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Mini Local Reg'd Mother Board for those 321/729 Cards - Group Buy Interest Check

Hi, I just finished two TRegs (not the MB but for a phono preamp) and got following values (unloaded and resistors as of Neil-BOM for MB):
32V HP PSU: 30,7 V
LMT317: 28,6 V
TRegs: 26,5 V
Are the 26,5 V Ok for the 321s, 729s and for the 322 (MM phono cards) :confused:

Thank you in advance !
Olivier

PS: I put the HP PSU and the Tregs on the scope and watched them for a while, very interesting ... I was very surprised to see so many ripples at the output of the HP PSU .... by chance attenuated by a factor 10 after the TRegs. The 24V of the HiCap was not so quiet as the output of the TRegs even with the HP PSU.
Watching TRegs is better than watching TV :D
 
binnie said:
...LMT317: 28,6 V...TRegs: 26,5 V[/B]
Click to expand...
Sounds about right...
binnie said:
Are the 26,5 V Ok for the 321s, 729s and for the 322 (MM phono cards) ...
Click to expand...
It should be OK - but if you are using the 25v Oscons you may want to drop it another volt on the gyrator (change R3 to 120 - 140K), especially of you remove the 27R series drop resistor...with it in there I've not had any problems so far but...
 
Thank You Neil !!!

For the rail decoupling I planned to use the same winners as for the TRegs:
10 µF Tant bypassed by a 10nF Film Wima.
For the Feedback I will first go for the Wima 22µF (6 dB) until I have the Oscons (or other to give them a try). Will change the resistor accordingly of course.

Olivier
 
It just occurred to me that since I ran the resistor for the LED off the main unregulated rail you may need to uprate the resistor to 1W if you run the amp of a 36/37v rail from a SNAPS os the like. So far I haven't seen an issue off a 32v HP supply...but a higher rated resistor wouldn't do any harm here either.
 
I finished yesterday the 321s (with the caps as mentioned two posts above).
I just checked some typical values with the scope and fired the NAP140.

They worked perfectly (I had the impression that I listened the CD player, but it was the tuner :cool:) but after 4 hours, the level of one of the channel decreased dramatically with lot of distortions.
I switched the output signal cap (thought it was the bad guy) but the same scenario happened again. This morning it took only 10 minutes after inserting them again :rolleyes:
Only one card makes troubles, the other one works a treat.
Both cards are identical (even the orientation of the resistors and the caps on the cards are identical !). All components coming from the same lot ...
I just checked the voltage accross the decoupling cap and the feedback cap: 24V and 13V resp. so this seems to be OK.

Have somebody any idea ???
Thanks in advance !
Olivier

P.S.:
Somehow, I dont mistrust the caps but the transistors instead, I will begin to switch them first ... (instability increasing with temp. ???).
 
What caps are you using in signal coupling (C2 & C4) Film or polar, if the latter check the polarity, The cards are not marked for polarity because i was assuming film caps but if you are using a polar it's important to get them in the right way round (-ve leg to input/output).

Also make sure you don't have a BC550 where are BC560 should be or vice versa - fundamental but easy to do with such indistinct markings on some of these transistors (I've done it!)

And of course just check every solder joint - especially on the transistors.

Good luck and a very Happy New Year...
 
Thank you Neil, I hope you had a good evening !

Signal caps are the marvelous Wima 10µF film caps so no pb here.
Yes BC550 and 560 are the correct ones (difficult to see but they are labeled).
As said the card work perfectly for a while and suddenly distortions appear ...

I took my phonostage apart, took the 322 out and connected the 321 to the TRegs.
I then measured every points on the 321s with the great hope that the distortions would appear soon (otherwise no chance to detect any differences).
I was (very, very) lucky :)
The voltage at the TR2 (BC560) collector and thus ~ at the TR5 basis turned to 5,5 V instead of 12,70 V :eek:
There are still ~0,6 V accross the base-emitter of TR2.
Therefore I suppose that the junction base-collector may turn defect after a while. Maybe this junction suffered to high temperature as I soldered the BC560 (even if I was very carefully).

I will swap it and report back.
Thanks a lot again :)
Olivier
and happy new year to All of You here !

PS: such a problem is in fact disappointing on the first moment but afterwards it is a real enrichment since you learn a lot !
 
It was not TR2,
not TR5 either,
was also not TR4,
was not the cap C6 (just change it because on the working card it was turn the other way),
was not C3 either,
and it was not TR1, and ... it was late !
Not only that removing a component is not funny, but after replacing it I had first to wait until "Miss" 321 accepted to go wrong ... and it took each time a while :mad:)
After TR1 I decided to give up and to build another card.
Did it this morning.
They are both working a treat since 12 hours, no signs of distortion ... yet :rolleyes:.
The first hours they were a litle bit harsh (easy to ear when listening to news speakers) but it is better now.
From my last experiences with Wima (especially in the NAP140) they need 4 or 5 days to become smooth and 2 or 3 weeks to become marvelous smooth.
Next step: the 729s (still lack the 22pF Styroflex) and then the NJ-Motherboard :).
Good evening,
Olivier

@sq225917: if you asked me, I haven't Oscon yet, I use 22µF Wima as feedback and 10µF Tant bypassed with 10nF Wima as rail decoupling.
 
neiljadman said:
What caps are you using in signal coupling (C2 & C4) Film or polar, if the latter check the polarity, The cards are not marked for polarity because i was assuming film caps but if you are using a polar it's important to get them in the right way round (-ve leg to input/output).

Good luck and a very Happy New Year...
Click to expand...

Thanks for that, Neil. I had one pair of tants the wrong way round in my second pair of 729s and had some peculiar effects. Noisy volume control, fuzzy sound...
 
I've now got my motherboard up and running, well sort of. No relay section as yet - still can't find a supplier. (Digikey's website says PRMA 2A12 out of stock and obsolete) I nearly broke one of the printed earth/ground tracks on the board; :eek: and there is horrible hum when I connect the TT source :( but this is probably a simple earthing fault.

It's installed in a NAC42 case and powered from an old transformer, of unknown rating but it's quite big and heavy, and bridge rectifier board with new smoothing caps.

So preliminary results only. But CD sounds fantastic - alive and attention-grabbing. :cool: I have not heard any of the distortion I often notice when 721s are used in a NAC72 with a Hicap or an externally stabilised supply.

Must get the hum problem sorted. And if it is to be domestically acceptable then I shall have to get an olive case from a 62 or 72. But very encouraging and worth all the effort!
 
Gerontius said:
... No relay section as yet - still can't find a supplier. (Digikey's website says PRMA 2A12 out of stock and obsolete)
Click to expand...
Ownership has changed hands at least twice and these are now made by Coto Technology. They are available from Newark here is the US. And if there is enough interest I could buy a few and send them on. But it's only really going to work if 5 or 6 people want them.

The price is about $4.60 each plus $8 shipping - which would get split 5-6 ways perhaps. Then add $3.50 for packing and airmail to the UK. So if 5-6 people wanted them they'd be about $10 each delivered to your door.

Gerontius said:
...and there is horrible hum when I connect the TT source :( but this is probably a simple earthing fault.
Click to expand...
Sounds like it - did you take the earth binding post to power ground inside the amp?

Gerontius said:
...But CD sounds fantastic - alive and attention-grabbing. :cool
Click to expand...
:)
 
Whilst I don't have the motherboard I have a 72 with TRs on each cards and I agree that CD is indeed alive and attention grabbing. It has the ability to keep things hanging together when the music gets rythmically complex, I LOVE it!

Neil and Teddy are the dogs bollocks!!!
 
Neil, I might take up your offer if enough other people do.

But do you know whether this relay from Hamlin would do? It seems to be very similar and there are both 12v and 24v versions.

Still to investigate the hum; I may have missed earthing the phono input leads altogether! However perseverance has paid off so far with this project.
 
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