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Power amplifier on NE5532 - ty.ytka

tytka 21117 79

TL;DR

  • A stereo power amplifier built from NE5532 operational amplifiers replaces a conventional power stage with an op-amp-based experiment.
  • Each channel uses four op-amps in the voltage stage, 64 op-amps in parallel as the output buffer, and one op-amp for DC-servo control.
  • The supply is stabilized at +/-18 V with LM338 regulators, and speaker protection uses a uPC1237 circuit.
  • The finished amplifier delivers 2×14 W into 8 ohms and sounds detailed, clean, and surprisingly strong in the bass.
  • Cooling matters, because the regulators dissipate a lot of heat and the op-amps reach about 45-50°C during operation.
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  • #61 20658140
    yogi009
    Level 43  
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    katakrowa wrote:
    To make it modern, it begs to be built on op amps in class D


    What to do, it's best to buy any Chinese D-class module for PLN 8.88 and off you go.
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  • #62 20658145
    katakrowa
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    austriackimalarz wrote:
    I would suggest converting some polyphase converter from the GPU power supply to the amplifier

    Today, in fact, the effect would probably be similar, but as you can see, the heat emitted by the WO is a big problem, as evidenced by this whole topic.
    I bet that within 10 years there will be such class D WOs that will be indistinguishable from analog ones in the audio band.
  • #63 20658147
    austriackimalarz
    Level 26  
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    katakrowa wrote:
    I bet that within 10 years there will be such WOs in class D, which in the audio band will be indistinguishable from analog ones.

    They are like that today. Interestingly, these are still "single-phase" models, and they do not switch at megahertz, but closer to the standard 300-500kHz.
  • #64 20658155
    katakrowa
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    austriackimalarz wrote:
    They are like that today. Interestingly, these are still "single-phase" models, and they do not switch at megahertz, but closer to the standard 300-500kHz.

    Can you provide some model?
  • #65 20658177
    marweg1967
    Level 15  
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    yogi009 wrote:
    I wouldn't get into quad dice for several reasons. Cooling, crosstalk, the ability to replace the system with another

    In theory you're right, but:
    1. The sum of the power dissipated will be rather similar in each case, so the surface area of the heatsink will also be. In the absence of a heatsink, double, and even better single, will do better.
    2. Crosstalk... But in each opamp will be the same...
    3. I was thinking about the SMT version, so no one will play with resoldering ICs. At most, it would be possible to use the design of the board.
    In general, I treat the project as a curiosity, with the option of making two or more versions, e.g. "high end" on NE5532 and better components (no exaggerations in the style of kondy for several hundred zlotys) and "popular" on SMT and just TL074 in such a version. It will be interesting to compare such constructions both in terms of measurement and hearing. :)
    Why such opamps? Let's say I'll trust Douglas Self, who quite clearly justifies the lack of sense in using "better" chips than the NE5532 in general and the TL07x in applications requiring input FETs.
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  • #66 20666706
    Jaro
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    austriackimalarz wrote:
    We settled on the TL071HIDBVR, which is the well-known TL071 in the SOT-23 housing


    I'm not sure it's a good choice. The documentation contains only a functional diagram, but if the modern versions do not differ much from the earlier TL06x TL07x and TL08x, they have a primitive and inescapable "short-circuit protection" in the form of a final stage with 100-ohm emitter resistors and another 200-300 Ohm resistor connected in series with the WO output to load. It does not matter much in typical applications of these WO, but here we have an unusual application, because even for the parallel connection of several dozen or even several hundred such circuits with a load in the form of a loudspeaker, this will have an impact limiting the output power and the Damping Factor.
  • #67 20666709
    marweg1967
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    Jaro wrote:
    austriackimalarz wrote:
    We settled on the TL071HIDBVR, which is the well-known TL071 in the SOT-23 housing


    I'm not sure it's a good choice. The documentation contains only a functional diagram, but if the modern versions do not differ much from the earlier TL06x TL07x and TL08x, they have a primitive and inescapable "short-circuit protection" in the form of a final stage with 100-ohm emitter resistors and another 200-300 Ohm resistor connected in series with the WO output to load. It does not matter much in typical applications of these WO, but here we have an unusual application, because even for the parallel connection of several dozen or even several hundred such circuits with a load in the form of a loudspeaker, this will have an impact limiting the output power and the Damping Factor.


    Thanks for the warning. In fact, in this situation you would have to go into thousands of WO. But a fellow Austrian painter has just such an intention. I'm even more curious about the end result :)
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  • #68 20713538
    tytka
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    marweg1967 wrote:
    Will your colleague share details about this security? Input diodes? Because this Behringer makes a really bad noise and I'm getting ready to etch the board to use the workaround described by my friend (I already have the parts). So I would add this protection right away.


    Please check the topic again link , I posted new information.
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  • #69 20713587
    marweg1967
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    tytka wrote:
    marweg1967 wrote:
    Will your colleague share details about this security? Input diodes? Because this Behringer really hums badly and I'm getting ready to etch the board to use the workaround described by a colleague (I already have parts). So I would add this protection right away.


    Please check the topic again link , I posted new information.


    I looked :) I imagined something more or less like that, except that I was thinking about an anti-parallel connection of sets of ordinary diodes (3-4 in series), or JFETs working as diodes. I wonder if these Zener tubes don't make any noticeable noise, although probably not since you left it like that?

    I would like to thank my colleague for keeping his word and best regards :)
  • #70 20795827
    austriackimalarz
    Level 26  
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    Hi.
    So I had a vacation. I will say this - expect an article "The end of a thousand amplifiers" within a week or two :P It turned out beautiful.
  • #71 20795920
    tytka
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    In that case, I'm waiting for my colleague's article. I'd love to see a different approach to this ending than mine.
  • #72 20796883
    Anonymous
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  • #73 20840893
    Anonymous
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  • #74 20841073
    tytka
    Level 23  
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    w3501yyyy wrote:
    A block of 250 TL072 units connected in parallel, a total of 500 amplifiers, consumes 1A of current when powered by +-18V.

    Just enough? And maybe not more?
    And that's only at rest. When you drive this, the demand will be even greater.
    I power my "baby" (probably only 140 WO in total) from a 100W transformer.

    I signaled that it was heating up :)
  • #75 20841106
    Urgon
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    AVE...

    With 250 TL072, the maximum quiescent current can be up to 1.25A. The minimum is 625mA. 1A is a good result. Fortunately, with typical speaker impedances and this supply voltage, the maximum power consumption will not increase significantly above this value. For a speaker with an impedance of 4Ω, the maximum power will be approximately 30W. This means additional current consumption of ~840mA per channel. A transformer for such a stereo amplifier should have a current efficiency of ~4.1A and a power of ~150W, with up to 90W dissipated in the ICs in the idle state. It'll be warm...
  • #76 20841361
    Anonymous
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  • #77 20841399
    Urgon
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    AVE...

    Well, in such a scenario you will need a transformer of at least 400W, but the output power of the amplifier will be 110W per channel into 4Ω. It will definitely be an interesting construction...
  • #78 20841410
    Anonymous
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  • #79 20841460
    Urgon
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    AVE...

    According to Note, you will lose about 3V of voltage relative to the power supply, i.e. in the bridge, 36V will become 30V. I calculated it for you exactly, because just two hours ago I was editing a text about bridge amplifiers, and I calculated it based on it. So you will need 400W, 200W per channel, assuming that the WO quiescent current will be maximum for each piece. Always assume the worst possible scenario...
  • #80 20841463
    Anonymous
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Topic summary

✨ The discussion revolves around the construction of a power amplifier using the NE5532 operational amplifier, achieving a power output of 2×14 W at 8 ohms. The project, inspired by Douglas Self's article in Elektor magazine, is described as an experimental endeavor rather than a commercial product. Participants share insights on the design, including the use of a uPC1237 for protection and LM338 for voltage regulation. Various contributors express interest in replicating the project, discussing the challenges of sourcing components, particularly the NE5532, and the implications of using clones versus originals. The conversation also touches on measurement techniques, noise reduction through parallel connections of op-amps, and the practicality of such designs in audio applications. Some participants suggest alternative components and configurations, while others highlight the potential for high power outputs with larger setups.
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FAQ

TL;DR: “It sounds quite detailed,” and the builder measured 2×14 W into 8 Ω from a power amplifier made with parallel NE5532 op-amps. This FAQ helps DIY audio builders understand the topology, measurements, thermal limits, part choices, and why this experiment works despite its obvious inefficiency. [#20640831]

Why it matters: This thread shows how a seemingly impractical op-amp array can become a usable audio power stage, while exposing the real limits in cooling, idle power, measurement method, and device selection.

Option What the thread says Main trade-off
NE5532P Used in the featured build; 2×14 W into 8 Ω; praised for clean, detailed sound Higher chip count and heat [#20640831]
TL07x Considered for very large SMD builds; lower current per amp in some variants Questions about output resistance and suitability [#20654388]
LM833 Mentioned as sonically stronger than TL07x in listening tests Not developed into a full build here [#20657278]
LM358/LM324/LM2904 family Explicitly warned against for this push-pull output use Output crossover “dead” zone harms performance [#20643524]

Key insight: Paralleling op-amps can lower noise and raise output current, but in this thread the limiting factors were not headline wattage. They were idle dissipation, regulator heat, measurement method, and the output-stage behavior of the chosen op-amp family.

Quick Facts

  • The finished amplifier used three boards: one PSU/protection board with ±18 V rails, plus two channel boards; each channel had 4 op-amps in voltage gain, 64 op-amps in parallel as the output buffer, and 1 op-amp for the DC-servo. [#20640831]
  • The builder reported 2×14 W into 8 Ω with both channels driven, and the op-amps themselves reached about 45–50 °C during operation, so cooling was identified as mandatory for practical use. [#20640831]
  • The chosen parts were TI NE5532P devices bought from TME for under 1.9 gross per piece at the project quantity, which kept the experiment financially plausible despite the large chip count. [#20642244]
  • A later large-scale variant showed the thermal penalty clearly: 250 TL072 packages connected in parallel per block drew about 1 A at ±18 V at idle, meaning a 1000-op-amp amplifier could waste roughly 60 W before delivering signal. [#20840893]

How was this NE5532 power amplifier built to deliver 2×14 W into 8 Ω using so many op-amps in parallel?

It used many small op-amp stages to share the output job. Each channel had 4 op-amps in the voltage amplifier, 64 op-amps in parallel as the output buffer, and 1 more op-amp for the DC-servo. A separate board provided stabilized ±18 V rails and loudspeaker protection, and the whole amplifier was split across three PCBs. The builder simplified the original Elektor-inspired concept by removing balanced inputs and bridge mode, then measured 2×14 W into 8 Ω with both channels driven. [#20640831]

What is a DC-servo in an audio power amplifier, and why was an extra op-amp used for it in each channel?

A DC-servo is a control circuit that corrects output DC offset without putting a large capacitor in the audio path. The builder used one extra op-amp per channel for this function, separate from the 4 gain-stage op-amps and the 64 parallel output devices. “DC-servo” is an audio correction circuit that monitors slow DC error at the amplifier output, injects a compensating signal, and keeps the speaker near 0 V without altering normal audio-band gain. That choice fits a design built for direct-coupled listening tests. [#20640831]

Why does paralleling dozens of NE5532 op-amps reduce noise, and how does that differ from using them to increase output current?

Paralleling op-amps reduces equivalent input noise by averaging many uncorrelated noise sources, while also letting many outputs share load current. One commenter quantified the noise effect: with N devices in parallel, noise voltage falls by √N, so 2 TL071s drop from 15 nV/√Hz to 10.6 nV/√Hz, and 2000 devices reach about 0.335 nV/√Hz. The same topology can also raise output current, but another commenter stressed that noise reduction is the classic reason for this technique, not power drive. [#20654463]

What measurement setup was used for this amplifier, and how do asymmetrical and differential load measurements change the results?

The amplifier was measured asymmetrically, not differentially, and that matters. One commenter warned that asymmetrical measurement creates a ground loop through the interface output, amplifier, load return, and interface input ground. He reported that switching configuration improved the noise result from 102 dB dynamic range to 110 dB. A practical check is: 1. measure the audio interface alone, 2. compare asymmetrical and differential load wiring, 3. confirm where the measurement floor sits before judging the amplifier. [#20641108]

How was the Behringer UMC202HD modified to get better reference measurements, and what was wrong with the stock Midas input stage?

The interface was modified by stripping the input path down to a minimum because the stock Midas input amplifiers were described as the main weakness. The builder said those factory input amps were “a total flop” and the reason the UMC202HD underperformed as a measurement front end. After the modification, he also added input protection because he had already burned one AD8694 on the input stage. The thread does not list the full schematic here, but it clearly states the rationale and the failed part. [#20643545]

Where can you buy a working uPC1237 loudspeaker protection IC today, and what risks come with sourcing it from China?

The builder bought a working uPC1237 from China and said that only Chinese sources now seem to produce these chips. He also warned that buying them there involves risk, so the thread treats availability as possible but uncertain. The practical takeaway is simple: you can still source uPC1237-based protection, but expect authenticity and consistency risk when the supply chain is limited to Chinese sellers. [#20641164]

Why do LM321, LM358, LM324, and LM2904-family op-amps perform poorly in this kind of parallel push-pull audio output stage?

They perform poorly here because their output stage can momentarily “die” when output current changes direction. One commenter explicitly warned against LM321, LM358, LM324, and related parts for this topology, and later explained that the problem comes from a push-pull output stage with no quiescent current. That creates a switching interval between the upper and lower transistor, which shows up as distortion. Another commenter then confirmed LM2904AQTH behaves like LM358 in this respect and is therefore unsuitable for this amplifier style. [#20645984]

NE5532 vs TL07x vs LM833 for an op-amp power amplifier: which one makes more sense for sound quality, noise, and current draw?

In this thread, NE5532 is the safest proven choice, TL07x is a scalable experiment, and LM833 is praised mainly on listening quality. The finished amplifier used TI NE5532P and was judged clean and detailed, while one commenter said listening tests gave NE5532 or even LM833 a clear quality advantage over TL07x. For current draw, another large-scale build using TL072 showed the downside clearly: 250 packages per block drew about 1 A at ±18 V at idle. That makes TL07x attractive for packaging experiments, but not automatically for efficiency. [#20657278]

What is damping factor in a loudspeaker amplifier, and why might TL071 or TL072 output-stage resistance reduce it in a parallel op-amp design?

Damping factor is the amplifier’s ability to control speaker motion through low output impedance. One commenter warned that older TL07x-family behavior can add substantial effective output resistance because the final stage includes emitter resistors and another resistor in series with the op-amp output. “Damping factor” is a loudspeaker-control metric that compares load impedance to amplifier output impedance, so a lower output impedance gives tighter electrical control over the driver, especially at low frequencies. In a parallel speaker-driving array, that extra resistance can limit both output power and damping factor. [#20666706]

How do you estimate transformer size, idle power loss, and heatsinking for a large parallel-op-amp amplifier running on ±18 V?

Start with idle current first, because it dominates the thermal budget. In one large TL072 example, 250 packages per block drew about 1 A at ±18 V, so a 1000-op-amp amplifier could waste about 60 W at idle. Another commenter estimated that a stereo bridge design at this scale would need roughly a 400 W transformer, while even a smaller stereo variant could need about 150 W and dissipate up to 90 W in the ICs at idle. That is why the thread repeatedly treats heatsinking and airflow as design requirements, not accessories. [#20841106]

Why did the author use LM338 stabilizers and large output capacitors, and how could 2200 µF on an LM338 output affect regulator performance?

The builder used LM338 stabilizers to create the amplifier’s regulated ±18 V rails and credited the strong bass partly to PSU quality. A later commenter challenged one detail and said 2200 µF on the LM338 output is too large, arguing that it worsens regulator behavior and that 1 µF is enough at the output in this case. So the thread presents both views: the regulated supply helped listening impressions, but very large output capacitance on LM338 may degrade regulator performance rather than improve it. [#20656289]

What is a bridge amplifier configuration, and how would bridging large blocks of TL072 or TL071 op-amps change voltage swing and output power?

A bridge amplifier drives the load from two opposite-phase outputs, doubling voltage swing across the speaker. In the thread, one builder described using two 250-TL072 blocks to form one bridge, then two bridges for stereo. Another commenter estimated about 110 W per channel into 4 Ω in that kind of stereo bridge arrangement and said a transformer around 400 W would then be appropriate. The thread also notes a real limit: output swing loses several volts versus the rails, so bridge power is high but not idealized. [#20841399]

How should you cool a commercial-style version of this amplifier built with SOIC or SMD op-amps on a double-sided PCB?

Mount the op-amps on one side, place the remaining SMD parts on the other, apply thermal paste, and bolt the PCB to a heatsink. That was the specific commercial-style suggestion made in the discussion for a SOIC or SMD version. The idea matters because the original through-hole build already heated the op-amps to about 45–50 °C, and larger arrays showed even worse idle dissipation. The proposed double-sided board turns the whole PCB into a heat-spreading interface instead of relying on free air alone. [#20652784]

What kind of input protection can be added to a modified UMC202HD after burning an AD8694, and how do Zener diodes compare with anti-parallel diode strings or JFETs used as diodes?

The thread points to clamp-style protection, but it does not fully settle the best device choice. The builder said he added protection after burning an input AD8694, then later linked updated information using Zener-based protection. Another commenter said he had expected either anti-parallel strings of 3–4 ordinary diodes or JFETs used as diodes, and asked whether the Zeners added audible noise. The thread records that question, but it does not report a measured noise penalty from the chosen Zener approach. [#20713587]

Which class D op-amp or audio amplifier models already sound indistinguishable from analog in the audio band, as mentioned in the discussion?

No specific class D op-amp or amplifier model was named in the discussion. One commenter claimed such devices already exist today and said they are still single-phase designs switching around 300–500 kHz rather than at megahertz frequencies. When another participant asked for a model number, none was provided in the quoted thread. So the only reliable answer here is that the claim was made, but no concrete product was identified. [#20658147]
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