop email to "[email protected]" and ask about below models -

NYS367-x
where x has following values - : 0-Black, 2-Red, 4-Yellow, 5-Green, 6-Blue, 9-White


PS: I don't have any affiliation with this person.

 

[duncan]

OK Guys, I think I have a serious problem here.

Norge amp owners may know that the Norge amp has no earthing (just a two pin plug); that's point no 1

Point no 2 is that, if I hold a tester to the -ve input of the Norge that's connected or not connected to the SSP, it flashes brightly; and when I turn the amp off it gets dim and goes off.

Now since I can only listen to the SSP via the Norge amp, is it that the hum is present because of this?