[individual6891]

So I figured why everyone was having difficulties fitting the MINT into the smallest hammond with a 9V, it seemed logical to me how it should all go in. Not the easiest of jobs, but at least it'd do-able!

Standard Mint with 1.5mA CRD, jumpered R8, 0.22uF MK4 input caps, Panasonic FC 220uF capacitance, 0.1% 15ppm TruOhm resistors, silver plated PTFE wire...

High quality macro shots soon

 

[Nisbeth]

Nice Job!

I've been meaning to try that for quite some time, beacuse i would really love a small protable amp like that. Only problem is that I would prefer to have the charger built in...

/U.

 

[n_maher]

Nicely done! I've actually got plans to do one myself as the cmoy that I tried to shoehorn into that case failed miserably.

Nate

 

[Super-Gonzo]

Brilliant idea to heat shrink the whole circuit board!

I've done nearly the same thing with my mint... but I have problems with things shorting out too easy in such a small case. I'm gonna have to give the heat shrink a go.

Looks like I'll have to lay down the big caps like you've done, that might take a little creativity.

On the plus side, I was able to squeeze in dual 9V's, using the longer version of this case, the 1455C1201.

Nice work!

 

[digitaldave]

Nicely done

.

I agree about heat shrinking the board - a simple but effective idea.

 

[Magsy]

Good job!

I have one of those hammonds waiting to be filled too!

Where did you get the crd in the uk?

 

[individual6891]

Thanks everyone, the heatshrink does make things really tight, but it's all snug and nothing shakes around - so I guess thats ok. The tallest component was the input caps, and I used a SIL header to separate the boards... Most annoying thing now is that I'm reconsidering jumpering R8... The amp's designed for portable headphones, and how many portable headphones are high impedance?!

Gonna stick a 47R in there now, and also set the gain from 2.3 -> 4.2. Oh the fun of desoldering the two boards!..

The CRD I got from Rapid, but the 1.5mA axial is discontinued, and the SMD is getting to low stock. I got the SMD version, and it wasn't very difficult to solder to the board at all ... just use a lot of solder

The 2mA axial i think is available, but I didn't want to draw too much current.

Gonzo, if you look closely at the 2nd to last pic you can see one of my cap's legs are bent a lot!

Amp sounds fantastic with the AD8620 - just need to get rid of the small hum as said above..

 

[Edwood]

Well, of course a Mint + a single 9V can be crammed in there. WIth some sacrifices made, particularly with regards to electrolytic capacitance.

Wish Wima caps were more plentiful here in the US, they are quite a bit smaller.

-Ed

 

[individual6891]

I settled on 220uF/10v FC's in the end cos that's what I had in my box.. They're the same size as the 330uF/10v ... just that I didn't want to pay £5 getting 110uF extra

. Hell you can even use 470uF/6.3V if you're sure your virtual ground remains stable.

I can't hear the difference between 220uF and 470uF unless I bring out the HD650 , and I wouldn't want to use this amp for those cans anyways

I don't think there's much sacrifice for this amp, other than the lack of R11, but that's true for all single 9v amps...

Just finished replacing R8 jumper with 47R, and replaced R4 for higher gain. Amp sounds absolutely fantastic for such a small size...this is my first DIY amp , so I'm pretty surprised it worked first flick... Only problem was battery polarity was borked but spotted it when testing the rail splitter - battery and diode were almost smoking

.. Also knobbed the potentiometer, and thumbscrewed the battery plate.

Final pictures (custom cabled HD497s, and mini jack - mini jack)...

 

[Syzygies]

Very nice! I had been using my MINT boards for soldering practice, I couldn't accept having the volume knob on the side for a shirt pocket amp. You've convinced me to finish a couple.

A careful parts list (for anything that could possibly influence fit; you've told us most of it already) would probably go over big here, e.g. my favorite 3.5mm stereo jacks instead of yours might be the reason mine doesn't fit!

So where did you get the TruOhm resistors? I could only find the larger, 0.4W ones at Precision Electronics.

As for charging, it looks like there's room for a power jack in back. A simple resistor charging circuit, tuned for the one power supply you're likely to already have with you (for me, the iPod power supply), would take very little room at all. This doesn't preclude using an outboard LM317 charging circuit most of the time to guarantee a constant trickle charge, it would just have to push a fixed current through the resistor and the battery. This raises the voltage overhead somewhat.

Edit The thumbscrews are clever. I just see myself wanting to open one of these up without tools, in the middle of a long flight, you've just solved that problem.

 

[individual6891]

Quote:

Originally Posted by Syzygies Very nice! I had been using my MINT boards for soldering practice, I couldn't accept having the volume knob on the side for a shirt pocket amp. You've convinced me to finish a couple. A careful parts list (for anything that could possibly influence fit; you've told us most of it already) would probably go over big here, e.g. my favorite 3.5mm stereo jacks instead of yours might be the reason mine doesn't fit! So where did you get the TruOhm resistors? I could only find the larger, 0.4W ones at Precision Electronics. As for charging, it looks like there's room for a power jack in back. A simple resistor charging circuit, tuned for the one power supply you're likely to already have with you (for me, the iPod power supply), would take very little room at all. This doesn't preclude using an outboard LM317 charging circuit most of the time to guarantee a constant trickle charge, it would just have to push a fixed current through the resistor and the battery. This raises the voltage overhead somewhat.

No way will a LM317 fit in there

.. DC jack should be able to I think, but it should be a switched socket, cos there's no way you'll fit another switch on the front panel unless you use really small microminiature switches..

The TruOhm's I got from Rapid Electronics in UK... www.rapidelectronics.co.uk ... they're equivalent to the Welvyn RC55 0.1% 15ppm, but at quarter of the price

Parts worth noting...

All resistors: TruOhm 0.1% 15ppm ...standard values a'la Tangent, except R4 = 820, which gives me a gain of 4.7ish - R8 is populated for low impedance load, R11 is not populated to increase battery time. RLed draws 2-3mA through the LED.

Power Supply caps: 220uF / 10V FC though you can fit 470uF in here if you mount the caps sideways like my configuration.. or even fit 560uF / 6.3V

Input caps: Wima MK4 0.22uF, though a 1uF version is available but not in stock at the time (also not convinced about height). You could probably leave this out and jumper across it for most sources, but I'd rather be safe than sorry.

As for the 3.5mm jack sockets - they are the same that Nisbeth used on his Disco LED mint - I got them from www.maplin.co.uk

 

[Syzygies]

Are your caps 8x11.5mm? Panasonic FMs come in 16V 330uF for this form factor. NiMH 9V cells will certainly exceed 10V in charging, a very fresh alkaline 9V could exceed 10V. I'd want 16V caps.

One doesn't need a switch for charging, just a resistor to protect the batteries. If the amp is on it will draw current away from the charging batteries, the amp might work, it won't self-destruct as long as the caps are ok.

 

[individual6891]

Quote:

Originally Posted by Syzygies Are your caps 8x11.5mm? Panasonic FMs come in 16V 330uF for this form factor. NiMH 9V cells will certainly exceed 10V in charging, a very fresh alkaline 9V could exceed 10V. I'd want 16V caps. One doesn't need a switch for charging, just a resistor to protect the batteries. If the amp is on it will draw current away from the charging batteries, the amp might work, it won't self-destruct as long as the caps are ok.

Well, since the caps are horizonatally mounted, the most important thing is diameter - you don't want it to overlap the input caps (which at the moment are the biggest things sticking out). I'm using 10V, because the total voltage from the power supply is split between the two supply caps. Yes I know the rail splitter might fail and might short out the caps and blast the total supply voltage across one of them, but that's my risk - and I'm pretty certain everything inside the heatshrink is clean enough with no stray strands..
If the TLE2426 does fail, you'd need to replace it - and the panasonic FCs aren't exactly expensive, so why not just replace them at the same time as the TLE2426? Hassle yes, but the priority here is space

Anything thats 8mm diameter, 11.5mm height should fit in here no probs (side mounted). I think 10mm diameter would be a tight fit.. There's no significant audible difference on rail capacitance over 220uF on the mint board, so I guess the smaller physical size the better

 

[Syzygies]

What size heat-shrinking?

Are the TruOhm "standard" sized? What did you do for the buffer bandwidth resistors, which need to be smaller? Welwyns are oversized, they'd never fit a MINT.

 

[Syzygies]

Others have separated the two halves of the Mint board some distance from each other, e.g. for the Hammond C12 board. A variant on your approach would be to hang both caps side-by-side off the end of the board, and wire them to the cap holes using short leads. Can this possibly be worse than separating the board halves some distance, involving more and more sensitive leads? Looks tidier to me, in mockups.

This way one could use a pair of Panasonic FM 25V 470uF 10x16mm caps in a Hammond C12 case, leaving plenty of room for an LM317 charging circuit.

Why didn't you board-mount the pot? Is it not the Panasonic EVJ?