I've just installed my third A2451 amp module into my DYI subwoofer. The two previous modules both exhibited popping and clicking for a few months before they eventually died.
This makes 3 modules in just 2 years. Before you say turn the volume down... The unit has an auto on/off feature that I never use and I only turn on for limited applications and never/ever loud. So given my use I don;t understand why they are burning out.
The chaps at "The Loud Speaker Kit Company" (Perth WA) said they have had a few returned and have identified some resisters (that burn out) that have been upgraded in the replacement models.
Circled in picture attachment. In the original units these resisters were quite small and when I opened up the dead unit they were burnt black. In the second unit they are much larger presumably to handle the heat.
This doesn't seem to have alleviated the problem however. They are not black but the second unit exhibited the exact same symptoms the first module did.
Lets see how long the third one lasts!
Has anyone else had any experience with these amps?
Are there any suggestions!
Walter
This makes 3 modules in just 2 years. Before you say turn the volume down... The unit has an auto on/off feature that I never use and I only turn on for limited applications and never/ever loud. So given my use I don;t understand why they are burning out.
The chaps at "The Loud Speaker Kit Company" (Perth WA) said they have had a few returned and have identified some resisters (that burn out) that have been upgraded in the replacement models.
Circled in picture attachment. In the original units these resisters were quite small and when I opened up the dead unit they were burnt black. In the second unit they are much larger presumably to handle the heat.
This doesn't seem to have alleviated the problem however. They are not black but the second unit exhibited the exact same symptoms the first module did.
Lets see how long the third one lasts!
Has anyone else had any experience with these amps?
Are there any suggestions!
Walter
Attachments
What driver?
The A2451 subwoofer module powers a
Woofer Material: Polyproylene
Woofer Diameter: 300mm (12")
Sorry no other specs (web link below)
S150 Kit Subwoofer - The Loud Speaker Kit
The A2451 subwoofer module powers a
Woofer Material: Polyproylene
Woofer Diameter: 300mm (12")
Sorry no other specs (web link below)
S150 Kit Subwoofer - The Loud Speaker Kit
I've had exactly the same problem. Replaced those resistors, but no luck. Also going to replace the other resistors and those diodes as well..
Anyway, the specs of the amp (available from Altronics) are:
Features
Auto power on/off with signal presence
High and low level inputs
High level outputs
Volume control
Short circuit output protection
Active crossover variable from 20Hz - 200Hz
Phase reversal switch
Specifications:
Power Output: 180 Max @ 4Ω (0.5% THD)
Frequency Response(Variable): 20Hz - 200Hz
Roll Off Rate: 6dB/Octave
S/N Ratio: >64dB
Auto Turn On Sensitivity: 21mV
Auto Power Off Time: 15-20 Minutes
Input Impedance: (Line) 47k Ω, (Speaker) 200 Ω
Anyway, the specs of the amp (available from Altronics) are:
Features
Auto power on/off with signal presence
High and low level inputs
High level outputs
Volume control
Short circuit output protection
Active crossover variable from 20Hz - 200Hz
Phase reversal switch
Specifications:
Power Output: 180 Max @ 4Ω (0.5% THD)
Frequency Response(Variable): 20Hz - 200Hz
Roll Off Rate: 6dB/Octave
S/N Ratio: >64dB
Auto Turn On Sensitivity: 21mV
Auto Power Off Time: 15-20 Minutes
Input Impedance: (Line) 47k Ω, (Speaker) 200 Ω
Looks familiar, I had a $99 plate amp do the same thing: the board turned black near 2 "large" resistors and stopped working.
I threw it out, which I don't like to do. Seems like they would use larger resistors; i.e. I'm not buying anymore plate amp, not the $99 ones anyway.
I threw it out, which I don't like to do. Seems like they would use larger resistors; i.e. I'm not buying anymore plate amp, not the $99 ones anyway.
Hi Walter.
Not sure if you still have this plate amp, but I might be able to shed some light on what's happening, as I've had the same problem.
The 2 resistors are part of a voltage dropping circuit in conjunction with the two transistors (Q120, Q121) just below the resistors in your picture and the two 12v zener diodes between the resistors and transistors.
This drops a rectified voltage from + - 55v down to + - 12v and feeds the preamp board and what looks like some kind of thermal sensor on the main heatsink.
If your amp is the same components as mine, the transistors are S8550 and S8050. For reasons unknown to me (laziness? incompetence?) they are running them out of spec, with Vce around 43v, datasheet I found said 40v.
My amp was popping and burping about every 2 mins.
When I opened it up, I found that the -12v rail had collapsed to -0.75v, and the S8550 was dead.
I replaced these 2 transistors with BC640 and BC639 (be careful, the first datasheet I found said S8050 was PNP, it is definitely NPN, caused me some grief), and I replaced the 2 resistors with 5 watt types, stood off from the pcb. While I was at it, I replaced the nearest small electrolytic caps as well.
Seems to be working fine now, although the 2 transistors get pretty hot. If they fail again, the next try might be to add in a pre-regulator eg: Pre-Regulator and just use LM7812 and LM7912.
Of course, all these issues could have been avoided if they had just run a more appropriate second winding on the transformer. Starting with + - 55v seems ridiculous when you want to end up with + - 12v. The rails don't appear to power anything else
I guess the answer might be to not buy it in the first place, as it's pretty rubbish. It's cheap, but seems false economy. I won't be getting another, that's for sure. Maybe try a class d from parts express?...
Anyway, hope this might help somewhat. Good luck.
Cheers,
Mark
Not sure if you still have this plate amp, but I might be able to shed some light on what's happening, as I've had the same problem.
The 2 resistors are part of a voltage dropping circuit in conjunction with the two transistors (Q120, Q121) just below the resistors in your picture and the two 12v zener diodes between the resistors and transistors.
This drops a rectified voltage from + - 55v down to + - 12v and feeds the preamp board and what looks like some kind of thermal sensor on the main heatsink.
If your amp is the same components as mine, the transistors are S8550 and S8050. For reasons unknown to me (laziness? incompetence?) they are running them out of spec, with Vce around 43v, datasheet I found said 40v.
My amp was popping and burping about every 2 mins.
When I opened it up, I found that the -12v rail had collapsed to -0.75v, and the S8550 was dead.
I replaced these 2 transistors with BC640 and BC639 (be careful, the first datasheet I found said S8050 was PNP, it is definitely NPN, caused me some grief), and I replaced the 2 resistors with 5 watt types, stood off from the pcb. While I was at it, I replaced the nearest small electrolytic caps as well.
Seems to be working fine now, although the 2 transistors get pretty hot. If they fail again, the next try might be to add in a pre-regulator eg: Pre-Regulator and just use LM7812 and LM7912.
Of course, all these issues could have been avoided if they had just run a more appropriate second winding on the transformer. Starting with + - 55v seems ridiculous when you want to end up with + - 12v. The rails don't appear to power anything else
I guess the answer might be to not buy it in the first place, as it's pretty rubbish. It's cheap, but seems false economy. I won't be getting another, that's for sure. Maybe try a class d from parts express?...
Anyway, hope this might help somewhat. Good luck.
Cheers,
Mark
Pre regulator
Hi Bikeman,
Using your info (thanks) I've installed the pre-regulator on the heat sink using the existing tapped holes on the heat sink for the MJE 3055 and MJE 2955 transistors. So far I've been reducing the output of the pre-regulator to plus and minus 20 volts and the transistors on the board run a lot cooler. I've bypassed the on board resistors. I'm thinking of reducing the volts even further by using 15 volt Zeners.
John
Hi Bikeman,
Using your info (thanks) I've installed the pre-regulator on the heat sink using the existing tapped holes on the heat sink for the MJE 3055 and MJE 2955 transistors. So far I've been reducing the output of the pre-regulator to plus and minus 20 volts and the transistors on the board run a lot cooler. I've bypassed the on board resistors. I'm thinking of reducing the volts even further by using 15 volt Zeners.
John
Hi Walter.
Not sure if you still have this plate amp, but I might be able to shed some light on what's happening, as I've had the same problem.
The 2 resistors are part of a voltage dropping circuit in conjunction with the two transistors (Q120, Q121) just below the resistors in your picture and the two 12v zener diodes between the resistors and transistors.
This drops a rectified voltage from + - 55v down to + - 12v and feeds the preamp board and what looks like some kind of thermal sensor on the main heatsink.
If your amp is the same components as mine, the transistors are S8550 and S8050. For reasons unknown to me (laziness? incompetence?) they are running them out of spec, with Vce around 43v, datasheet I found said 40v.
My amp was popping and burping about every 2 mins.
When I opened it up, I found that the -12v rail had collapsed to -0.75v, and the S8550 was dead.
I replaced these 2 transistors with BC640 and BC639 (be careful, the first datasheet I found said S8050 was PNP, it is definitely NPN, caused me some grief), and I replaced the 2 resistors with 5 watt types, stood off from the pcb. While I was at it, I replaced the nearest small electrolytic caps as well.
Seems to be working fine now, although the 2 transistors get pretty hot. If they fail again, the next try might be to add in a pre-regulator eg: Pre-Regulator and just use LM7812 and LM7912.
Of course, all these issues could have been avoided if they had just run a more appropriate second winding on the transformer. Starting with + - 55v seems ridiculous when you want to end up with + - 12v. The rails don't appear to power anything else
I guess the answer might be to not buy it in the first place, as it's pretty rubbish. It's cheap, but seems false economy. I won't be getting another, that's for sure. Maybe try a class d from parts express?...
Anyway, hope this might help somewhat. Good luck.
Cheers,
Mark
Hi Guys, I'm new here, but I have a few problems with th A2451 as well. I have it driving an 18" Goodmans Audiom 18P, from the late 1970s that a Pommie friend (now gone) left me, & with it's value currently being over $1,000 (if you can find one!), I'm worried that getting this amp (A$180 from Altronics) is going to put it at risk. I checked it in "off" mode, & oddly the voice coil output puts 80mV on an open circuit (speaker not connected) condition, which drops to under 50mV when "on". Why would it be loading the VC with 80mV on "idle"?
I am just rebuilding the chipboard cabinet with a larger unvented unit in MDF & veneer, with Alpaca wool fibre pillows (Alpaca only because a friend has a herd of them just outside Sydney!). As such, I want to put a repeater bi- indicator LED on the front grille, to duplicate the rear bicolour green/blue LED, which is as useless as tits on a bull when it is facing ther wall. This will be along with a very neat 20-segment 3-colour bar graph (http://www.barmeter.com/en/showpic.asp?filename=vu120p-5712s.jpg) for level indicator I found on the net, but problem is how to power the bargraph, which needs 12vdc, & how do I get the LED on/standby indicators Wired up? The LED on the A2451 has a 2-wire arrangement, & has a 3.3KΩ resistor feeding from a rail of +/- 12vdc, depending on the on/off state. When the voltage was fed to an outrigger bicolour LED for putting on the front panel, it was too dim to be useful, & a parallel 3.3KΩ resistor across the back of the preamp board to increase current wasn't particularly effective.
Since I want to run the board's 12vdc to the bar graph only when signal is detected & it turns on, I tried to find a connection on the power board that actually comes alive when the preamp board supposedly turns everything on, but could not find anywhere where voltage conditions changed when I turned the unit on manually from off to on! Those transistors (Q120 & Q121) & the larger-wattage resistors seem to run just as hot in both on & off conditions. With no venting, I am worried that the total heat build-up in an unvented & wool-filled cabinet just may fry some components or even catch fire, given that the heatsink in the unit is on the inside, not the outside like better plate amps.
Simple summary Qs:
>Does this amp have sufficient design safety that it won't cook the VC on my irreplaceable monster Axiom speaker?
>What sections of the power board go on standby, in the absence of signal, that I can tap off a 100mA/12vdc supply for the bar graph, & a green "on" LED? (I can get a power indicator LED supply from the existing 12vdc supply to the preamp & leave the amps on-board rear bicolour LED alone).
>What's the consensus on having a supposedly standby-condition plate amp producing quite a bit of heat in the power supply components in an unvented & wool-packed enclosure with very little external heat dissipation provision?
Any help here would be gratefully accepted. Unfortunately there is no service manual nor circuit diagramme available for the rotten thing!
Thanks & Best Wishes,
Jeff Thompson,
Sydney, Oz.
I am just rebuilding the chipboard cabinet with a larger unvented unit in MDF & veneer, with Alpaca wool fibre pillows (Alpaca only because a friend has a herd of them just outside Sydney!). As such, I want to put a repeater bi- indicator LED on the front grille, to duplicate the rear bicolour green/blue LED, which is as useless as tits on a bull when it is facing ther wall. This will be along with a very neat 20-segment 3-colour bar graph (http://www.barmeter.com/en/showpic.asp?filename=vu120p-5712s.jpg) for level indicator I found on the net, but problem is how to power the bargraph, which needs 12vdc, & how do I get the LED on/standby indicators Wired up? The LED on the A2451 has a 2-wire arrangement, & has a 3.3KΩ resistor feeding from a rail of +/- 12vdc, depending on the on/off state. When the voltage was fed to an outrigger bicolour LED for putting on the front panel, it was too dim to be useful, & a parallel 3.3KΩ resistor across the back of the preamp board to increase current wasn't particularly effective.
Since I want to run the board's 12vdc to the bar graph only when signal is detected & it turns on, I tried to find a connection on the power board that actually comes alive when the preamp board supposedly turns everything on, but could not find anywhere where voltage conditions changed when I turned the unit on manually from off to on! Those transistors (Q120 & Q121) & the larger-wattage resistors seem to run just as hot in both on & off conditions. With no venting, I am worried that the total heat build-up in an unvented & wool-filled cabinet just may fry some components or even catch fire, given that the heatsink in the unit is on the inside, not the outside like better plate amps.
Simple summary Qs:
>Does this amp have sufficient design safety that it won't cook the VC on my irreplaceable monster Axiom speaker?
>What sections of the power board go on standby, in the absence of signal, that I can tap off a 100mA/12vdc supply for the bar graph, & a green "on" LED? (I can get a power indicator LED supply from the existing 12vdc supply to the preamp & leave the amps on-board rear bicolour LED alone).
>What's the consensus on having a supposedly standby-condition plate amp producing quite a bit of heat in the power supply components in an unvented & wool-packed enclosure with very little external heat dissipation provision?
Any help here would be gratefully accepted. Unfortunately there is no service manual nor circuit diagramme available for the rotten thing!
Thanks & Best Wishes,
Jeff Thompson,
Sydney, Oz.
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