Increasing amplifier auto-turn on sensitivity.

DcibeL · 18th November 2005, 08:50 PM

I'm not really sure where I should have posted this, but anyway...

I have a the SUB-250R subwoofer amplifier from Solen which is the same design as the smaller subwoofer amplifiers you will find at Parts Express, ApexJr, and Rythmik Audio. The problem I have with the amplfier is that it will not automatically turn on when the volume is at a very low level. In fact it is quite annoying in that the turn on level for this amp is at the point where if I watch TV at a normal volume, the sub will turn off during the show, and turn on during the ads (which are louder).

Is there a possibility to change a part or two in the input module to increase this amplifiers auto turn-on sensitivity? It has been a few years since I have worked with transistor circuits, so I'm not really sure about this circuit. You'll see the on-auto-off switch in the lower left of the following image:

moamps · 18th November 2005, 10:15 PM

Hi,
Use higher value for R37 or/and smaller value for R36.
Also, if the timeout is too short, use higher value for C19 and/or higher value for R46.

Regards,
Milan

DcibeL · 18th November 2005, 11:23 PM

Change that voltage divider, got it. Thanks.

It'll be a few days before I will have the time to test it out, but I'll let you know how things work out. Something like double the value of R37, and half the value of R36 should work out, as long as the sensitivity is not so low that the amp is being turned on by line noise.

DcibeL · 24th November 2005, 02:25 AM

Crap. My PCB, having the model with the remote control, has different designation numbers for the resistors. I guess I am out of luck for this modification.

wintermute · 25th November 2005, 08:11 AM

maybe not all is lost

I'd assume that the remote basically controls the level of the sub??? meaning that the rest of the circuit is probably the same??? how many 2.7K resistors are there in series with a 20K resistor (with pin 2 of an opamp connected to the middle) in the circuit?? without checking the entire schematic I'd guess probbaly only the one!! should be relatively easy to track it down on the pcb, and then a bit of tracing should show you whether you are in the right spot...

Tony.

richie00boy · 25th November 2005, 10:49 AM

moamps you got that the wrong way round. The 2.7k (I thought it was 2.7M but doesn't really matter) should be made smaller to increase the gain.

wintermute · 25th November 2005, 11:05 AM

maybe it is 2.7M I had trouble readning the value on the schematic, and made no attempt to work out the actual circuit

Tony.

DcibeL · 25th November 2005, 12:44 PM

Yea, I'm sure with a little looking around on the PCB I could find the resistors. R36 and R37 on my board are at almost opposite ends on my board, which is odd because I used the same schematic to remove the bass-boost on this amp and the resistors had the same designation. Hopefully I will have some time today to look at it.

richie00boy · 25th November 2005, 01:38 PM

Just check that what you are removing is a 2.7k or 2.7M resistor

DcibeL · 25th November 2005, 08:10 PM

R36 is definately and M, and R37 is most likely and M. They better both be M's because that's the size of resistors I grabbed from school today. I'm looking at the board right now. Stay tuned

18th November 2005, 08:50 PM	#1
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	Increasing amplifier auto-turn on sensitivity. I'm not really sure where I should have posted this, but anyway... I have a the SUB-250R subwoofer amplifier from Solen which is the same design as the smaller subwoofer amplifiers you will find at Parts Express, ApexJr, and Rythmik Audio. The problem I have with the amplfier is that it will not automatically turn on when the volume is at a very low level. In fact it is quite annoying in that the turn on level for this amp is at the point where if I watch TV at a normal volume, the sub will turn off during the show, and turn on during the ads (which are louder). Is there a possibility to change a part or two in the input module to increase this amplifiers auto turn-on sensitivity? It has been a few years since I have worked with transistor circuits, so I'm not really sure about this circuit. You'll see the on-auto-off switch in the lower left of the following image: __________________ The power of Science compels you!

18th November 2005, 11:23 PM	#3
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	Change that voltage divider, got it. Thanks. It'll be a few days before I will have the time to test it out, but I'll let you know how things work out. Something like double the value of R37, and half the value of R36 should work out, as long as the sensitivity is not so low that the amp is being turned on by line noise. __________________ The power of Science compels you!

24th November 2005, 02:25 AM	#4
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	Crap. My PCB, having the model with the remote control, has different designation numbers for the resistors. I guess I am out of luck for this modification. __________________ The power of Science compels you!

25th November 2005, 08:11 AM	#5
wintermute just another diyAudio Moderator Join Date: Aug 2003 Location: Sydney Blog Entries: 22	maybe not all is lost I'd assume that the remote basically controls the level of the sub??? meaning that the rest of the circuit is probably the same??? how many 2.7K resistors are there in series with a 20K resistor (with pin 2 of an opamp connected to the middle) in the circuit?? without checking the entire schematic I'd guess probbaly only the one!! should be relatively easy to track it down on the pcb, and then a bit of tracing should show you whether you are in the right spot... Tony. __________________ Any intelligence I may appear to have is purely artificial! Some of my photos

25th November 2005, 10:49 AM	#6
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	moamps you got that the wrong way round. The 2.7k (I thought it was 2.7M but doesn't really matter) should be made smaller to increase the gain. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more


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18th November 2005, 10:15 PM	#2
moamps diyAudio Member Join Date: Oct 2002 Location: Croatia	Hi, Use higher value for R37 or/and smaller value for R36. Also, if the timeout is too short, use higher value for C19 and/or higher value for R46. Regards, Milan

25th November 2005, 11:05 AM	#7
wintermute just another diyAudio Moderator Join Date: Aug 2003 Location: Sydney Blog Entries: 22	maybe it is 2.7M I had trouble readning the value on the schematic, and made no attempt to work out the actual circuit Tony. __________________ Any intelligence I may appear to have is purely artificial! Some of my photos

25th November 2005, 12:44 PM	#8
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	Yea, I'm sure with a little looking around on the PCB I could find the resistors. R36 and R37 on my board are at almost opposite ends on my board, which is odd because I used the same schematic to remove the bass-boost on this amp and the resistors had the same designation. Hopefully I will have some time today to look at it. __________________ The power of Science compels you!

25th November 2005, 01:38 PM	#9
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Just check that what you are removing is a 2.7k or 2.7M resistor __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

25th November 2005, 08:10 PM	#10
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	R36 is definately and M, and R37 is most likely and M. They better both be M's because that's the size of resistors I grabbed from school today. I'm looking at the board right now. Stay tuned __________________ The power of Science compels you!

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