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His Master's Noise: A Thoroughly Modern Tube Phono Preamp
His Master's Noise: A Thoroughly Modern Tube Phono Preamp
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Old 3rd January 2018, 07:08 PM   #481
luis.martins is offline luis.martins  Portugal
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Join Date: Sep 2006
[QUOTE=lehmanhill;5275989f you are looking for something a little different, I used Amtrans AMCO caps for the 0.1 uF positions. I usually wouldn't recommend a metallized PET cap, but Amtrans does a nice job. It sounds very neutral with a little more high frequency clarity than the Wima MKP4.[/QUOTE]

Hi Jac,

Thanks for the tip. I'll look into those Amtrans caps. I need to order a few parts from HiFi Collective and will probably get those too.

--
Luis
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Old 3rd January 2018, 07:28 PM   #482
luis.martins is offline luis.martins  Portugal
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Default CCS Resistor Values

Hello everyone,

Last evening I finally started working on my build which felt great after so long studying the circuits and sourcing parts.

I started by testing the CCSs on a breadboard, trying to match the MOSFETs and checking the current for the given values in the schematic.

In the first post, SY wrote:

Quote:
R5, R14, and R18 set the CCS currents, 20mA for the first stage, 10mA each for the next stage and the buffer. The values may have to be adjusted slightly, depending on the particulars of your batch of MOSFETs; this is most easily done by attaching the + end of the CCS to a power supply (24V or more) and the – end to a 100R dummy load resistor connected to ground. The 20mA CCS should be adjusted to get 2V across the dummy load, and (naturally) the 10mA CCS adjusted to get 1V. Exactitude isn't critical.
And now I have a few questions:

With R5 = 120R I could only get around 12mA on the CCS, which is quite far from the 20mA. I had lower this value to 82R, not a slight adjustment, and was able to find two pairs of MOSFETs that would give 19.35mA and 19.65mA with this value.

Does this sound about right? My workbench power supply only does as high as 23.5V, could this be a problem and cause the tests of the CCS to deliver much less current than expected?

For the 10mA CCSs I had to change R14 ad R18 from 300R to 200R, 220R and 240R. The MOSFETs I got are far from matched but using values in this range I was able to get CCSs with a current ranging from 9.5 to 9.9mA.

Will this be a problem? Having CCSs with different resistor values? Or the only thing than matters is that the current is right. I guess different resistor values are fine as long as the current meets the target spec. I wasn't expecting to have to change the resistor values this much. This the 300R value I was only getting around 6.5mA for these CCSs.

Other than that everything went well. I used masking tape to stick the MOSFETs pairs on a sheet of paper and labeled everything so I can solder then once I clear these questions.

Cheers,
Luis
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Old 3rd January 2018, 07:34 PM   #483
luis.martins is offline luis.martins  Portugal
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Another quick question:

Do I need to get the CCS currents perfectly matched or is 0.3mA an acceptable tolerance? I could get the closer, but I'll have to use resistors in series / parallel instead of the standard values I found would that give close current values.

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Luis
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Old 3rd January 2018, 07:53 PM   #484
Freecrowder is offline Freecrowder  United States
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His Master's Noise: A Thoroughly Modern Tube Phono Preamp
Are there boards available for order on this preamp? If so who do I talk to?
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Old 3rd January 2018, 08:00 PM   #485
frankwilker is offline frankwilker  Germany
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Location: Duisburg
Hi freecrowder,
if you´re interested, you can boards from me.
regards Frank
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Old 3rd January 2018, 08:02 PM   #486
frankwilker is offline frankwilker  Germany
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Join Date: Nov 2011
Location: Duisburg
Hi freecrowder,
there are some boards available; PS and Mainboard.
send me an PN, please.
regards Frank
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Old Yesterday, 05:45 PM   #487
jackinnj is offline jackinnj  United States
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Location: Llanddewi Brefi, NJ
His Master's Noise: A Thoroughly Modern Tube Phono Preamp
Quote:
Originally Posted by Globulator View Post
Would a pentode like a 6j51p/EF184 be a reasonable sub. for the D3a?
6EJ7 ?
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