A visual guide to the Rothacher/Pass Zenductor 2
The Zenductor 2 is a mono block, single-ended, zero-feedback, Class-A audio amplifier. You need two for stereo.
Nelson’s article can be found here - https://www.diyaudio.com/community/threads/burning-amp-2024.414636/post-7820909
All photos in this guide will show one amplifier being built.
Parts for one amplifier.
Let's look a little closer at al the various bits -
The circuit board everything attaches to.
Zenductor 2 is powered by a 16v 4.5A brick-style Power Supply.
Here's the magic... the big device is the choke (inductor) that loads the output stage. The darling little transformer is used for voltage gain.
Please note the little circular notch in the plastic closest to the camera, this denotes pin 1.
L to R, RCA input jack, DC power connector, power switch
Capacitors. there are 2 different values that look quite similar. The physically bigger can is 4700uF 25V, the smaller is 6800uF 10V. Make sure you have the right one when stuffing the PCB.
Electrolytic capacitors are polarized. It matters which way they are installed. The long lead is positive (+). The can has negative (-) marked on the heatshrink.
This photo show the 4700uF 25v
1000uF 25v
10uF 35v SILMIC input capacitor.
This is a small value poly capacitor used in the notch network, it's not polarized and can be inserted any way.
Speaker jacks.
Nifty rectangular LED
The input section uses an array of 8 matched Jfet.
Output section is comprised of these two matched Mosfet.
Mosfet heatsinks.
M3 hardware for heatsinks.
Assembly will look like this.
The Zenductor 2 is a mono block, single-ended, zero-feedback, Class-A audio amplifier. You need two for stereo.
Nelson’s article can be found here - https://www.diyaudio.com/community/threads/burning-amp-2024.414636/post-7820909
All photos in this guide will show one amplifier being built.
Parts for one amplifier.
Let's look a little closer at al the various bits -
The circuit board everything attaches to.
Zenductor 2 is powered by a 16v 4.5A brick-style Power Supply.
Here's the magic... the big device is the choke (inductor) that loads the output stage. The darling little transformer is used for voltage gain.
Please note the little circular notch in the plastic closest to the camera, this denotes pin 1.
L to R, RCA input jack, DC power connector, power switch
Capacitors. there are 2 different values that look quite similar. The physically bigger can is 4700uF 25V, the smaller is 6800uF 10V. Make sure you have the right one when stuffing the PCB.
Electrolytic capacitors are polarized. It matters which way they are installed. The long lead is positive (+). The can has negative (-) marked on the heatshrink.
This photo show the 4700uF 25v
1000uF 25v
10uF 35v SILMIC input capacitor.
This is a small value poly capacitor used in the notch network, it's not polarized and can be inserted any way.
Speaker jacks.
Nifty rectangular LED
The input section uses an array of 8 matched Jfet.
Output section is comprised of these two matched Mosfet.
Mosfet heatsinks.
M3 hardware for heatsinks.
Assembly will look like this.
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More parts -
0.47ohm 3W resistors
62ohm resistor
Various small resistors
50K potentiometer for setting bias
You need a bit of wire, this is more than enough.
The bigger hardware is used for mounting the choke and also as feet.
Note the bigger hardware and the smaller hardware are pretty close in size. try to keep them separate.
So what does all this mean when looking at the schematic? Let's take a look and break it down...
This image shows most everything except the small resistors, placed near their symbol on the schematic.
Here's just the transistors
The magnetics
Capacitors
Resistors
Jacks and mechanicals
0.47ohm 3W resistors
62ohm resistor
Various small resistors
50K potentiometer for setting bias
You need a bit of wire, this is more than enough.
The bigger hardware is used for mounting the choke and also as feet.
Note the bigger hardware and the smaller hardware are pretty close in size. try to keep them separate.
So what does all this mean when looking at the schematic? Let's take a look and break it down...
This image shows most everything except the small resistors, placed near their symbol on the schematic.
Here's just the transistors
The magnetics
Capacitors
Resistors
Jacks and mechanicals
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Let's assemble.
First, there is one housekeeping item on the BAF 2024 boards. This will almost certainly be corrected subsequently, but the camp bards have the error in the silk...
"R9" is on the PCB twice. The correct R9 is up near the heatsink and inductor in the far corner.
This one is "R0"
----------------
The very first step in building the amplifier is to measure and label your small resistors. Please do so now.
If you have a lead bender, 0.5" is the proper spacing for the small resistors.
Small resistors sit flush on the PCB
Bend the leads outwards underneath to keep them in place for soldering.
Solder
Trim off the lead
The bigger resistors get hot, and elevating them off the PCB is a good idea. You can use one of the nuts as a spacer. It's a lot easier to solder one of the leads from the top when you mount these.
Here's the PCB with all the resistors stuffed and soldered.
Generally when stuffing the PCB, you want to go from the shortest to the tallest components. We will generally be following that.
The little red capacitor can be stuffed. No polarity to worry about.
The input cap. Remember, long lead into +
Potentiometer. It's 3-leg and keyed, very hard to get this wrong.
DC jack. Make sure it's flush witht the PCB.
The RCA jack is keyed, make sure is flush.
LED. Like a polarized capacitor, long leg into +
Also, this is a neat photo, it shows that inside the plastic the cathode is bigger... why? It's the part that actually lights up.
Next is the small transistors. The transistors are a match set, and all the same - any transistor can go into any position. Just make sure the flat of the transistor body matches the flat of the symbol on the silkscreen.
What works best is to place the PCB on a flat surface, preferable with a piece of paper ir two underneath, and insert the transistors, and soldering just the outside leg from the top. This gives a chance to get everything all lined up.
You can see the single leg soldered here. Yes, the solder joint on the further away transistor could be a little prettier... but this is not an issue as there's an opportunity to clean it up later.
Continue until all transistors are stuffed and the outside leg, I.E., the one easiest to get to, is soldered. Make everything line up as pretty as you can get them.
...and I'm out of images in this post, so on to the next -
First, there is one housekeeping item on the BAF 2024 boards. This will almost certainly be corrected subsequently, but the camp bards have the error in the silk...
"R9" is on the PCB twice. The correct R9 is up near the heatsink and inductor in the far corner.
This one is "R0"
----------------
The very first step in building the amplifier is to measure and label your small resistors. Please do so now.
If you have a lead bender, 0.5" is the proper spacing for the small resistors.
Small resistors sit flush on the PCB
Bend the leads outwards underneath to keep them in place for soldering.
Solder
Trim off the lead
The bigger resistors get hot, and elevating them off the PCB is a good idea. You can use one of the nuts as a spacer. It's a lot easier to solder one of the leads from the top when you mount these.
Here's the PCB with all the resistors stuffed and soldered.
Generally when stuffing the PCB, you want to go from the shortest to the tallest components. We will generally be following that.
The little red capacitor can be stuffed. No polarity to worry about.
The input cap. Remember, long lead into +
Potentiometer. It's 3-leg and keyed, very hard to get this wrong.
DC jack. Make sure it's flush witht the PCB.
The RCA jack is keyed, make sure is flush.
LED. Like a polarized capacitor, long leg into +
Also, this is a neat photo, it shows that inside the plastic the cathode is bigger... why? It's the part that actually lights up.
Next is the small transistors. The transistors are a match set, and all the same - any transistor can go into any position. Just make sure the flat of the transistor body matches the flat of the symbol on the silkscreen.
What works best is to place the PCB on a flat surface, preferable with a piece of paper ir two underneath, and insert the transistors, and soldering just the outside leg from the top. This gives a chance to get everything all lined up.
You can see the single leg soldered here. Yes, the solder joint on the further away transistor could be a little prettier... but this is not an issue as there's an opportunity to clean it up later.
Continue until all transistors are stuffed and the outside leg, I.E., the one easiest to get to, is soldered. Make everything line up as pretty as you can get them.
...and I'm out of images in this post, so on to the next -
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post 4
Line them up
Twist, poke, prod, as necessary to get as straight as possible
Still a lot of unsoldered holes
Flip the board over
And solder them all. Avoid solder bridges. Didn't like a solder joint from before? here's the opportunity to reflow and make pretty.
Ok, moving on! Grab the small transformer and put into it's place. Remember the little notch key thing? You can see it printed on the PCB as well, for proper alignment.
Now we need to install the first standoff that acts as a foot for the amp. Now is a good time, and we'll see why in the next step.
One complaint from previous Camp Amps is the small output connections. Zenductor 2 has full size posts. (If you want to use the smaller style, there are pads provided.) In our example we'll mount the big ones.
There are a lot of washers and nuts on this set of posts. This photo shows the order. the PCB is sandwiched between the two plastic ovals. Note there is a washer under the post on the top side, and yes, two gold washers on the bottom before the lock washer.
Get the posts installed, and align & tighten with one nut.
The 2nd nut acts a lock for the first, tighten separately.
Reliable continuity cannot be guaranteed with these posts through the PCB, so we're going to add some leads to make good and sure. Trim a price of wire as shown,
Solder to the post.
Repeat on the other side. Nice!
Stuff and solder the bigger blue capacitors
Time to mount the choke. The 6/32" hardware is used for this. Note the fender washers. Also not the electoral tabs on the choke point to the left.
The bolts and nuts are used on the inner set of mounts.
However the remaining standoffs are used on the outer mounts.
Connect the two electrical tabs to the PCB via two pieces of wire
Board should look something like this now.
Please continue on post #8 https://www.diyaudio.com/community/threads/zenductor-2-amp-camp-24-version.418631/post-7813870
Line them up
Twist, poke, prod, as necessary to get as straight as possible
Still a lot of unsoldered holes
Flip the board over
And solder them all. Avoid solder bridges. Didn't like a solder joint from before? here's the opportunity to reflow and make pretty.
Ok, moving on! Grab the small transformer and put into it's place. Remember the little notch key thing? You can see it printed on the PCB as well, for proper alignment.
Now we need to install the first standoff that acts as a foot for the amp. Now is a good time, and we'll see why in the next step.
One complaint from previous Camp Amps is the small output connections. Zenductor 2 has full size posts. (If you want to use the smaller style, there are pads provided.) In our example we'll mount the big ones.
There are a lot of washers and nuts on this set of posts. This photo shows the order. the PCB is sandwiched between the two plastic ovals. Note there is a washer under the post on the top side, and yes, two gold washers on the bottom before the lock washer.
Get the posts installed, and align & tighten with one nut.
The 2nd nut acts a lock for the first, tighten separately.
Reliable continuity cannot be guaranteed with these posts through the PCB, so we're going to add some leads to make good and sure. Trim a price of wire as shown,
Solder to the post.
Repeat on the other side. Nice!
Stuff and solder the bigger blue capacitors
Time to mount the choke. The 6/32" hardware is used for this. Note the fender washers. Also not the electoral tabs on the choke point to the left.
The bolts and nuts are used on the inner set of mounts.
However the remaining standoffs are used on the outer mounts.
Connect the two electrical tabs to the PCB via two pieces of wire
Board should look something like this now.
Please continue on post #8 https://www.diyaudio.com/community/threads/zenductor-2-amp-camp-24-version.418631/post-7813870
Attachments
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A MoFo with M2 gain stage - what's not to like!
Yes please. Is there a wait list where I can sign up and/or can I buy some boards at BAF?
Yes please. Is there a wait list where I can sign up and/or can I buy some boards at BAF?
Fabulous work as always, Mr. T. 😎
Note that after listening tests into my evil load speakers, the two 100 ohm resistors
have been changed to 475 ohms. No performance hit, but better high frequency stability.
Note that after listening tests into my evil load speakers, the two 100 ohm resistors
have been changed to 475 ohms. No performance hit, but better high frequency stability.
Really appreciate the laying out of components on the schematic. Thank you.
Build continued
Remember this photo from earlier? Attach the mosfets to the heatsinks with the M3 hardware and get things squared up and torqued. If you have heatsink goop, use some. If not, don't worry about it. Attach and snug these up now because getting to the nuts later is inconvenient.
Make sure the wires on the choke and PCB are attached properly before installing the heatsinks. Once the heatsinks are soldered on, getting to these wires would be a very large pain in the posterior.
Right heatsink first, then left.
Soldering heatsinks isnt that hard as the pins are nicely tinned at the factory. It just takes some time to warm everting up because they are, well, heatsinks...
Place wetted iron to pad and pin, add some solder so there's more flux, and once you can bely fresh solder on the top of the pin, it's hot enough.
Solder both pins first.
Then solder the transistor pins.
Trim leads.
Everything should be on by now. All we need to do is set the bias.
Multimeter is set to DC Volts and placed across the tabs of the big choke.
You can see the meter clip leads on the choke tabs.
Set bias between 1.3 - 1.4 V. Move the pot slowly, small movements make big changes. Things will not get truly stable until it's up to temperature. These heatsinks run pretty darn hot in operation, getting close to incandescent lightbulb temps. (not a big one, but still...)
Enjoy! This little amp sounds fantastic!
🙂 🙂 🙂
Remember this photo from earlier? Attach the mosfets to the heatsinks with the M3 hardware and get things squared up and torqued. If you have heatsink goop, use some. If not, don't worry about it. Attach and snug these up now because getting to the nuts later is inconvenient.
Make sure the wires on the choke and PCB are attached properly before installing the heatsinks. Once the heatsinks are soldered on, getting to these wires would be a very large pain in the posterior.
Right heatsink first, then left.
Soldering heatsinks isnt that hard as the pins are nicely tinned at the factory. It just takes some time to warm everting up because they are, well, heatsinks...
Place wetted iron to pad and pin, add some solder so there's more flux, and once you can bely fresh solder on the top of the pin, it's hot enough.
Solder both pins first.
Then solder the transistor pins.
Trim leads.
Everything should be on by now. All we need to do is set the bias.
Multimeter is set to DC Volts and placed across the tabs of the big choke.
You can see the meter clip leads on the choke tabs.
Set bias between 1.3 - 1.4 V. Move the pot slowly, small movements make big changes. Things will not get truly stable until it's up to temperature. These heatsinks run pretty darn hot in operation, getting close to incandescent lightbulb temps. (not a big one, but still...)
Enjoy! This little amp sounds fantastic!
🙂 🙂 🙂
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Banana plugs are the Monoprice Affinity.
https://www.monoprice.com/product?p...ufg-grevOZIoNsqnEraBO1V8ePiWU-vJBGkPAL0T9dNGx
I’ve always liked banana plugs over all other solutions, bought a whole bunch of them, and haven’t looked back. Highly recommended.
https://www.monoprice.com/product?p...ufg-grevOZIoNsqnEraBO1V8ePiWU-vJBGkPAL0T9dNGx
I’ve always liked banana plugs over all other solutions, bought a whole bunch of them, and haven’t looked back. Highly recommended.
I like big posts and I can not lie
You other builders can't deny
when an amp comes in with ity bitty posts
and your cables are bigger than most
you get irate, and wanna abort
cause you noticed those cables short
Great work Jim and Nelson! Would you be able to tell me the PCB size? I’m hoping I get the chance to get the miter saw out this weekend and make a wood base for them.
Very nice ideas with the circuit! I wonder if the 8x input JFets could be changed for 2x depletion mode MOSFET's?