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 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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PostPosted: 21 Nov 2011, 10:23 
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Joined: 09 Feb 2011, 15:25
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Tom!!.....Everybody makes mistakes......It's hard enough for me to keep that "squirrel's nest" of wires straight and I have the amp right in front of me....Sorting this thing out over the internet like you are doing is not an easy task!!

I have one more question....When you speak of the RCA jacks on the back of the amp you call one "red" and one "yellow"........but they are red and white.....Did you mean white when you wrote yellow?....Don't think I am nickpicking....I just want to be sure I have everything straight.

Be Cool and Danke!!-Rusty


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PostPosted: 21 Nov 2011, 11:47 
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Location: Duesseldorf, Germany
Yes,

also Red and White. White was meant as I wrote Yellow.

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 07 Dec 2011, 10:04 
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Hey Everybody!!

Thought I'd give a quick update.....The necessary parts are ordered.....From all corners of the globe.....But mostly from Hong Hong.....Ha!

Here's what I went with:

Obbligato metalized film in oil caps from DIY Hifi Supply.....Tom I hope you will forgive me..... :xfingers:

50K Ladder Attenuators....These have 23 positions and feature Vishay/Dale resistors.....CMF series I believe.....I got these from DIY AudioKit(Analogue Metrics).....8 Audio have some very nice ones too...and they are a little cheaper but use a mix of resistor brands and Taiwan mostly....Sill very good I'm sure....I just decided to go with the Dales.....Besides these come with knobs....(which I don't intend to use)......

I was also able to buy the other required resistors from DIY AudioKit......They appear to be the same stock that the attenuators are made from......Keepin' it all in the Vishay family...

Lastly....Well for now.....I bought a couple of very nice knobs from 8 Audio......40 mm in diameter......Shoud give the steppers a nice feel......

I also have pretty much decided to fashion a new faceplate out of 3/8" 6061 aluminum.....This will take care of the now un-used holes in the stock faceplate problem....I have a small lathe(a Craftsman from the 40's).....And access to a larger one(a South Bend).......And with the 40 mm knobs to inspire me maybe I can do something fairly nice...

Well, now we wait.....Be cool!!-RAA


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PostPosted: 08 Dec 2011, 12:14 
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Folk:

The output transistors(Toshiba Mosfets) on this amp are mounted to a piece of aluminum channel which serves as a kind of sub heatsink that is in turn is fastened to the chassis/enclosure which is a clam shell combination of two aluminum extrusions that doubles as the main heatsink for the amp.....The faceplate and backplate hold the arrangement together via eight screws.

Okay, now that I have explained all that, what I am actually writing about is that it has occurred to me that I will need some heat sink compound to replace the stock material between the sub heatsinks and the enclosure when I re-asemble my amps. I was surprised to find so many products offered to do this task. After reading what seemed like a million customer opinions on this product and that, I settled on Masscool Shin-Etsu. It supposedly was rated the best by test of 80 of these compounds.

Any of you folk ever used it?......Do you think it's suitable for my application?-RAA


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PostPosted: 09 Dec 2011, 16:04 
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Hi Rusty,

I think this compound paste is OK. Usually the simple cheap white aluminum oxide or ceramic compund is used.. Now, as you only need a little
of these paste it's OK. Remember not to apply too much. The paste only has to fill air gaps between the MosFets and the heatsink.
Are there no mica or silicone insulators mounted between the transistors and the heatsink??

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 10 Dec 2011, 09:40 
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Hi Tom,

Yeah, there is a membrane of some sort isolating the MosFets from the "sub" heatsinks to which they are attached.....The need for the compound comes where the "sub" heatsinks(which appear to be nothing more than some short pieces of aluminum angle stock) attach to the aluminum extrusions that form the amps enclosure and serve as the major heatsink....

The Shin-Etsu might be overkill here, but it wasn't any more expensive than a tube of compound from the local Radio Shack....It was "only" about $5.00 from Newegg...and that includes shipping....Of course you don't get much for that price, but as you said I don't need much....

Tom, on a related topic, is it desireable that in an amp design, such as mine, that the enclosure be well grounded? I would assume that, that is the intention of this amps designers since there is a green gounding wire attached to each of the amps two "sub" heatsinks(visible in the Flickr pics), but I suspect that there is not a good connection between the these units and the main heatsink/enclosure due to the fact that they are anodized black and therefore non conductive on their surfaces....Would it be a good idea to take steps to make sure the entire enclosure is uniformly grounded?....Or do you think the enclosure should "float"?

Danke, Rusty


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PostPosted: 12 Dec 2011, 15:41 
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RAA wrote:
Or do you think the enclosure should "float"?
Hi Rusty, I assume that the enclosure is earthed properly. As far i could see, the protective earthing is tied to both heat sinks, the PCB and the enclosure.
The enclosure earthing can float - relative to the circuit ground. This is very common and often used to minimize ground / earth loops.
But, I am sure your enclosures do not float. You can check the enclosure-earthing and the circuit ground for continuity.
I believe a DMM will beep like crazy when you stick one probe to the amp's power socket earthing tab and the heatsink or some screws.
I can not imagine there could occur a problem with the earthing and the circuit ground. The wiring and the isolation also seems to be good.
Don't worry...
Quote:
The need for the compound comes where the "sub" heatsinks(which appear to be nothing more than some short pieces of aluminum angle stock) attach to the aluminum extrusions that form the amps enclosure and serve as the major heatsink....
Ah, now i got it right.
At this point, a good thermal compound is a very good idea. You're surely right. The better the contact between the surfaces - the better the cooling :wizard: .

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 13 Dec 2011, 09:20 
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Hi Tom, thanks for the insight on the grounding issues.....I just want this amp to be a "quiet" as possible and looking for potential areas of improvement. I'll investigate the grounding as you described when I get a chance. Oh, by the way, what do you think the input impedance will be on these amps with the modifications? It was listed in its published specs as being 10K single ended or 20K balanced stock. From what I have been reading that seems a little low and therefore hard to drive. That may explain why this amp sounded kind of flat and lifeless but very clear when connected directly to a source component such as a CD player.....and better but still lacking when connected to the headphone output on my Philips MP3 player.....Thanks Rusty


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PostPosted: 17 Dec 2011, 02:38 
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Hi Rusty,

The input impedance is about 20k. It is a common value and should be easy to drive from a line level source like a CD / DVD player
or a computer sound card. Sources like mp3 players or portable CD players often don't provide a good voltage and current level to drive
line level inputs.

A "flat and lifeless" sound often comes from to many signal conditioning and Op Amps. Modern Op Amps can sound very dynamic and
lifelike, but to many of them in one path can flatten the sound as each has its own input conditioning. Let's say that each Op Amp linearizes
the signal.

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 20 Dec 2011, 16:12 
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Hi Tom,

What you said about the "linearizing"(read gimping up) characteristic of op amps makes me optimistic about the sound of these amps after the mods are made.....Thanks to you two of these offenders will be eliminated from the signal path along with the electrolytic coupling caps....I can't wait to hear the results!!

I have received all of the electronic parts I ordered to reconfigure the amp's input. Here's a few thoughts on each of them and their suppliers:

Obbligato Poly Film in Oil Caps, 4.7 uF, 630V 5 percent tolerance- These appear to be very good quality pieces with the capacitor encased in a metal "can" which is then layered by a plastic cover. The leads are solid copper wire of a substantial guage(I'd guess 20 or 22) and insulated. They are sealed at their entry point to the interior of the cap by resin. They are BIG....but luckily in this instance I think I can make them fit.....They WILL require brackets. I got these from D.I.Y HiFi Supply, Hong Kong for around $7.00 apiece.....Service was prompt and shipping no more than what a domestic supplier would charge and arrived suprisingly quick....About $ 8.00

Ladder Attenuator featuring Vishay/Dale Resistors, Log Taper, 50K, 23 Volume Steps - Really satisfied with these units.....The soldering is beautiful....I was also heartened that they employ Dale's CMF/RN models which Vishay claim to exhibit exceptionally low noise(typically 0.10 uV/V.....Whatever that means.....)and also excellent high frequency characteristics. It appears that 1/2 watt units were used as well. I got these also from Hong Kong through D.I.Y. Audio Kit which appears to be part of Analogue Metrics. Again service was good, shipping fair($8.00) and quick. Communicating with them was best done through their Analogue Metrics address....I never got a response with the D.I.Y. Audio kit addie. I also purchased the other required resistors for the mod and was glad to see that they were the same variety as used in the attenuators. Attenuators went for about $52.00 for a pair with the resistors going for $4.50 for 10 pieces any combination of values.

40 MM Solid Aluminum Knobs- These are very nice......But not quite as nice as they appear in the website's pictures. They are machined from a casting, which is fine, but they could have stood a little more machine work. For instance the knurling, which appears to be machined in the pictures is actually a cast in detail.....Still nice and I am satisfied, but a true machined detail would have been more elegant. They do, however, have three machined rings/grooves cut across the faux knurling that add a touch of sparkle to the units.....They also have nice and secure set screw attachment to hold them securely in place......All in all....They're pretty cool....and definitely worth the $10.00/pair price.....With $8.00 shipping. Available from 8 Audio.....Thanks Matt for turning me on to this outfit.....Good service, good communication, fast shipping.

Well, that's kind of where I am now....I hope the insight on these products might help anyone else who was wondering about these items....Of course I will have a lot more to say about how they perform after the install is complete and the amp is back up and running.

The next thing to buy will be the aluminum stock for the new front panel.....next stop Online Metals.......-Rusty


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