DIY Audio Projects Forum

I was very curious when I read Mark Houston project when he built the Zero Amp Components. I've never had a SE amp, but I've listened to the SE Amp in some Audio Stores when they show High End Audio System. They said the system using SE Amp. Sounds good. But when I asked about the price, I got an answer that can make a heart attack.

So, I decide to make it for my own. SE Amp with Mosfet. I go to Mark Houston project. Seems its very simple. But, in my town I never found audio grade MOSFET like 2SK1058. I search over internet for another ZCA schematic and found this schematic using NPN transistor 2SC3281 that I think it close to Mark Houston ZCA schematic.


Fortunately, I found several small BD139 transistor in dead CDMA fax machine. When see the datasheet, its can be using an audio amplifier and its seems same like 2SC3281. So, I follow Mark Hosuton schematic, but try to simplify it. Here is my schematic.


When start this project, I'm pesimistic to got the best result like Mark Houston describe on
his project. Because, I cannot found High grade component for audio system in my town and no budget to make an order from another country. (Like choke 10mH, and big Caps for PSU).But, experimentation is fun !

I have :
- 2 Tranformer from dead UPS (that rated 3 Amp) with 15 Volt DC at secondary.
- 2 pair 2200uF caps from old Desktop Amp.
- 1 pair PSU Kits with 4700uf Auricaps from Analog Metrics (I buy one years ago from Hongkong)
I buy:
- 1 pair bridge dioda 25 Amp.
- 1 pair 10k Pot .
- 10 1k resistor .
- 8 27R 10watt resistors.

I built Dual Mono Mini SE Amp.

The first setup, I try using one BD139, the sounds is purest but too light with audible hum.
Using PSU which produce 19VDC (when I check with my DMM). And then setting the bias about
9.5 Vdc. So, I try to make paralled 3 BD139 and the sound was improved but still with
audible hum. About this hum, I have no Idea before. Because I think on Marks project he is
using choke to reduce hum.

After several hour testing this amp, I was curious how to got the best performance for that
amp ??? I think, I must check from PSU. Using my DC watt meter , I check for one channel,
how much its can drawn the current and produce the voltage to this Amp. I checked it when I
playing this Amp about 1 hour with my laptop as source and cheap Sharp 2 Way Loudspeaker
with 8 Ohm impedance.

It's shown, the PSU cannot suply a stabil voltage. Its shown around 17 - 19 VDC. So, I try to adjusting pot on PSU to obtain 19Vdc. But after several adjusting, I found my PSU can be suply a stable voltage at 17 Vdc. Therefore, I set the bias voltage to 8.5 Vdc. I set and reset for several time till watt meter and my DMM shown stable voltage from PSU and stable voltage for biasing.

And guess what??? Believe it or not! There is no HUM anymore. This methode not reduce
HUM, but really remove HUM from that Amp. And sure, a clean sounds! I think, I no need choke anymore for SE Amp. I think with stable voltage can remove hum .But, I'm not sure about that. I just trying. Am I right ??? Mark, please help me to explain why the HUM is gone with this methode. This methode can be working with another transistor ???

Note : I always using my laptop to try my DIY Amp. Because, laptop is a bad source as audio player (with too many noise). When the amp can produce a good sound (no fatigue for a long time listening) from my laptop it's mean the amp must be good with CD Player or another audio source.

_________________
Small is enough. Clean is good. Simple is easy. Small, Clean and Simple is ZCA. And this is so beautiful....

Salam,
Arie

This is some pic about Mini ZCA


BD139 Transistor

PSU Kits from Analog Metric

_________________
Small is enough. Clean is good. Simple is easy. Small, Clean and Simple is ZCA. And this is so beautiful....

Salam,
Arie

SE amps can be troublesome in this way; either they cost an arm and a leg or they are underpowered. For the same budget, you can build a class AB amp with more power. Some people are enamored with class A and will listen to nothing else.

Let me give you some insight real quick. I can explain in greater detail another time. If you are satisfied with the construction of this amp, you can use these tips in your next amp.

-I am assuming that the input and output capacitors are electrolytic. That is fine; it will be hard to find a film cap with that sort of value unless you are willing to pay a fortune. What I do suggest is to place a small cap in parallel with each one. Use a 1 uF, 50v monolithic ceramic cap. They come in small packages and are usually coated in yellow epoxy. You should be able to find them on eBay, ten for $1. What this does for you is bypass the electrolytic capacitor's series inductance, allowing higher frequencies to get by. You may not experience a difference but the part is so cheap it's worth trying.

-That resistor of 27 ohms makes your amp less efficient. If you replace it with a constant current source, you should experience an increase in efficiency as well as more linearity, more gain, and more rejection of power supply noise. The reason is that it acts like a low-value resistor at DC frequencies but has a very high AC impedance. Some tube preamps use a single stage with a current-source as the plate load. This is the very same principle and it supposedly lowers distortion quite a bit. If you want to know more about how to do this, I'll explain it in my next post.

Anyway, it looks good and I hope you enjoy. If you have any more questions I know a few things.
Ed

_________________
Completed Projects:

6L6G / 12AX7 25W Guitar Amplifier
TLC272CP/2N3904/3906 Headphone Amp (Can Man)
MPF102/IRF630 Headphone Amp (FETZilla)
12AU7 / IRFX Headphone Amp (x2)
TIP31C/32C 5W Stereo
More to come...

Bow to Ed!!

Hi Ed, Many thanks for your suggestion. So, to get more power efficiency I must change the load resistor ? How low I can go ? 15 Ohm or 10 Ohm ?
If my Trafo rated 3 Amp and can supply a stable voltage at 17 Vdc , can I use 10 Ohm resistor to get 7.2 watt per channel ?

_________________
Small is enough. Clean is good. Simple is easy. Small, Clean and Simple is ZCA. And this is so beautiful....

Salam,
Arie

I would check on your transistor's dissipation rating first. It would be the limiting factor. If you have a bias voltage of 8.5, that means your bias current is 0.315A. If you changed the resistor to 10 ohms that puts your current at 0.85A, allowing for more power but also generating more heat. Be careful.

The current source I am talking about is more complicated. It involves getting a PNP transistor and putting it in place of the load resistor. I will draw you up a schematic tomorrow or Friday and show you what you could do.

If I were you, I would keep your amp the way it is. Then, get some parts and build another amp so you can compare them. If getting parts is a problem, then I can understand why you would want to take one apart to build the next one.

Ed

_________________
Completed Projects:

6L6G / 12AX7 25W Guitar Amplifier
TLC272CP/2N3904/3906 Headphone Amp (Can Man)
MPF102/IRF630 Headphone Amp (FETZilla)
12AU7 / IRFX Headphone Amp (x2)
TIP31C/32C 5W Stereo
More to come...

Bow to Ed!!

Redsky you have now joined the ranks of the ZCA fraternity. We are many (haha). The ZCA is meant to be an easy to build low power amp and if you want more build something else. Class A SE is the purest sounding amp to build and though simple in design it can be the hardest to build. It has no Ripple rejection. Any PS hum comes out your speakers. No that's wrong "all" PS hum comes out your speakers.

If you want to build a very good amp build a better PS. The PS is the hart of any amp and get it right you have a small chance of building a great amp. Get it even a little wrong and your amp will be no better than every body elses. I build a lot of SET amps and sometimes use 94db efficient speakers. You can hear electrons moving in quiet passages of the music (thermal noise). For tube amps I always use tube rectification and choke filtering. There are many reasons to use this combo but for me, I like the sound of tube rec. and choke filter. Changing a rec tube alters the tone of the amp.

To get my ZCA quiet I went for choke filtering. Choke filtering adds a level of channel separation possibly not obtainable without it (prepare for pending riot). A SS amp builder friend of mine who sells his wares all over the world agrees with me, though for him choke filtering is far to costly and heavy to employ.

There are many ways to build a ZCA and many variations on my ZCA. Every component in every amp "bu**g#gers" the sound. Every piece of wire, solder joint or even chassis, adds distortion to the original signal. For ME low power, two stage, class A, SE tube amps have the best sound because they change so very little of the original sound. In my system from CD player (Oppo BDP-95 Audiophile) to speakers I only have two capacitors and three active devices in the signal path. I employ all component-2-component wiring (very little to no hook-up wire). The ZCA attempts to demonstrate that a simple low power amp can produce excellent sounding music into the right speakers. It is simple to build and good to listen to. After all, for me, it's all about the music.

_________________
Projects: Oatley K272C - headphone amp in a tin can | "K272C" - Oatley's newest headphone amp | "VoXItBassO" - stereo 12" sub-woofers ]
Website: [ retro-thermionic ]

Here is a schematic of one way to do what I was saying. I modeled this in TINA-TI and only got a little less than a watt with an 18v supply. I tried different levels of bias current in the output amplifier.

T2 and T3 are the constant current source which holds a constant voltage across R2. When you have a constant voltage across a constant resistance it then follows you have a constant current. You adjust P1 to make the voltage at T1's collector half the VCC. I used a 4700u capacitor in the output circuit but it's bypassed with a 1u ceramic. Your mileage may vary with whatever parts you may or may not get.

How did you find the output power of your amplifier?
Ed

_________________
Completed Projects:

6L6G / 12AX7 25W Guitar Amplifier
TLC272CP/2N3904/3906 Headphone Amp (Can Man)
MPF102/IRF630 Headphone Amp (FETZilla)
12AU7 / IRFX Headphone Amp (x2)
TIP31C/32C 5W Stereo
More to come...

Bow to Ed!!

Hi Mark, I'm really a proud become a one of ZCA fraternity. Yap, you're right. The point is how to minimalize the component to avoid a noise source. I do believe that. The simple is good. And for my condition, ZCA is the best way to get "high end" system.

For me, low power amp is really enough to enjoy the musics. I try my mini ZCA (direct connect to My laptop) to drive low sensitivity 8 ohm Sharp speaker (2 way parallel ). The sound very clean and purest. And after adjusting PS voltage and bias voltage to get stable voltage, the HUM is gone.

You're right again Mark, the hum is audible (just when I hear closest to Speaker) when I drive my Primus II 150 Infinity with sensitivity 88 db (2 way in series) and nominal impedance 8 ohm. And when try to connect to CD Player, the sounds is worst. It's seems the signal from CDP is too weak?? Do I need a preamp ? Or it's because My ZCA not enough power to drive that speaker when in data specification shown the recomended power Amp is 10 - 100 Watt ?

And another stupid question, can I use small coil as choke for filtering PSU ?

Many Thanks

_________________
Small is enough. Clean is good. Simple is easy. Small, Clean and Simple is ZCA. And this is so beautiful....

Salam,
Arie

Hi Ed, thanks for your help. Really to learn about CCS. And think to build another more ZCA with CCS to see the different.

Ed, I try to understand about your CCS schematic . I try to simplify it like this. Thinking it's just simple change of the resistor load for my Mini ZCA ???

Am I right Ed ?

First , using my DC Watt Meter ( tools from my aeromodelling Hobby) . I connet it from PSU output (as source) to resistor load (as load) its shown power consumption about 1 - 2 watt with current drawn at 0.2 - 0.3 Amp. Maybe I take a pic again for the next post.

Second, using Electric Caculator http://www.sengpielaudio.com/Rechner-ohm.htm to make sure what I did. I make calculation for 8.5 Voltage and 27 Ohm. Do I right ?

Regards,

arie

_________________
Small is enough. Clean is good. Simple is easy. Small, Clean and Simple is ZCA. And this is so beautiful....

Salam,
Arie

I'm glad you find this hobby so entertaining. If I can help, I want to so I can further you along in your mission to understand what you are building.



That's more or less what the CCS is...it's a load for your power transistor and it is active. That allows you to get more efficiency out of your power supply. The theorhetical maximum efficiency for a class A amplifier is 50%; to get that you have to use a transformer as the collector load. With a CCS load, you can get higher than 25%. I wouldn't try to use a class-A for anything more than 2 watts of audio power, as I'm a big fan of class AB and I'm working on learning class D.

I have a project on this list entitled Insane Hybrid Headphone Amplifier. Take a look.



The circuit you have drawn is accurate except for one thing...you will need a resistor from the base of the lower transistor to ground. Make the value 1K at 0.5w. The 500m ohm resistor should be 2w or more.

Remember, some audio people believe that simplicity is better. They would specifically not use the CCS because they believe the 27-ohm resistor is better. The ZCA people believe the ideal amplifier is a piece of straight silver wire with gain.



If you are wanting to get an accurate measurement of power, run a sinewave through the amp. Make sure the amp is not clipping. Now, use a DMM and measure the AC RMS voltage into an 8 ohm resistor (not a speaker). Multiply that voltage by itself and then divide by 8. That is your output power. Some people say the power formula is Vcc * Vcc / 2R where R is the load.

The reason I asked is because I modeled something similar in TINA-TI and only got about 0.9w into an 8-ohm speaker. If you are measuring 2.6w into a speaker then use a load resistor instead. If you still get 2.6w then my simulation was wrong.

Good luck!
Ed

_________________
Completed Projects:

6L6G / 12AX7 25W Guitar Amplifier
TLC272CP/2N3904/3906 Headphone Amp (Can Man)
MPF102/IRF630 Headphone Amp (FETZilla)
12AU7 / IRFX Headphone Amp (x2)
TIP31C/32C 5W Stereo
More to come...

Bow to Ed!!