DC Blocker

[Reeltarded]

I swear to God if that is a a Pokemon thing I am never coming back.

[Cathode Ray]

I just want a kikisui pcm4000m

Who doesn't ?

[WhopperPlate]

I swear to God if that is a a Pokemon thing I am never coming back.

If I get that one I will have caught them all
….except for that tone dragon …chase

[R.G.]

Looking for a schematic for a DC Blocker - a device that will clean any DC and noise from the mains coming into an amp.

Want to build something in a small enclosure that I can plug into the wall outlet, then plug amp into the DC Blocker.

There are two and only two DC blockers that come to mind - a series capacitor or an isolation transformer.
A capacitor is the obvious choice for blocking DC, as that's fundamentally what it does. The problem with caps is that they have an ac impedance that reduces the effective AC line voltage. The impedance of a cap is Xc = 1/ (2*pi*F*C). The full AC current of your amp's power supply flows through the series cap, so the capacitance need to be big. For particulars, you'd probably prefer that the line voltage be dropped less than about 5% by the cap. If your amp pulls 3A, 5% of 120V is 6Vac, so the impedance of the cap needs to be less than
Xc = 6Vac/3A = 2 ohms. So working backwards C = 1/ (2*pi*F*Xc) = 1/ (6.28*60*2) = 0.00133F. That's 1300uF.

The voltage rating is problematical. Ideally it would be more than the peak value of the AC line, about 180Vdc. It ought to be rated for continuous current duty - that is, a film type motor run cap. The capacitor gets to being a problem if it's really doing its job.
An isolation transformer is simpler. An E-I lamination isolator can withstand minor DC offsets pretty well, although more than 10V or so gets the isolation trannie in trouble too.

Goal is to quiet down hiss/hum when running high gain.

Just curious - why do you think DC offsets on the AC line cause hiss? Hum I understand.

[Cathode Ray]

Just curious - why do you think DC offsets on the AC line cause hiss? Hum I understand.

As I said earlier in this thread, an amp builder in Germany posted a thread on another forum, and pictured a new amp he is selling.

In the photo was an AudioLabs DC Blocker. Never seen one, so I asked him what is was, what it did. The answer was a cryptic, "It makes the amp sound better."

Started looking around and located a schematic and some hi-res gutshot photos of the DC Blocker. Tried asking this guy some questions about what I had come up with, and his response was, "Never use polarized electrolytic capacitor on AC line!! That's a bomb !"

Showed him a gut-shot image of the AudioLabs DC Blocker, with a couple of polarized electrolytic capacitors inside it.. and he goes quiet.

-

I think Sluckey is correct about saying the device I need is a line filter, rather than DC Blocker.. but this all raises a question; Since I use a variable autotransformer (variac) between my amp and the wall outlet, wouldn't that keep any DC (that may or may not be on the mains) from ever reaching the amp ?

In your description, wouldn't the variac (being a transformer) act as an isolation transformer - and therefore, a DC blocker ?

[Reeltarded]

Variac is not an isolation device. You can probe your variac and find DC.

Also, the thing RG asks is to think about. This won't balance anything or remove hiss, only the hum that should be nil or nearly nil audibly when wide open.

[Cathode Ray]

Variac is not an isolation device. You can probe your variac and find DC.

Thanks RT !

Just getting a lot of answers saying DC cannot pass thru a transformer.

It finally clicked to ask about my variac.

[Reeltarded]

The IEC line filters are a good thing to use. I have a few and those amps maybe sing marginally better when I bend strings insanely.

[Cathode Ray]

The IEC line filters are a good thing to use. I have a few and those amps maybe sing marginally better when I bend strings insanely.

Since the DC Blocker circuit adds up to about $50 in parts, I will probably build it anyway and see what (if anything) it does for my rig.

Already ordered a power entry module with RFI filter for this amp.

[sluckey]

...wouldn't the variac (being a transformer) act as an isolation transformer - and therefore, a DC blocker ?

Most variacs are an autotransformer and do not provide any isolation, therefore no DC blocking. A few variacs are isolated types (separate primary and secondary windings) and do provide isolation. They will be labeled as isolated. If your variac does not say isolated, then it probably is not isolated. Easy to check. Use your ohm meter and check for continuity from the hot wire input to the hot wire output. Continuity means it's not isolated.

[Cathode Ray]

...wouldn't the variac (being a transformer) act as an isolation transformer - and therefore, a DC blocker ?

Most variacs are an autotransformer and do not provide any isolation, therefore no DC blocking. A few variacs are isolated types (separate primary and secondary windings) and do provide isolation. They will be labeled as isolated. If your variac does not say isolated, then it probably is not isolated. Easy to check. Use your ohm meter and check for continuity from the hot wire input to the hot wire output. Continuity means it's not isolated.

Using a Tenma 72-110

Will check, but I don't think it's isolated based on what I've read.

[sluckey]

Your Tenma 72-110 variac is an autotransformer. No isolation.

[gktamps]

Since the DC Blocker circuit adds up to about $50 in parts, I will probably build it anyway and see what (if anything) it does for my rig.

Yikes! Using the board I showed earlier, cost is one bridge rectifier and two caps, plus the board and terminal blocks. Cheap. I'll sell you a board for a few bucks.

Read more: https://sound-au.com/articles/xfmr-dc.htm
and a ton of other articles/reviews online.

Again, these tend to be used with toroidal transformers because large ones tend to be affected by DC offset.

[Cathode Ray]

Yikes! Using the board I showed earlier, cost is one bridge rectifier and two caps, plus the board and terminal blocks. Cheap. I'll sell you a board for a few bucks.

Read more: https://sound-au.com/articles/xfmr-dc.htm
and a ton of other articles/reviews online.

Again, these tend to be used with toroidal transformers because large ones tend to be affected by DC offset.

pm sent.

[Reeltarded]

The IEC line filters are a good thing to use. I have a few and those amps maybe sing marginally better when I bend strings insanely.

Since the DC Blocker circuit adds up to about $50 in parts, I will probably build it anyway and see what (if anything) it does for my rig.

Already ordered a power entry module with RFI filter for this amp.

I have bought them on ebay in lots for about 3-5 dollars each with switches and wired. I will pull one out and take a pic later.