Minimalist Pimeta

[heady 0]

Bram, the virtual ground is wrong. It is not connected to the BUF, only the Signal Ground is connected after the 2134 to the BUF634.

 

Is this in Visio? I have just installed Visio Pro but it doesn't have this type of template.

 

Thanks,

[bpribadi 0]

Can explain a bit more? Virtual ground and signal ground should be the same right?

Edited September 30, 2004 by bpribadi

[heady 0]

Bram, in CMOY, virtual ground and signal ground are the same. In Pimeta and PPA, the output ground is supposed to be isolated from virtual ground so as to isolate the (theoretical?) effects of the L/R opamp on it. The input ground has a connection with the virtual ground but it is input into R1 and then fed into the Signal Ground opamp, the output of which goes to the output signal ground.

 

In the PPA, the isolation is further carried to the power supplies and virtual ground of all the channels, with each channel having their own virtual grounds and TLE. Which is the difference between the Pimeta and PPA.

 

That's what I think the schematics in Tangent's site meant.

 

Paul.

[bpribadi 0]

Hi Heady, yes you're right, I overlooked the Pimeta and PPA schematic. Thanks for the correction !

 

I'm still learning of the effect of the ground isolation and what will be the impact to the sound quality.

 

Anyway, for either the input and the output ground, at the end the R&L will be joint together at the headphone socket, so I don't see the effect on the left and right channel seperation, but more to the power supply transient of current, which might be improved with other ways.

 

It is said "Isolated power rails reduce rail-modulated crosstalk". I don't really understand it. Anyone can explain it to me?

Edited September 30, 2004 by bpribadi

[heady 0]

Just a report of a change of the Nichicon cap to an Elna cap of same capacity. I changed the Nichicon 1000uF 35V cap (sorry not FineGold, thought it was) to an Elna 1000uF 25V (not a Silmic) yesterday and left it running over night and didn't like the sound from the beginning. Till now it still sound dark although bass has improved. I expected the bass to change but not the higher frequencies. ??? Anyway, I changed back to the Nichicon, I like its sound better.

 

Bram, you are right about the joining of the L/R channel at the socket. Now I remember the explanation from the site but you know, I am not electronic trained so I don't really understand it. I just follow the schematics and let the people who know do the thinking. When I did this Pimeta clone, I wondered if I did anything wrong but turned out my interpretation of the schematic was ok and the built worked. Phew!

[bpribadi 0]

Tangent's explanation of Virtual Ground:

http://www6.head-fi.org/forums/showthread.php?t=87569

[heady 0]

Bram, do you understand it? Not really sure except that it reduces cross talk.

[bpribadi 0]

Roughly

 

He says that, the current flow to the amp's ground is high. And because our ground is not completely 0 ohm, it might (it will) cause I x R = V some voltage on the ground. This voltage might disturb the source.

 

Since the source ground only deal with tiny current, so the isolation will prevent those high current on the amp's ground to disturb the source ground.

 

I hope my interpretation correct

[heady 0]

Bram, Makes sense to me.

[heady 0]

Update.

 

I have dropped the idea of fitting this into a Hudson tin because I found the Pimeta can sound A LOT BETTER with the caps which was originally specified. So I added more capacitors to it and it won't fit into a Hudson tin anymore. This picture is after I folded the two halves of the board and secure it with ties.

 

I will show the update Pimeta in the larger box I found for it when it is done. Hopefully this weekend.

 

Thanks.

Edited October 7, 2004 by heady

[bpribadi 0]

Still looks pretty small to me You can add more caps

 

Where did you buy the casing?

[heady 0]

Bram, the pic is before adding more caps. The plastic box came with a MagLite and belong to a friend who from whose fingers I pried it away from.

 

I have unfolded the amp as the box has sufficient space and it is plastic so won't conduct heat away from buffers. Hopefully will update the pic later. I burned another TLE2426 when I connected the V+ and V- in reverse. Poof, there goes $5.00. Bad to do diy late at night.

[aaa 0]

federal component only charge me $3.50 for each TLE2426 less than a month ago.

I bought 3, but that Mary originally mistaken as 2, so it should be $3.50 each when you buy two.

On farnel catalog it is $2.41 for one and $1.92 for 25 or more.

All price without GST though.

[heady 0]

Alamak, when I asked Federal, they said they never heard of it. I searched Farnell on their site and it reported not found. So I had to buy from RS Components and drive to Tuas and getting lost to collect and pay more for it. Of course this is about two months ago. Thanks for the info, aaa, save me agro if I need to re-order, I have 5 more. I ordered more since it was so difficult to get. Argh.

[bpribadi 0]

On farnel catalog it is $2.41 for one and $1.92 for 25 or more.

 

aaa, are you refering to Singapore Farnell, or US Farnell? I searched Singapore one, they don't have it.

 

Looks like the best hope is on Federal