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PostPosted: 23 May 2011, 12:13 
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Gio wrote:
Les wrote:
I'm using a Bud Ind. 7x12x3 aluminum case. It's unpainted and is economy style. Some exposed seams will get a coating of epoxy to cover and smooth, then the case will be primered and then finished in a gloss black enamel.
Take photos of the seam work. Sounds interesting.

No probs Gio! I'll be using a product called J.B. Weld. There is a quick curing type of this product, but I'll be using the regular stuff which will give me plenty of time to work it. I'm in the process of hole punching / cutting right now (well, not right now, but rather in the evening).

_________________
The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
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LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


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PostPosted: 24 May 2011, 12:21 
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Les wrote:
No probs Gio! I'll be using a product called J.B. Weld.

Nice tip. I will have to give this product a go. In Canada you can find this at Princess Auto and Canadian Tire and the generic name is cold weld.

Cheers

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PostPosted: 25 May 2011, 09:07 
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Some more pics: These are just some pictures showing case detail and my layout. I have not yet finished the seams, and there fore the case has not been prep'd for paint. Yes. the screws will be painted as well.

Inside layout. The whole of the left side, where the pre-amp will live, will be packed with sound / vibration deadening foam. Pictures of that will come later. If you look hard enough, you can see the separator shield I have installed to shield the PS from the amp. I'm hoping that, in addition to locating the transformer as far over as possible, that shield will keep induced hum from the PS out of the amp.
You can also see the mods I've made to the amp to remove the original on-board PS. The LED mounted on the new PS is temporary. It will be removed when I connect the indicator lamp of the power switch. A nylon wire tie will be placed around the transformer prior to final mounting as well. This transformer was a plug-in type - that is, it had the prong for a wall plug made in to it. For mounting on the PCB, I cut the prongs short enough to solder to the PCB. At this point, that joint is all that holds the transformer to the PCB. Granted, it is a silver soldered joint and very strong, I still want the extra insurance of a wire tie to secure the transformer to the board. I've also hatched an idea that may add a little extra insurance against hum by wrapping the JAN6418 tubes with enameled bell wire and connecting that wire to GND. I don't believe that will upset any capacitance with in the tube and cause instability, but do invite comment on that..
Attachment:
layout.jpg

In the upper left of the picture, you can see the phono jack PCB. After drilling the holes for it and see how it looks, those are going bye-bye. I will instead clean-up the holes that I drilled for that concept and make it a square cut-out and then fabricate a new jack PCB using nice new jacks. I have some 1/8" acrylic that will be use in conjunction to strengthen that concept, if necessary. That's primarily why I didn't show you the back side where the jacks and IEC receptacle will be mounted. Those jack holes are UGLY.
Attachment:
outside.jpg

Picture of the seam detail. For this reason, I'll not purchase anymore Bud boxes. The price was right and the size was good, now I know why the price was lower than a good quality Hammond box.
Attachment:
seam detail.jpg

The IEC ground will be connected to case. The rest of the circuitry will be isolated from case. By doing this, I should be able to avoid any system ground loops.

While I'm thinking about it.. My phono, like most, has a separate grounding wire. Should this wire be earthed, or isolated from earth?
.....stay tuned! :up:


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_________________
The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
_________________________________
LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


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PostPosted: 25 May 2011, 12:19 
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hi Les, since your turntable has a grounding wire you should include a grounding lug on your phono preamp. This will give you have the option of grounding the two together.

Cheers

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PostPosted: 25 May 2011, 14:16 
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Hi.
Les wrote:
Should this wire be earthed, or isolated from earth?
Gio wrote:
since your turntable has a grounding wire you should include a grounding lug on your phono preamp. This will give you have the option of grounding the two together

Yes, Gio has said it. The ground wire of yr TT MUST be hooked up to the metal case of yr phonostage.
If yr all-purposed metal case does not have a ground bolt, Install one & only one on the metal case immediately next to the phono cartridge I/P jacks. The IEC green ground wire should be connected directly to the ground bolt.

I installed a ground bolt to ALL the phonostages I built, glass or sand regardless
though they get only 2-wire power plugs. The TT ground wire after hooked up to the ground bolt of my phonostage does take care of the ground noise when not connected. Audibly! :idea:

c-J

PS: not intend to complicate the ground issue, I always add RFI devices (as previously posted) btween the signal reference ground of the phonostage & the ground bolt.

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PostPosted: 25 May 2011, 17:08 
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Gio wrote:
since your turntable has a grounding wire you should include a grounding lug on your phono preamp. This will give you have the option of grounding the two together.

I knew that. The question was whether that should be earth grounded, ie bolted to the case, or just grounded to the amp ground, which I am keeping isolated from case ground. :)
CJ wrote:
If yr all-purposed metal case does not have a ground bolt............

Thanks CJ. That's the answer I was looking for.
RFI has already been considered and addressed. :up:

_________________
The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
_________________________________
LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


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PostPosted: 25 May 2011, 19:17 
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Looks like you are good to go. I like the PS improvements you have made and the shielding between the PS and RIAA section. That should help make for a nice quiet phono preamp.

What have you done with the mounting of the RIAA PCB to the chassis? Are you using grommets to damp the PCB from the standoff? You can also use a couple of stacked grommets as standoffs.

A good pair of (soft / absorbing) rubber feet will help too. The 6418 tubes don't like vibration and RFI so shielding and damping will be worth the extra effort on this build.

Cheers

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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PostPosted: 25 May 2011, 21:36 
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Gio wrote:
Looks like you are good to go. I like the PS improvements you have made and the shielding between the PS and RIAA section. That should help make for a nice quiet phono preamp.

Thanks! Means a lot coming from people with way more experience in DIY than myself.
Gio wrote:
What have you done with the mounting of the RIAA PCB to the chassis? Are you using grommets to damp the PCB from the standoff? You can also use a couple of stacked grommets as standoffs.

That's a good question, Gio. I enlarged the mounting holes of the K301 PCB and fitted small rubber grommets. I am using plastic mounting bushings as spacers about 6mm long, however, I like your suggestion and will probably use that method instead - THANKS! In addition to that, I have a quantity of high density foam that will be packed all around the PCB.
Gio wrote:
The 6418 tubes don't like vibration and RFI so shielding and damping will be worth the extra effort on this build.

Boy howdy, you're not kidding about that! The JAN6418s are SUPER MICROPHONIC. You just breathe on them and they'll ring! I have some nice felt feet to apply to the base plate.
__

I have begun finishing the case. I've cleaned up the cut-outs for the IEC and soon to be built phono-jack pad. The corners have been epoxied and must now dry for at least 24 hours before I can begin sanding to smooth. The bottom plate has already been sanded and 1st primer coat applied.

More pictures!
Attachment:
back.jpg

Attachment:
cornerwork.jpg


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_________________
The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
_________________________________
LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


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PostPosted: 26 May 2011, 10:36 
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Hi.

Sorry, somewhat O.T. again.
Les wrote:
The JAN6418s are SUPER MICROPHONIC. You just breathe on them and they'll ring! I have some nice felt feet to apply to the base plate.

Yes, microphony can be a pain. The most effective damping, IMO, is get a ring damper fitted around the 'waist' of the tubes in question.

While many spend a bundle in buying brandname vibration dampers, I did my cheapie DIY way by fitting a thick rubber ring tightly around the body of the tubes in question. This rubber ring is cut to shape & the tube diameter size out of a $1 mouse rubber pad.

The next thing to do is to hot-proof the rubber ring - wrapping a few round of Hi-temp resistant tape tightly around the tube before fitting on the rubber ring.
Where to find the heat resistant tape? A little thinking tells me plumbers Teflon sealer tape will do the job, available dirt cheap from any hardware stores. :idea:

Yes, these penny costing tailor-made dampers work bigtime.

But make sure the dampers do not overkill the vibrations - killing the music as well. It depends on how mcirophonic are the tubes, of course.

I've found it so effective that such rings damp down the music as well. The music gets slow down & loses brilliance with my phonostage tubes overdamped.

So I simply removed the rubber rings but left the Teflon tape in-situ from day one. Then the music bounced back to its live & vitality !! :smoking:

c-J

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PostPosted: 26 May 2011, 11:02 
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I notice there are comments regarding the 6418 being microphonic . This type is a directly heated battery pentode with 1.25V 10mA filament . That specification alone tells me microphony will be a major issue ! I find with directly heated types a slight backing off of the filament voltage can benefit . If applying damping I would suggest wrapping elastic bands around the tube , heat won't be an issue so it could be completely covered . Wrapping a strip of sorbothane around the tube and securing with a tywrap may also be worth trying , this worked for me with 1LE3

The 6418 does not seem a very good choice for a phono stage in my opinion :(

BDA


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