capacitor polarity in a phono stage project

[giltas]

Hi guys, I don't have much knowledge about electronics so I got kinda confused in a few things in this project I'm working on.
ok so the project is a phono stage I'm making for my turntable. It's a project found here: http://www.tnt-audio.com/clinica/solidphono_e.html

I uploaded the schematics of the PSU and Phono preamp that were given.

anyway I would like to know what would be the right way to connect the electrolytic capacitors because it is not shown in the schematics (the symbols are like of film capacitors).

Also, I'm a bit confused with the 0v shown in the PSU schematic, as there are only two voltage cables coming out from the toroidal transformer (well, two for each channel). do I need to connect anything there? should there be a connection between the two different boards grounding (the project is made of two different units- each in it's own enclosure)

 

[Arouse1973]

Electrolytic capacitor as you know have to be connected the correct way. They normally have a printed white or grey stripe on one side although SMD devices have a black bar it's the same thing. This stripe connect to the lower voltage. Another give away is for a new capacitor there will be one long leg, this leg connects to the positive potential of the circuit.

The 0V point is the centre of where the two windings of the transformer join. Everything on the schematic that has this symbol should be connect there. The other power rails are + and - voltages

Adam

 

[giltas]

ok so I take it that in the PSU schematic, the electrolytic capacitors in the upper part should be connected with the longer pin to the upper line and the shorter pin to the ground? (and in the lower part of the schematic it should be the opposite) am I right?

about the 0v- do you mean that the ground should be connected to the body of the transformer? that heavy ring of wire? it's wrapped in plastic, should I take it off?

 

[(*steve*)]

The power supply you have there requires a transformer with a centre tap -- this means a secondary with 3 wires. If yours only has 2, you need to get another transformer as the one you have is wrong.

What you need is a 36VCT, or a 18-0-18V transformer (both mean the same thing).

It is possible that you have two windings on your transformer (4 secondary wires, 2 for each winding). If these are both 18V windings, you can connect these in series to get 36VCT. However you need to connect them the right way or you'll get 0V (but that won't hurt anything).

I also think you can pretty much ignore all of what that guy says about one power supply sounding better than the other. When he says he maybe doesn't trust his ears, it's not his ears but his brain that is fooled.

 

[giltas]

Yeah I believe the difference between the two is insignificant but I don't care doing the second one just in case (already got the components anyway). Are you sure there is no way to connect the transformer I have? It costed pretty much and would be a bummer to get another one...
As you said it does have 4 secondary wires coming out- 2 sets of 2 18v. I figured that I was probably supposed to connect each couple to a different channel (left right channels).

 

[(*steve*)]

As you said it does have 4 secondary wires coming out- 2 sets of 2 18v. I figured that I was probably supposed to connect each couple to a different channel (left right channels).

It's simple.

1) use your multimeter to determine which wires are pairs (you may not need to do this)

2) connect one wire from each pair together.

3) apply power to the transformer (careful!) and measure the voltage across the remaining pair of wires.

4) if you measure something > 30V -- congratulations you have wired the transformer up as 36V centre tapped. The joined wires are the centre tap.

5) if you measure < 18V then you have one pair around the wrong way. Undo the join and swap one wire for it's opposite pair. Repeat step (3) and you should have success.

Note: there are several risks:

A) electrocuting yourself on the mains
B) connecting the mains to the secondary and generating a very high voltage on the primary
C) shorting a winding

To prevent (C) measure the resistance between any pair of wires you join in step (2) or (5) and make sure that there is no connection between them before you join them.

 

[giltas]

ok I tried it. I connected one wire of one pair to another wire from the second pair. measuring the voltage across the other two wires gave me around 41-42v. it makes sense since the transformer actually gives out about 20v instead of 18.
would this solution work, however, for two channels? can I split each wire so that it connects parallel to both channels?

 

[(*steve*)]

You only need a single power supply. It provides power to both channels.

 

[giltas]

you mean that I only need to solder the PSU schematic once?
I realized that the phono preamp schematic has to be doubled cause it has only one OUT connection (so I soldered it twice on the same vero)

 

[(*steve*)]

you mean that I only need to solder the PSU schematic once?

Without looking at the project details, I would say yes. It is a little unusual (although not unheard of) to have separate power supplies for each channel. In general it's cheaper to make one large power supply instead of two smaller ones.

 

[(*steve*)]

I have to warn you, every time I read that page I cringe at something they say.

Take this for example:

[FONT=Arial, Helvetica]There is no mains switch: in facts power supply takes quite a long time to get stable and sound continues improving for a long time after switching it on: so it is far better to leave it always on.

Complete male bovine excrement.
[/FONT]

 

[KrisBlueNZ]

I agree Steve. This is some of the worst audiophile wank I've ever read. I was tempted to ask him for reports from the double blind testing sessions he's done to confirm that it's not just all in his head.

I'm subscribed to a couple of Yahoo groups for old English "hi-fi" toob amplifiers - Leak and Radford - because my father was heavily into that stuff. I asked that question - quite diplomatically, I thought, but quite explicitly too - on the Leak mailing list:

Hi all, (...)

In audiophile circles, I often hear opinions like "Mullard valves sound the best" (recently), or that a particular brand or series of capacitor sounds better than a different one.

I've been wondering for a long time whether anyone making these claims has done any controlled tests to validate these judgements. For example, it would only take a couple of friends and a few hours' listening time to do a fairly thorough double blind test to compare, say, two different brands of valves that you think sound significantly different.

I'm aware that complicated psychological factors are at work when making judgements based on listening experiences. If the listener knows what component they're listening to on each listening, their subjective experience cannot fail to be affected by this knowledge, so clearly non-blind tests are the least reliable; single-blind tests are better, but double-blind is currently the best way to test for what you think you're testing for.

I would be very interested to hear from anyone who has taken a disciplined approach to listening tests.

The only response I got was from a guy in Aussie offering to lend me a selection of different toob brands so I could confirm the differences for myself!

The lack of responses certainly doesn't disprove my suspicion that these people just have overactive imaginations, and that their ears are in fact not golden, but brass plated.

 

[davenn]

and add OFC speaker cables to the list of woo woo improvements

Dave

 

[giltas]

I also believe that such tiny difference as different capacitor brands doesn't make an audible difference. It just seemed to me (from recommendations in posts) that this specific project will get me a decent preamp for my turntable and that was enough for me.

 

[(*steve*)]

I also believe that such tiny difference as different capacitor brands doesn't make an audible difference. It just seemed to me (from recommendations in posts) that this specific project will get me a decent preamp for my turntable and that was enough for me.

Different brands actually do make a difference in some circumstances, and different types of capacitor certainly do. Go with the same type of capacitor as recommended and purchase from a reputable source (mouser, digikey, RS (Radio Spares, NOT radio shack), etc).

Just don't make us read any more of that page than we have to, OK?

 

[KrisBlueNZ]

Different brands actually do make a difference in some circumstances, and different types of capacitor certainly do

Steve, do you know of any properly tested cases where these differences were detectable by a listener, or are they only measurable?

 

[(*steve*)]

Steve, do you know of any properly tested cases where these differences were detectable by a listener, or are they only measurable?

Not audible differences, but poor quality electrolytics failing or having the wrong capacitance/voltage.

The obvious thing is the premature failure of low ESR caps (or capacitors in a high ripple-current environment). But there are also images going around of large metal can capacitors being filled with... a much smaller capacitor and something to make them feel heavy.

The important thing is to get quality parts where substitutions of fakes is less likely.

 

[giltas]

hey guys, so I completed the two units, PSU and Phono stage.
PSU seems to be alright, gives out the requested voltage. However, once I connect it to the phono circuit the output voltage of the PSU drops to 1v. I tried connecting the turntable to the amp through the project but couldn't hear anything. any ideas?

 

[BobK]

Many years ago, Popular Electronics tested to see if audiphiles could tell the difference between their beloved tube amplifiers and a good solid state one. Sure enough they could tell the difference and they all picked the tube one as sounding better. Then they (PE) analyzed the outputs of the two amps. The modified the solid state amp to have the same amount of 60Hz hum and the tube amp and added high frequency rolloff to match the output transformer of the tube amp. After that the audiophiles could not tell the difference in a blind test.

Bob

 

[BobK]

hey guys, so I completed the two units, PSU and Phono stage.
PSU seems to be alright, gives out the requested voltage. However, once I connect it to the phono circuit the output voltage of the PSU drops to 1v. I tried connecting the turntable to the amp through the project but couldn't hear anything. any ideas?

You have a short. You may or may not have damaged some of your components.

Bob