Chipamp output power with overdriven input - Page 1
Forum section: electronics / beginners

author: dazz
author_rank: Frequent Contributor
timestamp: August 10, 2018, 11:59:04 am
content: Hi guys, quick question please.I'm trying to figure out what the power output capabilities of chipamps are when the input signal is overdriven/distorted, as in a guitar amp with overdrive/distortion effects. So let's take theseTPA3116D2 or TPA3118D2which are the ones I have in mind for my guitar amp. At 20V supply, 4ohms load, in PBTL mode, both chips should be able to put out about 40W with THD below 1%. But if the chipamp poweramp input signal is distorted by the preamp, does that increase the output power of the chipamp without further distorting the signal? Or is the distortion a function of the output power (instead of the gain/amplification at the power amp)?LONG STORY:I've built a SS guitar amp using a preamp design by phatt from ssguitar.com and an aftermarket TDA7297A poweramp board. That theoretically gives me some 5W on the output power on 8ohms, 12V supply.Now I'm considering upgrading the power amp to aTPA3116D2 or TPA3118D2that I would be powering with a 20V laptop brick for some extra output power. The plan is to go up to some 40-50W on 4ohms and 20V which both the TPA3116D2 and the TPA3118D2 should be able to cope with in PBTL mono mode.But, the TPA3118D2 doesn't have an external heatsink, so I fear I might cook it when using distortion effects if the distortion considerably increases the output power, and also that pushing the output power of the chipamp may add extra, unwanted distortionHope that's not too much of a mess. Thanks

author: Paul Price
author_rank: Super Contributor
timestamp: August 11, 2018, 11:25:33 pm
content: Over-driving any power amplifier will very significantly "color" the output sound produced, and most likely create unwanted distortion and other unexpected sound effects, and the distorted sound heard quality will depend on over-drive level as well as power amp input waveform shape, complexity and frequency spectrum. Will probably work best for all listeners when the power amp is not over-driven.Not over-driving the input will most likely be best to achieve loudness without harsh audible artifacts.Class A tube amps are a completely different story.You mention you would be building the higher power "D" amp without using a heat sink. No workee.TPA3116D2TPA3118D2TPA3130D2These chipamps require a significantly large heat sink.Refer to section 10.3, about the EVM module. A large heat sink is always needed and used with all high power chipamps.

author: dazz
author_rank: Frequent Contributor
timestamp: August 12, 2018, 08:29:36 am
content: Quote from: Paul Price on August 11, 2018, 11:25:33 pmThanks Paul. I don't want to overdrive the power amp, the overdriven signal comes from the preamp or effect pedals. What I'm asking is how that will affect the output power of the power amp.So if I put a sine wave in the chipamp input and I increase it's amplitude till it hits the +/24V rails in the output of a TPA3118D2 loaded with 4ohms, I get some 60W of power before it starts distorting.Now let's say a put a clipped signal with an RMS value 1.5 times the RMS voltage of the sine wave, and the same amplitude as the sine wave when it hit the rails at the output. Now the output power is 90W.The question is, when does the power amp start to introduce extra distortion? when the output signal hits the rails or when the output signal exceeds a certain level of power (60W in the example above)If the former, I need to be careful not to exceed the thermal dissipation capabilities of the chip/board. According to the datasheet, theTPA3118D2can run 4ohms loads without heat sink on a dual layer PCB

author: iMo
author_rank: Super Contributor
timestamp: August 12, 2018, 09:02:52 am
content: QuoteThe power amp starts to introduce an extra distortion when it operates outside recommended limits as per datasheet (ie. max/min input signal amplitude, max/min input frequency, max/min power supply voltage, max chip/package temperature, max power supply ripple, poor decoupling, max/min output impedance, low quality RLC parts, self oscillations and ringing, etc.)

author: dazz
author_rank: Frequent Contributor
timestamp: August 12, 2018, 10:53:44 am
content: Quote from: imo on August 12, 2018, 09:02:52 amUnderstood, thank you