Biasing the Op-Amp into Class A

The MINT board allows you to use a CRD to bias the op-amps into class A. (See this article for more information on this topic.) I recommend that you use one in the 0.5 to 2 mA range for most op-amps. The 1.1 mA 1N5298 is the canonical CRD for the MINT. There is a wide range of other values in that series available from several manufacturers.

If you don't have access to this line of CRDs, there are other lines mentioned in the article I linked to above. If none of those are available or suitable to your purpose, don't worry about it; this is not a night-and-day improvement anyway.

Increasing the Bandwidth of the Buffers

Most of what you need to know about this subject is covered in the BUF634 datasheet. The bandwidth resistor referred to in the datasheet is called R11 in the MINT circuit.

One important thing to note is that there is less space on the board for R11 than for the other resistors. Its pin spacing is only 200 mils. Standard 1/8W resistors are small enough to work with this pin pitch. If you're using Vishay-Dale RN55 series resistors for the other positiions, don't be confused that they're specified as 1/8W; at moderate temperatures they are in fact 1/4W resistors, so they are big enough to require 300 mil pin spacing.

Before you put something in R11, be sure you understand how this will affect the current draw of your amp. If you simply jumper the R11 position, current draw per buffer increases tenfold! Since the MINT is intended for portable use, I envision the vast majority of MINT amps having nothing in R11, and the minority having some resistor here so that you don't increase current draw too much.

Some people have done testing and have found that this resistor shouldn't be lower than 220 Ω for best sound. That's right: shorting R11 is actually worse sounding than having a small resistor value here. The highest useful value is probably 4.7 kΩ.

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Updated Fri Dec 16 2022 12:23 MST Go back to Audiologica Go to my home page