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Doug Self Preamp from Linear Audio #5
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Old 9th December 2015, 09:59 PM   #261
still4given is online now still4given  United States
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Doug Self Preamp from Linear Audio #5
Hi guys,

Populating the boards and i came across R47L/47R.I can't find them in the BOM or schematic. Can someone tell me what it is?

Thanks, Terry
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Old 9th December 2015, 10:09 PM   #262
Carl_Huff is offline Carl_Huff  United States
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Quote:
Originally Posted by georgebrooke View Post
Here is one that I found.. I guess you found it too? Assuming it is not a Chinese copy what are the quality issues that you find?
ALPS Quad rotary Potentiometer RK27114MC motorized pot 10K or 50K logarithmic | eBay
Sorry George,

But those won't work. They are log taper pots. You need linear pots.
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Old 9th December 2015, 10:42 PM   #263
Rick G is offline Rick G  United States
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Doug Self Preamp from Linear Audio #5
Terry,
I don't remember seeing any R47L/R47R on my board. can u post a pic of the area on the board. Here was my board with all Resistors installed.
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File Type: jpg SAM_2642.jpg (154.4 KB, 523 views)
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Old 9th December 2015, 11:24 PM   #264
Carl_Huff is offline Carl_Huff  United States
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Originally Posted by still4given View Post
Hi guys,

Populating the boards and i came across R47L/47R.I can't find them in the BOM or schematic. Can someone tell me what it is?

Thanks, Terry
Terry,

If your PCB is marked v1.2 and not v1.2c you were inadvertently shipped a first generation PCB. I had not intended to do that, but it's no big deal if that is the case. The first PCB had two resistors (R47 & R48) that were decided to not be needed. Other than that the PCBs are identical. The fix is easy. Put a jumper in place of R48R & R48L and don't put anything in the R47R & R47L locations.

The details are shown here ...

Click the image to open in full size.

You want to end up with only R49R & R49L resistors south of the A8 op amps.
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Old 9th December 2015, 11:58 PM   #265
still4given is online now still4given  United States
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Doug Self Preamp from Linear Audio #5
Oops, I meant to say C47l/C47b.
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Old 10th December 2015, 01:36 AM   #266
Carl_Huff is offline Carl_Huff  United States
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Default Problem solved ...

Well good!
From your PIC I see that you are working with the latest PCB. My concern over shipping you the wrong PCB was unfounded.

C47 is on page #2 of the schematic. It is 220uF at 35 volts.
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Last edited by Carl_Huff; 10th December 2015 at 01:43 AM.
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Old 10th December 2015, 01:40 AM   #267
Carl_Huff is offline Carl_Huff  United States
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Default ** ALL KITS HAVE SHIPPED **

Incidentally,

All purchased project kits have shipped. The last of them went out this last Saturday morning. Those of you in the continental US should be receiving them now. International buyers should see them next week.
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Old 10th December 2015, 06:20 AM   #268
georgebrooke is offline georgebrooke  United Kingdom
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Default Another one bites the dust

Quote:
Originally Posted by Carl_Huff View Post
Sorry George,

But those won't work. They are log taper pots. You need linear pots.
And there I thought I had a solution... so far I have not been able to find a linear version of the quad motorised 10k pot...any suggestions..non-Alps...?

George
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Old 10th December 2015, 02:28 PM   #269
georgebrooke is offline georgebrooke  United Kingdom
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Default Moving on .. the 10k pot vs. the 5K pot

Jan Didden was kind enough to put me in touch with Hans Polak, who performed some analysis on the likely results of using a 10K pot instead of a 5K. (Remember, this question arises when trying to include a motorised pot for remote volume control. 5K linear are very hard to find). Hans wrote "Setup for the volume control chosen by DS, magnifies the equivalent noise at the taper of the pot (generated by the op-amps and the volume pot) by a factor 3.
This makes this circuit very sensitive for the value of the pot as far as noise is concerned.
Most noise will be generated with the pot in the middle position, in this position giving the volume-control some -4 dB of gain.
The equivalent noise generated by the op-amps calculated as being completely at the taper of the pot is ca 5,1 nV/rtHz.
When using a 5k pot its equivalent noise at the taper in mid position is 7.1 nV/rtHz, giving an increase in total noise of 4.6 dB.

Now when using a 10K pot instead, its equivalent noise at the taper in the mid position is 10 nV/rtHz, increasing the total noise with 6.8 dB.

So the difference between the two pots in mid position is an increase of 2.2 dB in total noise, not something to become very nervous, and hardly noticeable.
However all stages before the volume-control are also generating noise adding up to this, so in practice when using a 10K pot noise increase will most likely be below a humanís level of discrimination of ca 1.4 dB.

To conclude: using a 10K instead of a 5K stereo pot is not a problem at all, forget about a quad version."

So, this means that any of the 10K-based remote control systems can be considered for inclusion in the build. And with that, I shall return to my bathroom renovation :-)

My thanks to Hans and to Jan for providing this analysis.

George
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Old 10th December 2015, 06:12 PM   #270
jan.didden is online now jan.didden  Europe
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And I have to thank Carl for a sterling job with the PCBs. First rate, thanks Carl!

Now there'a balanced phono pre to be published in L|A vol 11....

Edit: is there a BoM for the power supply? Type of xformer?

Edit edit - found it!

Jan
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Last edited by jan.didden; 10th December 2015 at 06:20 PM.
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