thanks Patrick .. one more thing to be sure
I ordered BL jfets from Diya store (the BOM of the user guide asks for BL grade 8mA idss) - the jfets received don't have any idss marking on them . you mentioned before
I ordered BL jfets from Diya store (the BOM of the user guide asks for BL grade 8mA idss) - the jfets received don't have any idss marking on them . you mentioned before
so changing to E562 is the way to go , right ?i am a little bit confused ... sorry
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Quick question from a newbie learning on the go. I am planning to use this CEN IV with a PCM63 DAC (Miro). I am considering running it without a preamp and saw a note in the older thread that it may be possible to adjust the output by varying the IV_R value. Is this feasible/advisable or would it be better to add something like a Mesmerize buffer?
Wanted to double check against the BOM, if we wanted to use this for the TDA1541A (-/+2ma) we need to replace the 2k resistors to 2.4k?
It seems like this fix was detailed for both 2ma dac outputs and a high-Idss 170/74 input pair, just wanted to make sure. 6-8ma input devices and 2k in the R51/61 spots would be for -/+1ma?
It seems like this fix was detailed for both 2ma dac outputs and a high-Idss 170/74 input pair, just wanted to make sure. 6-8ma input devices and 2k in the R51/61 spots would be for -/+1ma?
My apologies for missing your post altogether.
The output voltage is given by output current of the DAC x Riv.
For 2mA output current, a Riv of 1.4k will give you 2Vrms output voltage.
The CEN IV is designed for this output level.
Increasing the output further will increase distortion, eventually leading to clipping.
The Circuit has built-in JFET buffer.
There is no need for additional buffer unless you want to drive loads <10k.
Patrick
Have you read post #60, 80, 85, 86 ?
What is the Idss of you JFETs ?
And what is the actual current of your CRD ?
Patrick
So :
For a DAC with 2mA output current, such as PCM63, it is advisable to use a high Idss JFET pair for Q1,2.
Let's assume Idss is 10mA.
Also the current through Q3,4 should be at least 3x of I_DAC, in this case 6mA.
Therefore total bias current through Q5b,6b should be 16mA or higher.
The voltage across R52,62 should be <6V, and voltage across R51,61 should be <6.3V.
To find the optimum value for R51,53,61,63, you will have to measure the actual current by applying 12V across the C452.
The resistance is then given by 6.3V x 2 / I_C452, which is between 2.4k & 3.2k.
Choose the cloest to the calculated value.
The ratio between R51 & R52 is given by the current ratio between C452 and Q3,4.
If we assume C452 to be measured at 4mA, the ratio should be 4.
If R51 is 2.7k, then R52 should be 680R.
IMHO, because of the wide tolerance, you cannot avoid measuring the C452, if you want to do this right.
Patrick
For a DAC with 2mA output current, such as PCM63, it is advisable to use a high Idss JFET pair for Q1,2.
Let's assume Idss is 10mA.
Also the current through Q3,4 should be at least 3x of I_DAC, in this case 6mA.
Therefore total bias current through Q5b,6b should be 16mA or higher.
The voltage across R52,62 should be <6V, and voltage across R51,61 should be <6.3V.
To find the optimum value for R51,53,61,63, you will have to measure the actual current by applying 12V across the C452.
The resistance is then given by 6.3V x 2 / I_C452, which is between 2.4k & 3.2k.
Choose the cloest to the calculated value.
The ratio between R51 & R52 is given by the current ratio between C452 and Q3,4.
If we assume C452 to be measured at 4mA, the ratio should be 4.
If R51 is 2.7k, then R52 should be 680R.
IMHO, because of the wide tolerance, you cannot avoid measuring the C452, if you want to do this right.
Patrick
Hello Patrick
about resistor R58 the suggested part is 71-RN55D3001FTR . This is 100ppm/C .
Wouldn't it be better a lower ppm resistor there ? something <25ppm ?
like this : https://gr.mouser.com/ProductDetail/279-H83K0BYA ?
What about Riv ? is Holco Η8 a good candidate ? I read nice specs .
about resistor R58 the suggested part is 71-RN55D3001FTR . This is 100ppm/C .
Wouldn't it be better a lower ppm resistor there ? something <25ppm ?
like this : https://gr.mouser.com/ProductDetail/279-H83K0BYA ?
What about Riv ? is Holco Η8 a good candidate ? I read nice specs .
Has this circuit been published somewhere? Which FETs, bot upper and lower FET cascoded?