Hi all,
I don't know whether this thread is in the wrong place or not but musical instruments forum seems a bit dead so i decided to post here...
I have been designing this low power amplifier for guitar and the design is now in the part where i'm open for suggestions of improvements. There are also some issues to which i need clearance. This circuit is mainly a test to see what kind of tone some circuit's will produce since my research has shown that most of solid state guitar amplifiers that have a reputation of having a good tone have 1. an active tone shaping stage, 2. quasi-complementary power stage, 3. smallish decoupling caps, 4. no negative feedback from output to previous stages.
Also, there seems to be a lot controversy about the amplitude range of guitar pickups. The common belief is that they produce a peak voltage of 100mV (peaks) and when the note decays the amplitude is typically about 30mV.
My research has shown that some pickups can easily do 400mV peaks and some effect pedals even put out a line level signal. 1V is quite much when compared to 30mV. When i tested my guitar's pickups by plugging them straight into mixer's input they were almost equally as loud as a line level signal. What is the truth here? To what peak voltage you people usually base your design into?
Another design issue is the frequency curve which is not flat in guitar amplifiers. Since the slope's centerpoint in the curve is usually located around 400-600hZ the amplitude in 1kHz (the typical measurement frequency) can easily be around -12dB less than the amplitude in for example 2kHz or 80Hz. Doesn't this lead into awful amount of distortion if you base your design on 1kHz sine wave, especially with 60mVpp signal? What methods you people use in designing these amplifiers?
I tried to find some discussion about this from the internet but strangely there doesn't seem to be any. I guess it's time for it now and more the merrier if it can relate to circuit i'm posting as attachment.
Thanks in advance,
Teemu K
I don't know whether this thread is in the wrong place or not but musical instruments forum seems a bit dead so i decided to post here...
I have been designing this low power amplifier for guitar and the design is now in the part where i'm open for suggestions of improvements. There are also some issues to which i need clearance. This circuit is mainly a test to see what kind of tone some circuit's will produce since my research has shown that most of solid state guitar amplifiers that have a reputation of having a good tone have 1. an active tone shaping stage, 2. quasi-complementary power stage, 3. smallish decoupling caps, 4. no negative feedback from output to previous stages.
Also, there seems to be a lot controversy about the amplitude range of guitar pickups. The common belief is that they produce a peak voltage of 100mV (peaks) and when the note decays the amplitude is typically about 30mV.
My research has shown that some pickups can easily do 400mV peaks and some effect pedals even put out a line level signal. 1V is quite much when compared to 30mV. When i tested my guitar's pickups by plugging them straight into mixer's input they were almost equally as loud as a line level signal. What is the truth here? To what peak voltage you people usually base your design into?
Another design issue is the frequency curve which is not flat in guitar amplifiers. Since the slope's centerpoint in the curve is usually located around 400-600hZ the amplitude in 1kHz (the typical measurement frequency) can easily be around -12dB less than the amplitude in for example 2kHz or 80Hz. Doesn't this lead into awful amount of distortion if you base your design on 1kHz sine wave, especially with 60mVpp signal? What methods you people use in designing these amplifiers?
I tried to find some discussion about this from the internet but strangely there doesn't seem to be any. I guess it's time for it now and more the merrier if it can relate to circuit i'm posting as attachment.
Thanks in advance,
Teemu K
Attachments
Hello Teemu
General this amp shoul work fine
it is good that the poweramp does not have a global feedback - the distortion will be much better during overdrive it and easier for overdrive!!! Good to isolate it from the speaker, you know what I mean?
IMO using of opamps is not a good solution, try use jfets configured as tubes to get good distortion and the spectrum like in a valve amp.
One more: try to use at the input and at every stage high pass filter with the frequency~100Hz.
To get hmetal-like distortion try to overdrive signal shaped in pass filter ~1kHz.
General this amp shoul work fine
it is good that the poweramp does not have a global feedback - the distortion will be much better during overdrive it and easier for overdrive!!! Good to isolate it from the speaker, you know what I mean?
IMO using of opamps is not a good solution, try use jfets configured as tubes to get good distortion and the spectrum like in a valve amp.
One more: try to use at the input and at every stage high pass filter with the frequency~100Hz.
To get hmetal-like distortion try to overdrive signal shaped in pass filter ~1kHz.
hi teemuk
i m tryin to buil an amp too ! but for my bass guitar ...
better to take look in this site , it has several good schematics and power amp and etc .. http://www.albertkreuzer.com/start.htm
i wanna try the jfet bass guitar preamp that shown in this site .. u too better take a look at it , it may satisfy u ...
good luck
i m tryin to buil an amp too ! but for my bass guitar
... better to take look in this site , it has several good schematics and power amp and etc .. http://www.albertkreuzer.com/start.htm
i wanna try the jfet bass guitar preamp that shown in this site .. u too better take a look at it , it may satisfy u
... good luck
Re: Re: Help designing a guitar amp
Hi
your requirements about guitar amp assume getting distotrion from power amp. Another attitude is to add all the tube-like coloration and/or hard distortion from preamp and run power amp in 'linear' mode. This eliminates x-over dist.
My observations are the same, pass-boost 700-1600Hz before distortion gives nice results. £adna pogoda siê zrobi³a w tym pieprzonym kraju, nie?
Hi
your requirements about guitar amp assume getting distotrion from power amp. Another attitude is to add all the tube-like coloration and/or hard distortion from preamp and run power amp in 'linear' mode. This eliminates x-over dist.
padamiecki said:
.....
To get hmetal-like distortion try to overdrive signal shaped in pass filter ~1kHz.
My observations are the same, pass-boost 700-1600Hz before distortion gives nice results. £adna pogoda siê zrobi³a w tym pieprzonym kraju, nie?
Re: Re: Help designing a guitar amp
Hi all,
thanks for your answers but i still think there's room for more discussion.
Well, i'm not really looking for distortion from this amplifier. If i'd want that i would rather use outboard effects. Distortion is nice and often associated with guitar amplifiers that are usually driven harder than "home" amplifiers but implementing a "distorter" to this amplifier would need a whole new circuit (channel) since distortion tone shaping is very much different from typical tone shaping, especially in solid state devices. And what if you want to have a clean tone?
Totally another question is how to make the distortion that WILL occur in any amplifier mellow and nice sounding. That seems to be quite tricky with solid state devices and since this is low power amp it might become an issue. A compressor stage before the final voltage amp possibly...?
What do you mean by configuring jfets as tubes? The jfets can be configured as jfets - nothing else. Solid state is solid state - tube is tube and the sonic spectrum is unique in every case.
The lowest E in guitar is 80Hz. Dropped tunings put out even lower frequency and same thing happens when you play damped strings so why put low pass on 100Hz?
I have to disagree with you since i'd rather use frequncy shaping in the signal path as less as possible since this is the easiest way to get nasty sounding distortion besides overdrive. Truly some is needed to cut down lowest and highest end and to avoid oscillation. As you notice i do this with small decoupling caps and negative feedback in opamp stages. However, i don't agree with you on 100Hz.
Personally i see nothing wrong in using opamps as long as they're not overdriven. That could happen in the last voltage amplifiying stage unless the input sensitivity is not set correctly. Anyone have idea of how to do it? (Frequency curve and pickup issue).
I tried jfet's in a 1/2W practice amplifier that i built few months ago. It had a chip amp otput stage (lm386) and a jfet preamp. I have to say that i liked the distortion characteristics of jfets when compared to opamps but at the end all comes down to clipping power amplifier which then should have fets too and that's a whole new story.
I didn't want to take that path this time since this is my first try in designing a discrete power stage and i wanted to keep things as simple as possible. Also, i find opamp design easier because you can avoid of using large amount of discrete components. As long as you don't overdrive them they don't seem to differ that much from jfets or any other discrete circuits.
Teemu K
Hi all,
thanks for your answers but i still think there's room for more discussion.
padamiecki said:To get hmetal-like distortion try to overdrive signal shaped in pass filter ~1kHz.
Well, i'm not really looking for distortion from this amplifier. If i'd want that i would rather use outboard effects. Distortion is nice and often associated with guitar amplifiers that are usually driven harder than "home" amplifiers but implementing a "distorter" to this amplifier would need a whole new circuit (channel) since distortion tone shaping is very much different from typical tone shaping, especially in solid state devices. And what if you want to have a clean tone?
Totally another question is how to make the distortion that WILL occur in any amplifier mellow and nice sounding. That seems to be quite tricky with solid state devices and since this is low power amp it might become an issue. A compressor stage before the final voltage amp possibly...?
padamiecki said:
What do you mean by configuring jfets as tubes? The jfets can be configured as jfets - nothing else. Solid state is solid state - tube is tube and the sonic spectrum is unique in every case.
padamiecki said:
The lowest E in guitar is 80Hz. Dropped tunings put out even lower frequency and same thing happens when you play damped strings so why put low pass on 100Hz?
I have to disagree with you since i'd rather use frequncy shaping in the signal path as less as possible since this is the easiest way to get nasty sounding distortion besides overdrive. Truly some is needed to cut down lowest and highest end and to avoid oscillation. As you notice i do this with small decoupling caps and negative feedback in opamp stages. However, i don't agree with you on 100Hz.
padamiecki said:
Personally i see nothing wrong in using opamps as long as they're not overdriven. That could happen in the last voltage amplifiying stage unless the input sensitivity is not set correctly. Anyone have idea of how to do it? (Frequency curve and pickup issue).
I tried jfet's in a 1/2W practice amplifier that i built few months ago. It had a chip amp otput stage (lm386) and a jfet preamp. I have to say that i liked the distortion characteristics of jfets when compared to opamps but at the end all comes down to clipping power amplifier which then should have fets too and that's a whole new story.
I didn't want to take that path this time since this is my first try in designing a discrete power stage and i wanted to keep things as simple as possible. Also, i find opamp design easier because you can avoid of using large amount of discrete components. As long as you don't overdrive them they don't seem to differ that much from jfets or any other discrete circuits.
Teemu K
Re: Re: Re: Help designing a guitar amp
Dear Teemu,
80Hz is low E maybe for the bass,
when you are using 6string better put 100Hz high pass filter, the sound would be quicker especialy during palm mute technique.
Besides this lowers a little hum and ripple from supply section.
Many people use opamps, but look at the forum - you have to know which opamp to use!
If you are going to build just an amp please ignore my posts!
A w Krakowie na wysokoœciach pod Kopcem Pi³s. pieprzona zima, dopiero ni¿ej czuæ wiosnê!!! Ale czu³emj¹ du¿o wczeœniej w koœciach i dobrym samopoczuciu!
Dear Teemu,
80Hz is low E maybe for the bass,
when you are using 6string better put 100Hz high pass filter, the sound would be quicker especialy during palm mute technique.
Besides this lowers a little hum and ripple from supply section.
Many people use opamps, but look at the forum - you have to know which opamp to use!
If you are going to build just an amp please ignore my posts!
A w Krakowie na wysokoœciach pod Kopcem Pi³s. pieprzona zima, dopiero ni¿ej czuæ wiosnê!!! Ale czu³emj¹ du¿o wczeœniej w koœciach i dobrym samopoczuciu!
Re: Re: Re: Re: Help designing a guitar amp
Low E on the guitar is 82.5 Hz, trust me! Why would a 100 Hz filter affect the sound of the guitar otherwise?
But yes, turning down the bass can be beneficial to the sound, particularly if like the sound with less bass
You really need an input sensitivity control that sets the gain of the first stage. Guitars are a varied lot, as you have discovered. Many guitar amps have Hi/Lo inputs for this reason.
Switchable resistors or a potentiometer is a good thing. I'd make U1 a non-inverting stage to make the values of resistors more manageable.
Rune
padamiecki said:
Low E on the guitar is 82.5 Hz, trust me! Why would a 100 Hz filter affect the sound of the guitar otherwise?
But yes, turning down the bass can be beneficial to the sound, particularly if like the sound with less bass
You really need an input sensitivity control that sets the gain of the first stage. Guitars are a varied lot, as you have discovered. Many guitar amps have Hi/Lo inputs for this reason.
Switchable resistors or a potentiometer is a good thing. I'd make U1 a non-inverting stage to make the values of resistors more manageable.
Rune
Re: Re: Re: Re: Re: Help designing a guitar amp
Yep, i think the main question is how much the low frequncy has to be cut? Too much bass is poison for low power amplifier and damped notes easily fart out. This thing can also be compensated with a good speaker cabinet but too much is too much. Where would you put the -3dB point?
That´s what i figured out too. I´t´s quite easy to replace a resistor with a trimmer but still there´s a huge difference between 30mV @1kHz and 1V at, say, 82.5Hz. So what would be the starting point? 30mV on 1kHz and lowering the gain from there?
Also, has any comments of the amplifier circuit in general?
Teemu K
runebivrin said:Low E on the guitar is 82.5 Hz, trust me! Why would a 100 Hz filter affect the sound of the guitar otherwise?
But yes, turning down the bass can be beneficial to the sound, particularly if like the sound with less bass
Yep, i think the main question is how much the low frequncy has to be cut? Too much bass is poison for low power amplifier and damped notes easily fart out. This thing can also be compensated with a good speaker cabinet but too much is too much. Where would you put the -3dB point?
runebivrin said:
That´s what i figured out too. I´t´s quite easy to replace a resistor with a trimmer but still there´s a huge difference between 30mV @1kHz and 1V at, say, 82.5Hz. So what would be the starting point? 30mV on 1kHz and lowering the gain from there?
Also, has any comments of the amplifier circuit in general?
Teemu K
Re: Re: Re: Re: Re: Re: Help designing a guitar amp
Can't say I have a general opionion. I like my bass deep. It's something I'd consider making adjustable.
30mV is a probably not necessary. I'd start at 100mV, maybe. In my opinion the operative word is headroom, as in headroom before the master volume. That way, when it does clip you know it's the power amp that's doing it. If you're playing Sultans Of Swing style there's gonna be a lot more than a 1:3 ratio beween peak and decay levels.
As I said earlier, I'd consider a non-inverting input stage for gain adjustment.
What is R25 doing? 1miliohm is hard to buy
J1 seems a bit superflous as a whole. Surely U1 can drive the 33k impedance of U3?
U1 has no DC negative feedback.
Rune
teemuk said:
Can't say I have a general opionion. I like my bass deep. It's something I'd consider making adjustable.
teemuk said:
30mV is a probably not necessary. I'd start at 100mV, maybe. In my opinion the operative word is headroom, as in headroom before the master volume. That way, when it does clip you know it's the power amp that's doing it. If you're playing Sultans Of Swing style there's gonna be a lot more than a 1:3 ratio beween peak and decay levels.
Well, there's a bunch of 6.8k resistors from the op-amp outputs. What are they doing there? I know som op-amps were designed to be resistor loaded, but what are you using?teemuk said:
As I said earlier, I'd consider a non-inverting input stage for gain adjustment.
What is R25 doing? 1miliohm is hard to buy
J1 seems a bit superflous as a whole. Surely U1 can drive the 33k impedance of U3?
U1 has no DC negative feedback.
Rune
About those high-pass filter question, I have to say that in general guitar amps have a -3dB point at 60Hz, that's to cut lower frequencies to prevent them to distort, fart, or just steal power from the higher frequencies. And jes, the guitar low E is 82Hz...
However, i suggest to you to use jfets. Yes, using them "normally", like you use opamps "normally", it is the same sound. But there are jfets experts that can do about anything with those transistors, search for some on the usual fx forums (www.diystompboxes.com). Some of them are really impressive in creating a CLEAN tube sound (I understand that you want to add pedals for overdrive ). You know, a warmer clean amp is better for pedals, because they tend to give a punchier sound with more sustain. Just put a Rat in fron of an hi-fi amp and then in a clean Fender amp... you'll hear the difference, even when the THD is under 2%. Clean tube sound is better for pedals than clean hi-fi opamp sound, even with lo-pass filters and all the like. Simple lo-pass sound like lo-pass, not "warm sound".
Maybe trying some tubes in the preamp? That would be the best... Some clean 12AX7... Plate voltage took with a voltage doubler... search the net if the idea intrigues you.
Keep posting your results!
However, i suggest to you to use jfets. Yes, using them "normally", like you use opamps "normally", it is the same sound. But there are jfets experts that can do about anything with those transistors, search for some on the usual fx forums (www.diystompboxes.com). Some of them are really impressive in creating a CLEAN tube sound (I understand that you want to add pedals for overdrive
). You know, a warmer clean amp is better for pedals, because they tend to give a punchier sound with more sustain. Just put a Rat in fron of an hi-fi amp and then in a clean Fender amp... you'll hear the difference, even when the THD is under 2%. Clean tube sound is better for pedals than clean hi-fi opamp sound, even with lo-pass filters and all the like. Simple lo-pass sound like lo-pass, not "warm sound".Maybe trying some tubes in the preamp? That would be the best... Some clean 12AX7... Plate voltage took with a voltage doubler... search the net if the idea intrigues you.
Keep posting your results!
Re: Re: Re: Re: Re: Re: Re: Help designing a guitar amp
Thanks for your comments Runebivrim. The non-inverting input stage seems to be a good way to add a trimmer resistor to control the input sensitivity. I will work on that. Also, i do believe that the circuit needs a bass control.
The resistors are there to bias the opamps to operate in class A.
Depending of the opamp that is used in the circuit it can either make the tone better or worse - or possibly it won't have any audible effect. Yes, they can be omitted unless i want to use them.
Hehe. Actually it's a "potentiometer" with R26. LTspice, which i use to make schematics and simulate circuits, doesn't have a model for potentiometer so i skip it that way.
Not really. U1 forms an active frequency shaping circuit that will need a low output impedance, which is 1.5k on J1's grid. Varying impedance would cause drastic variation in the frequency curve unless the J1 buffer stage would be there. Without the buffer it would also be hard to add a volume control potentiometer (R25 & R26) and the "high" input impedance of U3 to the circuit.
Teemu K
Thanks for your comments Runebivrim. The non-inverting input stage seems to be a good way to add a trimmer resistor to control the input sensitivity. I will work on that. Also, i do believe that the circuit needs a bass control.
runebivrin said:
The resistors are there to bias the opamps to operate in class A.
Depending of the opamp that is used in the circuit it can either make the tone better or worse - or possibly it won't have any audible effect. Yes, they can be omitted unless i want to use them.
runebivrin said:What is R25 doing? 1miliohm is hard to buy
Rune
Hehe. Actually it's a "potentiometer" with R26. LTspice, which i use to make schematics and simulate circuits, doesn't have a model for potentiometer so i skip it that way.
runebivrin said:J1 seems a bit superflous as a whole. Surely U1 can drive the 33k impedance of U3?
U1 has no DC negative feedback.
Rune
Not really. U1 forms an active frequency shaping circuit that will need a low output impedance, which is 1.5k on J1's grid. Varying impedance would cause drastic variation in the frequency curve unless the J1 buffer stage would be there. Without the buffer it would also be hard to add a volume control potentiometer (R25 & R26) and the "high" input impedance of U3 to the circuit.
Teemu K
Re: Re: Re: Re: Re: Re: Re: Re: Help designing a guitar amp
I see. C6 and R12 form a hi-pass filter with a -3dB point at 156 Hz. Still, effectively adding a resistor parallel with R12 varying from 19387 ohms to 47000 ohms (R26//R4) would vary the total resistance from 1392 ohms to 1453 ohms, which results in a -3dB point moving from 161 to 168 Hz. Hardly earth shattering, in my opinion. But maybe J1 adds some subtle colouring, I don't know.
However, I still fail to see how U1 has any negative feedback at DC.
Rune
teemuk said:
I see. C6 and R12 form a hi-pass filter with a -3dB point at 156 Hz. Still, effectively adding a resistor parallel with R12 varying from 19387 ohms to 47000 ohms (R26//R4) would vary the total resistance from 1392 ohms to 1453 ohms, which results in a -3dB point moving from 161 to 168 Hz. Hardly earth shattering, in my opinion. But maybe J1 adds some subtle colouring, I don't know.
However, I still fail to see how U1 has any negative feedback at DC.
Rune
Re: Re: Re: Re: Re: Re: Re: Re: Re: Help designing a guitar amp
Ok, i'm posting the updated schema.
Whoops, good point there. The only reason why the previous circuit seemed to work (at least in simulation) was that it biased the output only to -12v. Not good practice, higly unstable circuit and doesn't leave much overload capacity since most opamps clip at -13v! ...So i had to redesign the circuit.
The "fender-marshall-vox-whatever"-tonestack seems to have a quite big insertion loss so i guess that "solved" the issue about the jfet buffer. Any opinions about using a baxandall stack instead of this one - other than it has more control and an ability to boost midrange?
Comments are welcomed.
Teemu K
Ok, i'm posting the updated schema.
runebivrin said:
Whoops, good point there. The only reason why the previous circuit seemed to work (at least in simulation) was that it biased the output only to -12v. Not good practice, higly unstable circuit and doesn't leave much overload capacity since most opamps clip at -13v! ...So i had to redesign the circuit.
The "fender-marshall-vox-whatever"-tonestack seems to have a quite big insertion loss so i guess that "solved" the issue about the jfet buffer. Any opinions about using a baxandall stack instead of this one - other than it has more control and an ability to boost midrange?
Comments are welcomed.
Teemu K
Attachments
I really have little to say on the tone stack issue. The typical hifi Baxandall tone stack is usually not particularly useful, but that is mainly a frequency issue, not a fundamental topology thing.
Otherwise it look quite good, except I would keep the stage with adjustable gain as close to the input as possible. Preferably the first stage. That way you'll be able to have maximum headroom, while keeping the noise to a minimum.
Rune
Otherwise it look quite good, except I would keep the stage with adjustable gain as close to the input as possible. Preferably the first stage. That way you'll be able to have maximum headroom, while keeping the noise to a minimum.
Rune
Teemu,
Take a look at Rod Elliott's project 27
http://sound.westhost.com/project27.htm
I built this one, (actually mine is more like project 27B) and it sounds pretty good for a solid state guitar amp. I ended up convering this into a bass amp and it is used twice a week for 4 years, no problems whatsoever. I built it on perfboard with flea clips, this was before Rod offered a PCB for this project.
Some other interesting preamp ideas are at runoffgroove
http://www.runoffgroove.com/index.html
Basically they use classic tube circuits with Jfets and variable drain resistors to set the operating point. Jfets are very inconsistent in their characteristics. It works surprisingly well. Sound clips available.
Also check out the Jfet mu-amp.
http://www.geofex.com/Article_Folders/foolwfets/foolwfets.htm
This circuit has a soft clipping characteristic similar to a tube being driven to saturation ( not cutoff).
As mentioned before, the real killer with solid state guitar amp circuits is the small amount of headroom available with low voltage power supplies. As you have observed, the output of a guitar pickup can easily exceed 1v RMS especially with picking transients, and that is enough to drive most op-amp circuits to clipping. And most op-amps are very nasty sounding when clipped. That is one of the main reasons for the popularity of the JFET circuits, when they do clip, it tends to be less harsh than an op-amp.
That said, I've experimented with Fets, BJTs, op-amps, germanium diodes, LEDs, modelling amps, etc. and none of them can compare to a good tube amp. They might sound ok, but don't RESPOND like a tube amp.
By the way, there is a potentiometer model available for LTSpice. It is on the LTSpice yahoo group, you have to join the group to get the downloads. http://groups.yahoo.com/group/LTspice
Good luck with your project.
Regards,
Mike D.
Take a look at Rod Elliott's project 27
http://sound.westhost.com/project27.htm
I built this one, (actually mine is more like project 27B) and it sounds pretty good for a solid state guitar amp. I ended up convering this into a bass amp and it is used twice a week for 4 years, no problems whatsoever. I built it on perfboard with flea clips, this was before Rod offered a PCB for this project.
Some other interesting preamp ideas are at runoffgroove
http://www.runoffgroove.com/index.html
Basically they use classic tube circuits with Jfets and variable drain resistors to set the operating point. Jfets are very inconsistent in their characteristics. It works surprisingly well. Sound clips available.
Also check out the Jfet mu-amp.
http://www.geofex.com/Article_Folders/foolwfets/foolwfets.htm
This circuit has a soft clipping characteristic similar to a tube being driven to saturation ( not cutoff).
As mentioned before, the real killer with solid state guitar amp circuits is the small amount of headroom available with low voltage power supplies. As you have observed, the output of a guitar pickup can easily exceed 1v RMS especially with picking transients, and that is enough to drive most op-amp circuits to clipping. And most op-amps are very nasty sounding when clipped. That is one of the main reasons for the popularity of the JFET circuits, when they do clip, it tends to be less harsh than an op-amp.
That said, I've experimented with Fets, BJTs, op-amps, germanium diodes, LEDs, modelling amps, etc. and none of them can compare to a good tube amp. They might sound ok, but don't RESPOND like a tube amp.
By the way, there is a potentiometer model available for LTSpice. It is on the LTSpice yahoo group, you have to join the group to get the downloads. http://groups.yahoo.com/group/LTspice
Good luck with your project.
Regards,
Mike D.
Time for an update.
I followed few suggestions and replaced some opamp stages with jfets. It seemed to make the tone a bit more "punchier". Unfortunately, side effect is increased noise and distortion. However, i prefer the spicier tone a bit more than having an ultra quiet amp.
I also added the secondary side of the power supply circuit, which (during simulation) helped to reveal some weaknesses in first designs: There wasn't enough capacitance on power rails in first two versions. Some capacitance is also needed before the regulators (C36 & C35), otherwise the amount of ripple is unbearable.
I also added snubbers to the supply rails. It didn't seem to make any difference to the tone or to circuit's behaviour. In flesh things might be different.
Comments on the design are welcomed and appreciated.
Teemu K
I followed few suggestions and replaced some opamp stages with jfets. It seemed to make the tone a bit more "punchier". Unfortunately, side effect is increased noise and distortion. However, i prefer the spicier tone a bit more than having an ultra quiet amp.
I also added the secondary side of the power supply circuit, which (during simulation) helped to reveal some weaknesses in first designs: There wasn't enough capacitance on power rails in first two versions. Some capacitance is also needed before the regulators (C36 & C35), otherwise the amount of ripple is unbearable.
I also added snubbers to the supply rails. It didn't seem to make any difference to the tone or to circuit's behaviour. In flesh things might be different.
Comments on the design are welcomed and appreciated.
Teemu K
Attachments
oooooh that's starting to look good. The problem here is that if you use a jfet as first gain stage, you'll get it's warm compression (or better, limiting) but also BIG noise. Selecting fets would help in this case: remember to put a trimmer to control the bias of the fets, as they tend to vary their parameters very much from device to device... Good idea that tone cap switch.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.