A homemade workshop sine-wave generator provides 100 Hz, 1 kHz, and 10 kHz outputs for servicing amplifiers and receivers.
It uses a Wien bridge oscillator with a dual TL082 op-amp, a 60V/20mA telephone bulb for amplitude stabilization, and a buffer stage.
The power supply runs from 230 V mains, uses a TS2/14 transformer with a Delon doubler, and delivers about 14 V DC plus 11 V AC.
The output level is adjustable from zero to about 4 Vrms, and the project cost only a dozen zlotys.
Recycled materials kept the price low, but missing parts stretched the build to about one year.
Generated by the language model.
Hello,
Necessity is the mother of invention, sometimes the right equipment is needed for servicing, such as a low-frequency signal generator used to repair amplifiers and receivers. There are a lot of devices on the market, both new and used, but their price is unacceptable to me. So I thought that in order to save costs I would build something like this. The choice fell on a simple sine wave generator with three frequencies: 100 Hz, 1 kHz and 10 kHz, powered from the 230 V mains. I found a description of the electronic circuit on the Internet. It comes from the popular magazine Elektronika Praktyczna 1/95.
The mechanical construction consists of a base made of steel sheet with two sides riveted to it. The lid is also cut from the same material. The metal pieces were cut with a hacksaw and then bent with a vice in my dad's garage. On it, the power supply is screwed with M3 screws through distance sleeves a few millimeters long. The front panel is made of plastic. On the latter, the so-called a small chassis with a generator board, a dependent isostat switch with frequency selection RC elements, a control lamp and a BNC output socket. The inscriptions were made with a thin waterproof marker. Before final assembly, the steel parts were painted with anti-corrosion paint. The box is permanently connected to the PE conductor of the power cable.
The modules on the boards are connected by thin wires. The power supply includes a TS2/14 domestically produced transformer and a rectifier with a Delon doubler equipped with two filtering capacitors. From it comes the DC voltage of approx. 14 V and the alternating voltage of approx. 11 V to power the control lamp with the telephone bulb. The boards were etched in a solution of sodium persulfate heated indirectly by solar energy, the process for the power supply circuit took about 40 minutes. The Wien bridge generator contains a double TL082 operational amplifier placed in a socket. The first stage produces a sinusoidal signal with the selected frequency, the second is a buffer. A 60V/20mA telephone bulb is used to stabilize the amplitude, and the Telpod CN-15 cermet potentiometer is used to set it. The signal is regulated by a Telpod SP 1.2 carbon potentiometer from zero to approx. 4 Vrms. On the back there is an output ground switch.
The approximate cost is a dozen zlotys and is low due to the use of recycled materials and parts, e.g. a three-core power cord with a plug is made of electronic scrap, the casing sheet was purchased at a local scrap yard, and the plastic is recycled. The rest of the used parts I had from my own stock. The elements that I bought myself are a mains transformer in a stationary store, two electrolytic capacitors (TME) low-SR Panasonic 470 uF/25 V/105 °C and a double operational amplifier TL082 (Allegro). Due to the shortage of some parts, work on this device took about one year.
I add some photos of the project:
About Author
żarówka rtęciowa wrote 3910 posts with
rating 390 , helped 364 times.
Live in city Pelplin.
Been with us since 2005 year.
The switch is visible in some photos, and in others it is not. BNC is also ordinary, not isolated, so it is at PE potential - the same as in most function generators. So what does this "output ground switch"... [Read more]
żarówka rtęciowa
04 Jul 2023 14:51
Hello,
The switch is designed to break the ground loop when the output ground of the generator is connected with the tested circuit and the analog oscilloscope, in which its input socket is is permanent... [Read more]
CosteC
04 Jul 2023 14:56
Can you make some diagram because I don't understand. I have, perhaps mistakenly, the impression that the ground loop break is in the wrong place. [Read more]
Hello,
Factory-made Polish devices with these transformers, e.g. power supplies for radio receivers or emergency lighting modules. they have no mains fuses on the mains supply side. So there is no need... [Read more]
CosteC
04 Jul 2023 16:12
And what happens if the transformer gets a short circuit of, say, 200 ohms and starts to heat up to the point where it can ignite?
I still don't understand what the switch does. Can you make a d... [Read more]
prosiak_wej
04 Jul 2023 19:48
I believe it cuts the PE wire from the mains cord from the housing. [Read more]
pawlik118
04 Jul 2023 19:55
The front panel is made of plastic - it is non-conductive.
Added after 1 [minutes]:
I like. A reasonably maintained compromise of aesthetics to the amount of work.
It is neat and looks decent.
... [Read more]
CosteC
04 Jul 2023 20:24
I don't know such a recipe... It would be very strange, besides it assumes that there will be no magical failure anywhere else in the device that could lead to a fire..
The fuse has two roles - protection... [Read more]
123104
04 Jul 2023 21:29
The author wrote: "The front panel is made of plastic." [Read more]
CosteC
04 Jul 2023 21:38
I'm honored, yes. I missed it.
Still somehow I feel bad without a fuse ... Indeed, a wire in a tiny power transformer should not fall out of the transformer and strongly limits the current ... But... [Read more]
pawlik118
04 Jul 2023 21:47
I'd probably give a fuse, just to feel good. Some time ago, an older colleague, a designer, told me about the "lack of its requirement" in small transformers, and it concerned certified medical equipment... [Read more]
acctr
04 Jul 2023 23:27
Why this tension? Have you checked its characteristics for voltages equal to the amplitude present in the generator system? [Read more]
prosiak_wej
04 Jul 2023 23:29
A board made of foamed PVC?
As for the fuse - recently I have been resuscitating Carel controllers from Liebherr MediLine freezers. The controllers have a converter, which is an independent module on... [Read more]
^ToM^
05 Jul 2023 09:47
Nice product.
I made such products myself somewhere in the 80s, following the example of Maria and Wojciech Nowakowski's systems. All the devices presented in their books were built by them and worked... [Read more]
pawlik118
05 Jul 2023 09:49
I do not know, there is info in the description, only that it is a material. Is PVC still an insulator? [Read more]
^ToM^
05 Jul 2023 09:51
The bulb is correct because the key parameter is its current, not voltage. Use a light bulb with as little current as possible. Its non-linearity is used for stabilization. This solution was used even... [Read more]
szeryf3
05 Jul 2023 10:30
Cool, useful, cheap DIY. Well, and from the goodies.
I know that the transformer should have thermal protection, but I would put a fuse. Just for my peace of mind. What you will do is up to you to de... [Read more]
pikarel
05 Jul 2023 16:05
The generator is the basis in the electronics studio for testing acoustic devices, and the circuit from the subject has an almost immeasurable value of distortion.
Foamed PVC is a grateful material for... [Read more]
FAQ
TL;DR: This DIY workshop generator delivers about 4 Vrms and uses a TL082 Wien bridge; as one commenter put it, "the bulb is correct." It is for amplifier and receiver servicing when commercial low-frequency generators cost too much. The practical issues are grounding, output hum, and whether to add a primary-side mains fuse. [#20642550]
Why it matters: This thread shows how to build a very low-cost audio test source that is useful in real bench work, while also exposing the safety and grounding decisions that matter most.
Option
Waveforms
Frequency approach
Complexity
Best use from thread
TL082 Wien bridge
Sine only
100 Hz / 1 kHz / 10 kHz
Very simple
Low-distortion servicing source
ICL8038
Three waveforms
Wider range
Slightly more featured
More versatile bench generator
Key insight: In a mains-powered metal generator, the enclosure should stay bonded to PE. The only switch that helps measurement problems is the one that interrupts the signal return path to reduce a ground loop, not the protective-earth bond.
Quick Facts
Output frequencies are fixed at 100 Hz, 1 kHz, and 10 kHz, selected by an isostat switch with RC elements. [#20641443]
The power supply uses a TS2/14 transformer and a Delon doubler, giving about 14 V DC plus about 11 V AC for the indicator lamp. [#20641443]
Output level adjusts from 0 to about 4 Vrms with a Telpod SP 1.2 potentiometer; amplitude is stabilized by a 60 V / 20 mA telephone bulb. [#20641443]
The enclosure cost was about a dozen zlotys, thanks to recycled sheet metal, reused mains cable, scrap plastic, and stock parts. [#20641443]
Bought parts explicitly named in the thread were 2 × 470 µF / 25 V / 105 °C Panasonic electrolytics and one TL082 dual op-amp. [#20641443]
How does the output ground switch work in a mains-powered signal generator with a non-isolated BNC socket and PE-connected metal chassis?
It works by interrupting the generator’s output return path, not by disconnecting protective earth from the metal case. The author said the chassis is permanently connected to PE, while the rear switch is used when the generator, tested circuit, and analog oscilloscope would otherwise create a loop through their grounded connections. With a standard BNC and metal case, that switch only makes sense in the signal ground path. [#20641606]
Why can a ground loop appear when a workshop generator and an analog oscilloscope are both connected to protective earth?
A ground loop appears because both devices can reference the same circuit through separate PE-linked paths. In the thread, the analog oscilloscope input socket was described as permanently connected to PE, and the generator chassis was also bonded to PE. When both then connect to the tested amplifier, loop current can flow in the signal return and add hum or misleading measurements. [#20641606]
What is a Wien bridge generator and why is it used to generate low-distortion sine waves at 100 Hz, 1 kHz, and 10 kHz?
A Wien bridge generator is an RC sine-wave oscillator that uses a frequency-selective bridge and nonlinear amplitude control, giving low distortion without complex circuitry. Here it was chosen because the EP 1/95 design is simple, uses a TL082, and provides three practical service frequencies: 100 Hz, 1 kHz, and 10 kHz. One commenter called its distortion value “almost immeasurable,” which captures why this topology is popular for audio servicing. [#20642995]
What is a Delon voltage doubler and how does it work in a simple transformer power supply?
A Delon voltage doubler is a rectifier circuit that uses two diodes and two capacitors to stack charging peaks, producing a higher DC output from an AC secondary. In this build, it follows a TS2/14 transformer and, with two filter capacitors, provides about 14 V DC for the generator while a separate roughly 11 V AC path feeds the indicator lamp. [#20641443]
How do you build a simple low-frequency sine wave generator based on the Elektronika Praktyczna 1/95 circuit with a TL082 op-amp?
Build it as a two-board mains device with a TL082 Wien bridge oscillator, a buffer stage, and a simple transformer supply. 1. Assemble the TS2/14 transformer supply with the Delon doubler. 2. Build the TL082 board with RC selection for 100 Hz, 1 kHz, and 10 kHz plus the lamp stabilizer. 3. Add the output level pot, BNC socket, and PE-bonded metal enclosure. The author completed the project over about one year because of parts shortages. [#20641443]
What role does a 60V/20mA telephone bulb play in amplitude stabilization in a Wien bridge oscillator?
It provides automatic gain control by changing resistance as the filament warms. In this generator, the 60 V / 20 mA telephone bulb sits in the Wien bridge feedback path, so a rising output increases lamp temperature and resistance, which reduces loop gain and stabilizes amplitude. The result is a cleaner sine wave than a fixed-gain RC oscillator usually gives. [#20641443]
Which bulbs work best for amplitude stabilization in RC audio generators, and which types should be avoided?
Use low-current incandescent bulbs, typically about 5–20 mA, because the thread stresses current more than rated voltage. Examples given were 12 V bulbs at 5–20 mA and telephone bulbs such as 24 V / 20 mA or 60 V / 20 mA. Avoid high-current lamps, because they are less sensitive in this role and make amplitude control poorer. As one reply put it, “the key parameter is its current, not voltage.” [#20656920]
Why are people concerned about the lack of a mains fuse in a generator powered by a TS2/14 transformer?
They are concerned because a fault in the transformer or wiring can overheat the device before anything external trips. Several replies challenged the author’s no-fuse choice and explicitly raised fire risk, including a case where a controller board burned until the installation protection operated. The concern is not only transformer failure, but any internal short on the 230 V side. [#20642060]
What are the fire and shock protection arguments for adding a primary-side fuse to a small mains transformer device?
A primary-side fuse limits fault energy and can reduce both fire risk and some shock scenarios. One commenter stated that a fuse has two roles: fire protection and, in specific cases, shock protection, though that second benefit depends on plug orientation because the fuse may end up in the neutral line. Even when small transformers sometimes omit a fuse, the thread repeatedly argues that adding one improves safety margin. [#20642060]
How does a plastic front panel made from ABS affect grounding and safety when the enclosure itself is metal and connected to PE?
It keeps the user-facing front surface non-conductive while the metal enclosure remains safely bonded to PE. The author later confirmed the front panel material is ordinary ABS plastic, and the original post states the box is permanently connected to the protective-earth conductor. That combination reduces accidental contact with grounded metal at the controls without removing chassis earthing. [#20647191]
What output level can you expect from this TL082-based generator, and how do you adjust it from zero to about 4 Vrms?
You can expect an adjustable output from 0 to about 4 Vrms. The thread says the level is set with a Telpod SP 1.2 carbon potentiometer, while a separate Telpod CN-15 cermet potentiometer sets the stabilized amplitude inside the oscillator. In practice, one control trims oscillator behavior and the other acts as the front-end output level control. [#20641443]
ICL8038 vs a Wien bridge TL082 generator — which is better for a simple workshop signal source for amplifier and receiver servicing?
The TL082 Wien bridge is better when you want a simple, low-distortion sine source for audio servicing. The ICL8038 was suggested because it offers three waveforms, wider range, and even offset adjustment, but that is a different priority. For amplifier and receiver alignment at 100 Hz, 1 kHz, and 10 kHz, the thread favors the Wien design’s simplicity and sine quality over broader feature count. [#20648594]
How can you wire the generator output and oscilloscope connections to avoid hum and grounding problems during amplifier testing?
Use one clear signal-return path and avoid duplicating the earth-referenced return through both instruments. 1. Keep the metal generator enclosure bonded to PE. 2. Connect the oscilloscope and generator grounds to the tested circuit carefully, watching for duplicate return paths. 3. If hum appears, use the generator’s output-ground switch to open the signal-return loop, not the chassis PE bond. This method addresses the exact loop problem discussed for analog oscilloscopes with PE-linked inputs. [#20641606]
Why is bulb current considered more important than bulb voltage in amplitude-stabilized sine wave generators?
Current matters more because the stabilization depends on how easily the filament’s resistance changes with heating. The thread explicitly says to choose a bulb with “as little current as possible,” and explains that its nonlinearity is what stabilizes the oscillator. That is why bulbs such as 20 mA telephone types are preferred even when their printed voltages differ, such as 24 V or 60 V. [#20642550]
What low-cost recycled materials and parts can be used to make a DIY workshop signal generator enclosure and power supply?
Use scrap steel sheet for the case, reused three-core mains cable, recycled plastic for the front panel, and stock components wherever possible. The author built the chassis from hand-cut and bent sheet metal, used a locally bought scrap sheet, and reused a mains cord from electronic waste. That kept the total cost to about a dozen zlotys, with only the transformer, TL082, and two 470 µF capacitors clearly bought new. [#20641443]
Comments
The switch is visible in some photos, and in others it is not. BNC is also ordinary, not isolated, so it is at PE potential - the same as in most function generators. So what does this "output ground switch"... [Read more]
Hello, The switch is designed to break the ground loop when the output ground of the generator is connected with the tested circuit and the analog oscilloscope, in which its input socket is is permanent... [Read more]
Can you make some diagram because I don't understand. I have, perhaps mistakenly, the impression that the ground loop break is in the wrong place. [Read more]
And what about the mains fuse? [Read more]
Hello, Factory-made Polish devices with these transformers, e.g. power supplies for radio receivers or emergency lighting modules. they have no mains fuses on the mains supply side. So there is no need... [Read more]
And what happens if the transformer gets a short circuit of, say, 200 ohms and starts to heat up to the point where it can ignite? I still don't understand what the switch does. Can you make a d... [Read more]
I believe it cuts the PE wire from the mains cord from the housing. [Read more]
The front panel is made of plastic - it is non-conductive. Added after 1 [minutes]: I like. A reasonably maintained compromise of aesthetics to the amount of work. It is neat and looks decent. ... [Read more]
I don't know such a recipe... It would be very strange, besides it assumes that there will be no magical failure anywhere else in the device that could lead to a fire.. The fuse has two roles - protection... [Read more]
The author wrote: "The front panel is made of plastic." [Read more]
I'm honored, yes. I missed it. Still somehow I feel bad without a fuse ... Indeed, a wire in a tiny power transformer should not fall out of the transformer and strongly limits the current ... But... [Read more]
I'd probably give a fuse, just to feel good. Some time ago, an older colleague, a designer, told me about the "lack of its requirement" in small transformers, and it concerned certified medical equipment... [Read more]
Why this tension? Have you checked its characteristics for voltages equal to the amplitude present in the generator system? [Read more]
A board made of foamed PVC? As for the fuse - recently I have been resuscitating Carel controllers from Liebherr MediLine freezers. The controllers have a converter, which is an independent module on... [Read more]
Nice product. I made such products myself somewhere in the 80s, following the example of Maria and Wojciech Nowakowski's systems. All the devices presented in their books were built by them and worked... [Read more]
I do not know, there is info in the description, only that it is a material. Is PVC still an insulator? [Read more]
The bulb is correct because the key parameter is its current, not voltage. Use a light bulb with as little current as possible. Its non-linearity is used for stabilization. This solution was used even... [Read more]
Cool, useful, cheap DIY. Well, and from the goodies. I know that the transformer should have thermal protection, but I would put a fuse. Just for my peace of mind. What you will do is up to you to de... [Read more]
The generator is the basis in the electronics studio for testing acoustic devices, and the circuit from the subject has an almost immeasurable value of distortion. Foamed PVC is a grateful material for... [Read more]