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Bride of Zen, Bride of Son of Zen
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Old 20th December 2016, 04:54 AM   #21
MNYankee is offline MNYankee
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Quote:
Originally Posted by Zen Mod View Post
P5 trimpot (set and close the lid) 500R

what with 2.1mV ?

typo?
My bad, I had a brain fart as I was in a hurry to get to work. I meant 2.1 VRMS out put of the DAC. Which is about standard.

Thanks for pointing that out.

I will post pics and a review when we are done in about 4-5 weeks. I have most of the parts on order from Parts Connexion, HiFi Collective and Digikey. I need to decide on a power transformer and a metal chassis. I was thinking about going with a Chassis from Class D Audio and using one of their SDS amp chassis and drilling holes for the volume pot and selector switch in the front plate. I like the fact that it has the holes for XLR and RCA's already punched out. I might be able to remove the Class D Audio silk screening. I am open to other suggestions.

http://www.classdaudio.com/sds-chass...o-sds-chassis/

By the way, what are people using for hook up wire? I am not sure that it matters. I was going to use 22 awg silver coated copper PTFE or just 22 awg tinned copper stranded wire. I am not sure that the PTFE stuff is worth the hassle to work with, although solder does flow better with the silver coating.

I do have Cardas silver solder.

Larry

Last edited by MNYankee; 20th December 2016 at 05:03 AM.
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Old 20th December 2016, 07:45 AM   #22
Zen Mod is offline Zen Mod  Serbia
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Bride of Zen, Bride of Son of Zen
PTFE and coated is good

I'm usually using solid core , thinnest I can practically use

you choose your own
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Old 23rd December 2016, 06:54 PM   #23
MNYankee is offline MNYankee
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Thanks,

I am considering using this R-Core transformer. It has the recommended 30v + 30V

110V 30W high quality R Core Transformer 30V+30V | eBay

instead of the torroidal. Are there any problems with this?

Also, is there any real benefit to shunting the Blue Alps 10K remote volume pot with a resistor of 90% of the value that I am going to use at P1-2? I read that it can improve the sound. Is it worth the trouble?

This should be a fun build with my son over his school break.

Merry Christmas and Happy Holidays to all!

Larry
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Old 23rd December 2016, 08:30 PM   #24
Zen Mod is offline Zen Mod  Serbia
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good xformer , it seems

shunting pot with resistor ? I know for that trick from Rod Ellio's site , but that's for linear pot ...... when you shunt wiper pin with appropriate sized resistor , you're getting usually damn good log. pot

shunting pot with 90% resistor is , well , BS
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Old 24th December 2016, 05:49 AM   #25
ColinA is offline ColinA  United Kingdom
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Not to argue with mighty Zen Mod BUT!
Shunt mod to a pot can make quite a difference to the sound.
It allows the use of selected resistor in the audio path.

There was much discussion on the old World audio site and many tried and liked the idea.

Shunt Pot Volume Control for Better Sound and/or Gain Reduction - World-Designs-Forum
This is a volume control which uses a fixed resistor as the series part of the potential divider and a log pot as an variable resistor for the shunt part. Note that the pot is "inverted" from its normal wiring; the signal-in and earth connections are the other way around from standard.

It gives the signal an elegant hard wired path. The earth connection is made via the pot wiper. Any noise at the wiper junction with the track will be isolated/reduced by the track resistance between the wiper and signal.

(Subjective comment - the sound is noticeably clearer. A metal film resistor used as series gives a brighter more detailed sound whilst a carbon film type gives a warmer sound. Some of the pot character remains and pot/resistor combinations can be tried to taste. An Alps Blue with a metal film series resistor makes a very enjoyable control with sweet and open high frequency detail and warm bass.)

To keep a similar "feel" to the volume control law choose a series resistor approx 90% the value of the pot track, so 91k with a 100k pot, 47k with a 50k pot, or 18k with a 20k pot. (Only small wattage resistors are needed, eg 1/4W or 1/2W will be fine.)
Attached Images
File Type: gif ShuntMod2.gif (10.3 KB, 423 views)
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Old 24th December 2016, 08:24 AM   #26
AndrewT is offline AndrewT  Scotland
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Colin,
your sketches are wrongly labelled.
There is no ground on either.
There is a common terminal, i.e. common to both the input and the output.

Left Diagram
Two wires bring in the signal to pins 3 & 1.
Two wires take out the signal from pins 2 & 1.
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Last edited by AndrewT; 24th December 2016 at 08:27 AM.
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Old 24th December 2016, 10:30 AM   #27
ColinA is offline ColinA  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
Colin,
your sketches are wrongly labelled.
https://www.youtube.com/watch?v=oU6zpAMBDOI
Perhaps
if you want to be pedantic about it.
but most people understand them as drawn!
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Old 24th December 2016, 12:50 PM   #28
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Colin

long day yesterday ...... I didn't understood using pot as variable series resistor ...... even if I know for that

agree 100% , but I'm also sure that Eliot's trick is better , you get virtues of improved channel ballance too , simply because linear pots are usually better in that area

presuming that in solution you posted , log pot is in use
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Old 24th December 2016, 06:50 PM   #29
MNYankee is offline MNYankee
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I plan on using a 10K Motorized Blue Alps pot. I have a TKD MC2511 50K motorized pot laying around but I found it too bright and edgy compared to the Blue Alps when I tried it in my Pass B1.

If I do this mod, I was thinking of using a Shinkoh Tantalum or Audio Note non magnetic Tantalum 9K1 resistor. Or possibly an Amtrans 10K or 820R carbon. I want to keep a warmer sound.
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Old 24th December 2016, 07:26 PM   #30
MNYankee is offline MNYankee
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I have another question. I plan on using a resistor in place of the pots at P3 and P4. I read that this preamp has a lot of gain. It is going to be used with a Parasound A21 amp. The input impedance is as follows-

Input impedance:
33 k Ω unbalanced; 66 k Ω balanced

Input sensitivity:
1 V for 28.28 V, THX Reference Level

I was planning on using a 5K resistor at P3-4. Would I be better off using a different value, like a 2.2K or 3.3K to cut down on some of the gain? I was thinking about trying different values and swapping them out to see what works best. The Parasound actually has external gain controls on the back of it but Parasound recommends running it with the gain turned all the way up and I would rather not mess with them.

Thanks,

Larry

Last edited by MNYankee; 24th December 2016 at 07:48 PM.
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