replace the tl074s

[dreuf]

it is possible to replace the tl074s, to make a midiboxfm with only 0-5v?

I want to build a little keyboard for travelling with a 9v battery.

thanks

[seppoman]

replacing the tl074s wouldn´t help. OpAmps generally need a bipolar supply as long as you don´t redesign the whole cirquit to an unipolar setup. The easiest solution: use two 9v batteries, connect + of one to - of the other and use this junction as your ground. The tl074 will run fine from +/- 9V. Probably you should change the 22k resistors around IC6 to 10k or 15k. They adjust the amplification and with 22k, the peak output would go over +/- 7V which is around the max output you can get off +/- 9V supply.

In this setup, it could be a good idea to use a third 9V battery (with - also connected to the mentioned junction) to drive the 7805, because otherwise the "plus" battery of the pair would be flat long before the "minus" battery. And think about using a LCD without backlight cause backlight draws a lot of current.

Seppoman

[napierzaza]

So wait, let's say I have a 5v power supply, how long would this 9+- volt supply (in conjunction with the 5v PSU) last? I recall Thorsten saying that they 12+- line draws very little current.

[seppoman]

I think there´s no sense in using 9V batteries in stationary equipment. Without load, a 074 draws around 5-10 mA (from the data sheet). So standby/silence would be around 20-30 mA. When playing this goes up a bit. 9V rechargeables mostly have very low mAh rating because they´re built from small 1.2v cells like for watches. I guess with rechargeables you´d get perhaps 5 hours of playing (if you buy good ones). Alkalines should last longer. But after a few weeks the price for alkalines will reach the price of a new bipolar PSU (as does the price for two sets of accus and a charger). And you have to bother with recharging/exchanging all the time.

Seppoman

[napierzaza]

_IF_ it didn't cost as much as it does to ship such a PSU.

[seppoman]

:o At which remote place of the world do you live? even if you can´t find such a PSU for sale in your part of the world, there has to be someone that sells 2x12V transformers? Then build your own linear -/- 9V PSU from that. That would be safer than poking around in a broken switcher like you do ATM. A self-repaired switching PSU can make a nice fire or high voltages if you don´t really REALLY know what you´re doing! So be careful :)

[napierzaza]

Well my mouser order cost was increased by about 50% because of shipping,taxes,holding fees.

If you have any specific recommendations for a place that might sell transformers, or better yet a linear 12+,12-,and 5+ PSU I'll check it out. But even just shipping to Canada really slagged my project.

Personally I really don't want to build a PSU, I'm hoping that the one I fix will be easier, but if I could just buy one for a decent price I would.

[dreuf]

Thanks, but if i want an unipolar setup, what should i do?

[jrp]

To my knowlege and experiance any opamp can be used with a single supply.

But: For an inverting opamp you need a voltage referance that is in the middle of the two rails. In an symetrical setup this is ground, in an unipolar this has to be created (voltagedivider)

Here we have noninverting amps, so that´s nothing to worry.

But: Most amps are not rail to rail. So they will not be able to go down to ground when powerd between + and ground.

Depends on what comes out of the ya chips.

About the +-12v supply

A regulated psu is easy to build. very easy. But care should be taken and it´s maybe better not to have to deal with mains. especially if you transport the synth, never know who´ll step on it, tear a cable and get shocked.

I wrote a message to tk about this idea already:

The easiest, safest and most available solution are AC supplys (whats the english word for steckernetzteil? Plug-psu?)

They are more rare than dc, but you get them. Conrad in germany has one with 14VAC. Perfect for us. lots of comercial stuff, phone stations etc have psus like that.

Plug it in and you get 14v without dealing with any mains supply.

14V can be one way rectified and regulated with 7812/7912 for a +-12v supply. We don´t need much current, so one way rectification is no problem here, but don´t forget to use cabs twice as large than witch bridge rectification.

Opter possibility: Two 12v dc supplys. Cheap and in every household. Should be two of the exact same type. Prefer regulated ones. If you use cheap unregulated ones you will get more hum and noise. A RC filter and a gyrator on each rail will fix that.

hey napierzaza. greetings to canada. I once lived in vancouver for a year, loved it! There must be some vendors that you can order from in canada. Can´t belive.....

[AndrewMartens]

There must be some vendors that you can order from in canada. Can´t belive.....

I order from Digikey all the time up to Canada, and never have to deal with any shipping/cross-border hassles.  I think there's about a $7.95 flat shipping charge on any order over $32, and that's about it.  So just order a whole bunch of crap so that it's a smaller percentage of your order.

That said, their selection is somewhat more limited than Mouser...

[Echopraxia]

I just got some quad op amps from local radio shack. The pin connections are the same but wanted midiboxers input if there is anything wrong with using these instead of the tl074

LM324    4 internally compensated high gain op amp.

Regards,

echo

[fluke]

The LM324 has lower bandwidth (1MHz vs 4MHz), is slower (0.5V/us vs 13V/us) and is probably noisier than the TL074.  But they'll work, so have a listen and see how you like them.  Just remember to socket them so you can change them later.

[Echopraxia]

Cool I just wanted to test them out to see if I broke my tl074s. I can take them back to radio shack if needed.

[RoyalScam]

You could try this to get a  bipolar power supply from a 9volt battery

I hope I can do this in text;

    ________________ +

    |      |        |

    |    10k    10uF

    |      |        |

    +      |        |

  9V    ------------  GND

    -      |        |

    |      10k    10uF

    |      |        |

    -----------------  -

Just be sure to use at least 5% resistors.  This circuit may work, but the battery won't really last that long.  Also the MBFM uses a 12v bipolar supply and as such 9volts(or a bit less in this case) will decrease the headroom and prob raise the noise floor.

Regards,

Dean

RoyalScam

[stryd_one]

Thanks :)

I hope I can do this in text;

If you use the 'code' tags (The # button up there ^ ), it will render in a fixed width font - handy for ASCII art (which I love)

[nILS]

And then it could look as pretty as this:

    .-------.--------.---- +
    |       |        |
    |      10k     10uF
    +       |        |
   9V        >-------+---- GND
    -       |        |
    |      10k     10uF
    |       |        |
    `-------^--------^----  -[/code]
And I totally don't understand why some people would prefer sth. like it's attached ;)

[Antix]

Hi,

Anyone used TL084 instead of 074?

I am asking because i have a lot of 084 in my drawer and

it will be fine use them.

Thanks and regards.

Antix

[seppoman]

TL084s are pin compatible AFAIK, they only have slightly different specs but that shouldn't make any difference in this case. So just try them out :)

S