3-5 watts classA amp

[adason]

I was bored over the holidays so I made small amp. Just for fun. From spare parts. Its from this site:

http://www.redcircuits.com/Page80.htm

Sounds good. Definitely worth exploring.

ed

 

[davidallancole]

This amp is similar to the JLH Class A amp.

http://www.tcaas.btinternet.co.uk/jlh1969.pdf

 

[Minion]

Hi, I have looked at that circuit before but never got arround to Trying it because I have had problems with many of the circuits on that site.....But now that i know someone else has tried it I am more inclined to build it.....

I just quickly did up a PCB design for this amp and was wondering if someone could look at it and see if I made any Mistakes....

An externally hosted image should be here but it was not working when we last tested it.

I used the Pinout for the Output transistors after the Tip transistors as that is what I have on hand (B,C,E) and I used the pinout for the other Transistors as a BC560 which I have...

The PCB is 2in x2.1in....

Thanx

PS, I also used an Input resistor for the P1 pot to set the Input impedance...

 

[adason]

I just want to add one more information. Amp prefers regulated supply. It works with both just fine, but you need way too much capacitance for unregulated supply to be hum free. Than it kinds of defeats the purpose of cheap amp, does not it, if you have to use tons of filtration.
ed

 

[Minion]

Filtration is cheap.....I have a Box full of 10,000uf caps that I got for $1 each, also with a LM317 regulator and a cheapo Pass transistor you can make a regulated supply that supplies serveral amps of Current.....

😀

 

[adason]

Filtration is cheap.....

yes and no....
I was testing unregulated suply, started with one 27000 uF, big hum, obviously its simple classA amp, that is expected. I needed to add six (6) of those 27000 uF caps. Now that is not a cheap solution.
On the other hand, if you use just 5000 uF before, than regulator, and 1000 uF on the output, it will be much less money.

ed

 

[Zen Mod]

or 27KuF , then cap multiplier , then 27KuF

that's even better than reg

 

[adason]

Hi Choky,

that would increase voltage. I started with the voltage I wanted, 22-24 V. Just wanted to filter it.

By the way, when you use multiplier, does not that reduce current capability? You know, each time you double the voltage, you half the current?

This amp takes 1.5A.

ed

 

[Zen Mod]

Hi Choky,

that would increase voltage. I started with the voltage I wanted, 22-24 V. Just wanted to filter it.

By the way, when you use multiplier, does not that reduce current capability? You know, each time you double the voltage, you half the current?

This amp takes 1.5A.

ed

not voltage multiplier ;

cap multiplier .......... google for it or go to ESP site and read tutorial

 

[adason]

I see, Choky, great. I was in Elliotts page. I got it.
ed

 

[Zen Mod]

I see, Choky, great. I was in Elliotts page. I got it.
ed

cap multiplier a-la Pass (with mosfet) is also goood replacement for choke - less expensive , fast to make and pretty good if you have few un-needed volts in your PSU ......because of Vds of mosfet - you'll have 4 volts less on output of multiplier

but I always say that is best as choke replacement in CLC config .

nothing replaces big cap on end of PSU

 

[Minion]

I built this amp a couple days ago useing the PCB I designed and it sounds REALLY Good..... I used 2n3055 Transistors for the output and the BC560 at the input and used a regulated PSU useing a LM317 and a Pass Transistor and 10,000uF of filtering and a fair quality Elna 2200uf at the output for DC Blocking....

I believe I am getting over 10w out of it as my Preamp puts out up to 9v and it gets quite loud....I"m going to use it as a Practice guitar amp.....

Definately worth building.....and absolutely no Hum....

Cheers

 

[tiefbassuebertr]

This amp is similar to the JLH Class A amp.

http://www.tcaas.btinternet.co.uk/jlh1969.pdf

No. in opposite to JLH this is a SRPP circuit. Additional there is a equalizer function in the globale NFB (two feedback pads) to enhance the aera arround 100 Hz (see attachements of simulation results). The ZEN amp also inside to the aim of camparsion.

 

[Bigun]

I wonder if this kind of bass boost is good for overall performance - does it not contaminate the feedback signal with some phase shifts that increase overall distortion ?

 

[mindutis]

I am working on this amp construction for about five months already. And it's done and siting in the amp chassis. Now trying three different power supply schematic. Cap filtering, capacitance multiplier, and regulated with LM317 plus pass transistor. Tried cap filtering with 20.000uF, and the hum still exists, but not so loud. Cap multiplier depends much on gain of chosen transistors.Acted kind of weird. Now working on filtered PS. If the 20kuF will be enough, I'll keep it. The only disadvantage - heat.

Does anyone matched the hfe of transistors? How much the output transistors had? And when talking about loud sound, dont forget output voltage, ok 😉 I used 4700uF for output.

 

[Bigun]

Cap multiplier depends much on gain of chosen transistors.Acted kind of weird.

Can you say more about the weird part ?

 

[mindutis]

Voltage drops if not high hfe transistor is used with a higher load.

 

[Bigun]

OK - well this isn't weird, it's an expected behaviour, you are ultimately limited by the ability of the transformer's internal impedance. I was worried that it somehow ruined the sound.

If simulations can be trusted I don't think you should be limited by the impedance of the cap multiplier. There are some ways to minimize voltage drop:

a) use a BJT not a FET (Vgs of 4V !)
b) the resistor supplying the base current to the BJT will add to the voltage drop (V = Ib X R) so this should be set at the lowest possible value - just high enough to stop the ripple getting to the amplifier. This means using a larger capacitor.
c) you can reduce the output impedance of the supply / increase hfe if you make a Darlington pass device - the extra Vbe voltage drop is likely to be compensated by the lower base current which allows you to use a lower valued resistor feeding current to the base.

 

[mindutis]

yes, best is to use a darlington pair, plus power BJT transistor. As you wrote - c. Have just finished an LM317 plus pass transistor, plus "soft start", or time delay circuit (you can find example in datasheet). Voltage rises up in few seconds after powering on PS. Everything worked same as simulated with program. Gonna try soon with the amp.

 

[russel]

I was bored over the holidays so I made small amp. Just for fun. From spare parts. Its from this site:

3 - 5 Watt Class-A Audio Amplifier - RED - Page80

Sounds good. Definitely worth exploring.

ed

The attachment may work, tried it quickly on LT Spice. For added current stability an extra transistor could be added to the PFET, does go rail to rail which is an advantage.