If you were going to remove fuses i would keep the fuses after the capacitors/before the amps, and the primary side fuse. If the diodes or caps short, it'll blow the primary side fuse. If the amps fail, they blow the fuses after the capacitors which means the capacitors then dont dump power into the speaker.
edit: my mistake, I thought F4 and F5 were after the main capacitors.
edit: my mistake, I thought F4 and F5 were after the main capacitors.
Hmm they like capacitors in the signal path :x with fet based opamps, most of these would be unneccesary. I'd keep C14/C25 and possibly C3/C37 depending on how much offset there was. If you don't use the tone control i'd bin C19/C29 and R52/R54.
You could try removing C22/C38 but I wouldnt - just make sure there's a good quality capacitor there.
Replace C12/C13 if they are ceramic. Either a good polypropylene or a silvered mica would be ideal here.
Back the decoupling caps for the LM3886's with some 100nF capacitors. I'm undecided whether ceramic or polyester is best there.
Opamp power supplies - replace with LM317/337 but these are not straight drop ins - you would have to make up a small PCB or use some stripboard for this.
You could try removing C22/C38 but I wouldnt - just make sure there's a good quality capacitor there.
Replace C12/C13 if they are ceramic. Either a good polypropylene or a silvered mica would be ideal here.
Back the decoupling caps for the LM3886's with some 100nF capacitors. I'm undecided whether ceramic or polyester is best there.
Opamp power supplies - replace with LM317/337 but these are not straight drop ins - you would have to make up a small PCB or use some stripboard for this.
mikesnowdon said:
Yeah - that is what I would call the bare minimum of safety. I have 1 in the primary and then a set per rail per channel after the main capacitors. That way, if an amp goes DC, the rail fuses blow and stop the capacitors discharging into the speaker. I doubt there is much if any sonic penalty for having fuses there.
See for example: here and here
Heres the schematic for the 'input buffer' currently I have Mundorf MKP's at C25-14. Nichicon muse 100Uf 25v at C7-8 (local decoupling). The opamp is lm4562.
I have 0.003 AND 0.005v DC on the output of the opamp with the above set up.
Next time I have the amp open I will check for DC at the speaker terminals with C3/C37 removed.
I'll also check for DC with the feedback caps removed (C12/C13). Peter Daniel has no NFB cap in his set up so I think It might be ok. If not then I'll replace with something nice. Any suggestions on type and value?
Mike.
I have 0.003 AND 0.005v DC on the output of the opamp with the above set up.
An externally hosted image should be here but it was not working when we last tested it.
Next time I have the amp open I will check for DC at the speaker terminals with C3/C37 removed.
I'll also check for DC with the feedback caps removed (C12/C13). Peter Daniel has no NFB cap in his set up so I think It might be ok. If not then I'll replace with something nice. Any suggestions on type and value?
Mike.
I thought a snubber was when you bypass the Diodes with a small cap?
Based on the information in this thread I was thinking of adding a 1000uF good quality low ESR cap to the main smoothers. With additional Film bypass around 0.1 to 10uF? If I needed to add resitors I could do easily.
Or I could replace those big caps with a pair of 4700/6800uF caps per rail, just zip tie them together and solder the leads of one cap to the other. Then feed the legs through the existing holes in the PCB and solder in place (obviously making sure there are no shorts).
Which of the above would be best?
Mike.
Hi Mike,
Leave the fuses in there. The manufacturer would not include them unless they had to. They are a source of expense plus service calls, so they had no choice.
What you are concerned about seems to be max. power. Into clipping. This is like chasing that last 2% of performance and not really suited to this build. You would need to add actual wire to help. Messy and prone to shorting.
Keep your eye on the entire amplifier when deciding what to do. On your own build, take full advantage of everything you can. At least you will get value for money spent. Consider this as a light upgrade for your everyday driver, the sports car is another matter entirely. I am trying to keep your current amp in good, reliable condition. Complete with all factory options.
Hi jaycee,
-Chris
How many DIY builds are done with full knowledge of safety and electrical laws? Not many.
Leave the fuses in there. The manufacturer would not include them unless they had to. They are a source of expense plus service calls, so they had no choice.
Local bypass caps will help that situation.
Soldering over the foil won't buy you much.
What you are concerned about seems to be max. power. Into clipping. This is like chasing that last 2% of performance and not really suited to this build. You would need to add actual wire to help. Messy and prone to shorting.
Alps pot. Why? Doesn't fit I don't think. More basically, you have a solid state input switch. That messes up the sound quality more than a volume control. Ditto for the balance control.
Keep your eye on the entire amplifier when deciding what to do. On your own build, take full advantage of everything you can. At least you will get value for money spent. Consider this as a light upgrade for your everyday driver, the sports car is another matter entirely. I am trying to keep your current amp in good, reliable condition. Complete with all factory options.
Hi jaycee,
I think I saw some NP0 / C0G types in a picture a while back. They would be okay, but mica would ensure a good sound. I'd leave them for now if the are zero tempco.
Probably ceramic or polypropylene here. Polyester caps have a much higher tan.
-Chris
These last posts are really useful Mike 
WRT to small film caps, they're unlikely to do anything good in my experience but at least they're cheap. My most honest advice would be to get some 1uF 63V polyester caps as they might have low enough ESR to do something that the electrolytics you're going to install won't. Put them right on the pins of the LM3886.
Simon
WRT to small film caps, they're unlikely to do anything good in my experience but at least they're cheap. My most honest advice would be to get some 1uF 63V polyester caps as they might have low enough ESR to do something that the electrolytics you're going to install won't. Put them right on the pins of the LM3886.
Simon
C12/C13 are not DC feedback caps - they are there to reduce the opamp's gain at high frequency to avoid oscillation. In fact, this is probably why the LM4562 is stable in this circuit. Don't remove them.
The DC offset of the output seems very low, so you should be able to get away with removing the capacitors in the signal path I talked about.
i wouldn't try and fit more power supply capacitors - its going to be unstable attaching them when the PCB is only designed for 2 of then. As the traces are thin, its not going to make much difference.
With regards to adding ceramic capacitors over C40-C43 it seems Cambridge might have revised the PCB and added these. Looking at Stream's picture, there is C72/C73 which would seem to be in the right spot. Check your actual PCB.
One thing that would be worth doing is getting some 18AWG wire (or Maplins Equipment Wire (24/0·2)) and running wires from C24/C27 to the power pins on the LM3886 chips. You must be neat about it though, otherwise you will cause a lot of damage.
The DC offset of the output seems very low, so you should be able to get away with removing the capacitors in the signal path I talked about.
i wouldn't try and fit more power supply capacitors - its going to be unstable attaching them when the PCB is only designed for 2 of then. As the traces are thin, its not going to make much difference.
With regards to adding ceramic capacitors over C40-C43 it seems Cambridge might have revised the PCB and added these. Looking at Stream's picture, there is C72/C73 which would seem to be in the right spot. Check your actual PCB.
One thing that would be worth doing is getting some 18AWG wire (or Maplins Equipment Wire (24/0·2)) and running wires from C24/C27 to the power pins on the LM3886 chips. You must be neat about it though, otherwise you will cause a lot of damage.
I've ordered some components.
100uF 50v BG Std for the local decoupling on the powerchips.
1000uF 35v Panasonic FC for the preamp PSU (Before regs).
MUR860 OnSemi Diodes.
If I get time this weekend I'll see if I can de-bug this buzzing problem I have before I make any changes. Details here.
Mike.
100uF 50v BG Std for the local decoupling on the powerchips.
1000uF 35v Panasonic FC for the preamp PSU (Before regs).
MUR860 OnSemi Diodes.
If I get time this weekend I'll see if I can de-bug this buzzing problem I have before I make any changes. Details here.
Mike.
Im curious if there is any way the microprocessor for the input switching could be used to control a relay board? There are a few relay boards I have seen for DIY projects but so far I have only seen the type that are controlled by a rotary switch?
Are there any 'push button' type input relay switch 'kits' for the DIY market?
Mike.
Are there any 'push button' type input relay switch 'kits' for the DIY market?
Mike.
Hi hope your all having a nice weekend so far.
In an earlier post it was suggested to incerase the value of the feedback caps (C22/38) to around 100/220uF. If so then what type of cap would be good here?
Ive decided not to alter the circuit around the LM3886 chips, rather to replace critical components for better ones and maybe tweak values a bit.
Is there any way I can improve on the input selector chip?
Mike.
In an earlier post it was suggested to incerase the value of the feedback caps (C22/38) to around 100/220uF. If so then what type of cap would be good here?
Ive decided not to alter the circuit around the LM3886 chips, rather to replace critical components for better ones and maybe tweak values a bit.
Is there any way I can improve on the input selector chip?
Mike.
Hi Mike,
Leave the selector chip as is. The rest of your plan seems sound enough. Remember, you are only trying to improve the performance a bit here. Any more requires some ugly work and you can't really go all out with this one. Like putting a 350 CID engine in a Ford Pinto. They used to do this in the 70's and it ended up with a car that was loud, but did nothing else well at all.
Go nuts on your complete build.
There are projects around to use a uP to control input relays and even volume controls. I built a push button control selector for my bench years ago (in the 80's). It was all SSI and MSI CMOS stuff. I wonder where it is now? Two banks of eight inputs each with memory backup. I used TACT switches with LED indicators above each switch. TO-5 transistor cases made up the buttons after I removed the writing on the cases. I'm sure you can use something nicer these days. However, a rotary switch has built in memory and controls relays in a much easier manner to build.
Happy hunting and I wish you success this weekend!
-Chris
Leave the selector chip as is. The rest of your plan seems sound enough. Remember, you are only trying to improve the performance a bit here. Any more requires some ugly work and you can't really go all out with this one. Like putting a 350 CID engine in a Ford Pinto. They used to do this in the 70's and it ended up with a car that was loud, but did nothing else well at all.
Go nuts on your complete build.
There are projects around to use a uP to control input relays and even volume controls. I built a push button control selector for my bench years ago (in the 80's). It was all SSI and MSI CMOS stuff. I wonder where it is now? Two banks of eight inputs each with memory backup. I used TACT switches with LED indicators above each switch. TO-5 transistor cases made up the buttons after I removed the writing on the cases. I'm sure you can use something nicer these days. However, a rotary switch has built in memory and controls relays in a much easier manner to build.
Do this first. You need to borrow or get access to an oscilloscope. You may have an oscillating op amp. A 'scope will allow you to troubleshoot and try different things until the buzzing goes away. If there are two instruments that you really need, they would be a good meter (DVM, new or used Fluke is the best - or the new Agilent) and an oscilloscope. A 20 MHz model would be fine and there are many available used. Even really good ones by Tektronix can be had for around $100, and that's a 100 MHz model, like a 2235 or 475. Expect dirty switches in these. The 2235 has bad connections on the power triac (easy fix). A new 'scope at 20 MHz would be a great instrument. Keep in mind that I started with a single, 500 MHz Stark. It cost me around $45 or $55 in the early 70's. I remember I saved up for a while and got it at Crown Assets Disposal (government surplus). You really ought to get a 'scope at some point in time soon.
Happy hunting and I wish you success this weekend!
-Chris
Thanks Chris.
I dont think its a bad opamp as I have tried disconnecting the supplies to all opamps and it still buzzes. Also if I remember correctly I tried lifting the input caps to the power stages and there was no buzz so the LM3886 are ok.
Maybe you could take a look at my de-bugging thread here.
By the way I do have a DVM and also a scope but I need to get leads for it and learn how to use it first.
Mike.
I dont think its a bad opamp as I have tried disconnecting the supplies to all opamps and it still buzzes. Also if I remember correctly I tried lifting the input caps to the power stages and there was no buzz so the LM3886 are ok.
Maybe you could take a look at my de-bugging thread here.
By the way I do have a DVM and also a scope but I need to get leads for it and learn how to use it first.
Mike.
Hi jaycee,
It's different over here. Mind you, most things off of Eeekbay need service before they will work. Rarely I have received stuff that actually works!
I imagine leasing companies would be worth checking out. Universities as well. Most companies will gladly sell off equipment to hobbyists, the good ones anyway.
Hi Mike,
Okay, you have an excellent start. Your first leads can be less expensive. I would recommend fixed X10 probes. Buy better ones later. Leads are very important! The ones for my HP are about $60 a set, but worth it. I also use cheaper sets, knowing what their limitations are. When the measurement is important, use good leads. This goes for both 'scopes and meters!
-Chris
It's different over here. Mind you, most things off of Eeekbay need service before they will work. Rarely I have received stuff that actually works!
I imagine leasing companies would be worth checking out. Universities as well. Most companies will gladly sell off equipment to hobbyists, the good ones anyway.
Hi Mike,
Okay, you have an excellent start. Your first leads can be less expensive. I would recommend fixed X10 probes. Buy better ones later. Leads are very important! The ones for my HP are about $60 a set, but worth it. I also use cheaper sets, knowing what their limitations are. When the measurement is important, use good leads. This goes for both 'scopes and meters!
-Chris
I'll check out getting some leads for the scope soon.
Im looking to replace the 2 resistors in the feedback with a single 12k Caddock as Peter Daniel uses. I'll be soldering it directly to the chips pins. Also If I have space under the heatsinks I'll try and solder the new decoupling caps direct too. The reason for dropping the value to 12k is to reduce gain as there is allready far too much as with most commercial kit. This mod was suggested to me by Greg Ball of SKA audio.
Here is what he said:
"This has the added advantage of reducing noise as higher signal levels are maintained through the volume / tone controls and into the main amp. Also there is 6dB extra feedback around the power amp chips for lower loop distortion and a 6dB PSRR improvement on their weaker -Vs supply. (Greg Ball)"
For the cap in the feedback I have some 100uF Tants and 100uF Rubycon ZLH in my kit box which I'll try out. I fancy the Tants might give it a warmer funky 'naimlike' sound where the Rubys might be better for micro detail and timbre, either cap should be an improvement so I'll see which I prefer.
SKA Audio
Mike.
Im looking to replace the 2 resistors in the feedback with a single 12k Caddock as Peter Daniel uses. I'll be soldering it directly to the chips pins. Also If I have space under the heatsinks I'll try and solder the new decoupling caps direct too. The reason for dropping the value to 12k is to reduce gain as there is allready far too much as with most commercial kit. This mod was suggested to me by Greg Ball of SKA audio.
Here is what he said:
"This has the added advantage of reducing noise as higher signal levels are maintained through the volume / tone controls and into the main amp. Also there is 6dB extra feedback around the power amp chips for lower loop distortion and a 6dB PSRR improvement on their weaker -Vs supply. (Greg Ball)"
For the cap in the feedback I have some 100uF Tants and 100uF Rubycon ZLH in my kit box which I'll try out. I fancy the Tants might give it a warmer funky 'naimlike' sound where the Rubys might be better for micro detail and timbre, either cap should be an improvement so I'll see which I prefer.
SKA Audio
Mike.
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