Minimalist Pimeta

[heady 0]

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UPDATE - I dropped idea of fitting this into a Hudson tin. See post dated 7 Oct 2004.

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Hi all,

My humble project cannot compare to bpribadi's work. Here is my board of a pimeta clone, without the extras, only one 1000uF electrolytic cap and one 1.5uF film cap for the power rails only. I am now listening to it with a AD8620 for left and right channels while the other OPA2134 is for the virtual ground and the signal ground. 3 BUF634s for L/R/G.

 

Surprising it sounds quite good. I am scratching my head at moment trying to figure a way to fit the cap into the tin. Somehow, my measurement is always slightly out, I am no engineer. Sigh!

 

The boards are meant to fold one on top of the other and so use the base of the tin as heat sink for the buffers. Of course I need to insert insulator sheet inbetween the folded boards.

 

I am trying to see if this is a significant improvement over my 3-channel CMOY. And my initial finding is, yes the sound is better. I can hear the sound is much cleaner. with better separation and sense of the "air" around the voices and instruments. The bass is punchy, dynamic and deep which is surprising as there is only one cap for the whole board. Maybe I just have very imaginative ears.

Edited October 7, 2004 by heady

[digi01 0]

good.your amp is not humble at all.

you have very imaginative ears and very imaginative layout ideas

 

[heady 0]

Thanks digi01.

[bpribadi 0]

Well, I think we all agree that 'comparison' is not the theme here, the Fun of DIY, that's the theme !

 

I don't really understand how you combine the BUF634s and the OPA2134 for the pseudo ground. Don't mind to share the connection?

 

I want to try it when we meet up later

[heady 0]

Bram, we compare to learn from one another. Otherwise each will be in our own little island. Having said that, I must say that your handicraft is superb and truly a blessing for the eyes. I don't think I can ever approach it but I will do what I can for the fun of it. Besides the music is so enjoyable thru our little creations.

 

I used one side of the dual OPA 2134 as buffer for a TLE rail splitter, for the virtual ground. Strictly speaking, it is probably overkill. The other side of the OPA is used for the signal ground, as per the PPA/Pimeta schematic. I just changed computer and have no Visio to draw the circuit I used but I can take a digital pic of my drawing to share with you what I did.

 

Hope to see you.

 

[domi33 0]

Nice design! did you draw a schematic? Or can we take the pimeta schematic and add your modifications? Waiting to see your enclosure

Edited September 29, 2004 by domi33

[heady 0]

domi33, I used the pimeta schematic from Tangent but adapted it to my own layout. I don't know any easy way to draw the layout except by using Visio and I don't have that at the moment. I am now thinking whether to keep the Nichicon FineGold cap or substitute it with a smaller Elna cap of same uF. Problem is the FineGold is just a lttle too fat but it sounds fabulous and the Elna is smaller but I wonder if the sound will change. Decisions, decisions.

[bpribadi 0]

Heady, you can fax or send the photo of your grounding schematic, I can make the Visio drawing for you

 

Did you biased the AD8620 into class A with jfet cascode? I only see one transistor... or are they hiding

 

Where did you bought the Nichihon FineGold? Don't mind to share the price with us?

 

I think your pimeta will looks great in Hammond die cast alluminium My2Cents

I can pass you the photocopy of the Hammond casing sizes from the Farnell catalog if you need it.

[heady 0]

Bram, I can send you a photo of the layout but it need some explanation. I also found a mistake as I was building it.

 

I did not bias it to Class A, no room. The transistor you saw is the TLE. I am keeping the JFETs for my desktop amp.

 

I got the Nichicon FineGold from Koba, I think it is $2 each.

 

I am trying to fit this into a gold coloured Hudson tin I don't think I want to spend too much on a Hammond. I did buy some enclosures from Koba but will keep them for the full size Pimeta or PPA clone. They also look so nerdy.

 

 

[bpribadi 0]

A photo of the layout would be difficult Hand drawing of the schematic is easier I think I understand your explanation, I will draw them in Visio if I have time and post it here.

 

I guess for cheaper solution, you can replace the TLE with 2 equal value of resistors, to create voltage divider. My2Cents

 

Let me know if you go to KOBA, I want to go with you if the timing right

[heady 0]

Bram, I am re-drawing the layout on paper, bigger so clearer. I like the idea of TLE instead of using the resistors after I saw the voltage imbalance when using battery. TLE allow battery to drain more before getting distortion. Cost about $4.50 each but the drive to Tuas to collect was insane, so I bought 10 pcs. Now left 5pcs. Burnt one when I connected the power in reverse.

 

Let's have lunch and go to Koba next week. PM me your preferred day (except Fri and weekends). I pick you up.

 

[heady 0]

Re-drawn the layout schematic so is clearer but still a little too crowded. If you are thinking of using this layout, please pm me for the original pic, this is too low res. Until I can get help from bpribadi to provide a Visio version (thanks) , this is the best I can do.

[bpribadi 0]

I would say it is a good layout, I can see that you plan it very carefully on where you should cut/remove the PCD copper lines

[heady 0]

Thanks Bram, before this I tried to do what you did with your Black Amp, ie soldering wires to back of perf board to simulate the strips. It was a mess, so I went back to this type of perf board. Must learn from you.

[bpribadi 0]

Heady, I tried to draw the schematic for you, I hope it's correct: