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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, 06:08 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, 06:28 PM   #482
luis.martins is offline luis.martins  Portugal
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Join Date: Sep 2006
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, 06:34 PM   #483
luis.martins is offline luis.martins  Portugal
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Join Date: Sep 2006
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.

--
Luis
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Old 3rd January 2018, 06:53 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, 07:00 PM   #485
frankwilker is offline frankwilker  Germany
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Hi freecrowder,
if you´re interested, you can boards from me.
regards Frank
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Old 3rd January 2018, 07:02 PM   #486
frankwilker is offline frankwilker  Germany
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Location: Duisburg
Hi freecrowder,
there are some boards available; PS and Mainboard.
send me an PN, please.
regards Frank
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Old 17th January 2018, 04:45 PM   #487
jackinnj is offline jackinnj  United States
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Join Date: Apr 2002
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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Old 1st February 2018, 08:47 AM   #488
luis.martins is offline luis.martins  Portugal
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Hello everyone,

Can someone shed some light on my question above regarding the CCSs?

Cheers,
Luis
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Old 1st February 2018, 09:29 AM   #489
mrdave45 is offline mrdave45  United Kingdom
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Join Date: Oct 2010
Location: Kent
Quote:
Originally Posted by luis.martins View Post
Hello everyone,

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
The mosfets are quite variable. Dont worry if the resistor values are quite different.

I used a trim pot set up as a variable resistor to find the value of resistor i needed to set the current. Once set, take trim pot out and measure with multimeter. It really doesnt matter if you use combinations of series/parallel to get the value you require although I would start with the first resistor value higher than the trim measured eg, if the trim measures 110r, then use a 120r, and use higher values of resistors in parallel to knock it down. In the case of 110r you may find 2 220r in parallel is a better bet. Again, try several different resistors of the same value to get the perfect match.

THere are 2 mosfets in the circuit. 1 position is sensitive to the variance of the mosfet, the other isnt. I cant quite remember which though. If you are OCD about matching the mosfets, figure which mosfet changes the current and then you can swap it out to find another that matches. (probably turning off the power supply first).

23.5v is fine for testing, they start doing their thing around 14v or so. I think the test circuit in the article suggested 2x 9v batteries. As you monitor the voltage across the test resistor youll see that it suddenly starts working correctly and stabilizes.

The current matching is the issue here. Absolute value isnt too critical. There was a long discussion about this earlier in the thread and a lot of people are running the CCS considerably lower than whats suggested in the article.

Hope this helps.

D.
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Old 11th April 2018, 10:32 PM   #490
guo5598 is offline guo5598  United States
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Default Board

Quote:
Originally Posted by frankwilker View Post
Attachment 625020

Attachment 625021

These are my board. If someone interested, PM me.
May I buy a set from you?
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