Holton DC Blocker's impact in my system

[GaryT]

All power transformers vibrate, so a slight hum doesn't necessarily mean there is a problem. But it doesn't hurt to try one of these, since they are a simple device and it is obvious if it works or not. thankfully most sellers would be happy to refund if it doesn't help, particularly if you get one from an established and trusted source like Holton.

[Furutechfan]

On 11/08/2020 at 8:43 PM, Aussieamps said:

Very Old Model

The new Holton DC blocker looks very streamlined inside now. I believe the caps are a different brand and larger in value? I'll let Anthony chime in. 

[andyr]

On 12/08/2020 at 8:31 AM, mbz said:

My starting point would be to use the trusty tektronix CRO. If the Vdc is not detectable by the CRO then I would research "best practices" for measuring low Vdc on mains and consider building/purchasing necessary test equipment

 

I'm interested to know, Mike, how you go about connecting up a CRO to a mains socket.

 

I tried this a couple of weeks ago as I wanted to see whether my mains supply looked as awful as the clipped sine wave that @Ittakuposted a couple of weeks ago.

 

A friend told me simply to put the CRO's signal lead on the Active terminal of a bare plug inserted into a wall socket - NB: with a 0.47uF film cap inserted in series - and the earth lead on the Neutral terminal.

 

So I did this but as soon as the earth lead touched the Neutral ... the RCD tripped back in the distribution box ... and the circuit went off.  And this was before I had switched on the wall socket!

 

So I am at a loss how to look at the mains. 

 

Andy

 

[Telecine]

30 minutes ago, andyr said:

 

I'm interested to know, Mike, how you go about connecting up a CRO to a mains socket.

 

I tried this a couple of weeks ago as I wanted to see whether my mains supply looked as awful as the clipped sine wave that @Ittakuposted a couple of weeks ago.

 

A friend told me simply to put the CRO's signal lead on the Active terminal of a bare plug inserted into a wall socket - NB: with a 0.47uF film cap inserted in series - and the earth lead on the Neutral terminal.

 

So I did this but as soon as the earth lead touched the Neutral ... the RCD tripped back in the distribution box ... and the circuit went off.  And this was before I had switched on the wall socket!

 

So I am at a loss how to look at the mains. 

 

Andy

 

Sounds like you did what is pictured in my avatar. You haven't made it this far in life by poking metal objects in power points, don't start now.

Edited August 15, 2020 by Telecine

[mbz]

16 hours ago, andyr said:

I'm interested to know, Mike, how you go about connecting up a CRO to a mains socket.

Connect probe ground connection to third/earth/GND pin. Use probe to measure active pin. Use either open ended plug or terminated power plug rather than inserting probes into socket.

[andyr]

1 hour ago, mbz said:

Connect probe ground connection to third/earth/GND pin. Use probe to measure active pin. Use either open ended plug or terminated power plug rather than inserting probes into socket.

 

Aah, OK - so I measure across Active & Earth.  Thanks, Mike.

 

Yes, i will use an 'open' plug.

 

Do you think a 0.47uF cap in series with the Active connection does anything?

 

Andy

 

[mbz]

On 12/08/2020 at 6:30 AM, mbz said:

keep in mind 240Vac can be lethal.

The 0.47uf cap is intended for dc blocking, possibly to to limit any hi order harmonics.  The measurement should be done with oscilloscope set to AC coupling which probably connects an internal cap. I'd try without the 0.47uf. Assumes you have a reasonable oscilloscope not some ebay toy (while they do have there place, ok for audio fault finding)

Edited August 15, 2020 by mbz
0.47uf cap

[andyr]

1 hour ago, mbz said:

The 0.47uf cap is intended for dc blocking, possibly to to limit any hi order harmonics.  The measurement should be done with oscilloscope set to AC coupling which probably connects an internal cap. I'd try without the 0.47uf. Assumes you have a reasonable oscilloscope not some ebay toy (while they do have there place, ok for audio fault finding)

 

Thanks, I'll try this later.

 

Andy

 

[mbz]

20 hours ago, andyr said:

and the earth lead on the Neutral terminal.

Never connect earth and Neutral. The earth/GND lead of the oscilloscope will be connected to the chassis and the 3rd pin/protective earth from the power cord. Making the earth wire live (connecting to neutral) also makes the oscilloscopes chassis, buttons etc live (for a few mS?) and a serious operator risk to electric shock. Easiest to think of neutral as the AC return wire and should/must be handled as a live wire.

[Aussieamps]

4 hours ago, mbz said:

The 0.47uf cap is intended for dc blocking, possibly to to limit any hi order harmonics.  The measurement should be done with oscilloscope set to AC coupling which probably connects an internal cap. I'd try without the 0.47uf. Assumes you have a reasonable oscilloscope not some ebay toy (while they do have there place, ok for audio fault finding)

Guys you need to be very careful doing anything like this unless you know exactly what you are doing!

There are a number of things you need to know, CRO amplifier input stages will only handle 300Volts typically on maximum attenuation, Australian AC mains is typically 240VAC its peak voltage is 340VAC. All AC mains measurement using a CRO; should be used with a suitable AC mains isolation transformer. If you do not have a 240vac to 240vac isolation transformer, use a 240vac to 12vac transformer or anything in the so called low voltage range. It is very important to electrically isolate your CRO from the Active and Neutral unless you want to potentially electrify your CRO at mains potential. This is no joke guys! Clearly none of you know what you are doing! Best to leave this kind of thing alone, no body wants anybody dead here, because of doing things out of ignorance !

Using a 0.47uf cap in series just lowers the amount of current that can pass on to the CRO inputs, its simply the capacitive reactance of the 470nf capacitor at 50hz that is protecting you, it does not provide Galvanic isolation.

 

Edited August 16, 2020 by Aussieamps

[mbz]

12 minutes ago, Aussieamps said:

CRO amplifier input stages will only handle 300Volts typically

TEK2215, 2220, 2235

[Aussieamps]

3 minutes ago, mbz said:

TEK2215, 2220, 2235

I think Mike you are missing the point, I will leave it at that!

[andyr]

1 hour ago, Aussieamps said:

Guys you need to be very careful doing anything like this unless you know exactly what you are doing!

There are a number of things you need to know, CRO amplifier input stages will only handle 300Volts typically on maximum attenuation, Australian AC mains is typically 240VAC its peak voltage is 340VAC. All AC mains measurement using a CRO; should be used with a suitable AC mains isolation transformer. If you do not have a 240vac to 240vac isolation transformer, use a 240vac to 12vac transformer or anything in the so called low voltage range. It is very important to electrically isolate your CRO from the Active and Neutral unless you want to potentially electrify your CRO at mains potential. This is no joke guys! Clearly none of you know what you are doing! Best to leave this kind of thing alone, no body wants anybody dead here, because of doing things out of ignorance !

Using a 0.47uf cap in series just lowers the amount of current that can pass on to the CRO inputs, its simply the capacitive reactance of the 470nf capacitor at 50hz that is protecting you, it does not provide Galvanic isolation.

 

Appreciate your post, Anthony - I won't try it.

 

But I'm interested to know what tool/meter I need to buy in order to look at my mains "sine wave".

 

@Ittakuposted this pic of his mains supply a couple of weeks ago (the input screen of his power regenerator) ... and it has got me worried: 

 

 

 

 

Andy

 

[Aussieamps]

37 minutes ago, andyr said:

 

Appreciate your post, Anthony - I won't try it.

 

But I'm interested to know what tool/meter I need to buy in order to look at my mains "sine wave".

 

@Ittakuposted this pic of his mains supply a couple of weeks ago (the input screen of his power regenerator) ... and it has got me worried: 

 

 

 

 

Andy

 

Hi Andy

 

if you already have a CRO then you can use almost any transformer you have on hand to do a basic observation of the ac mains. As i mentioned connect your CRO probe to the floating secondary winding and primary winding to ac Mains.

the CRO probe ground lead gets connected to the other secondary winding wire. 
this ensures not only low voltage to the CRO but correct isolation for total safety. I hope this helps? I might do a quick diagram so anyone can visualise it.

 

[Guest rmpfyf]

1 hour ago, andyr said:

 

Appreciate your post, Anthony - I won't try it.

 

But I'm interested to know what tool/meter I need to buy in order to look at my mains "sine wave".

 

@Ittakuposted this pic of his mains supply a couple of weeks ago (the input screen of his power regenerator) ... and it has got me worried: 

 

If you are really super keen and when next your sparkie visits, install a power analyser. 

 

These are usually stupidly expensive when new though usually come out of power stations and the like at the sub-$1k mark .

 

They will not give you 1HGz sampling though they will compute harmonics and the rest of it to a very accurate level. What's more they're permanent - simply log in when you need to. 

 

Check out the Schneider ION range from the 7650 up.

[Aussieamps]

38 minutes ago, Aussieamps said:

Hi Andy

 

if you already have a CRO then you can use almost any transformer you have on hand to do a basic observation of the ac mains. As i mentioned connect your CRO probe to the floating secondary winding and primary winding to ac Mains.

the CRO probe ground lead gets connected to the other secondary winding wire. 
this ensures not only low voltage to the CRO but correct isolation for total safety. I hope this helps? I might do a quick diagram so anyone can visualise it.

 

Here is a diagram I got off the net for a 1:1 ratio isolation transformer when connecting a CRO input, use the same principle using a transformer isolation with lower AC voltages. 

There are other methods of connecting the CRO to meaure ac mains as well, one other method is to connect or power the CRO from the 1 to 1 ratio isolation transformer secondary

and connect the CRO probe directly to AC mains, but again you need to know excatly what you are doing.

 

Edited August 16, 2020 by Aussieamps

[stereo coffee]

On 12/08/2020 at 10:11 AM, Steffen said:

I’m curious too. This is not a straight-forward thing to measure, due to the huge potential difference. Being DC, it also cannot be characterised/measured easily as distortion. The closest I’ve got so far was using the Average function of my oscilloscope, but likely without any semblance of precision. Given that the DC component is supposedly around a couple hundred millivolts, this goes hard up against the dynamic range of a typical 8-bit sampling oscilloscope.

Usual cautions are NEVER to use a conventional oscilloscope to measure mains directly, this is because the scopes earthing probe is earthed exiting via the scopes IEC earth potential. There are inductive probes and scopes that can do this that will scale the higher potential appropriately , but direct measurement should never be attempted with a standard scope, as it can easily result in a short of active via the earthed probe to safety earth.  

 

Rather it is quite safe to use a transformers secondary fused at low voltage like 12v AC to assess the incoming mains.  

[Snoopy8]

How did this thread get so far OT???? I thought we were discussing the Holton DC Blocker but it seems to have evolved to an electronics school lesson?   

[andyr]

2 hours ago, Aussieamps said:

Hi Andy

 

if you already have a CRO then you can use almost any transformer you have on hand to do a basic observation of the ac mains. As i mentioned connect your CRO probe to the floating secondary winding and primary winding to ac Mains.

 

 

Thanks, Anthony - worked like a charm! 

 

I had a 2x 15v secondaries toroid lying around - so I connected up the primary winding to a mains plug ... and put my CRO leads across one of the secondaries (taking care not to short the other secondary winding).

 

Hell - my mains looks even worse than @Ittaku's!    At least his was symmetric - mine:

• was also clipped at the top and bottom ... except that my clip-line was not horizontal - it slopes down to the right! 
• and the rest of the supposed 'sine' wave wasn't smooth ... but was a wavering line. 

 

Thanks a lot, Uncle Jeff!    (I am told, when he sold the SEC to private interests, Jeff Kennett relaxed the power quality specs that the SEC had followed, so the new owners could make more money by driving their street transformers closer to the max.)

 

Andy

 

Edited August 16, 2020 by andyr

[Aussieamps]

1 hour ago, Snoopy8 said:

How did this thread get so far OT???? I thought we were discussing the Holton DC Blocker but it seems to have evolved to an electronics school lesson?   

yes best to get back to the thread,

[Guest rmpfyf]

1 hour ago, andyr said:

Thanks a lot, Uncle Jeff!    (I am told, when he sold the SEC to private interests, Jeff Kennett relaxed the power quality specs that the SEC had followed, so the new owners could make more money by driving their street transformers closer to the max.)

 

OT but you were told wrong. Happy to discuss offline.

[Cardiiiii]

I have little to no electrical knowledge, but, if you had a seperate circuit that was powered by a Tesla Power Wall or similar battery, would that result in a perfect sine wave?

[sir sanders zingmore]

3 hours ago, andyr said:

Hell - my mains looks even worse than @Ittaku's!    At least his was symmetric - mine:

• was also clipped at the top and bottom ... except that my clip-line was not horizontal - it slopes down to the right! 
• and the rest of the supposed 'sine' wave wasn't smooth ... but was a wavering line. 

 

I know it probably looks ugly but is there any reason to suggest that this actually affects your sound quality?

[Telecine]

1 minute ago, sir sanders zingmore said:

I know it probably looks ugly but is there any reason to suggest that this actually affects your sound quality?

Not if you have equipment that has a well designed power supply.

[sir sanders zingmore]

5 minutes ago, Telecine said:

Not if you have equipment that has a well designed power supply.

I agree.

 

Back on topic, my active woofers had a hum coming from their amps. This was almost completely removed via Holton DC blockers (there is some residual - not sure why)