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PostPosted: 20 Apr 2014, 04:07 
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Here is an update. No pics as it is still raining. Now that the varathane has had some days to cure on the wood I have started to do some measurements. The high volt supply i am loading with 3.17K (2.7K+470/10W) given a 160 v supply will draw 50.5mA and all is looking as it should. The 6.3v heater supply however has me perplexed. I am using the Hammond 270FX which has a 6.3vac at 5A rating. With heaters driven i am getting 5.3vDC. So i jumper ed the two 0.15 ohm and it comes to exactly 6.3vDC. This should not be right. With heaters unplugged so, no load, AC is 6.125vac and the dcv is only hitting 7.7vdc.
. To me this points to a short. All i have in the cir is 4 of 6A diodes for the bridge, 1 of 33000uF + 22000uF. So far nothing is heating up Time for a beer.


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PostPosted: 22 Apr 2014, 22:51 
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Location: Vancouver Canada
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I have been listening to this amp for a few hours now and i like it. I realize discerning the sound of phones is a skill that takes time. (like picking the voice from static on a ham radio) I'm not fully there but i now can tell differences that i would not have a short time ago. My test was to watch a movie in full listening to phones plugged into comp. Then watch again with the amp driving the phones. Crummy way to test since it's aim is primarily music but this is what i experienced. First time threw, i watched on the screen and listened to the phones. Then, with the amp, without even realizing it at first, I was in the same room as the actors. The sound stage opened up and i was there. This is a very new experience and one i shall now strive for. Have read it from many people but never exp till now. truly a pleasure and a privilege.
I think i should explain that this amp is a full wood build and NOT something i would ever suggest for a newbie. One must be many times "experienced" and fully aware of power, and fire concerns. I do have a 12vDC fan on the bottom of the PS mounted on an aluminum plate used as a cover. It runs on the 6.3vDC producing no noise I can hear. The wire hanging off the back of the PS is to gnd the trans after it has the paint off to make good connections between end caps and core. The umbilical cord used i bought for $1 Can. attached to a European travel iron rated for 230v/500watts. (thrift store item)
I would also like to say, (for people thinking they have no room to do such work), this entire build ele and wood was done in a very small room with about 5' x 5' working space for wood cutting and drilling. I did it with a pre-WW2 saw 16" x 16" table driven with a motor salvaged from a kitchen blender i bought at garage sale for $1.50 Can. missing the utensils. It CAN BE DONE. Now i can do some tube rolling and breaking in. After hours of being on,, it is just warm. Most of the heat is in the tubes and trans, both located on the top. Leaving the heat producing resistors only, inside the cab. Venting is working ex as well. Now to save my pennies for a good pair of phones. Any questions or comments are welcome.


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PostPosted: 23 Apr 2014, 07:57 
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Location: Australia
Excellent build. Looks gorgeous well done.

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PostPosted: 30 Apr 2014, 09:42 
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This almost feels like it should be a new thread but it does have to do with this amps cir so i apologize if i am out of place.
I am making a mental list of the different noises an amp can make. Not by choice or design but more experiences that i can relate to from my youth about tubes. Namely A low slow rushing sound, A higher freq and pitched hiss, any osc's, and finally hum, which, here, is 60 or 120 Hz..I have no hum injection at all so no 60 or 120Hz. Thankfully no high hiss or wining so no RF getting in and no osc's inside..

The slower, lower rushing however is present at any volume, well I am being extreme fussy here but it is something i notice (very low db) and i am a cat at heart so impossible to let go of. I noticed if i brought my hand close to amp it went away some. Left, front, top, even cupping tubes with hands/fingers resulted in only some reduction, On the right side however, I tried hand open, closed in fist, and 4,3,2,1 finger. Even 1 would sustain absolute quiet, but, if aloud to get started again, then try and quiet by re-introducing 1,2,finger etc I needed to be up to 3 before enough was present to stop the rushing. Such a curious and perplexing thing. What to do? So i moved the amp and problem solved. If off,,it makes no less noise. The joys of being beside a Cell repeater station i guess as nothing on that wall but paint and plaster then air outside. Funny thing is, now, it's surrounded by test equipment and monitor/comp.lamps etc and no influence.


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PostPosted: 30 Apr 2014, 10:51 
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laurie54 wrote:
This almost feels like it should be a new thread but it does have to do with this amps cir so i apologize if i am out of place.
I am making a mental list of the different noises an amp can make. Not by choice or design but more experiences that i can relate to from my youth about tubes. Namely A low slow rushing sound, A higher freq and pitched hiss, any osc's, and finally hum, which, here, is 60 or 120 Hz..I have no hum injection at all so no 60 or 120Hz. Thankfully no high hiss or wining so no RF getting in and no osc's inside..

The slower, lower rushing however is present at any volume, well I am being extreme fussy here but it is something i notice (very low db) and i am a cat at heart so impossible to let go of. I noticed if i brought my hand close to amp it went away some. Left, front, top, even cupping tubes with hands/fingers resulted in only some reduction, On the right side however, I tried hand open, closed in fist, and 4,3,2,1 finger. Even 1 would sustain absolute quiet, but, if aloud to get started again, then try and quiet by re-introducing 1,2,finger etc I needed to be up to 3 before enough was present to stop the rushing. Such a curious and perplexing thing. What to do? So i moved the amp and problem solved. If off,,it makes no less noise. The joys of being beside a Cell repeater station i guess as nothing on that wall but paint and plaster then air outside. Funny thing is, now, it's surrounded by test equipment and monitor/comp.lamps etc and no influence.

As audiophile hobbyists we are met with many challengers. Wait until you encounter demonic possession. That's a hard one to fix on the fly. Keep a bible handy.

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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PostPosted: 30 Apr 2014, 11:12 
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laurie54 wrote:
On the right side however, I tried hand open, closed in fist, and 4,3,2,1 finger. Even 1 would sustain absolute quiet, but, if aloud to get started again, then try and quiet by re-introducing 1,2,finger etc I needed to be up to 3 before enough was present to stop the rushing. Such a curious and perplexing thing. What to do?
What you are describing is a classic grounding/shielding problem. There is an external interaction with the amplifier and then when high frequency problems get going, ungrounded metal parts pick up a charge (much like a capacitor) and feed the problem. There are some simple things you can do to help.

    1.) ALL metal parts not tied to signal ground need to be tied to chassis ground. Even if it's just a piece of metal vent screening like on either side of your driver tube.
    2.) All signal grounds need to be tied together with a VERY low impedance connection. This is why people use either a "star ground" concept or a heavy copper signal ground.
    3.) Tie the signal ground and chassis ground together at one and ONLY ONE point.
    4.) Shielding the components on the underside of the amplifier will help with external interactions. Even if it's not a complete enclosure, shields will help.
    5.) Eliminate RF "traps". These include looped wires, long paralleled conductors, and small encasing metal parts (like the shell of a potentiometer). Make very sure that all potentiometer shells, inductor housings, and transformer housings are tied to the chassis ground.
    6.) And finally, eliminate all carbon and or carbon film resistors in the driver stage. These resistors (especially carbon composition resistors) can cause all kinds of problems with amplifier noise down stream in the signal path.

I hope this helps.

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PostPosted: 30 Apr 2014, 11:51 
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Location: Vancouver Canada
It does help thank you suncalc. The amp and PS both conform to 1,2,3,4,5,6, so i am on the right path in these regards. Actually, given the bottom brass plate is all the shielding there is, i was expecting more "interference / injection" and i guess the relatively low gain helps in that regard. I have noticed also the 6.3vdc leaving the PS is only 6vdc at the heaters. So 300mv loss in the Umbilical cord. with about 2.6A draw given the 6as7 at 2.5A and ECC88 drawing 345/365mA and fan at 70mA. I will be shortening the 4ft cables in the future though. I just cut iron cord in 1/2 for now. Couldn't resist using the cloth covered wires. I am very pleased with the outcome of this build.
Now I'm all fired up so, maybe soon the 4S Pre-Amp or the RIAA phono amp or both. Any wood cabs here will have to be "encasing" the metal enclosures though.


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PostPosted: 30 Apr 2014, 18:55 
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I didn't have a buzz hum or anything until you guys started talking about it. I have just hooked up my latest preamp (Parley - posted on the forum) and find when cranked it has a buzz. Good news is it drives my cranky UX-171A amp (Intermezzo) very well where I thought it wouldn't. Now to chase down this buzz. At this point HT ground, filament ground (DC on the 12AU7) and mains earth are all separate and though most of the chassis is connected to mains earth one panel does read high resistance to ground.

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PostPosted: 30 Apr 2014, 22:18 
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I have noticed from the few amps i now built and others that tubes will produce different sounds as they age/break in/settle down. I am not so spry first thing in the morn anymore either so now i am wondering what noises i am making before my eyes open in the morn.
You must keep us informed as to your progress. It's frustrating, but every one of these little problems is producing a wealth of knowledge. So think of it as a good thing. mwhustn we can all sympathize and relate i am sure to the first sentence of your last entry.
P.S. thank you for the comic relief.


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PostPosted: 30 Apr 2014, 23:41 
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OK you can all sleep tonight the preamp now works 100% and drives Intermezzo beautifully. Listening to it now. No buzz hum or anything else. Took the whole morning but very worth it. I have never heard Intermezzo sound so good.http://www.diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4786&p=40555#p40555

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