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Improving a Maple Tree Audio PS 2 power supply
Improving a Maple Tree Audio PS 2 power supply
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Old 26th January 2010, 02:09 PM   #11
316a is offline 316a  England
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Quote:
Originally Posted by diamondsouled View Post
Thanks Eli!

I did check it fairly thoroughly before I sent it back to Lloyd at Maple Tree and again when I got it back and it was still humming. Maybe temporarily replacing one leg of the 100/100 JJ with a motorrun might tell me what I need to know. Actually I have a humongous 100uF 750V Electronic Concepts Metalized Poly that will do the trick. If that gets rid of the hum the choke should do it as well, .

Cheers

Lar
You're suppose top chase down the issue rather than hack the unit to pieces ! What level of B+ ripple is present ? What amount of hum/buzz do you measure at the output jacks ? What is the frequency 60 or 120Hz . What about with source/amp connected or disconnected ?

316a
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Old 26th January 2010, 03:00 PM   #12
diamondsouled is offline diamondsouled  Canada
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Quote:
Originally Posted by 316a View Post
You're suppose top chase down the issue rather than hack the unit to pieces ! What level of B+ ripple is present ? What amount of hum/buzz do you measure at the output jacks ? What is the frequency 60 or 120Hz . What about with source/amp connected or disconnected ?

316a
I wasn't suggesting that I install the humongous cap but simply put it into the circuit temporarily ;^). Good way to trouble shoot in my experience.

Cheers

Lar
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Old 26th January 2010, 03:04 PM   #13
diamondsouled is offline diamondsouled  Canada
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Quote:
Originally Posted by budmaestro View Post
Lar,
I have the Maplewood line preamp and listen to it every day. No hum whatsoever. I am not an expert on electronics but you might post the rest of the schematic as there is another 100 uf electrolytic cap in the power supply stream that is inside the other enclosure (i swapped it out for a homemade multi-parallel mpk that sits on top of the unit-ugly but sounds better IMHO). Funny Lloyd said it checked out-could you have an incompatible source?
regards
dave
Hi Dave,

I tried a variety of sources with it. Even tried using my Tercel phono stage with it with the same results.

I'll do a scan of the other schematic and put it up.

Cheers

Lar
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Old 26th January 2010, 10:40 PM   #14
refference is offline refference  Brazil
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Hi Eli , Hi Lar , sorry for the delayed reply .

Quote:
Originally Posted by Eli Duttman View Post
The power trafo is good for but 25 mA. So, a large inductance is highly feasible. The 595 Ω DCR/40 mA. rated/40 H. Hammond 157G will put a serious dent in the ripple level.
Yes , I agree .

Quote:
Originally Posted by Eli Duttman View Post
I agree that the design is quite questionable. Apparently, the low current capability of the rectifier winding and the resistance of the rectifier winding are preventing arcing over.
Yes !! Fortunately . But I think that is not the only drawback in this design .

The Sylvania Technical Manual 12th edition ( 1958/59 ,I'm not sure ) says that the 6X5 GT ( electrically similar to type 6X4 ) ,connected in a capacitor input filter , does not may have the 1st cap , larger than 10 uF , and to have minimum effective impedance per plate of 525 ohms . As you can see it is a tube with a very limited capacity , and must be used with certain care .
This tube has a bad percentage of regulation , < 15 % .
Another thing that I do not agree ( IMO ) is the use of a 6K8 x 5W + 100 uF , not a good choice .
We can get BEST results , if spliting the 6K8 x 5W + 100 uF RC network , in 2 or 3 parts : 2 or 3 RC networks with 2K2 x 5W + 30/35 uF ( or even 50 uF ) one after another , being the 1st cap a 10 uf MKP unit .
( The Scroggie table ) .

I do not know , if you ( Lar and Eli ) are going to agree with me , but I have
two suggestions for this power supply :

1 ) Let the rectification stage stays as it is ( 6X5 GT + diodes ) , then a 1st
cap of 10 uF , then a filter choke as described above ( need to know the
coil DCR , to subtract it from the 6K8 ohms total resistance ) , then a 2nd
cap of 100 uF , then 2 or 3 RC networks , composed by +/- 2K2 x 5W +
30/35 uF ( or bigger , if available )
The total resistance R1 + R2 + R3 + Choke DCR must be equal to 6,800
ohms , to give the same voltage value at the output .
This is my favorite solution .

2 ) Replace the tube with DIODES as I (and Eli ) had said , a big 1st cap, then
a filter choke and then 2 or 3 RC networks , with BIG caps ( the BIG value
no longer matters , because there is no tubes in the path ) , the only pro-
blem is that you'll need to recalculate the total resistance , to give the
correct voltage value at the output .
This is NOT my favorite solution , but works well , too .

I hope it helps ,

Regards,

Carlos
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Old 27th January 2010, 02:44 AM   #15
Eli Duttman is offline Eli Duttman  United States
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Carlos,

I think you are slightly underestimating the capability of the 70 mA. vacuum rectifiers. Check out this French 7Y4 data sheet, which shows the type being electrically equivalent to the 6X5. Also, check out the TDSL page, which suggest up to 40 μF. in the I/P cap. are OK.

I think that a 22 μF. 1st cap. will be quite satisfactory. LCRC after the 1st cap. will make for an excellent low current supply.
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Old 28th January 2010, 08:49 PM   #16
refference is offline refference  Brazil
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Quote:
Originally Posted by Eli Duttman View Post
Carlos, I think you are slightly underestimating the capability of the 70 mA. vacuum rectifiers.
Hi Eli . Yes , may be . But the 6X4 / 6X5 family , was developed , to be used
with vibrators in car radios ,where the in rush current is very " gentle " , and the cap's values are low , thus , I am very conservative about its ratings.

Quote:
Originally Posted by Eli Duttman View Post
I think that a 22 μF. 1st cap. will be quite satisfactory. LCRC after the 1st cap. will make for an excellent low current supply.
Yes . I agree , I think that 10 uF or 22 uF in the 1st cap , makes no difference
in the rectifier functioning . BUT I still prefer one more section of RC , I mean
1st cap 22uF + L (high value ) + C2 ( may be 100 uf ) + R1 + C3 ( may be 100
uF again ) + R2 + C4 ( may be 100 uF again ) .
You will agree with me , that this power supply will be insuperable and Lar (diamondsuled ) will be free from any noise or any hum .

Regards ,

Carlos
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Old 12th February 2010, 11:11 AM   #17
Burnedfingers is offline Burnedfingers  United States
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Lar,

Could you drop me an email?

Thanks,
Joe
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Old 14th February 2010, 10:50 AM   #18
Burnedfingers is offline Burnedfingers  United States
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I would like to diy this phono preamp. Would anyone share the schematic?
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Old 29th June 2010, 07:51 PM   #19
thor61 is offline thor61
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Where the mods done as described ? If so what kind of improvement was had ? Also can someone post the finished schematic please ? Thanks !
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Old 7th January 2011, 02:34 PM   #20
Alexdad54 is offline Alexdad54  United States
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I also have this preamp and it seems to be causing a hum without any sources connected. Did anyone do the mods and, if so, how does it sound?
cheers,
Dave
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