Forums

Solderless audio amplifier

Started by John Smith January 29, 2014
The radio kit hasn't arrived yet (Thread of 18th Jan. Probably due to 
weather conditions here in Ontario) so I thought I'd try my hand at making 
my own audio amplifier kit.

The requirements were as follows:
1. Must use components I already have. I couldn't find any 1N4148 but did 
find packets of 1N4001 so that's what I used. Also I could only find one 
resistor under 1 ohm so another is made from two in parallel.
2. Must be simple enough to fit on one piece of breadboard but not be a 
trivial design.
3. Must deliver enough power to make an 8 ohm speaker cone move visibly.
4. Must run from a single 9V battery.
5. Must be quick to design with minimal calculation.
6. Any soldering must be done in advance of taking it into a school and 
getting a little guy to build it.
7. Doesn't need high voltage gain as it will be driven from an ipod so I 
designed for a gain of about 10.
8. Low distortion is not essential as long as there's no obvious issue below 
clipping level.

With those requirements in mind I got a piece of paper out and drew this:
www.pdelectronics.ca/sed/amp2014jan28/schematic.jpg
Then I did the layout:
www.pdelectronics.ca/sed/amp2014jan28/layout.jpg
Then I built and tested it:
www.pdelectronics.ca/sed/amp2014jan28/built.jpg
Actually there was much overlap between those three things.

I set VR2 to zero resistance and measured an idle current of 60mA, so I 
didn't adjust VR2.
I then connected a signal source from a computer, adjusted VR1 and the 
requirements seemed to have been met.

I'm aware that there are people here who can comment on my amplifier design 
skills, or lack of them, and maybe some component values can be tweaked for 
better performance.

Are there any free tools available which can run a simulation of this 
circuit?
What is the lower and upper 3dB bandwidth?
Is my wild guess at a value for C6 reasonable?

Old Guy 


On a sunny day (Wed, 29 Jan 2014 13:02:18 -0500) it happened "John Smith"
<invalid@invalid.invalid> wrote in <lcbfjq$i5p$1@dont-email.me>:

>The radio kit hasn't arrived yet (Thread of 18th Jan. Probably due to >weather conditions here in Ontario) so I thought I'd try my hand at making >my own audio amplifier kit. > >The requirements were as follows: >1. Must use components I already have. I couldn't find any 1N4148 but did >find packets of 1N4001 so that's what I used. Also I could only find one >resistor under 1 ohm so another is made from two in parallel. >2. Must be simple enough to fit on one piece of breadboard but not be a >trivial design. >3. Must deliver enough power to make an 8 ohm speaker cone move visibly. >4. Must run from a single 9V battery. >5. Must be quick to design with minimal calculation. >6. Any soldering must be done in advance of taking it into a school and >getting a little guy to build it. >7. Doesn't need high voltage gain as it will be driven from an ipod so I >designed for a gain of about 10. >8. Low distortion is not essential as long as there's no obvious issue below >clipping level. > >With those requirements in mind I got a piece of paper out and drew this: >www.pdelectronics.ca/sed/amp2014jan28/schematic.jpg >Then I did the layout: >www.pdelectronics.ca/sed/amp2014jan28/layout.jpg >Then I built and tested it: >www.pdelectronics.ca/sed/amp2014jan28/built.jpg >Actually there was much overlap between those three things. > >I set VR2 to zero resistance and measured an idle current of 60mA, so I >didn't adjust VR2. >I then connected a signal source from a computer, adjusted VR1 and the >requirements seemed to have been met. > >I'm aware that there are people here who can comment on my amplifier design >skills, or lack of them, and maybe some component values can be tweaked for >better performance.
Only thing is an emitter resistor in TR4 to make it a more of a real current source. I think R8 is asking for trouble, just short it, but keep C3. C4 is big relatve to the supply decoupling caps, maybe works with a good battery / voltage source.
>Are there any free tools available which can run a simulation of this >circuit?
LT spice.
>What is the lower and upper 3dB bandwidth?
LT spice will tell you, but if you use some soundcard with a sweep audio file any scope will tell you. If you do not have a frequency sweep audio file I can make one available for download.
>Is my wild guess at a value for C6 reasonable?
Yea, just try it...
On Wed, 29 Jan 2014 13:02:18 -0500, John Smith wrote:

> The radio kit hasn't arrived yet (Thread of 18th Jan. Probably due to > weather conditions here in Ontario) so I thought I'd try my hand at > making my own audio amplifier kit. > > The requirements were as follows: > 1. Must use components I already have. I couldn't find any 1N4148 but > did find packets of 1N4001 so that's what I used. Also I could only find > one resistor under 1 ohm so another is made from two in parallel. > 2. Must be simple enough to fit on one piece of breadboard but not be a > trivial design. > 3. Must deliver enough power to make an 8 ohm speaker cone move visibly. > 4. Must run from a single 9V battery. > 5. Must be quick to design with minimal calculation. > 6. Any soldering must be done in advance of taking it into a school and > getting a little guy to build it. > 7. Doesn't need high voltage gain as it will be driven from an ipod so I > designed for a gain of about 10. > 8. Low distortion is not essential as long as there's no obvious issue > below clipping level. > > With those requirements in mind I got a piece of paper out and drew > this: www.pdelectronics.ca/sed/amp2014jan28/schematic.jpg Then I did the > layout: > www.pdelectronics.ca/sed/amp2014jan28/layout.jpg Then I built and tested > it: > www.pdelectronics.ca/sed/amp2014jan28/built.jpg Actually there was much > overlap between those three things. > > I set VR2 to zero resistance and measured an idle current of 60mA, so I > didn't adjust VR2. > I then connected a signal source from a computer, adjusted VR1 and the > requirements seemed to have been met. > > I'm aware that there are people here who can comment on my amplifier > design skills, or lack of them, and maybe some component values can be > tweaked for better performance. > > Are there any free tools available which can run a simulation of this > circuit? > What is the lower and upper 3dB bandwidth? > Is my wild guess at a value for C6 reasonable? > > Old Guy
Wow. Lots of components for not much amplification -- but if you're eschewing op-amps and coils, and want a class-AB output stage, I guess that's what you need to do. Check out LTSpice, from Linear Technology. It's supposed to be a tool for marketing their power supply chips, but it's a great all-around simulation tool. I'd suggest you answer your questions about bandwidth and C6 with LTSpice, if you can't just do the circuit analysis yourself. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On 1/29/2014 12:02 PM, John Smith wrote:
> The radio kit hasn't arrived yet (Thread of 18th Jan. Probably due to > weather conditions here in Ontario) so I thought I'd try my hand at making > my own audio amplifier kit. > > The requirements were as follows: > 1. Must use components I already have. I couldn't find any 1N4148 but did > find packets of 1N4001 so that's what I used. Also I could only find one > resistor under 1 ohm so another is made from two in parallel. > 2. Must be simple enough to fit on one piece of breadboard but not be a > trivial design. > 3. Must deliver enough power to make an 8 ohm speaker cone move visibly. > 4. Must run from a single 9V battery. > 5. Must be quick to design with minimal calculation. > 6. Any soldering must be done in advance of taking it into a school and > getting a little guy to build it. > 7. Doesn't need high voltage gain as it will be driven from an ipod so I > designed for a gain of about 10. > 8. Low distortion is not essential as long as there's no obvious issue below > clipping level. > > With those requirements in mind I got a piece of paper out and drew this: > www.pdelectronics.ca/sed/amp2014jan28/schematic.jpg > Then I did the layout: > www.pdelectronics.ca/sed/amp2014jan28/layout.jpg > Then I built and tested it: > www.pdelectronics.ca/sed/amp2014jan28/built.jpg > Actually there was much overlap between those three things. > > I set VR2 to zero resistance and measured an idle current of 60mA, so I > didn't adjust VR2. > I then connected a signal source from a computer, adjusted VR1 and the > requirements seemed to have been met. > > I'm aware that there are people here who can comment on my amplifier design > skills, or lack of them, and maybe some component values can be tweaked for > better performance. > > Are there any free tools available which can run a simulation of this > circuit? > What is the lower and upper 3dB bandwidth? > Is my wild guess at a value for C6 reasonable? > > Old Guy > >
Google Zen amplifiers, they are low parts count, probably don't meet your criteria, but neat anyway. Many variations, here's one. https://www.passdiy.com/project/amplifiers/the-zen-amplifier Mikek
On Wednesday, January 29, 2014 1:53:39 PM UTC-5, amdx wrote:
> On 1/29/2014 12:02 PM, John Smith wrote:
>=20 > > >=20 > Google Zen amplifiers, they are low parts count, probably don't meet=20 > your criteria, but neat anyway. Many variations, here's one. > https://www.passdiy.com/project/amplifiers/the-zen-amplifier >=20 > Mikek
Wow.. I was just at that page... trying to recall how he did the class A th= ing. To John Smith.=20 I was going to say that if the students are going to understand it then a s= imple class A type design might be better. (though wastful of the battery)= =20 I wonder if you need any voltage gain at all? =20 Would using an audio transformer be OK? =20 One thing that struck me is that you are not going to get taht much power f= rom a 9V battery. (What's the internal resistance of the battery? I stuck= 100 ohms across a 9V and Vout dropped to ~8V, but this is an old battery t= hat's been sitting on my bench for a while) So perhaps a beefier battery o= r a higher impedance speaker. =20 George H.
"Jan Panteltje" <pNaonStpealmtje@yahoo.com> wrote in message 
news:lcbgpa$am8$1@news.albasani.net...
> On a sunny day (Wed, 29 Jan 2014 13:02:18 -0500) it happened "John Smith" > <invalid@invalid.invalid> wrote in <lcbfjq$i5p$1@dont-email.me>: > >>The radio kit hasn't arrived yet (Thread of 18th Jan. Probably due to >>weather conditions here in Ontario) so I thought I'd try my hand at making >>my own audio amplifier kit. >> >>The requirements were as follows: >>1. Must use components I already have. I couldn't find any 1N4148 but did >>find packets of 1N4001 so that's what I used. Also I could only find one >>resistor under 1 ohm so another is made from two in parallel. >>2. Must be simple enough to fit on one piece of breadboard but not be a >>trivial design. >>3. Must deliver enough power to make an 8 ohm speaker cone move visibly. >>4. Must run from a single 9V battery. >>5. Must be quick to design with minimal calculation. >>6. Any soldering must be done in advance of taking it into a school and >>getting a little guy to build it. >>7. Doesn't need high voltage gain as it will be driven from an ipod so I >>designed for a gain of about 10. >>8. Low distortion is not essential as long as there's no obvious issue >>below >>clipping level. >> >>With those requirements in mind I got a piece of paper out and drew this: >>www.pdelectronics.ca/sed/amp2014jan28/schematic.jpg >>Then I did the layout: >>www.pdelectronics.ca/sed/amp2014jan28/layout.jpg >>Then I built and tested it: >>www.pdelectronics.ca/sed/amp2014jan28/built.jpg >>Actually there was much overlap between those three things. >> >>I set VR2 to zero resistance and measured an idle current of 60mA, so I >>didn't adjust VR2. >>I then connected a signal source from a computer, adjusted VR1 and the >>requirements seemed to have been met. >> >>I'm aware that there are people here who can comment on my amplifier >>design >>skills, or lack of them, and maybe some component values can be tweaked >>for >>better performance. > > Only thing is an emitter resistor in TR4 to make it a more of a real > current source. > I think R8 is asking for trouble, just short it, but keep C3. > C4 is big relatve to the supply decoupling caps, maybe works with a good > battery / voltage source.
Thanks for your comments. Yes I think R8 can be smaller or shorted but useful for explaining decoupling. The roads are closed at my location so I'm going to spend this afternoon/evening looking at LT Spice. Old Guy
> >>Are there any free tools available which can run a simulation of this >>circuit? > > LT spice. > > >>What is the lower and upper 3dB bandwidth? > > LT spice will tell you, but if you use some soundcard with a sweep audio > file any scope will tell you. > If you do not have a frequency sweep audio file I can make one available > for download. > > >>Is my wild guess at a value for C6 reasonable? > > Yea, just try it... >
"Tim Wescott" <tim@seemywebsite.really> wrote in message 
news:4sCdnYrd7pPr2nTPnZ2dnUVZ5qOdnZ2d@giganews.com...
> On Wed, 29 Jan 2014 13:02:18 -0500, John Smith wrote: > >> The radio kit hasn't arrived yet (Thread of 18th Jan. Probably due to >> weather conditions here in Ontario) so I thought I'd try my hand at >> making my own audio amplifier kit. >> >> The requirements were as follows: >> 1. Must use components I already have. I couldn't find any 1N4148 but >> did find packets of 1N4001 so that's what I used. Also I could only find >> one resistor under 1 ohm so another is made from two in parallel. >> 2. Must be simple enough to fit on one piece of breadboard but not be a >> trivial design. >> 3. Must deliver enough power to make an 8 ohm speaker cone move visibly. >> 4. Must run from a single 9V battery. >> 5. Must be quick to design with minimal calculation. >> 6. Any soldering must be done in advance of taking it into a school and >> getting a little guy to build it. >> 7. Doesn't need high voltage gain as it will be driven from an ipod so I >> designed for a gain of about 10. >> 8. Low distortion is not essential as long as there's no obvious issue >> below clipping level. >> >> With those requirements in mind I got a piece of paper out and drew >> this: www.pdelectronics.ca/sed/amp2014jan28/schematic.jpg Then I did the >> layout: >> www.pdelectronics.ca/sed/amp2014jan28/layout.jpg Then I built and tested >> it: >> www.pdelectronics.ca/sed/amp2014jan28/built.jpg Actually there was much >> overlap between those three things. >> >> I set VR2 to zero resistance and measured an idle current of 60mA, so I >> didn't adjust VR2. >> I then connected a signal source from a computer, adjusted VR1 and the >> requirements seemed to have been met. >> >> I'm aware that there are people here who can comment on my amplifier >> design skills, or lack of them, and maybe some component values can be >> tweaked for better performance. >> >> Are there any free tools available which can run a simulation of this >> circuit? >> What is the lower and upper 3dB bandwidth? >> Is my wild guess at a value for C6 reasonable? >> >> Old Guy > > Wow. Lots of components for not much amplification -- but if you're > eschewing op-amps and coils, and want a class-AB output stage, I guess > that's what you need to do.
Thanks for your comments. I could have used an op amp but I think the breadboard area required would be roughly the same. There is probably a single chip power op amp available which could do it with no other active devices at all but that would talke some of the fun out of building it.
> > Check out LTSpice, from Linear Technology. It's supposed to be a tool > for marketing their power supply chips, but it's a great all-around > simulation tool.
I'll have a look at it today. Old Guy
> > I'd suggest you answer your questions about bandwidth and C6 with LTSpice, > if you can't just do the circuit analysis yourself. > > -- > > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com >
>"George Herold" <gherold@teachspin.com> wrote in message >news:d5896681-33aa-4ea2-b361->abba58eb1def@googlegroups.com... >On Wednesday, January 29, 2014 1:53:39 PM UTC-5, amdx wrote: >> On 1/29/2014 12:02 PM, John Smith wrote: > >> >> > >> >> Google Zen amplifiers, they are low parts count, probably don't meet >> your criteria, but neat anyway. Many variations, here's one. >> https://www.passdiy.com/project/amplifiers/the-zen-amplifier >> >> Mikek > >Wow.. I was just at that page... trying to recall how he did the class A >thing. > >To John Smith. >I was going to say that if the students are going to understand it then a >simple class A type >design might be better. (though wastful of the battery)
It's more about having fun bulding it and watching it work. The student isn't likely to be able to fully understand how it works yet.
>I wonder if you need any voltage gain at all? >Would using an audio transformer be OK?
Possibly but I don't have any audio transformers except those on some old amplifier boards I have from the days when designers were still thinking tubes and used both a driver tansformer and an output transformer with a pair of transistors, usually germanium devices.
> >One thing that struck me is that you are not going to get taht much power >from a 9V battery. >(What's the internal resistance of the battery? I stuck 100 ohms across a >9V and Vout dropped >to ~8V, but this is an old battery that's been sitting on my bench for a >while) So perhaps a >beefier battery or a higher impedance speaker.
It's true that the battery isn't likely to last long. It will be interesting to see what happens as it runs down. Old Guy
>George H.
On Wed, 29 Jan 2014 14:58:07 -0500, John Smith wrote:

> "Tim Wescott" <tim@seemywebsite.really> wrote in message > news:4sCdnYrd7pPr2nTPnZ2dnUVZ5qOdnZ2d@giganews.com... >> On Wed, 29 Jan 2014 13:02:18 -0500, John Smith wrote: >> >>> The radio kit hasn't arrived yet (Thread of 18th Jan. Probably due to >>> weather conditions here in Ontario) so I thought I'd try my hand at >>> making my own audio amplifier kit. >>> >>> The requirements were as follows: >>> 1. Must use components I already have. I couldn't find any 1N4148 but >>> did find packets of 1N4001 so that's what I used. Also I could only >>> find one resistor under 1 ohm so another is made from two in parallel. >>> 2. Must be simple enough to fit on one piece of breadboard but not be >>> a trivial design. >>> 3. Must deliver enough power to make an 8 ohm speaker cone move >>> visibly. >>> 4. Must run from a single 9V battery. >>> 5. Must be quick to design with minimal calculation. >>> 6. Any soldering must be done in advance of taking it into a school >>> and getting a little guy to build it. >>> 7. Doesn't need high voltage gain as it will be driven from an ipod so >>> I designed for a gain of about 10. >>> 8. Low distortion is not essential as long as there's no obvious issue >>> below clipping level. >>> >>> With those requirements in mind I got a piece of paper out and drew >>> this: www.pdelectronics.ca/sed/amp2014jan28/schematic.jpg Then I did >>> the layout: >>> www.pdelectronics.ca/sed/amp2014jan28/layout.jpg Then I built and >>> tested it: >>> www.pdelectronics.ca/sed/amp2014jan28/built.jpg Actually there was >>> much overlap between those three things. >>> >>> I set VR2 to zero resistance and measured an idle current of 60mA, so >>> I didn't adjust VR2. >>> I then connected a signal source from a computer, adjusted VR1 and the >>> requirements seemed to have been met. >>> >>> I'm aware that there are people here who can comment on my amplifier >>> design skills, or lack of them, and maybe some component values can be >>> tweaked for better performance. >>> >>> Are there any free tools available which can run a simulation of this >>> circuit? >>> What is the lower and upper 3dB bandwidth? >>> Is my wild guess at a value for C6 reasonable? >>> >>> Old Guy >> >> Wow. Lots of components for not much amplification -- but if you're >> eschewing op-amps and coils, and want a class-AB output stage, I guess >> that's what you need to do. > > Thanks for your comments. > I could have used an op amp but I think the breadboard area required > would be roughly the same.
In my experience that's always how I start, but when I actually try both I end up finding that the op-amp solution takes less space. I'm shooting off the cuff here, but I think you could take out everything from just to the left of C1 all the way to, and including, TR4 and C6, and replace it with an op-amp, possibly with an emitter-follower into the base of TR5. Some audio guy will come on and tell you that yes, I guessed right or no, I'm full of holes.
> There is probably a single chip power op amp available which could do it > with no other active devices at all but that would take some of the fun > out of building it.
I certainly agree for you and me. A kid raised on video games may run out of patience before they get your circuit hooked up, though. I'd go with one little black bug, then have an "advanced" class for the kids that stick around, or maybe have your protoboard with all the transistors ready to pull out and try. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
A little guy is going to build that?  Cut 'im some slack!  Do something 
like this:
http://webpages.charter.net/dawill/tmoranwms/Circuits/Blasphemy_For_Mark.gif

TIP29/30 or 31/32 will do for the outputs, 2N3904 will do for the gain. 
Umm, you'll want to adjust the values a little for 9V operation, and 
obviously it won't give 10W then.

Simple mod: "Q capacitor" to the top of the 1k (add another resistor in 
series) to bootstrap the pullup.

Tim

-- 
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com

"John Smith" <invalid@invalid.invalid> wrote in message 
news:lcbfjq$i5p$1@dont-email.me...
> The radio kit hasn't arrived yet (Thread of 18th Jan. Probably due to > weather conditions here in Ontario) so I thought I'd try my hand at > making my own audio amplifier kit. > > The requirements were as follows: > 1. Must use components I already have. I couldn't find any 1N4148 but > did find packets of 1N4001 so that's what I used. Also I could only find > one resistor under 1 ohm so another is made from two in parallel. > 2. Must be simple enough to fit on one piece of breadboard but not be a > trivial design. > 3. Must deliver enough power to make an 8 ohm speaker cone move visibly. > 4. Must run from a single 9V battery. > 5. Must be quick to design with minimal calculation. > 6. Any soldering must be done in advance of taking it into a school and > getting a little guy to build it. > 7. Doesn't need high voltage gain as it will be driven from an ipod so I > designed for a gain of about 10. > 8. Low distortion is not essential as long as there's no obvious issue > below clipping level. > > With those requirements in mind I got a piece of paper out and drew > this: > www.pdelectronics.ca/sed/amp2014jan28/schematic.jpg > Then I did the layout: > www.pdelectronics.ca/sed/amp2014jan28/layout.jpg > Then I built and tested it: > www.pdelectronics.ca/sed/amp2014jan28/built.jpg > Actually there was much overlap between those three things. > > I set VR2 to zero resistance and measured an idle current of 60mA, so I > didn't adjust VR2. > I then connected a signal source from a computer, adjusted VR1 and the > requirements seemed to have been met. > > I'm aware that there are people here who can comment on my amplifier > design skills, or lack of them, and maybe some component values can be > tweaked for better performance. > > Are there any free tools available which can run a simulation of this > circuit? > What is the lower and upper 3dB bandwidth? > Is my wild guess at a value for C6 reasonable? > > Old Guy >