TDA1514 based amplifier giving low power

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hello everybody , I am trying to repair a guitar amplifier based on TDA1514a , the amplifier on paper has a stereo power output of 40w +40w at 4ohms , but this amplifier is giving around 25w per channel before clipping, the supply rails are at +/- 20vdc ,the main filter capacitors are4700uf and 25volt rated and are OK , the shematic is below attached , I check everything on the amp , and it seems that everything is OK , I changed one channel TDA1514 and the power output is the same ,
Can anybody say me that if it is normal so less power from this TDA ??, the data sheet specifies up to 50watt

Thank you
Best regards
 

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In this amp the TDA1514 works in a rather different circuit that sugested on Philips Data Sheet aplicattion circuit , the values and configuration of many of the circuits asociated with the chip are rather diferent , bootstrap circuit or SOAR and Mute/standby are rather diferent ,
 
Nobody has used this Chip?
I only want to know if it is normal so less power from this chip on this circuit , perhaps something must be wrong on the amp ,.
I am a quite sure that the amp don't have any problem , but I need to verify it , with the opinion of someone that has work on any amp working on similar specs with this chip.

Thank you.
 
Thank you , but the load is 4 ohms.

If I am correct:
20/1.41=14.18v
(14.18)2=201
201/4ohms=50w

I am not sure if this is valid for these amps , because at 27.5 volt per rail , doing this gives around 100w at 4ohms.

The power supply sag at max power is 1to 2 volt , so total 18-19 volts per rail.
 
It is nearly valid. Replace the rail voltage in the formula by the sagged rail voltage minus the losses across the transistors and through ripple on the rails. They should be around 3-5 V.

25 W at 4 Ohm would be 10 V eff -> ~14 V peak. 18 - 4 brings you just there.

For comparison. National's Overture Design Guide predicts 24,48 W with 4 Ohm load for 20 V rails with the LM1876. Not too far off.
 
Hi,
what's the purpose of 10uF (C2) in series with 220nF (C3)?

Why do they attenuate through the first inverting opamp,
then apply gain through the second opamp (switchable between inverting and non-inverting),
then attenuate with 10k (R23) & 3k3 (R24),
then apply gain through the chipamp?
Seems nonsensical.

Is the 120k (R28) and 220nF (C15) at the input there to prevent electric shock through the guitar strings?
 
Their motto is "transistor distortions sound bad, while tube distortions sound good", so they try to make transistor amps that sound like distorted tube amps. Too much gain is supposed to bring each individual stage into distortion. Then they have to attenuate again, because they also don't want too much distortion.
The 10 µF is probably also there to create a certain type of distortion. Must be the secret of the typical Marshall sound.

The crossover for the tweeter is also very special. To think that Marshall is one of the most renowned and respected companies in that sector...
 
This amp isn't a typical marshall guitar amp , is to amplify acoustics guitar or electroacustic , The purpose of the amp is to amplify like "HI-FI" without any distortion , a large dinamics instrumet signal , the schematic ,it is only the power amp , the first Op-amp and the IC3 circuit work as a compressor limitter to avoid distortion from the large peaks on he input signal , the switch on the second opamp is for Phase- out of phase output , to avoid cancelations when mixing with other Miced instruments.
The compresor is not very well designed , in my humble opinion , it not takes the output stage on the peak detector circuit so the results are a little poor , other design options that you coment ,I think that , dont have any especific pupose , simply , the people that desing this come from other circuit topologies (hibrid valve and opamp circuits) this things are usual ,on most of their designs, I know the most Marshall desings , but this amp is quite rare ,
The tweeter is a piezo , that is conected on paralell with one channel , it only has a 10ohm for protection if it shorts.
Thats all .
 
I have a home made TDA1514A in dual mono configuration it's arnd 10 yr old , but i stil play it as an amp for my PC. Speakers though are new ones ( Polk audio RTi A1 ).This based on the philips application diagram however, plays pretty loud.
PCB was from a local kit supplier "visha".
supply voltage +- 25v regulated ( primitive pass transistor and zener )

here's a pic
 
I have a home made TDA1514A it's arnd 10 yr old , but i still play it as an amp for my PC. Speakers though are new ones ( Polk audio RTi A1 ).This is based on the philips application diagram however, plays pretty loud.
PCB was from a local kit supplier "visha".
supply voltage +- 25v regulated ( primitive pass transistor and zener )

here's a pic
 

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