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PostPosted: 20 Apr 2011, 16:36 
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Forgot to post a link :blush:

http://geek.scorpiorising.ca/GeeK_ZonE/ ... pic=3647.0

The amp pics are gone (for now), but the schematic is still there. I think it costed less than $200 and I had to buy EVERYTHING.

Cheers!

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PostPosted: 20 Apr 2011, 16:53 
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Hi Cheap for sure, I just hope the amp wasn't line powered with the chassis and signal grounds attached to the mains. I know it was a common practice in days gone by, but I really hate to hear of diyers fried by their projects. :hot:

Good listening
Bruce

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PostPosted: 20 Apr 2011, 22:20 
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Ugh, no, I learned my lesson on that.

Three acceptable ways IMO to safely link/isolate the two:

- Ground wire to chassis and how I do the noise bleed is a 100R/2W Metal Oxide (or carbon comp) between signal ground and chassis.
- Another common one is a pair of 6A Si diodes "chasing each other" and bridged with a 100n cap between signal and chassis ground.
- Third is a 100n cap in series with a 51 ohm resistor between the grounds.

I'd be happy to learn another if you have one :-)

Cheers!

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* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
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PostPosted: 21 Apr 2011, 09:16 
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Hi.

Caution should always be taken for any tube projects where HV is involved. Period. If you would not wire B+ to the chasses, how would you expect you would wire the AC live line to the chassis??

Geek wrote:
I'd be happy to learn another if you have one


However you isolate the earthed chassis from the signal reference ground of the amp, make sure the power cord gets polarized plug. So there will be no chance of plugging live wire to the chassis by mistake! I always do so with my tube projects.

Of course, you can always add an isolation line tranformer (110V:110V rated 100vA) for peace of mind in case yr power amp does not get an power transformer.

c-J

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PostPosted: 21 Apr 2011, 18:14 
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I always isolate.... and use a 3-wire IEC :)

Cheers!

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* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
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PostPosted: 26 Apr 2011, 09:42 
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Hi.
Geek wrote:
use a 3-wire IEC

Yes, 3-wire IEC is safe. BUT, repeat but, don't put 3-wire powering to every components in the same rig to avoid ground looping. Make sure only use one single 3-wire IEC plug for one single component, & all the other components only use 2-pin polarized power plugs.

Since the power amp consumes largest power. I use 3-wire IEC system only for my power amp. All other components, from phonostages/linestages, TT, cassette tape deck , CD-audio player, DVD-audio player use 2-pin polarized plugs to eliminate ground loops.

Even having done so, check out each component's grounding to ensure no grounding wiring reversed inside each components by reversing the polarity of the 2-pin power plug to ensure there is no ground loop humming with volume crank up to maximum.

This is how I tested all the components in my rig to avoid ground loop humming considering I play vinyl nearly all the time. I tried my best as not to allow any ground loop hum contaminating the music even with volume control set to maximum.

Yea, nothing comes easy. I'd take nothing for granted.

c-J

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PostPosted: 26 Apr 2011, 16:27 
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Hi

I'm interested in very cheap construction too - partly to save money, partly as an interesting engineering exercise. Some nice ideas here!

One method I liked to get HT and heater voltage from regular transformers is to wire two back to back. If you have a 6-0-6 winding you can also step up the HT if you need too to 2x supply voltage. I'm thinking about a 6n6p based tube amp for a low power triode amp, maybe 2W or so. It would be a 2-tuber though, maybe a 6n2p srpp driving the 6n6p srpp output into another 6V transformer (as suggested above), with the NFB loop going from the 6n6p anode to the unbypassed 6n2p cathode. So 4 small 6V toroids, + 4 cheap tubes and a few bits.

May not be the cheapest but it should be fairly cheap to build.


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PostPosted: 26 Apr 2011, 17:16 
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cheap-Jack wrote:
Hi.
Geek wrote:
use a 3-wire IEC

Yes, 3-wire IEC is safe. BUT, repeat but, don't put 3-wire powering to every components in the same rig to avoid ground looping. Make sure only use one single 3-wire IEC plug for one single component, & all the other components only use 2-pin polarized power plugs.


OK, I see what you mean now.

I'm going to have to test this at Audiofest (there's some real scary wiring there.... if we're gonna get hum and dropouts... :eek: )


Quote:
Since the power amp consumes largest power. I use 3-wire IEC system only for my power amp. All other components, from phonostages/linestages, TT, cassette tape deck , CD-audio player, DVD-audio player use 2-pin polarized plugs to eliminate ground loops.


I don't think I have 3-wires on anything else at the moment other than power amp and phono pre..... preamp is powered by a wallwart, phono is 3-wire, but the 100R method between signal and chassis ground keeps it quiet. I've tested 3-wire preamps upon repair, but my house is pretty quiet for loop currents.


Quote:
Even having done so, check out each component's grounding to ensure no grounding wiring reversed inside each components by reversing the polarity of the 2-pin power plug to ensure there is no ground loop humming with volume crank up to maximum.


Guh! Do you know how many commercial supposedly-CE-UL-CSA approved products I've found with the line/neutral backwards, or illegal wiring schemes (line straight to transformer, neutral switched, then to fuse, then to transformer. No X2 cap across switch)?

Disgusting! And they came from reputable department stores. I found one amplifier even full of knockoff components :down:

Quote:
Yea, nothing comes easy. I'd take nothing for granted.


Agreed there!

Cheers!

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* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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PostPosted: 27 Apr 2011, 08:48 
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HI.
Geek wrote:
line/neutral backwards, or illegal wiring schemes (line straight to transformer, neutral switched, then to fuse, then to transformer. No X2 cap across switch)?

Yea, say it again! It is all those factory screw-ups may cause hums to other components hooked up to it.

O.T. - Similar 'stupid' things you may find inside many loudspeakers, even famous brandnames.

If you got the gut to get access to the inside of a loudspeaker system box, you may find skinny hookup wires, lousy built like micky mouse X'over networks, inadequate bracing, etc etc. :down: You will see where the money we paid for the loudspeaker system go to - a gorgeously looking wooden box !
But doing so may void manufacturer's warranty on the loudspeakers.

c-J

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PostPosted: 27 Apr 2011, 09:22 
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Hi.
Globs wrote:
Hi... cheap construction too - partly to save money, partly as an interesting engineering exercise.

Yup, you've hit the bull's-eye !

This is the charm of the DIY game! It also serves as a challenge to whoever takes part in it.

I think I have succeeded my own challenge to build the simplest phonostage ever - one stage one tube - singing like a nightingale! Now I am taking up my another challenge to build a stand-alone PS for it - 6VDC heater PS using NMHi cells rechargeable by a built-in SMPS + 440V B+ regulated PS in a small plastic Hammond equipment box:- 7.5" x 4.25" x 2.25". Another mission impossible !? :lildevil:

Life is itself a challenge, anyway.

c-J

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