Question about minimum input voltage using Voltage Regulator L7809?

[Jasonmatthew911]

photos, so we can see what you are doing, cause it doesn't add up right. you need to bias pin 3 - bias to half the supply and the output will swing as much each way about halfway. so, 1M from pin 3 to the two 10k resistors forming the bias divider. pin 5 is also needing bias, so you need that other 1M already shown. and between pin 1 and pin 5, you seem keen on breaking the DC connection between, so use a cap - only one cap needed, and 10uF is waaaaaaaaaay big enough - and no 10k there because you already have the correct 1M connection shown.

oh, and I've just seen your pin 2 connection. it needs to go through the resistor to bias volts, as does pin 3 - OR - pin 2 resistor can go to ground, as you've drawn, only IF it has a capacitor to block DC. otherwise, the ground connection tells the opamp "GROUND", and nothing gets thru.

but you are telling us what you've done, instead of showing us what you've done. we'll get you there sooner or later.

BTW, would you maybe recommend trying some capacitors in the 2 Gain stages between Pins 2&1 and Pins 6&7?...If I put Caps there, depending on the value, the Caps would set the Frequency of the Gain being boosted right or wrong?...Let me know more things I can add to this PreAmp to make it sound a little better for guitar and Bass, like what components I can add to do a little fixed EQ'ing and maybe something to give me some extra clean boost with my Volume knob...Thanks again!

Also, what are your thoughts on TLC2272 and/or NE5532, are they better than TL072 or pretty much sound the same, or would they give less noise than a TL072 for a clean PreAmp circuit?

[Jasonmatthew911]

Hey guys, I decided to start experimenting and I added a J201 JFET at the output of the PreAmp, and wow what a difference, nicer more defined tone now, less muddy...Adding the J201 at input didn't do too much, but at the output it allowed me to lower my 2nd Gain stage a little more, for some louder clean before any distortion, it's pretty clean throughout volume range, at the end it adds a little saturation, but with the J201 at output it's nicer saturation...

It's working pretty nice now, sounds a lot louder than unity gain, more defined, and it sounds good/loud enough through the simple headphone amp as well...

Any recommendations to improve on this, or maybe I'm good to go if I'm happy with the result (See attachment of final)...Though I'm pretty happy with the results, I would like to know how I can affect the frequencies being amplified even more, just to really tailor it for guitar, bass and synth?...I tried swapping Caps with bigger and smaller and tried adding a resistor with Cap to GND to form a fixed Tone, I tried swapping values of those resistor/caps and I couldn't feel any significant difference...Let me know what I should be doing to control the frequencies I want emphasized a little more or less?...I only want to do something fixed, no extra Pots/trimpots...Also, let me know if you guys would recommend trying different Cap values in a specific section to optimize for Bass and Guitar, thanks!

[merlinb]

Any recommendations to improve on this, or maybe I'm good to go if I'm happy with the result (See attachment of final)...

The 1uF cap should not be on the gate of the J201, otherwise the gate receives no reliable bias. I'm guessing it's just a drawing error.

You don't really need all those coupling caps, but you can leave them since they provide you with the option of tweaking them to reduce bass. If you want to tailor the frequency response better, you will probably need to add a tone stack somewhere. You can use fixed resistors instead of pots, of course.

[Jasonmatthew911]

Any recommendations to improve on this, or maybe I'm good to go if I'm happy with the result (See attachment of final)...

The 1uF cap should not be on the gate of the J201, otherwise the gate receives no reliable bias. I'm guessing it's just a drawing error.

You don't really need all those coupling caps, but you can leave them since they provide you with the option of tweaking them to reduce bass. If you want to tailor the frequency response better, you will probably need to add a tone stack somewhere. You can use fixed resistors instead of pots, of course.

Thanks for the input...I learned about this simple J201 circuit back in 2006 from Brian Wampler...I was building a few circuits from his book on "How to Design, Customize, and Build Effects Pedals", and back then you could contact him when you had issues, so I did, and he's the one that told me the right values to bias the J201, he told me to add the voltage divider and to use 15K and 1K to properly bias the J201, in his book he has the 1uf Capacitor on the Gate, but he told me to add the Voltage divider, I don't recall him telling me to take the 1uf Cap out or if maybe the 1M resistor should be after the 1uf Cap...That makes more sense to me with what you're saying...As is, it seems to be working fine, but if you say I should go after the 1uf Cap or take it out completly for better bias, then I'll do that...

I've actually also added capacitors in both Gain stages to tame the highs a little, I put a 680pf between Pin 1&2 on 1st gain stage, and .0047uf between Pin 6&7...Those tamed unwanted highs through my headphone amp...It feels like these Caps help tame the amplified highs in Gain, making it a little cleaner...After adding the J201 at the output, I feel like I don't really need a Tone stack anymore, it sounds better and louder than just connecting direct to amp, so I guess I don't have to overdue it.

For some reason I don't feel like the low end is too much, so I wasn't sure about lowering the values of the Coupling Caps, I actually thought that maybe it helped with noise having the bigger coupling caps...Also, on the input cap, I tried .1uf through 1uf, and I barely felt any difference with the frequency response...Let me know where you specifically think I should lower the value to notice a difference in low end response and/or which coupling caps would you take out?...Also, consider these are supposed to be (2) separate Pre-Amps to be used with Guitar, Bass and synths in mono, so I need more of a full range frequency response, I don't think I should cut lows for the Bass and synth.

Last question...Are those (2) 10K resistors on the voltage divider going into the J201 also extra/not necessary?...I feel like I can just send that 1M resistor of the J201 to the (2) 10K resistors that are already connecting the 1M resistors of Pin 3 & 5 of the opamp, or would it be better for the J201 to have it's own 10K resistors for the voltage divider?

[antonis]

As it is, J201 receives bias only by negative signal waveform, 'cause Source stays at 0V without quiescent current..
If I take your word that it seems to work fine then 10k/10k & 1M resistors are totally useless..
(1μF cap blocks any DC path to Gate..)

Input cap forms a HPF with 1M bias resistor so to feel any difference you should try a much lower value (10nF -> 16Hz, 4.7nF -> 34Hz, 2.2nF -> 72Hz, 1nF -> 160Hz, etc..)

Same stands for 10μF coupling caps with 1M bias resitors respectively (-3db cut-off frequency at 0.016Hz..)

[Jasonmatthew911]

As it is, J201 receives bias only by negative signal waveform, 'cause Source stays at 0V without quiescent current..
If I take your word that it seems to work fine then 10k/10k & 1M resistors are totally useless..
(1μF cap blocks any DC path to Gate..)

Input cap forms a HPF with 1M bias resistor so to feel any difference you should try a much lower value (10nF -> 16Hz, 4.7nF -> 34Hz, 2.2nF -> 72Hz, 1nF -> 160Hz, etc..)

Same stands for 10μF coupling caps with 1M bias resitors respectively (-3db cut-off frequency at 0.016Hz..)

I took out the 1uf going into the Gate and replaced the 10uf coming out of Pin7 with the 1uf, it seems to sound a little bit better now...It was working pretty good though, the way it was, but I guess maybe the voltage divider wasn't doing anything, so thanks for pointing that out...I'm pretty satisfied with the results now...Thanks!

[Jasonmatthew911]

As it is, J201 receives bias only by negative signal waveform, 'cause Source stays at 0V without quiescent current..
If I take your word that it seems to work fine then 10k/10k & 1M resistors are totally useless..
(1μF cap blocks any DC path to Gate..)

Input cap forms a HPF with 1M bias resistor so to feel any difference you should try a much lower value (10nF -> 16Hz, 4.7nF -> 34Hz, 2.2nF -> 72Hz, 1nF -> 160Hz, etc..)

Same stands for 10μF coupling caps with 1M bias resitors respectively (-3db cut-off frequency at 0.016Hz..)

Hey, I'm an idiot, you were right about the cap on the Gate of the J201...I just redid my PreAmp again, because I just realized my J201 was connected backwards, letting signal through it, but it wasn't actually doing anything, so when I switched it around, it had too much gain...Now I ended up putting the J201 at the input, and taking out the 2nd Gain stage, to lower my Gain...Please let me know if this new schematic looks good to you guys?...So far after experimenting a few days, I think this is the best sounding version now that I switched the J201, moved it to input of TL072 and eliminated the 2nd Gain stage I think, let me know if all looks right or not?...Thanks again!

[duck_arse]

erm, well ..... see how you have now put the DC bias voltage on the J201 gate, via the 1M resistor? and see how there is now no capacitor between that voltage and the "IN" jack? you need to put a blocking cap there between. and NOT 10uF. seeing as you have set the input impedance at about 1M, you only need a small cap there - 22nF will be plenty.

same applies at pin 5 - that cap is 200 times big enough. and, as you've taken the gain leg away from pin 6, you might as well remove both the 10k and 10nF feedbackers and short pin 7 to pin 6 - now a unity gain non-inverting buffer. but it's buffering an opamp output, which can look after itself quite nicely, needs no buffer.

generally, we use the gain available in a dual oppie to overcome losses in tone shaping. you can use a cap [or a network of caps and resistors for a complex response] across the feedback resistor to tailor the  high-cut, and use the inverting input leg-to-ground [or Vbias] to set the low freq rolloff. again, you can make complex response with more than one resistor/cap leg to ground. then stick a lossy tone stack, or fixed tone shaper, between the two stages, and either buffer the tone stage, or make-up gain for the losses.

head over to Rod Elliot's ESP site and read up on opamps there, he's always got loads of good stuff.

[Jasonmatthew911]

erm, well ..... see how you have now put the DC bias voltage on the J201 gate, via the 1M resistor? and see how there is now no capacitor between that voltage and the "IN" jack? you need to put a blocking cap there between. and NOT 10uF. seeing as you have set the input impedance at about 1M, you only need a small cap there - 22nF will be plenty.

same applies at pin 5 - that cap is 200 times big enough. and, as you've taken the gain leg away from pin 6, you might as well remove both the 10k and 10nF feedbackers and short pin 7 to pin 6 - now a unity gain non-inverting buffer. but it's buffering an opamp output, which can look after itself quite nicely, needs no buffer.

generally, we use the gain available in a dual oppie to overcome losses in tone shaping. you can use a cap [or a network of caps and resistors for a complex response] across the feedback resistor to tailor the  high-cut, and use the inverting input leg-to-ground [or Vbias] to set the low freq rolloff. again, you can make complex response with more than one resistor/cap leg to ground. then stick a lossy tone stack, or fixed tone shaper, between the two stages, and either buffer the tone stage, or make-up gain for the losses.

head over to Rod Elliot's ESP site and read up on opamps there, he's always got loads of good stuff.

I did all the things you mentioned, except, when I add the small .022uf Cap between the input and 1M resistor on the Gate of J201, it attenuates the sound a lot...Is that suppose to happen...To me it sounds a lot better and much louder without that Cap at the input, I don't get why the Cap is attenuating at the input?

[antonis]

In case you've placed 22nF cap between 10M anti-pop & 1M bias resistors, you shouldn't experience any attenuation for signals of frequency higher than 7Hz..

[Jasonmatthew911]

In case you've placed 22nF cap between 10M anti-pop & 1M bias resistors, you shouldn't experience any attenuation for signals of frequency higher than 7Hz..

That's exactly where I placed the Cap, and I've tried different values, but they all attenuate the signal and it sounds louder/better without that Cap for some reason...When I input into Pin3 of TL072, the input Cap doesn't attenuate, but now I feel that the J201 sounds better at the input, rather than the output how I had it before, because I realized the J201 was only passing signal before, but doing nothing for the sound cuz it was backwards...Should I get rid of the input Cap going into Pin3 maybe, or would that not make a difference on attenuation of the Cap going into 1M and Gate of J201?...Just when I think I've finally reached a decent PreAmp there's always something odd.

[Jasonmatthew911]

In case you've placed 22nF cap between 10M anti-pop & 1M bias resistors, you shouldn't experience any attenuation for signals of frequency higher than 7Hz..

Running more tests, if I eliminate the 1M (Voltage divider) from the input of the J201, I can add the 22nf Cap and it attenuates a lot less than when it has the voltage divider as well, but using like this I would have to add my 2nd Gain stage back in again, cuz it's not to the loudness I want or had without the Cap on J201 Gate before 1M...The perfect loudness seemed to be keeping the Voltage Divider on the J201 Gate, but without the Cap between the 10M and 1M...BTW, what exactly will happen if I don't use that Cap on the input going into J201?

[duck_arse]

what will happen without the cap at the input to block the DC is - you will send 4V5 up your guitar lead to whatever is connected to the other end. will it like that voltage? who knows. will it fry and burn? you will find out.

photos, so we can see what you are doing, cause it doesn't add up right.

but you are telling us what you've done, instead of showing us what you've done. we'll get you there sooner or later.

...It's working fine now...I don't send pics of the Breadboard, because it's messy looking and you probably wouldn't see all the connections very well...

[nag_on]

a few things. a breadboard is a very ordered type of device, very rigid in its layout. there is no reason to be untidy on a breadboard, it's all straight lines and right angles.

there is no breadboard too untidy to show pictures of, especially when "a circuit" does not conform to standard parts changes and placements.

if you are too ashamed of how untidy your BB is, TIDY IT UP! do tidy from the start. just that might magik the circuit to work.

photos. show us. you are telling us one thing, but some other thing is happening on the bb. we will still get you there, this is not a complicated circuit.

[/nag_on]

[Jasonmatthew911]

what will happen without the cap at the input to block the DC is - you will send 4V5 up your guitar lead to whatever is connected to the other end. will it like that voltage? who knows. will it fry and burn? you will find out.

photos, so we can see what you are doing, cause it doesn't add up right.

but you are telling us what you've done, instead of showing us what you've done. we'll get you there sooner or later.

...It's working fine now...I don't send pics of the Breadboard, because it's messy looking and you probably wouldn't see all the connections very well...

[nag_on]

a few things. a breadboard is a very ordered type of device, very rigid in its layout. there is no reason to be untidy on a breadboard, it's all straight lines and right angles.

there is no breadboard too untidy to show pictures of, especially when "a circuit" does not conform to standard parts changes and placements.

if you are too ashamed of how untidy your BB is, TIDY IT UP! do tidy from the start. just that might magik the circuit to work.

photos. show us. you are telling us one thing, but some other thing is happening on the bb. we will still get you there, this is not a complicated circuit.

[/nag_on]

Haha...Ok, I'm just gonna sent the breadboard pic as is right now...At the moment it has the J201 going into the TL072, and then that's going into my 386 Headphone Amp...First I split the output of the J201/TL072 PreAmp to a 10K mixing resistor out to an unbalanced jack so that I can hear how the PreAmp sounds through an amplifier, and another 10K mixing resistor with the same PreAmp signal goes into the 386 Headphone Amp, so I can hear how it sounds through the headphones as well...If you zoom I guess you should be able to see everything, I'm not very neat when it comes to Breadboarding, so sorry if it looks messy...Hopefully you guys can find the problem in there, or give me tips as to moving things around, thanks.

[Jasonmatthew911]

Here's another angle of my Breadboard (PreAmp side), so you can see the PreAmp connections a little bit better...

[Jasonmatthew911]

Hey, I was wondering why this Tillman Pre-Amp only has a 3M resistor to GND at the Gate of J201?...I don't see a coupling capacitor?...How come?

[11-90-an]

I don't see a coupling capacitor?...How come?

Sometimes it isn't really needed. It's more on "good practice"... or something like that...

[PRR]

> ... Tillman Pre-Amp ...I don't see a coupling capacitor?...How come?

Are you applying DC bias to the FET gate or not?? You seem totally lost here. Once you decide that, the "need" for a cap may be clearer.

[Jasonmatthew911]

> ... Tillman Pre-Amp ...I don't see a coupling capacitor?...How come?

Are you applying DC bias to the FET gate or not?? You seem totally lost here. Once you decide that, the "need" for a cap may be clearer.

I had the 1M resistor going to the (2) 10K resistors as a voltage divider, and without the coupling cap it sounded loud enough, but once I added the Cap it attenuated the sound big time, so I guess the combo of voltage divider with cap was way too attenuated, so instead I tried going into the 10M to GND, then the 22nf Cap, then a 1M resistor going to GND on the Gate of J201...I suppose I can do it like this, with the 1M to GND instead of a voltage divider, right?

[Jasonmatthew911]

> ... Tillman Pre-Amp ...I don't see a coupling capacitor?...How come?

Are you applying DC bias to the FET gate or not?? You seem totally lost here. Once you decide that, the "need" for a cap may be clearer.

So this is where I'm at now, with the 1M going to GND instead of acting like a voltage divider...I think I'm good like this, input impedance is good right?...At least it seems to be working fine like this...Please let me know that everything looks good in this updated version of my PreAmp?...Thanks again