I guess not all venues have always had grounded plugs. Perhaps Ampeg included the switch for those places that had poor or missing grounds.
Enjoy the benefits of a premium membership!
Upgrade Account
-
TalkBass has been independent since 1998. Add your voice.
Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
Join free Log in
Want zero display ads or expanded classifieds tools? Compare plans.
Amp Guts Photos - Official Thread - Lets see those pics
- Thread starter svtb15
- Start date
I guess not all venues have always had grounded plugs. Perhaps Ampeg included the switch for those places that had poor or missing grounds.
Some companies do still have three position polarity switches even though they have three-conductor power cords. In the first and third position (at the extremes) a capacitor connected to chassis ground at one end, is connected to the hot (often black in North America) or neutral (white) power line wires. In the middle position, the capacitor isn't connected to anything. The middle position is equivalent to an amp that has a three-conductor power cord and no polarity switch. The first and third positions can under some conditions make the amp quieter. See the pic below.
Three-position ground switch like in the modern SVT.
Isn't that noise filter capacitor called the death (suicide) capacitor?
In the old days, yes. The noise filter capacitor could short which could result in a voltage on the chassis. If you are grounded or touch something like a mic that is grounded and you touch your chassis or indirectly by touching your strings, (your strings are grounded through the instrument cable to the chassis) you could get zapped.
Today modern capacitors are used that will not short if they go bad. They are called [Invalid or Expired Link Removed] capacitors. They are designed specifically for line filtering applications like in the pic above. In this case you would use a Y Class or an XY Class capacitor.
Bottom line, you can have a safe polarity switch in an amp and in some cases, using the polarity switch can reduce noise.
Three-position ground switch like in the modern SVT.
Isn't that noise filter capacitor called the death (suicide) capacitor?
In the old days, yes. The noise filter capacitor could short which could result in a voltage on the chassis. If you are grounded or touch something like a mic that is grounded and you touch your chassis or indirectly by touching your strings, (your strings are grounded through the instrument cable to the chassis) you could get zapped.
Today modern capacitors are used that will not short if they go bad. They are called [Invalid or Expired Link Removed] capacitors. They are designed specifically for line filtering applications like in the pic above. In this case you would use a Y Class or an XY Class capacitor.
Bottom line, you can have a safe polarity switch in an amp and in some cases, using the polarity switch can reduce noise.
That capacitor would have a reactance of around 56k Ohms. I'll have to wrap my head around how that can be safe, and how it wouldn't trip a ground fault interrupter. I found a couple of modern amp schematics at the Fender website, and they show a cap from hot to neutral, but not from either line to the chassis.
I modified my image above to remove the value of the capacitor. Sorry for the confusion. It was intended as an example to illustrate the three position polarity switch. Below is what Ampeg uses. Normally the switch is set to the center position.
In the case of the Fender schematic that has a capacitor connected from hot to neutral, you would use an X Class capacitor if you wanted to be safe.
Ampeg polarity switch:
Here are some specs on a Y Class cap from Vishay.
In the case of the Fender schematic that has a capacitor connected from hot to neutral, you would use an X Class capacitor if you wanted to be safe.
Ampeg polarity switch:
Here are some specs on a Y Class cap from Vishay.
And I see that the engineer has spec'ed a "UL" cap.
Thanks Chef! Ya, Hodgy rocked this amp good! Just wish the cabs were done...all I'm waiting on now.
So you're saying they might know what they're doing when it comes to making amps? You don't say...
- Mar 22, 2004
- 13,004
- 4,741
- Disclosures
- I play it all. Whatever works for the gig. Q+
Invalid Link Removed by Avus412Energy, on Flickr
Invalid Link Removed by Avus412Energy, on Flickr
Invalid Link Removed by Avus412Energy, on Flickr
Invalid Link Removed by Avus412Energy, on Flickr
Invalid Link Removed by Avus412Energy, on Flickr
D7K_2083 by Invalid Link Removed, on Flickr
D7K_2080 by Invalid Link Removed, on Flickr
D7K_2077 by Invalid Link Removed, on Flickr
Is the top one the Echolette BS-40?
How does it hold up in a gig situation?
One day I will get one, just for nostalgic reasons...
I run it through 2 high sens. 1x12" cabs. Works well for small to medium gigs. Of course, it depends on the general volume level of your band.
You should definitely get one. Great little amp. There was one on ebay just rescently which went for ~134 Euros.
So you're saying they might know what they're doing when it comes to making amps? You don't say...
Of course they know what they're doing, but best engineering practices have improved over the years. I wouldn't gig an historical amp that had a polarity switch and suicide cap. I don't trust anybody else's gear on stage.
Passinwind
I know nothing.
- Dec 3, 2003
- 23,079
- 46,050
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Mine's not nearly as purdy as yours, but I can't resist. It's my boo-teek 6 knob JFET preamp. (Gain, bass, treble, mid, mid-frequency, and master):
Passinwind
I know nothing.
- Dec 3, 2003
- 23,079
- 46,050
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Mine's not nearly as purdy as yours, but I can't resist. It's my boo-teek 6 knob JFET preamp. (Gain, bass, treble, mid, mid-frequency, and master):
Most impressive!! I love it!
