MINT Parts List - Suggestions/Advice

[n_maher]

Well, I love my little Cmoy that I built so much I have decided that my next DIY project will be a MINT. I don't feel like dumping the $$ into a PIMETA just yet and I like the fact that the mint has buffers and can be biased. Please bear in mind when making rec's that size w/ this MINT is not the driving force, it's basically being built as the ultimate Cmoy.

What I'm trying to decide is:

1. Is it worth using an ALPS pot for a MINT?
2. Is biasing worth it?
3. Are the Switchcraft jacks worth it?
4. Am I missing anything from the attached list?

Thanks for any help.

Nate

 

[guzzler]

The ALPS RK27 won't fit on the MINT board. The only way to use it is to mount it direct to the case and run wires to the MINT. The MINT uses the Panasonic EVJ pot from Mouser or Digikey, I can't remember which.

Don't bias initially, add it when you're satisfied with the amp and maybe want to experiment.

Might as well go for the switchcrafts, they're not terribly expensive and are a quality product.

You don't need a socket as the opamp is SMD and as such is soldered directly to the board and is about half the size of a DIP package. Other than that, looks dandy to me.

g

 

[MisterX]

Quote:

1. Is it worth using an ALPS pot for a MINT?

No, (mainly cause of the reasons Guzzler pointed out) but for the same price you can buy a few extra EVJs and pick the one that tracks the best so.....

Quote:

2. Is biasing worth it?

That depends on the opamp.
With the OPOS2227 yes it is worth trading the battery life for the sound.

Quote:

3. Are the Switchcraft jacks worth it?

Yes, cause the alternatives suck.

Quote:

4. Am I missing anything from the attached list?

R11... I would trade R11 for the class "A" bias anyday.
You are also missing a GOOD opamp (matter of taste) a DC-jack and an Elpac ... you WILL get sick of changing the batteries in that case very quickly
I would also suggest bigger PSU caps (#P10275) and also a pair of film bypass caps just in case.

 

[n_maher]

guzzler,

Yup, I know I'll have to wire up the Alps pot, which I don't think is any big deal. Just wondering if folks have noticed a $10 difference in performance.

I'll order the biasing parts (might as well) but that's good advice to see what I think of the amp before and after.

I want to use the socket so that if I want to swap out the amp in the future I won't need the iron. It seems to me that having this option would be nice.

And I'll take that as one vote for the switchcrafts.

N

 

[n_maher]

Quote:

Originally Posted by MisterX R11... I would trade R11 for the class "A" bias anyday. You are also missing a GOOD opamp (matter of taste) a DC-jack and an Elpac ... you WILL get sick of changing the batteries in that case very quickly I would also suggest bigger PSU caps (#P10275) and also a pair of film bypass caps just in case.

Feel free to suggest an alternate Opamp. And thanks for the tips on the caps and powersupply stuff, I'll look into it.

N

 

[MisterX]

What are you gonna solder that dip socket to?

What cans you using?
Knowing that goes a long way to helping us figure out what opamp will be best for your setup.

 

[Syzygies]

Quote:

Originally Posted by n_maher Please bear in mind when making rec's that size w/ this MINT is not the driving force, it's basically being built as the ultimate Cmoy.

Indeed, the MINT has some room to bounce around in the J12 case (I have some Illustrator files handy from playing with floorplans):

1. How about a switch for throwing some resistance in the way of your Ety 4p canalphones, making them 4s? I haven't done this, but it's a standard idea you can google to figure out.

2. The Shellbrook Labs "Maxi Moy" uses this case, look what they do for ideas:

http://www.shellbrooklab.com/maxi.htm

3. You'd have room for a trickle charge circuit for the two 9V batteries that just barely fit into this case. (Case height is tight; I'd be afraid they wouldn't fit, but Shellbrook Labs manages so they must.) If you use a DPDT toggle switch for amp power, in the "off" position it could separate the batteries for separate charging. If you figure the worst-case watts and match the ohms to your power supply and battery, it's hard to beat the simplicity of a resistor for each battery as a trickle charge controller. Let me know and I'll draw the DPDT circuit for this. I've devised and tested fancy circuits for reducing the voltage overhead using LM317 regulators, and in the end I came to prefer a simple resistor circuit, no contest.

One reason to consider this is it will be a pain to keep opening the case to feed it batteries?

4. The Alps won't fit, it's a 25mm cube:

http://tangentsoft.net/audio/pimeta/pguide.html
http://www.hammondmfg.com/pdf/1455J1201.pdf

 

[Syzygies]

I took a look at your CMoy gallery, nice work overall.

I truly mean this in the best possible spirit, you're asking for advice, I'd think twice about soldering a MINT until your solder work has moved on from the underside solder photo there?

(Gotta admire your courage in posting it, I've posted solder shots also, I'm always thinking I can't even see how bad my work is, it's like one of those dreams where you're walking around in your boxers...)

Believe me, we're in the same reading group. I ended up buying a digital Weller (WESD51; I also like good knives in the kitchen), but with practice I'm much better than I was even using an $8 RadioShack iron. Tangent's solder recommendations really help, too, along with a good gooseneck magnifying glass. Do some simple projects that cost a few bucks each in parts; I made a dozen charging circuits in different sessions.

If you have a cheap scanner, they have surprising depth of field for taking pictures of circuits. I got better at soldering by staring at my work blown up to fill my monitor.

 

[n_maher]

Okay, lots to address in this one but here goes:

Misterx:

1. Cans - see sig

, unless you have them turned off - in which case it's Ety Er-4p's and Senn 535's (probably 580's w/in a year).

2. Is there any reason that you can't mount a socket to the MINT board? Or did I pull a dumb*** move and pick the wrong socket (which wouldn't be surprising). Nothing is ordered so nothing lost, yet.


Syzygies:

3. I don't want to turn the 4p's into 4s's, just my choice in the matter.

4. The pic of the soldering that I'd done on my Moy was a work-in-progress type shot, I went back and "touched up" all the light spots. I sorta knew that some of it was sketchy but I was really just trying to get the outside-the-enclosure version working as both a friend and I had built Cmoy amps that weekend and neither worked. We were both idiots and had wired the inputs and outputs wrong. Mea Culpa. The end result of the bottom of my board looked every bit as good as the pic you posted, unless that's not good, in which case color me confused that looks like fine solder work to me. And I certainly appreciate the critique, it's hard to learn if you're not willing to listen. It took no courage to post that shot of the underside of my board, just no ego, I use the internet as a tool, which requires that I listen to at least some of the advice that I solicit.

My toolkit currently includes a Welder adjustable iron and Tangent's recommended solder. Certainly I could have spent more but the resulting kick to the curb by the SO would have cost a whole lot more.

5. The charging suggestion has been taken to heart and sounds like a great idea, any links where I can do some background reading. I think Tangent has some info on his site, which I'll read, but any other links would be great. And if you want to share a parts list or schematic for a charging circuit that'd be very helpful.

6. And thanks for the catch on the ALPS pot, that would have been a major bummer of the wallet variety.

Keep the info coming, it's all good.

Nate

 

[guzzler]

Regards the socket, there isn't a place to put one. The MINT uses surface mount chips to save on space. Basically, it means you're soldering has to be pretty good with steady hands as you're soldering at half the pitch of through hole stuff (eg, your CMoy), and while you're soldering it, it'll be skittering around. Look at the pictures on Tangents walk through and you'll see why you can't use a socket...

If you're using a 9V NiMH, the only thing you can do is implement a trickle charger as the cells in a 9V NiMH are too small to withstand the heat from a fast charge. Just a simple LM317 set to CC mode will do the trick, just make sure you don't charge them for too long...

g

 

[Syzygies]

To give you a sense of scale, this LM317 charger drops into the 8th slot in a pair of 4 AA holders glued back-to-back, and charges 7 AA cells off an iPod supply:

Each of the diodes has a leg jumpering a neighboring pad. This circuit is easy to build but less easy to analyze; I was trying to avoid having the LM317's 1.25V volt reference drop in the charge path, which you can afford with a 9V battery. At a minimum you'd need the LM317 and one resistor per 9V battery, or go with a resistor charger, pros and cons either way. I still need to draw for you the DPDT circuit to toggle between series powering the amp and parallel charging...

Meanwhile, study Tangent's NiMh battery board

http://www.tangentsoft.net/audio/ppa/bb/

but keep in mind they aspire to providing state-of-the-art, we aspire to the smallest, simplest thing that works and keeps us from having to unscrew the Hammond case. Read the LM317 data sheet

http://www.national.com/ds.cgi/LM/LM117.pdf

and read Eveready's datasheet on NiMh batteries

http://data.energizer.com/PDFs/nicke...dride_psds.pdf

For understanding a resistor charger, I like this graphical method:

This illustrates charging 8 NiMh AA cells through a 10 ohm resistor. A square is 5 ohms wide and 1 volt high, so a slope of -1 represents a charging current of 200 mA. The dots in the upper left model two different iPod power supplies as ideal voltage sources in series with resistors. The per-cell voltage is given on the right; as the cells charge, the dot representing the battery climbs to a peak of 1.45V or so. One draws a line between the battery dot and the power supply dot, to read off current. Currents between 1/10th and 1/20th the battery capacity ("C/10" or "C/20") are considered trickle charges, with pros and cons at each extreme; googling will turn up lots on this subject.

This graphic makes it obvious that as the battery charges, the charging current falls. (This is also obvious to plenty of people from the algebra, but I like to think graphically.) I'm still working on a complex numbers version of this to help me understand capacitors and resistors together, but this approach has helped me with everything I've designed so far, e.g. my binary stepped attenuator.

 

[james902]

Quote:

Originally Posted by MisterX What are you gonna solder that dip socket to? What cans you using? Knowing that goes a long way to helping us figure out what opamp will be best for your setup.

would you have suggestions for er4s's? i'm about to build my list of parts too, but finals are keeping me on my toes

i was thinking about the 8620.

 

[n_maher]

Syzygies,

Thanks for the info, time to do some more reading/research. Any pics of how you use the Ipod power supply to attach to the battery holders? And I think I'll build another Cmoy before I launch into the MINT for some additional soldering practice. It's probably $20 well spent in parts and labor.

James902,

For me this MINT is a balancing act. I want to build a better amp than the Cmoy that was my first project but at the same time I realize that it's still just a step towards either a PIMETA or a PPA. Putting a $15 opamp into a $40 amp doesn't seem to make a whole lot of sense to me.

Almost time to order parts.

N

 

[skyskraper]

why not just go straight to the pimeta? its not much pricier, and much easier to work with

 

[en480c4]

Quote:

Originally Posted by skyskraper why not just go straight to the pimeta? its not much pricier, and much easier to work with

A follow up question...

I used that spreadsheet that's floating around for pricing out a pimeta and came up with a HUGE difference between it and the mint. Granted I priced a maxed out versions of each...

So, here's the question:
Is it better to spend a little more for a very basic pimeta and have the easier layout to work with? And will building a "basic" pimeta result in a superior amp to a "maxed out" mint? This could be a better balancing act if it will sound similar, cost a little more and be easier to work with...

Thanks! Your input's appreciated...

Ian