| Nordic |
I worked myself into a corner on the little gainclone I started putting together for mom in law.
I have been modularly tinkering and assembling on it for the last 2 months or so.
The end result is that I kinda started running out of space, just as I decided I would like to make it an integrated amp includeing Nuuk's class A Valve Buffer. which is kinda like noteceing the nice desert at a buffet after you stuffed yourself on the main course.
There was no space for another transformer to power the lower voltage preamp, and the relay to power to amp on after delay.so I decided to try a circuit I saw about a year ago.
Rod Elliot's simple pre-regulator. He suggested it would work for dropping up to +and-70V rails to 24V after which he implemented fixed voltage regulators.
I chose to use LM317 and LM337 to give me variable supplies (not to mention the datasheet shows an extra 10db ripple rejection). In theory the supply thus have rails that are variable through a wider range than indicated above, but I like to stay within max of 10V diffirential i.e. up to 24 minus 10V. This means in theory we should never get close to the current limit for these 2 regs, with about a 5A ceiling between the 2 of them)
As far as I understand the prereg part will supply about 100mA with those transistors (biased at 20mA) per rail, which is more than enough for an opamp based buffer, and I hope for nuuk's buffer too. (work in progress short 1 transistor which I will only receive on Monday morning)
I have tested the build up pre-post reg assembly off my + and - 35V Gainclone supply, and it is the most steady output I have seen on my primitive testing equipment yet.
So I attach the neccecary schematics and board files in zip format along with some pictures....
The only thing I omitted on the files is the 10R resistor should be 1 to 2 W... the resistor is shown, just not the wattage...
Rod claims it should be cleaner than only using a regulator. |
|
|
| Nordic |
| Zipped file containing sch, brd files as well as instructions for calculating Rx. |
|
|
| Nordic |
| Hard to talk along without seeing a schematic I guess |
|
|
| Nordic |
Remeber the text file in the zip arhcive contains importnt info!!!
SO there you go folks, an easy way to power remotes, pic and what have you inside that case off the same transformer used for your amp.
PS. the heatinks were way overkill - I'm cheap, I sawed them out af a heatsink from an ATX psu that died. |
|
|
| davidlzimmer |
Nordic,
I am in a very similar situation. Throwing together a cheapo sub amp for my 14 year old. The Chip amp and op amp active crossover work surprisingly well but am using batteries to power the amp amp for testing.
I spent 3 hours searching on the subject (of which I am very ignorant) and came up with the same two chips you are using. Wish I had came here first! :D
Could I ask, what wattage pots are you using? And what if I just use the schematic on the LM337 data sheet?
Thanks! |
|
|
| Nordic |
I threw the packets away allready... these were pretty small Bournes trimpots, 1/4W on the outside... regular ones would work just fine in that position This little board would work pretty neat for you. But hold on until monday when I can actualy listen to something powered by it...
You could use just the second part of the board with just the 2 regulators on of course or use the firts half with fixed regulators too of course...
The problem with only using LM317 etc, is that the larger the drop you achieve, the less current it can provide without overheating. |
|
|
| Variac |
| Nice to see the holiday elves working , spreading DIY joy..... |
|
|
| davidlzimmer |
Ok. I can wait. This is not for Christmas. Just a little side job cause I had a chip amp and an op amp to play with. :D
I'm fairly new to op amps also (but beginning to really like them) but I'm only using one channel. I shouldn't draw much current. And I have plenty of heat sink as I am building on the plate of a defunct plate amp.
Anyway, this is the circuit I was going to use. The simpler the better for this job. ;) |
|
|
| Nordic |
| that looks just fine |
|
|
| Nordic |
| I would increase the 1 uf to 1000, unless you have a tantalum. |
|
|
| davidlzimmer |
I'm wondering about power up. I hope this won't require a delay for the power amp. Using the batteries, I power up the op amp first then the power amp.
Will be interested in your findings Monday. :D
This could really be a sweet solution for a lot of projects that I have day dreamed about, but tossed off thinking I'd have to build a separate supply. ;) |
|
|
| Nordic |
| Lol you should have asked, I made a relay board to use with this as well.... |
|
|
| davidlzimmer |
OK wise guy.;) What program do I need to open a .sch file? :D
Eagle? |
|
|
| Nordic |
While it is quiet, you could use the relay board with a 12V supply by bypassing the big resistor where the power conects through... it is currently set to operate off 30V. I.e. from the positive and negative rails from the prereg-reg board. (which prevents loading one rail more than the other)
Alternatively you could use larger voltages or voltages in between, by adjusting the resistor. |
|
|
| Nordic |
| Sorry, was unable to do promised testing today thanks to RS, once again screwing up... been like a running battle with them since Thursday. |
|
|
| davidlzimmer |
No problem. I'm in no hurry. Was given an old sub amp yesterday so, I'm mainly interested in this for future projects.
Have had an itch to build an integrated amp. This will be a sweet solution for powering the pre. |
|
|
| Nordic |
| I'd be interested in the crossover/filter you did for the sub, I have a dead Yahamaha here which the woofer still works fine in, it is only a 100W. |
|
|
| davidlzimmer |
This was submitted by some one months ago. It works just fine for what little testing I gave it. I just used two 10K resistors to sum the input which was taped from the input vol control of the mains amp.
I would imagine a couple of buffers for summing and a stage for a little gain would really improve the performance.
But for what it's worth, here it is. |
|
|
| Nordic |
Cool, will give it a shot, I tried useing another filter, but I fear at the time I was still a little dumber... and used an LM3875 which just could not handle the impendace dips on that woofer, it, would knock like someone was kicking against the woofer when it hit some frequencies... was very disheartening...
I got the service manual in the mean time, but getting hold of those chips and transistors at this stage looks harder than learning algebra all over and then learning filter theory. |
|
|
| davidlzimmer |
I was using a P2P LM3886 and a 4 ohm speaker. Worked fine but was only assisting a little 20 watt mains amp.
A parallel LM3886 configuration would probably suit your needs better. |
|
|
| Nordic |
| Yeah I'm no too worried about the amp part, even have some 100W TDA chips around here... jsut the filters I tried all drove me nuts at the time. |
|
|
| davidlzimmer |
Nordic,
I was just wondering. Were you using passive filters? I've had terrible luck experimenting them. Couldn't get rid of spikes that made farting sounds! :bawling:
The schematic a gave you, doesn't have a lot of "Q" but at least, in my testing, there were no spikes or clipping sounds comming out of the sub woofer.
Be interested in your findings.
Had time to check out the regulator circuit yet? |
|
|
| Nordic |
Yeha, speaking from memory I think that would be an accurate description....
Sorry for not giving feedback about the prereg project.... I completed another amp that was open to make the it possible to get the amp the buffer has to go into on my desk. - all done and playing now. I feel like a proud daddy.
I just have to beat the lazyness today and finish those buffers then I can test the prereg after some rearangeing of internal components. |
|
|
| Nordic |
| ok, it works, still haveing some problems with the stupid buffer pcb, but the channel that works is dead quiet. |
|
|
| Nordic |
| Ok got everything operating together now... under load the heatsinks DO get warm, especialy the transistor on the negative side... but not so that you cant keep your finger on the sinks... |
|
|
| davidlzimmer |
Way to go!
Guess I'll download Eagle so I can look over your schematics. Let me know if you make any changes. I'll probably wait until I make a larger order to get the parts. I hate to pay more for shipping than for the item! :D
Thanks for sharing the info!:) |
|
|
|
