[Vadi]

I would like to build an SMD Dynalo
The schematic I use is the Rev.C board.
I have some questions.

Are thin film chip resistors ok? (link)
Is the TL071ID ok as an OP amp? Do I have to change anything when not using the OPA227?
Do I need heatsinks on 2SA1015 and 2SC1815? Do you know if there are SMD equivalents for them?
I can't find an SMD 4.7uF poly film type cap for C11,12,21,22. Can I use another type (for example ceramic)?
Is this a monolithic ceramic cap?
Are these fine for C1-C4,C14-C17?
Is this trimmer ok?
Should I use 100uF or 150uF electrolytic caps?

Can someone point me to a good PSU for the Dynalo?

Is anybody interested in a group buy of SMD circuit boards? One would cost 81€ while ten would be 18€ each.

 

[balou]

-the resistors should be okay, as long as the wattage matches more or less (in the voltage gain stage, wattage almost doesn't matter, but in the output stage it sometimes does)
-TL072/071 has quite a bad reputation. an ultra cheap opamp from the eighties
-can't say anything about heatsinking
-maybe just leave them out - ceramics in a psu, I don't really know if that's so good
-yes, it's a ceramic cap
-they should work. as I see it, C1-4,14-17 are bypass caps to ground - ceramics would work too, 0.1uF C0G, NP0 or X7R should work. somebody with more experience with the dynalo please correct me on this, dunno if there are specific reasons here for film caps instead of ceramics
-trimmer looks fine
-that depends on preference

please keep in mind that a BOM is just some rough reference. the one for the dynalo was made with ample space and through-hole components in mind. you will have to change quite a bit if you're going SMD. don't just try to find smd equivalents of every component, choose components according to the changed situation (no space on board e.g.)
where would you order circuit boards? olimex.com has realy, really low prices. 18€ per board looks awfully expensive

 

[Vadi]

Thanks!

I found SMD transistors.
The TO-92 dissipates 625mW while the other does 1000mW on a 6cm2 mounting pad for the collector lead.
Maybe I won't need a heatsink then?
The SMD version has two collector leads. Should I connect both of them?

 

[beerguy0]

Quote:

Originally Posted by Vadi /img/forum/go_quote.gif Thanks! I found SMD transistors. The TO-92 dissipates 625mW while the other does 1000mW on a 6cm2 mounting pad for the collector lead. Maybe I won't need a heatsink then? The SMD version has two collector leads. Should I connect both of them?

Yes. The part relies on both collectors being soldered to the PWB to remove the heat, as well as for mechanical support. The die of the part is probably bonded to the collector tab, which helps to remove heat from the part quickly.

 

[ericj]

iirc in the dynalo the opamp is just a DC servo. It doesn't get involved in amplification. In this application, the tl071 may actually show superior performance.

 

[Filburt]

TL071 is just doing DC servo duty. You could use other parts, though, such as the OPA827.

 

[tyre]

Quote:

I would like to build an SMD Dynalo.

A layout has already been done by tobias_svensk (link).

 

[balou]

Quote:

iirc in the dynalo the opamp is just a DC servo.

my bad. in this case, the tl071 should suffice

from the pm:
Quote:

Could you please explain what you'd change for example when building an SMD Dynalo?

maybe my comment was confusing. I normally associate smd with portable and portable with low power consumption. if you just want to build a normal dynalo but with smd parts, then there is of course no reason to change anything.

 

[Vadi]

Thanks!

What do you think of routing under a resistor?

Also how thick should the routes be? I remember some tutorial for the diameter but I can't find it any more.

 

[Jambo]

Routing under components is standard practise, no problems there as long as it passes DRC with clearances etc.

Minimum track widths depend on the current you're wanting to transport and what the PCB house specify as their minimum. You'll probably be surprised how much current a thin track will take.

 

[Vadi]

I still have two questions:

Are these transistors ok?
NPN
PNP

I can't find 1.6V LEDs. Do I need to change resistors for using 1.85V I found (or even 2V-2.2V LEDs, which are more available)?

 

[Vadi]

I want to add a switch for bypassing the pot. Instead of the pot the signal goes through a resistor then (like in the Dynalo rev.C board).
What value should the resistor have? (I guess the value of the pot?)

Can I use 1% thick film resistors? They are rated +/-100PPM and cost 0.02€. The alternatives would be 0.1% 25PPM thin film resistors which cost 0.74€.
I'd use the better ones for the 500 Ohm positions since they should be matched well.


Regards,
Sladi

 

[balou]

hi vadi,
Quote:

What value should the resistor have? (I guess the value of the pot?

best thing would be 0 ohm, i.e. no resistor at all. it makes no sense to fix an amp at say only 80% of its max volume, you want the full volume.

Quote:

Can I use 1% thick film resistors? They are rated +/-100PPM and cost 0.02?. The alternatives would be 0.1% 25PPM thin film resistors which cost 0.74?.

the PPM value is the variance in resistance they have with temperature, in parts per million (one tenthousandth of a percent per degree celsius), and in this application, it doesn't really matter how big it is. I'd say buy the cheaper ones for everything, and hand match them. This has the advantage that you will have enough spares, for this or for your next project, for the same price.

I'm sure somebody will taunt you for your curved lines in your layout, but actually that's the best way to do it. Have you considered adding a ground plane? it will reduce the impedance of the ground, and also act as an additional EMI shield for the components

 

[Vadi]

Thanks!

According to the Dynalo Rev. C construction guide you should use a 511 Ohm resistor when omitting the pot. What should I use?

I don't have room for a ground plane also all parts are close to ground. I read that the input of op amps don't like ground planes too.

 

[_atari_]

Sorry for dropping in that late. I am very interrested in this project since I am trying to build a portable, wallwart powered dac/amp combo.

Would you like to share your schematics? Or are they in the zip file (it is somehow corrupt for me)?

I hope you don't mind that I will use your SMDization in my design.

Best regards

_atari_

ps: are the +/- 16v mandatory or does it also run from +/- 12V?