Hello all,
I decided to make another amplifier to power my Frugel Horn Mk3's and tried and failed with a solid state circuit.
So I decided to make a 'posher' chipamp and I was able to obtain a pair of LM3876T on eBay and these formed the basis of my new non-inverted amplifier. I can work with timber and am useless at bending metal so that is my choice of material, in this case plywood from our local DIY shop.
I mounted the heat sink on a piece of thick ply with a bit of MDF picture backing board for the pot. I've used 1/4 watt carbon resistors, as in the GainCard, matching them with my meter, the one metal film one that you can see is for the mute, this chip being similar to the LM3886. The caps are 100 uf and 0.1 uf and the FB resistor is 22k and the gain resistor Ri is 680R giving a gain of about 30.
Starting at the back a 300VA 12-0-12 toroid I bought on eBay this was for my failed SS amp, the drive units in my FH3's are Mark Audio CHP-70's and are 4 Ohm so the 12v should be enough. next are 2 35 Amp bridges and then 2.2K resistors across the supply, 4,700 uf caps, 10,000 uf caps, 0.1 uf caps, and the snubber, 2.7R and 0.1uf. The power grounds come together at the front of the Veroboard. The cap sitting in the Blue Tak is for the mute. The amplifier assembly is mounted over a vent hole. The Vishay 10k pot is in place and the Zobel is screwed across the output, the pot shaft will be connected to some 6mm dowel and out through the front.
I powered it up in stages and checked power voltages each time, first with the bridges, then with the power supply, then with the amplifier but with no input, then with an old speaker and then finally when that was OK to one of my FH3's.
With the input connected to my paused CDP and turning the pot full up then placing my ear at headphone distance from the CHP-70's there is no sound whatsoever.
As for what it sounded like it's quite warm, what did surprise me was the detail certainly a bit better than my other GC. More on that later when I have finished it I will leave it on for a week quietly playing a tuner to itself. Ohh and yes the 12V is 17V at the power supply output and will easily drive the CHP-70's to painful levels.
I think that lots of 1st time DIYer's are reluctant to start an amplifier because like me they cannot work metal. I hope this thread will give some of them a start.
Jim
I decided to make another amplifier to power my Frugel Horn Mk3's and tried and failed with a solid state circuit.
So I decided to make a 'posher' chipamp and I was able to obtain a pair of LM3876T on eBay and these formed the basis of my new non-inverted amplifier. I can work with timber and am useless at bending metal so that is my choice of material, in this case plywood from our local DIY shop.
An externally hosted image should be here but it was not working when we last tested it.
I mounted the heat sink on a piece of thick ply with a bit of MDF picture backing board for the pot. I've used 1/4 watt carbon resistors, as in the GainCard, matching them with my meter, the one metal film one that you can see is for the mute, this chip being similar to the LM3886. The caps are 100 uf and 0.1 uf and the FB resistor is 22k and the gain resistor Ri is 680R giving a gain of about 30.
An externally hosted image should be here but it was not working when we last tested it.
Starting at the back a 300VA 12-0-12 toroid I bought on eBay this was for my failed SS amp, the drive units in my FH3's are Mark Audio CHP-70's and are 4 Ohm so the 12v should be enough. next are 2 35 Amp bridges and then 2.2K resistors across the supply, 4,700 uf caps, 10,000 uf caps, 0.1 uf caps, and the snubber, 2.7R and 0.1uf. The power grounds come together at the front of the Veroboard. The cap sitting in the Blue Tak is for the mute. The amplifier assembly is mounted over a vent hole. The Vishay 10k pot is in place and the Zobel is screwed across the output, the pot shaft will be connected to some 6mm dowel and out through the front.
I powered it up in stages and checked power voltages each time, first with the bridges, then with the power supply, then with the amplifier but with no input, then with an old speaker and then finally when that was OK to one of my FH3's.
With the input connected to my paused CDP and turning the pot full up then placing my ear at headphone distance from the CHP-70's there is no sound whatsoever.
As for what it sounded like it's quite warm, what did surprise me was the detail certainly a bit better than my other GC. More on that later when I have finished it I will leave it on for a week quietly playing a tuner to itself. Ohh and yes the 12V is 17V at the power supply output and will easily drive the CHP-70's to painful levels.
I think that lots of 1st time DIYer's are reluctant to start an amplifier because like me they cannot work metal. I hope this thread will give some of them a start.
Jim
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Dear Tiger,
Alas I wouldn't know I just buy as many bargains as I can find on eBay to keep the costs down. I'm a pensioner [waving my stick]
Though thinking about it doesn't Mr Sakura use a specially made EI tranformer in the GainCard now.
I think I read somewhere on here in 2004 when I made my first GC that toroids reacted faster but I'm probably wrong. I would imagine that the power supply caps would make up any shortcomings of a transformer providing of course that it was powerful enough for the use it's put to.
No doubt someone will provide enlightenment.
Regards - Jim
PS I like your wooden boxes, very well done indeed.
Alas I wouldn't know I just buy as many bargains as I can find on eBay to keep the costs down. I'm a pensioner [waving my stick]
Though thinking about it doesn't Mr Sakura use a specially made EI tranformer in the GainCard now.
I think I read somewhere on here in 2004 when I made my first GC that toroids reacted faster but I'm probably wrong. I would imagine that the power supply caps would make up any shortcomings of a transformer providing of course that it was powerful enough for the use it's put to.
No doubt someone will provide enlightenment.
Regards - Jim
PS I like your wooden boxes, very well done indeed.
Nice one Jim.
That's reminiscent of my first GC build.
I built it on a piece of MDF with everything spaced out, because i expected all kinds of teething troubles. Thought it would be easier to work on.
As it happened the amp worked fine, and sounded so good that i wished i had made a better job of it.
So instead of rebuilding it, I put the whole thing in a large metal case.
Eventually it took the place of my MF A3 amp, because I preferred it.
Good luck.
That's reminiscent of my first GC build.
I built it on a piece of MDF with everything spaced out, because i expected all kinds of teething troubles. Thought it would be easier to work on.
As it happened the amp worked fine, and sounded so good that i wished i had made a better job of it.
So instead of rebuilding it, I put the whole thing in a large metal case.
Eventually it took the place of my MF A3 amp, because I preferred it.
Good luck.
Yes it was Point to point and quite crudely done.
But it was successful.
Certain parts like input/output caps should be arranged so they're easy to swap.
Thats part of the fun isn't it.
Hello all,
Hello all,
I've listened to my LM3876 for 7 years now and been quite happy with it.
But as one does I looked at Mick Feuerbacher's site occasionally
And in particular at his 2 resistor LM3886 amp
A couple of weeks ago I decided to have a go and found an old box with a couple of toroids and a pair of bridges that I was going to make into solid state amp and failed.
It's all P2P using single core wire.
Sonically it's better than the 3876
And I was quite surprised that there is no hum or RF interference
It cost me £16.74 in extra bits.
Cheers
Hello all,
I've listened to my LM3876 for 7 years now and been quite happy with it.
But as one does I looked at Mick Feuerbacher's site occasionally
And in particular at his 2 resistor LM3886 amp
A couple of weeks ago I decided to have a go and found an old box with a couple of toroids and a pair of bridges that I was going to make into solid state amp and failed.
It's all P2P using single core wire.
An externally hosted image should be here but it was not working when we last tested it.
Sonically it's better than the 3876
And I was quite surprised that there is no hum or RF interference
It cost me £16.74 in extra bits.
Cheers
to wood "cases"!
Hey!!! Love it!!!! 
And if it works ..... it works.
That said, I guess it lives in an (electrically) clean area, no nasty electromagnetic interference around it; personally I would cover case floor (at least) with a glued sheet of kitchen type aluminum foil ... grounded of course.
Yes, it may involve "metal cutting and bending" .... cuting with scissors or a hobby knife, bending with your fingertios and even "punching" (if necessary) with a pencil tip
Won´t interfere with basic structure woodworking of course.
Congratulations again.
PS: FWIW I make Guitar amps and related stuff, have been doing it for almost 50 years now, and when I started, way back then, a "breadboard" prototype was not built on a chocolate bar sized piece of white plastic full of holes and with snap in connectors, but a real *bread* - *board* meaning a real piece of wood with nails and bare wires with parts actually soldered to them.
More than once such flimsy prototypes were carried to a rehearsal room or even a Club, sitting on a table or even speaker cabinet itself, to try "live" a new idea or circuit tweak
And if it works ..... it works.
That said, I guess it lives in an (electrically) clean area, no nasty electromagnetic interference around it; personally I would cover case floor (at least) with a glued sheet of kitchen type aluminum foil ... grounded of course.
Yes, it may involve "metal cutting and bending"
.... cuting with scissors or a hobby knife, bending with your fingertios and even "punching" (if necessary) with a pencil tip Won´t interfere with basic structure woodworking of course.
Congratulations again.
PS: FWIW I make Guitar amps and related stuff, have been doing it for almost 50 years now, and when I started, way back then, a "breadboard" prototype was not built on a chocolate bar sized piece of white plastic full of holes and with snap in connectors, but a real *bread* - *board* meaning a real piece of wood with nails and bare wires with parts actually soldered to them.
More than once such flimsy prototypes were carried to a rehearsal room or even a Club, sitting on a table or even speaker cabinet itself, to try "live" a new idea or circuit tweak
Hello JMF,
You're right it does work!
If I do get any interference I'll use your idea, thanks for the suggestion. It's been OK for the last 7 years though.
Hello SJ,
May ask with great respect where else I may connect it?
Have you got Andre Previn and Itzhak Perlman's ragtime album, wonderful stuff you reminded me of it must have a listen to mine tonight.
Cheers
You're right it does work!
If I do get any interference I'll use your idea, thanks for the suggestion. It's been OK for the last 7 years though.
Hello SJ,
May ask with great respect where else I may connect it?
Have you got Andre Previn and Itzhak Perlman's ragtime album, wonderful stuff you reminded me of it must have a listen to mine tonight.
Cheers
Don't connect it at all, it's for safety only and since that doesn't appear to be an issue with your design, it would probably be better off without it. You wouldn't have problems with ground loops through the mains when connected to other equipment and you wouldn't be bringing in any external noise that might be on it.
I think I've heard that album online, I will check it out again, thanks.
Hello SJ,
Ahhh I see thanks very much for that, if I get anything untoward happening rest assured that I'll disconnect said wires, however it has been OK for the past 7 years with my 3876 amp.
The signature track 'The Entertainer' (well, it would be wouldn't it) to misquote Mz Rice-Davies.
YouTube
I must admit I'd forgotten just how good they are together
Cheers
Ahhh I see thanks very much for that, if I get anything untoward happening rest assured that I'll disconnect said wires, however it has been OK for the past 7 years with my 3876 amp.
The signature track 'The Entertainer' (well, it would be wouldn't it) to misquote Mz Rice-Davies.
YouTube
I must admit I'd forgotten just how good they are together
Cheers
You do realize that this so called 2 resistors design doesn't make any sense right ?
There is nothing to be gained by removing the high value input to gnd resistor. It's actually silly to call it a 2 resistors design. What is the volume pot but a resistor ? The only thing you gain is no defined reference point if the wiper disconnects.
edit: btw, why do you take the speakers returns to a common ground while the whole thing seems wired as dual mono ?
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Hello 00940,
Many thanks for your kind words nice of you to respond with so much enthusiasm.
May I be bold enough to point out that had you referred to a previous post in this thread you may have seen this link to the circuit: Mick Feuerbacher Audio Projects
I merely made it and it works superbly, I do take your point about the speaker returns, and as I have said before should I suspect anything untoward I will recall your words and move the connections an inch or two.
One recalls a USA homily; "If it ain't broke don't try to fix it".
Cheers
[edit] pardon me for asking, "There is nothing to be gained by removing the high value input to gnd resistor." your words would indicate that the item is superfluous anyway.
Many thanks for your kind words nice of you to respond with so much enthusiasm.
May I be bold enough to point out that had you referred to a previous post in this thread you may have seen this link to the circuit: Mick Feuerbacher Audio Projects
I merely made it and it works superbly, I do take your point about the speaker returns, and as I have said before should I suspect anything untoward I will recall your words and move the connections an inch or two.
One recalls a USA homily; "If it ain't broke don't try to fix it".
Cheers
[edit] pardon me for asking, "There is nothing to be gained by removing the high value input to gnd resistor." your words would indicate that the item is superfluous anyway.
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I have seen the link. The circuit I'm criticizing is indeed Mick's. I've truly no idea why anyone would want to copy his work.
I commend your enthusiasm but it has to be pointed out that Mick Feuerbacher's circuits are very poorly designed (if nicely executed). There are no good reasons not to use more resistors and caps around the lm3886 and many reasons to. The circuit might appear to perform superbly but have you actually tested it ? Not just hooked it to speakers but tested with a scope under harsher conditions ?
edit: to answer your question: when a potentiometer is in the circuit, the input resistor to gnd isn't doing much. It is in // with a much lower value resistor (the pot). It is there to reference the input to ground if the pot is ever disconnected, which can happen with a dirty wiper.
I commend your enthusiasm but it has to be pointed out that Mick Feuerbacher's circuits are very poorly designed (if nicely executed). There are no good reasons not to use more resistors and caps around the lm3886 and many reasons to. The circuit might appear to perform superbly but have you actually tested it ? Not just hooked it to speakers but tested with a scope under harsher conditions ?
edit: to answer your question: when a potentiometer is in the circuit, the input resistor to gnd isn't doing much. It is in // with a much lower value resistor (the pot). It is there to reference the input to ground if the pot is ever disconnected, which can happen with a dirty wiper.
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Btw, sorry for being blunt in the above posts. It's just that this has been discussed many, many times.
For the input resistor, have a look here for a more detailed explanation: Chipamp's LM3886: omitting R2
For the input resistor, have a look here for a more detailed explanation: Chipamp's LM3886: omitting R2
Hello 00940,
I accept your apology, in turn please accept mine for being a very non-techie person.
I say this with respect to all the techie people who read this and I don't mean that in a derogatory way, far from it. My final arbiter is my ears and what I hear is for me almost perfection.
Personally I would recommend Mick's circuit to anyone reading this who wants to make something simple and inexpensive that sounds excellent. And to anyone from the UK who lives not too far from M1Ju29 you would be more than welcome to pop round and have a listen.
Cheers
I accept your apology, in turn please accept mine for being a very non-techie person.
I say this with respect to all the techie people who read this and I don't mean that in a derogatory way, far from it. My final arbiter is my ears and what I hear is for me almost perfection.
Personally I would recommend Mick's circuit to anyone reading this who wants to make something simple and inexpensive that sounds excellent. And to anyone from the UK who lives not too far from M1Ju29 you would be more than welcome to pop round and have a listen.
Cheers
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