Reparing car amplifier - Page 1
Forum section: electronics / repair

author: dbernotas
author_rank: Newbie
timestamp: March 09, 2018, 09:14:48 am
content: Hi there,I am new here and this is my first post. I am trying to fix friends car amplifier. I have no experience in that kind of work, but I have some basic knowledge of electronics and know how to use google (I think). So, I’ll explain what I have done and what I am struggling with now.Testing set up:1. Car amplifier – Gladiator JSN-42000 (4 channel 800 watts (RMS 100Wx4) mosfet amplifier);2. Power supply for AMP: Switching power supply Mean Well – Model MW7H30GS (I use this because I don’t have anything else what gives 12v and at least 3A) output - 12V, 3000mA 45VA;3. Speakers – generic 4” 2-way car speakers 100 watts 4ohm (frequency range 30Hz-3Khz);4. Input – my smart phone with cheapest RCA to 3mm jack cable;5. Measurement equipment – only 2 generic DMM (don’t have anything else).6. In ON state, with no music it draws about 0,75 A of current. In OFF state (no remote signal) 0 A.- Attachments and other optionsNotify me of replies. Return to this topic. Don't use smileys.Attach:Let’s begin. At first when I got this amp it had blown up its all its IRFZ44n transistors, 2 TIP36C 0 and 1 TIP35C O transistor. I replaced them all with new ones, and amp started working.First question. I have heard that it is necessary to change all output stage transistors (don’t know if I am naming them properly) TIP36C/TIP35C, and they must be from the same manufacturer and same batch. Is it true, and what can go wrong if I didn’t change them like that?Second problem. Now if I use left input channel and try to tune HPF (its limits are 40Hz to 1kHz) with its pot to starting point of 40Hz my 1 speaker from that output starts to make what it looks like low frequencies harmonic sound, some sort of trembling and its very loud. On my right input I don’t have this problem. What can be wrong and where to look, can it be related to first question? OpAmp used in this amplifier is NJM4558L.And the last third problem is that: after changing all dead transistors I didn’t saw the second problem, so my friend installed it back to its car. When car engine isn’t running everything is fine and amp plays nice, but when starts engine we can here it is making some noise in speakers, depending on engines rpms. Where to look for problem here? Power supply capacitors looks good.

author: Anks
author_rank: Frequent Contributor
timestamp: March 09, 2018, 01:20:32 pm
content: All the transistors in parallel need to be the same. This is so they share the load equally.Hope this helps

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 09, 2018, 03:42:35 pm
content: Since the noise started after messing with it, it's most likely a bad connection somewhere. Just hope it's not a problem with the car.https://www.crutchfield.com/S-m0I1IUM52ku/learn/learningcenter/car/noise_suppressors_installation_guide.html

author: james_s
author_rank: Super Contributor
timestamp: March 09, 2018, 06:54:11 pm
content: Quote from: Anks on March 09, 2018, 01:20:32 pmWith MOSFETs this is not as critical, their resistance rises with temperature so they tend to automatically share current pretty well. It never huts to have matched parts but it's not nearly as critical as with BJTs or IGBTs.