MASantos

I was measuring L+ L- to GND. I didn't measure between L+ and L- I'll check that quickly. No single ended phones atm so I'm safe there.

Success! I managed to get offset to within +-1.5mV on both channels. Installed the servo jumpers and music is great! One question: I let the amp cool down and then measured offset during startup. It got very high, above 150mV and descended in about 20-30 seconds to +-1mV, is this behaviour normal even with the servos in the circuit? MIght this damage the headphones if plugged during startup?

This might be a dumb question, should I short the inputs?

Thanks!! Today was outside DIY with my 6yo, recycling some wine crates.

Channel to GND DC yes. So you just play with the 2 trimpots close to the LED's to adjust offset? I'll reset the 4 trimpots close to the input transistors to midpoint and go from there. I'll need to remove the 0 ohm resistors first.

I measured the bias across all the 20R resistors and they're all flowing between 270-340 after a few hours with the top plate on. there are some variations in each channel between the 20R resistors, some might go to 340 and the one next to it only to 310. could this be transistor variation? I had the DC offset dialed to about +-5mV before installing the jumpers on the back side of the board. I'll remove the jumpers tomorrow and reset the trimpots.

So I finally got to finish my dynalo mini build. It is playing nice with 2SK170/2SK79 input jfets, 420ohm led resistors and 255 bias resistors. Temperature with cover on is 103C on left side (- channels) and 81C on right side (+ channels) transistors, is this sort of difference normal? I checked bias and L- is around 340mV while R+ is around 290mV. could this have anything to do with the offset trimpots? All the bias resistors 255ohm and led resistors (420ohm) measure within spec. Voltage drop on the leds around 1.65V When I remove the lid the temperatures drop quite a bit to around 60C-75C which is understandable. Sounds great though with my sennheiser HD650 recabled with 4 pin XLR. I would just like to understand this diferrence between plus and minus channels

Hello guys, after a long time, and with a lot of time in my hands due to quarantine I finally finished my Dynalo MK2 mini and reterminated my hd650 with a 4 pin balanced plug. Transistors are a bit hotter than I wanted, at 90-100 degrees with the top panel on. I need to go read about reducing bias. Sounds good though! Source at the moment is a bluesound node, need to go and find a better DAC with balanced out that doesn't break the bank.

I fired up the mini this morning, no smoke or fireworks which is always great! I left it for half an hour to warm up with the case closed and measured the temperature over the transistors with an IR thermometer. I got temperatures between 90-100 celcius, which is very hot. This seems to be quite hot, much higher than what other members reported. Is this safe or should I look into reducing bias? I don't mind the heat, but don't want to have to replace transistors anytime soon.

I was mentioning the rega speakers story. I'll tell you another: I bought a lyngdorf audio amp and speakers about one year ago at the portuguese dealer, who gave me a 15% discount on a brand that has a fixed price list. the prices online are all the same everywhere, so I got a very nice deal. There are good dealers and bad ones everywhere!

Well it isn't fair for a dealer to spend money having a store, stocking products and employing people, having you go there to listen and choose products, and then go buy somewhere else. If one wants to do that then they should order the product from the shop with the great price and return it if they don't like it and the shop allows. One shouldn't have a cake and eat it too in this situation. I can't understand how supersonido gets away with some of the prices they practice, most brands have some sort of price list that dealers should abide.

Guys, a question for those who used AMB's o78/79 regulators. Do I need to isolate the PCB from the heatsinks?

@cspirou Arrow has free international shipping, so I just ordered from them. Thanks for you help anyway!

thanks, that would be great. I'll send you a pm later today.

It seems I have forgotten to order the MMBTA56 SOT 23 transistors. Does anyone have 6 of these by any chance that they would be willing to sell me? Ordering from mouser will cost me an arm and a leg in shipping and customs for 1 dollar worth of parts.

They should all point to the same side indeed, but I for some reason I can't understand I soldered them this way... ? Regarding the 0ohm jumpers, I didn't understand I should only install them after testing the amp, I'll remove them tomorrow as well then.

Underside of the dynalo mini done, just need to clean the flux residue when it's all done. Those 0805 resistors are starting to be the smaller I can solder without magnifying glasses. I just noticed looking at the picture that the tantalum capacitors don't have the positive to the same side of the board. I must hsve confused this somehow and will take care of it in the morning.

I'm starting building my dynalo mini next monday, I tryed to find info regarding DC offset adjustment, and how to adjust each pot, but couldn't find any info.

There is space inside for one of those ultra quiet computer fans. With a reduced voltage removing a bit of air from inside the box might help.

Have you measured the top.of the transistors without the sinks?

Regarding the output transistors heatsinks, what size should I look for?

Parts ordered for a mini dynalo, should be here in a couple of weeks.

Finally got my boards through customs. Great packing Steve, thanks and the quality is awesome!

Could someone point me to the latest bom for the mini? I had one but cant find it.

Got my package yesterday, great quality for the price! There were 2 silver screws and nuts, what are those for? Can't remember