Need Help with this Circuit Please

[tfs2015]

Dear Forum members,

I hope that you can help me out with this amp circuit, I cannot get it to work correctly even on +- 12 vdc supply. I end up with 10vdc between the speaker output and ground.

Thanks
Tom

[stj]

Re: Need Help with this Circuit Please

i'm not surprised, it has no bias ajustment or anything.
it looks like a classroom example of what not to try to build!

[Khron]

Re: Need Help with this Circuit Please

Might i suggest taking a look at some of Rod Elliott's projects? As a starting point, i'd like to point you towards his Project 3A - http://sound.westhost.com/project3a.htm

He has strived to make his designs as simple and forgiving (if not even bulletproof), using mostly "jellybean" parts, so they should make a decent starting point

[SteveNielsen]

Re: Need Help with this Circuit Please

Dear Forum members,

I hope that you can help me out with this amp circuit, I cannot get it to work correctly even on +- 12 vdc supply. I end up with 10vdc between the speaker output and ground.

Thanks
Tom

It's no wonder, there is no output DC decoupling. At least put a cap in series with the speaker before you burn out the voice coil.

[Khron]

Re: Need Help with this Circuit Please

At least in theory, it shouldn't need any, since at least on the schematic, it has +/-45v supplies, so...

[SteveNielsen]

Re: Need Help with this Circuit Please

Yes, if the circuit was really balanced but it doesn't look like it at a glance and the circuit is not drawn very well. It's not possible to tell how the transistors are biased without knowing what they are. One could look them up and redraw the diagram but I'm not gonna do it.

[budm]

Re: Need Help with this Circuit Please

Might i suggest taking a look at some of Rod Elliott's projects? As a starting point, i'd like to point you towards his Project 3A - http://sound.westhost.com/project3a.htm

He has strived to make his designs as simple and forgiving (if not even bulletproof), using mostly "jellybean" parts, so they should make a decent starting point

+1, great site for learning also.

[budm]

Re: Need Help with this Circuit Please

Dear Forum members,

I hope that you can help me out with this amp circuit, I cannot get it to work correctly even on +- 12 vdc supply. I end up with 10vdc between the speaker output and ground.

Thanks
Tom

Link to the site where you get this diagram from?

[SteveNielsen]

Re: Need Help with this Circuit Please

Here are a couple I found:
http://circuitdiagram.net/150w-power-amplifier.html
http://www.circuitdiagramworld.com/a...ram_16729.html

[budm]

Re: Need Help with this Circuit Please

The reason I want the link is to fiond out how many people or if the Author actually build the circuit.
I see the power supply circuit (http://circuitdiagram.net/150w-power-amplifier.html) suggested to use 35V-0-35V and the filter caps are rated at 50VDC (4500uF 50V), @35V, the DCV on the cap will be about 49VDC if the line Voltage stays still.
I found this:
http://pcb.jspayne.com/150wattamp.html

I would also implement speaker protection relay.
I.E. http://sound.westhost.com/project33.htm

[SteveNielsen]

Re: Need Help with this Circuit Please

The alternate schem is easier to read:

[tfs2015]

Re: Need Help with this Circuit Please

Link to the site where you get this diagram from?

I got the schematic from http://electronics-diy.com/electroni...tic.php?id=477

I simulated it MultSim and found out that with +- 12vdc power I would get about 10vdc on the + speaker output to ground. If I raised the supply voltage to +- 45vdv the vdc would drop to 950 mv which should not burn out the speaker. When I ordered the components I forgot about the TIP 141 and ended up using a TIP 142 in its place. According to the specs it has 100 watt handling capability where as the TIP 141 has 80 watt. I have a couple of 1200 uF 63v caps laying around, can I use one of those as a decoupling cap on the speaker output? I don't have a lot of money to spend on this project right now so I am hoping I can use what I have on hand.

[stj]

Re: Need Help with this Circuit Please

you will need a lot of aluminium - and probably a fan.
that is going to get real hot.

[SteveNielsen]

Re: Need Help with this Circuit Please

1200uF is a bit much at 8 ohms, that puts the resonant freq center at below 20Hz. Around 20uF at 8 ohms would center close to 1KHz.

http://www.calculatoredge.com/enggca...apacitance.htm

[tfs2015]

Re: Need Help with this Circuit Please

Which is going to get hot, the cap or the transistors? I have a heat sink to mount them on.

I need to clarify something: I am trying to rebuild the power amp on my Fender PD250 PA system since the original board is not able to be repaired.

The SMPS outputs +/- 52 vdc for powering the amplifier section. I need a circuit that has low component count, can use most of what I have on hand and is cheap and easy to build. The SMPS is already mounted to a very big heat sink and the power amp board also mounts to this heat sink as well. The orginal board had a lot of transistors and diodes on it plus trimmer pots for setting all of the volategs and currents correctly. I want to get away from that so I can just plug the circuit in and go.

Any help or recommendations would be greatly apprecaited.

Thanks
Tom

[stj]

Re: Need Help with this Circuit Please

the transistors will generate heat, your psu will need to be pretty capable too.

[SteveNielsen]

Re: Need Help with this Circuit Please

I don't think you're going to have a good time of it going that route. Please explain why the original board cannot be repaired. It might be the best and easiest solution and there are people here willing to help with that. I found a svc manual for the unit.

[stj]

Re: Need Help with this Circuit Please

the chinese probably sell a pre-built pcb for peanuts.

[keeney123]

Re: Need Help with this Circuit Please

Here is a link to a course on understanding amplifiers. http://www.learnabout-electronics.or...plifiers50.php
It even has tests to verify your understanding.

[tfs2015]

Re: Need Help with this Circuit Please

I don't think you're going to have a good time of it going that route. Please explain why the original board cannot be repaired. It might be the best and easiest solution and there are people here willing to help with that. I found a svc manual for the unit.

The circuit board traces are badly damaged due to repeated repairs to the board. I called Fender about obtaining a replacement board. They told me that the board is no longer available and that the new systems they make use a digital technology instead of analog. Therefore I am kind of stuck on what to do that is why I reached out for some help. Any help and recommendations would be helpful.