[Chet_Summers]

I've built both a MINT and Cmoy and the Cmoy sounds better to me. Have I done something wrong? The Cmoy seems to have a lot more power in the lows, and a bigger soundstage. The MINT sounds a bit smoother, not as shrill as the Cmoy.

I should mention that I listen to horrible music with horrible production, mostly grindcore, and my favorite headphones are Beyerdynamic DT 770 Pros and Grado SR225s. Sources are iPod, and Sony D-151 and D-EJ1000.

Is it simply a matter of my bad taste, or did I screw up the MINT, or would the MINT sound a lot better with two 9 volts instead of just one? I know I've done something right because they both sound a hell of a lot better than my Total Airhead (older version).

Thanks to Tangent for the how-tos and selling MINT PCBs. I couldn't have made either amp without him.

 

[meat01]

You could just prefer the OPA2132 opamp, to the AD8620. There are other improvements to the MINT over the CMoy, but the opamp is where most of the taste for sound comes from.

 

[tigger]

Quote:

Originally posted by meat01 You could just prefer the OPA2132 opamp, to the AD8620. There are other improvements to the MINT over the CMoy, but the opamp is where most of the taste for sound comes from.

The buffers and multi-loop topology in the MINT have as much to do with it's sound quality as the op amp.
The MINT should have a considerably smoother, more extended sound than the CMoy with noticeably less distortion.
Assuming the amp is correctly assembled with appropriate resistor values, and there are no defective parts, the apparent lack of power in your MINT could be a result of a difference in gain between the two amps.

 

[Chet_Summers]

Using Tangent's gain calculator, I have a gain of 10.88, which should be good. I do turn the MINT up more than the Cmoy, but they're different pots with different input voltage dividers, etc., so it's not that much of a difference.

I'm wondering if maybe my surface mount soldering wasn't as clean as it should have been. It seems to be okay because I don't hear any channel imbalance, but that may just mean that I screwed both up in the same way.

I'm using a 1.0 uF cap and 475 K resistor for the DC-blocking input filter, which gives me a corner frequency of 0.335 Hz. Doesn't get much lower than that.

 

[tangent]

Did you use different op-amps in each?

 

[Chet_Summers]

No, I used a Burr-Brown OPA2132 for both the MINT and the Cmoy, the only difference being the surface mount package for the MINT.

Thanks again for all the advice and guides and selling of PCBs.

 

[tangent]

How much quiescent current is the MINT drawing? Also, what is in R11?

Are you sure you're not confusing low-end power with low-end boominess? Listen to the two amps again, and see if the MINT sounds tighter yet still powerful, or simply less gutsy.

 

[Chet_Summers]

Sorry about the long delay in replying, R11 is not populated. After re-reading your parts selection guide, it looks like I should put something in there to increase the bandwidth.

This is embarrassing, but I'm not quite sure where to place the multimeter probes to measure the current draw.

 

[Pars]

Unhook the positive terminal on the battery connector. Jumper one probe end (+ or red) to the positive battery terminal, the other to the open terminal on the battery connector (i.e., put the meter in series with the positive battery lead). This will give you the current draw.

Something is wrong with the MINT, because even my kids (9 and 13) noticed that the CMoys I built for them weren't really much better than straight out of their Sony CDPs, but the MINT kicked the dog snot out of the raw CDP (CMoys were with OPA2132s, gain of 5.5, MINT with AD8620, stock gain, with Class A biasing, one with 470 ohm in R11, one with R11 open). Strangely, the MINT with a gain of 10 something in stock config, is not louder than the CMoys with the gain reduced to 5.5. Not sure why that is, cuz the CMoys at their stock gain of 11 were really loud (that is why I reduced the gain).

 

[tangent]

Quote:

it looks like I should put something in there to increase the bandwidth.

Not necessarily. I think the MINT sounds fine with the buffers in low-bandwidth mode. I just wanted to make sure you hadn't put something silly there.

 

[Chet_Summers]

I went ahead and threw in a couple 215 ohm resistors for R11.

The current draw is 23.7 mA.

Thanks again for all the help.