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PostPosted: 10 Mar 2017, 16:53 
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Have to agree, this is a very good listening amp. One which really draws you in. I have posted, some time back when I first built mine, that this amp is a better high frequency amp than low frequency. What I meant by that is it doesn't dig deep into the bass. But not onlay me but a few very critical friends have added they can hear nothing wrong with the bass.

As Suncalc pointed out, with OPTs of a small to reasonable size very deep bass may never happen. But bass is not why you build this amp. You build is because it will deliver good listening over a wide variety of music using a simple schematic with inexpensive easily obtainable tubes.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 12 Mar 2017, 00:24 
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Thanks for follow ups. Just finished the power supply tonight and it seems to work fine. Going to spend some time tidy-ing it up tomorrow before diving into the amps.


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PostPosted: 01 Apr 2017, 21:18 
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I can't believe it.... it works!!! Thanks for the nice write up and responses. Made some adjustments and it sounds wonderful.

Time to pick out some solid wood and figure out a neat way to pack it all up. It's going to be my dad's 60th birthday present.

In the coming weeks I'll also do some charz and see how I'm doing compared to Suncalc's plot on March 10.

Question regarding safety... in your 2.0 schematic drawing I see a tie for AC outlet GND to your local amplifier GND. Is there any concern here with leaving your box hot if neutral is severed? I'm not sure about the best way to wire the chasis here / if at all.

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PostPosted: 02 Apr 2017, 10:20 
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Wow! That's some prototype! Please be very careful.
johnyo wrote:
Question regarding safety... in your 2.0 schematic drawing I see a tie for AC outlet GND to your local amplifier GND. Is there any concern here with leaving your box hot if neutral is severed?
Thats not usually a concern. The fuse and switch should be on the "line" side of the service feed. The "neutral" side should go directly to the power transformer. And the "earth" should tie to the metal chassis. You'll notice that the "Earth" conductor on all plugs is longer than the other two. This is to ensure that it's the first to make contact when plugging things in and the last to break contact when things are unplugged.

The idea behind the earth ground is to ensure that the metal chassis is not a shock hazard. So all exposed metal with which someone could come in contact, with the exception of electrical contacts, are tied to the chassis/earth ground. The signal ground used by the electronics is a separate ground circuit. In any modern three wire system (i.e. line/neutral/earth like we use in the United States) these two ground systems should be tied together at one point within the chassis. Without this, it is possible for the entire electrical audio circuit to shift with respect to earth and present a personnel shock hazard and a potential damaging condition to other equipment. For more information on ground systems and equipment interconnection, see this post: http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4628&start=71

I am assuming that I am answering your question. If your question is really "How do I handle a two wire service feed?" that's a fundamentally different subject.

Does this helps?

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PostPosted: 06 Apr 2017, 20:17 
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Thanks, that is a very nice write up.

Quote:
In any modern three wire system (i.e. line/neutral/earth like we use in the United States) these two ground systems should be tied together at one point within the chassis.

But doesn’t this defeat the purpose of a GND fault interrupt circuit back at the house / circuit breaker / electric pole?

I know in Lacewood 2.0 you tie signal GND directly to chasis GND. But now, return current through GND is no longer indicative of a faulty appliance but rather just normal operating condition depending on impedance of the two possible return paths. Still new to this but do pros outweigh cons in this case, want to check my understanding.


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PostPosted: 06 Apr 2017, 21:23 
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johnyo wrote:
But doesn’t this defeat the purpose of a GND fault interrupt circuit back at the house / circuit breaker / electric pole?

I know in Lacewood 2.0 you tie signal GND directly to chasis GND. But now, return current through GND is no longer indicative of a faulty appliance but rather just normal operating condition depending on impedance of the two possible return paths. Still new to this but do pros outweigh cons in this case, want to check my understanding.

No. When using a transformer there is no connection between the neutral (i.e. the service feed current return path) and the earth ground except at the cross bar in the panel. All normal service current flows in the line and neutral wires. However, in the case of a fault in the appliance (in this case a failure in the transformer isolation or a short to chassis), the earth tie will keep the chassis at (near) earth potential level and any current to earth ground will flow through the Earth safety ground rather than a person touching the chassis. If there is a GFCI in the circuit, then the current in the earth ground line will trip the breaker and shut down power.

Remember that when I said "these two ground systems should be tied together at one point within the chassis" I was talking about Earth ground and signal ground not Earth ground and service neutral.

Does this make sense now?

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PostPosted: 06 Apr 2017, 22:58 
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Makes sense to me now. Thank you.

You always hear "tie at one spot" but now I know why.


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PostPosted: 17 Apr 2017, 13:58 
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Finished, packed up in a nice wood box. Thanks.

Currently using some 5W 8Ohm speakers from Mouser, any suggestions for nice speakers in this low power range?


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PostPosted: 17 Apr 2017, 19:15 
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johnyo wrote:
Finished, packed up in a nice wood box. Thanks.

Currently using some 5W 8Ohm speakers from Mouser, any suggestions for nice speakers in this low power range?


If you DIY some very efficient speakers try the Fostex 8" full range. Or want to spend a lot more for a lot more and even greater efficiency try the Beyma 15" concentrics. These will make any amp sound loud and very good.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 18 Apr 2017, 17:36 
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Thanks for the reply. Yes I will be making my own. I get a few watts max before I start getting distortion, do you think a 30W 8" Fostex driver is a good option? Thinking about the FE103En, looks like a nice option and some others have enjoyed it (http://diyaudioprojects.com/Speakers/Fo ... -Speakers/).


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