Hi,
I was given an old commercial amp in non-working condition. I have fixed it, the amp is singing now but I found that it lacks bass. Can someone help me to improve bass response of this amp.
Having not found the shematic I reverse engineered it from the circuit. I have checked many many times, I apologize for possible errors.
I was given an old commercial amp in non-working condition. I have fixed it, the amp is singing now but I found that it lacks bass. Can someone help me to improve bass response of this amp.
Having not found the shematic I reverse engineered it from the circuit. I have checked many many times, I apologize for possible errors.
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Usually you can do that by increasing the value of input or feedback capacitor, but in your schematic I don't see them.
This amp is DC coupled from input to output, there isn't any caps in signal path and it lacks of bass. Strange isn't it?
Somebody told me to connect to it high efficiency speakers, I have tried with a pair of 93 db speakers and the result is worst than with my old Bose 301!
Somebody told me to connect to it high efficiency speakers, I have tried with a pair of 93 db speakers and the result is worst than with my old Bose 301!
Hi NDV33,
what are the values of the filter caps on the output stage. If you beef them up considerably the bass will be more controlled and extend lower. This is the return path of the speaker current. 10 000uF would normally do. Without analysing the schematic, I find it interesting that the designer made the front end into an instrumentation amp.
Nico
what are the values of the filter caps on the output stage. If you beef them up considerably the bass will be more controlled and extend lower. This is the return path of the speaker current. 10 000uF would normally do. Without analysing the schematic, I find it interesting that the designer made the front end into an instrumentation amp.
Nico
Yes, small or bad/old PS caps in amplifier tend to produce that effect.
What's the capacitance of the elkos in PSU?
Also, 1 pair of bd249/250 is not what you'd call a powerfull output stage at +/-42V...
What's the capacitance of the elkos in PSU?
Also, 1 pair of bd249/250 is not what you'd call a powerfull output stage at +/-42V...
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When you say it lacks bass, do you mean you have measured the frequency response or just compared it by ear (directly or via your memory) with another amplifier? If the latter, is it possible that the other amplifier has too much bass but you have got used to it and assume it to be 'correct'?
With no capacitors in the forward path or feedback loop this amp ought to be dead flat from DC upwards. Are you sure there are no capacitors in the feedback path i.e. it is just feedback and not a DC servo? What is the DC offset voltage at the output?
With no capacitors in the forward path or feedback loop this amp ought to be dead flat from DC upwards. Are you sure there are no capacitors in the feedback path i.e. it is just feedback and not a DC servo? What is the DC offset voltage at the output?
Are you sure the inductor in front of the speaker isnt broken? Might produce less bass that way...
Hi guys,
Thanks for your replies, I didn't expect so much replies in such short times. I answer your post in reverse order (new posts to old posts)
1- Yes I know that 93 db is not really a high efficiency but as the result is worst with a 93db than my old Bose 301 I extrapolate the result. It is already bad at 93db with higher efficiency the result could not be improved right?
2- Inductors are OK, I checked it.
3- I didn't measure frequency response but compare by ear, it lacks bass compared to all amps I own. I confirm that there are no cap in the FB path. DC offset voltage at the output = 0 V as I can adjust by pot P1.
4- Filter caps are 10 000uF on positive rail and 10 000uF on negative rail. I have replaced old caps by news caps because the caps of the negative rail on both channels were dead. The sound was bad with new caps but has improved significantly since. But the bass.
Thanks for your replies, I didn't expect so much replies in such short times. I answer your post in reverse order (new posts to old posts)
1- Yes I know that 93 db is not really a high efficiency but as the result is worst with a 93db than my old Bose 301 I extrapolate the result. It is already bad at 93db with higher efficiency the result could not be improved right?
2- Inductors are OK, I checked it.
3- I didn't measure frequency response but compare by ear, it lacks bass compared to all amps I own. I confirm that there are no cap in the FB path. DC offset voltage at the output = 0 V as I can adjust by pot P1.
4- Filter caps are 10 000uF on positive rail and 10 000uF on negative rail. I have replaced old caps by news caps because the caps of the negative rail on both channels were dead. The sound was bad with new caps but has improved significantly since. But the bass.
Hello all,
Why do u think that there is a problem with capacitors? What is about the output impedance? It is playing important role to drive woofer in good way.
Why do u think that there is a problem with capacitors? What is about the output impedance? It is playing important role to drive woofer in good way.
Possibly due to the output stage being poorly designed with no means to suck out charge from the output bases.
I do not know well the VN88, I want to replace it with an equivalent component bipolar or Fet device.
No Tekko, tone control has nothing to do here I connect the source direct to the amplifier through only a volume control.
No Tekko, tone control has nothing to do here I connect the source direct to the amplifier through only a volume control.
Could be an impedance mismatch, that can lose bass.
Try it with a mixer attached and see if taht improves the situation.
OK, I will connect a preamp tomorrow and see what happen. I think that I have already done, I have made so many trials that I do not remember what I have done or not 😱
Thanks to all for taking your time,
Thanks to all for taking your time,
Yes in theory HF distortion will be worse, but you can get some funny effects in the bass as well.
What do you mean by removing charge from output bases?
I have tried to connect a preamp but same thing.
My idea is that it's comes from component choice. I plan to replace output pair BD249/250 by Toshiba equivalent and see if there is improvement.
I have tried to connect a preamp but same thing.
My idea is that it's comes from component choice. I plan to replace output pair BD249/250 by Toshiba equivalent and see if there is improvement.
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