Hi Everyone,
I was the lucky winner of the most interesting amp enclosure contest. I most graciously received the 3886 amp in the mail a couple weeks back and am ready to finish up this project - I am working it into a self-contained live rig.
I've built several SS amps before, but always used a thrifted DC power supply of one sort or another. I have no idea about making a power supply.
Honestly, I've been looking at chipamp.com and I am a little confused about which amp I even have. I believe it is the 3886 mono kit - though I think the PCB is different than what he shows there as it looks like on mine the power supply is included on the board (other than transformer), and on the site it shows them being seperate boards. There is no pic of just the 3886 mono kit though, and the PDF manual for building is confusing to me, again because the boards shown there all look different from mine.
SO all that out of the way - my questions:
1. How do I know what to look for in a transformer? As mentioned before, I have never built an AC->DC power supply and don't really know much about transformers in general. I read the choosing a transformer section of the PDF manual and it was largely greek to me...
2. If I found a suitable DC power supply, could I just use that and connect it into the power inputs on the board?
3. If this is possible and I were to look for a pre-made DC supply, could it be single rail, and what type of voltage and amperage output ratings would I be looking for? I have a knack for finding things at thrift stores. Also, if so which connections would go where AC1, AC2, gnd...?
FYI, my hope is for it to be "as loud as possible" so that is what I have in mind when looking for the above components.
Thanks
Hi,
The supply voltage would depend on the speaker load. Less voltage for lower speaker impedance to keep the max current down (and heat dissipation).
You'll need a split supply (+/-) - easily as much as +/-28VDC for 4 ohms and up to +/-38VDC for 8 ohms.
Here's a handy design calculator for these chipamps: http://www.national.com/vcm/national3/en_US/products/audio/files/Overture_Design_Guide15.xls
Works with Excel.
You won't find that board (or a manual for it specifically) on chipamp.com. It is essentially a mono LM3886, but it includes the PSU onboard. Here is the build thread for it: http://www.ssguitar.com/index.php?topic=1255.msg7766#msg7766
It shows how to hook it up properly. I had problems as well, it's an odd beast but works amazingly well. I hope Brian eventually starts selling them and makes a manual for that kit.
As for transformer ratings. For full power you will want a 22v+22v transformer rated 160VA or higher. I used a 330VA because I was planning on using another LM3886 eventually.
Ok thanks both of you for your responses. Haha, I had no idea that it was not a commercially available board. No wonder I was so confused about it.
I have access to a decent electronics surplus store, so I may be able to get the transformer I need. I don't think I will be able to dig up a bipolar DC supply at that high of a voltage, or at least I haven't seen one so far.
So I am sorry because I am really ignorant when it comes to transformers.
If you could give me as much detail about the type I should be looking for - I am a little confused, for example about what 22v+22v means? Is that for the output of the transformer? Would that be two outputs that are out of phase with eachother?
Or if you could point me to a commercially available transformer that meets the necessary specs, so that I can look them over and compare them to one I can buy locally?
Thanks so much again.
No worries. I can explain a bit better.
You don't need (nor could you use easily) a bipolar DC supply. The board handles that already. All you need is a transformer with dual outputs, 22v on each.
Here is a great example: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=122-615
The LM3886 puts out:
68w at 4ohms with +/-28v
38w at 8ohms with +/-28v
50w at 8ohms with +/-35v
When you rectify AC to DC you multiply it by 1.4. So for 4 ohms to get max power you only need a 20+20 transformer. For 8 ohms to get the max you would need a 25+25 transformer (I can't find these smaller than 250va, much larger than you need but won't hurt anything other than your wallet if you go that way). These specs are all for being on the bleeding edge of peak performance. 22+22 will get you most of the way there and is cheaper and available in a 160va size so I normally recommend that.
Please ask questions if you have them and I'd be more than glad to help.
This would be good for your amp if using 4 ohm speaker: http://www.antekinc.com/details.php?p=40
22-0-22 and 100VA
If using an 8 ohm speaker: http://www.antekinc.com/details.php?p=41
25-0-25, 100VA
Sorry for my absence/lag in response... I am getting back to this project.
So there has been links to transformers in this thread that are rated 160VA and 100VA. What does that rating mean?
At 100VA, will I not be able to get the full potential output of the chip?
Thanks again for your patience.
in a nutshell, the 100VA one is fine for a single 3886; the 160VA one handles two of them.
even if you'll use only one chipamp, often the price difference is small, and the larger one will always run cooler
I would go with the 25-0-25 100VA one that JP linked to. For $18 you can't beat it and you would get full output from your chip. At full bore it would be maxed out, but trust me, you will rarely if ever be full bore on it assuming you have a decent speaker hooked up - it is LOUD!
Quote from: joecool85 on June 01, 2011, 09:10:30 AM
I would go with the 25-0-25 100VA one that JP linked to. For $18 you can't beat it and you would get full output from your chip. At full bore it would be maxed out, but trust me, you will rarely if ever be full bore on it assuming you have a decent speaker hooked up - it is LOUD!
I ordered that one last night. I hope it is loud.
I am planning to use the amp for my portable pa system for my live setup. Currently I am using a 30W rat shack PA head from the 70's and it is not cutting it.
QuoteI am planning to use the amp for my portable pa system for my live setup.
I feel cheated. :grr
Why do you say so only now, after the fact?
50W is LOUD for any guitar, *moderately* loud for bass and maybe not enough for PA.
You will need *two* 3886 power amps, each driving at least a 12" efficient guitar type speaker plus 2 or 3 Piezos for highs in *each* enclosure.
If your 30W PA does not cut it at all, a 50W one won't be that much louder, now talking 100W plus two cabinets is closer to real-world needs.
There's not such a thing as too much PA power.
Quote from: J M Fahey on June 01, 2011, 11:04:39 PM
I feel cheated. :grr
Why do you say so only now, after the fact?
50W is LOUD for any guitar, *moderately* loud for bass and maybe not enough for PA.
You will need *two* 3886 power amps, each driving at least a 12" efficient guitar type speaker plus 2 or 3 Piezos for highs in *each* enclosure.
If your 30W PA does not cut it at all, a 50W one won't be that much louder, now talking 100W plus two cabinets is closer to real-world needs.
There's not such a thing as too much PA power.
I agree. 50w is more than enough for most guitar needs given an efficient speaker is hooked up to it. However, PA is totally different. I'd actually recommend 150-200w for a PA along with what Juan suggest for a cab (2 x 12" speakers plus some piezos).
Maybe I should clarify.
I have been using this radio shack 30W PA head (which I am sure is less efficient than a modern design) driving a couple of home made cabinets with dept store announcement speakers and car audio speakers (all thrifted) for about 1 year for live shows. It works, but it gets distorted at the levels I use it. I don't play super loud.
By PA I mean that I mix a couple of synths, a guitar, and a seldom used mic into one amp.
I'm going to see how this amp works. I can always add more in some way or another. Maybe I can use it alongside my rat shack PA.
This isn't to mix drums, amps and a full band of mics through. Maybe think of it more like a "keyboard amp."
Ok, now I understand you.
Rather than a regular PA, you are talking about a multi-instrument amp.
That's an easier task.
The main problem is, do you play with or without a rummer?
If without, you can barely make it, considering your amp serves 4 instruments, meaning you'll have 12W at most for each of them.(4x12=48)
If "with", he alone sets a certain volume standard or level you won't be able to match.
Simple Physics.
Quote from: J M Fahey on June 02, 2011, 09:48:58 PM
Ok, now I understand you.
Rather than a regular PA, you are talking about a multi-instrument amp.
That's an easier task.
The main problem is, do you play with or without a rummer?
If without, you can barely make it, considering your amp serves 4 instruments, meaning you'll have 12W at most for each of them.(4x12=48)
If "with", he alone sets a certain volume standard or level you won't be able to match.
Simple Physics.
No drummer.
At any one time, I usually have two instruments going at the most. One is a synth with a sequencer and several voices, so it is a little hard to say really how many instruments are playing at any one time... I have been thinking of splitting off my guitar to it's own amp at a miminum in addition to the "PA." I used to do it that way for a while, but then started using FX on a whole submix which includes my guitar.
From what you say, may I guess you don't have a Bass player either? (that part being played by a Synth?)
In that case the "PA" amp would carry only 2 Keyboards (one of them sequenced, as a background track) plus a single mic.
Well, that lightens the load a bit.
Sending the guitar to its own amp, even a 15W one, will help anyway.
Pity you told us so late, or we would have suggested the 160VA transformer instead, which would have allowed the future addition of another 3886 driving an extra box.
That would *sure* increase clean headroom.
Sounds like you might be ok. Especially if you decide to utilize both the new amp and the old Radio Shack one. Let us know how it works out.
Quote from: J M Fahey on June 03, 2011, 03:15:56 AM
From what you say, may I guess you don't have a Bass player either? (that part being played by a Synth?)
In that case the "PA" amp would carry only 2 Keyboards (one of them sequenced, as a background track) plus a single mic.
Well, that lightens the load a bit.
Sending the guitar to its own amp, even a 15W one, will help anyway.
Pity you told us so late, or we would have suggested the 160VA transformer instead, which would have allowed the future addition of another 3886 driving an extra box.
That would *sure* increase clean headroom.
My setup is not exactly "normal." It's not really rock music at all. My setup is nord micromodular with trigger-able sequences/sounds stored in it, guitar w/some FX, guitar to midi converter into a synth, home made synth/sequencer thing, home made sampler, banjo, microphone.
Usually the nord plays "backing" sequences and I play guitar or banjo parts on top, whistle, and guitar->midi into old yamaha FM synth for some other sounds, and then the other stuff for between song transitions. There's some bassy sounds in there and occasional synth percussion parts, but it's not a standard drums/bass/guitar kind of thing. More melodically based.
I have my home made TDA2005 based 2 output channel space-heater amp (which landed me this 3886 kit when I won the contest way back a couple months ago). I could start putting my guitar through that again, and keep the 3886 for the synths stuff. My main concern is keeping equipment hauling from getting totally out of hand.
This is kinda what this whole mess looks like at the moment:
http://www.youtube.com/watch?v=g2WVlSKIbLg
Well, if it's a kind of one-man-band, no drums, no real bass, then you can plug everything into that single multi-amp.
In this very particular case you don't benefit that much from putting that guitar through an external amp , specially since half of the time it's not "a guitar" but "a synth".
Pity you didn't state all this at the beginning.
It's as if I asked for dessert and cakes recipes at a cooking Forum, I received many sent by members with their best intentions , and after some time I stated : " thanks .... but I'm diabetic .... ".
Here's the thing: I already have the amp kit. Asking for a transformer to power it was not misleading at all. I am going to start by just building it regardless (not planning on building a double 3886 at the moment). So I am happy for the info provided so far 8) Also there is a 100 watt PA head/mixer sitting at my favorite mom and pop music store for $60, so there is a limit I am willing to spend on transformers and amp kits to make it myself.
Moving on...
My transformer arrived at my door today. I am going to check out the wiring to get it up and running. This is where I am going to need some help - I looked at RG's post in the thread linked by joecool in the beginning of this thread, but the description is a bit confusing to me because it refers to everything by terms I don't yet know, ie: "You can connect two identical secondaries into one centertapped secondary."
There's two sets of blue wires, two sets of green (two pairs outputs according to the label), and two sets of red, and two sets of black (inputs according to the label).
I've got this thing about death (not really my thing) so I want to make sure I understand how to wire it correctly even at the risk of appearing completely dense.
That's 8 wires that all have to go somewhere. Is there a diagram somewhere for what to do with these 8 wires?
OK... going to prod this one on a little bit with some pics.
After looking at the power supply diagram from that other thread, I wired up the secondaries (?) to the board in what I think is the right configuration.
(http://oi52.tinypic.com/28740nl.jpg)
PS diagram:
(http://www.chipamp.com/images/ps.gif)
Got a box to put it in, still need to pick up a heat sink tomorrow.
(http://oi54.tinypic.com/n6vwrc.jpg)
So the wall AC part, I am still a little stumped about. Four connections on my transformer, two in the diagram. Do I tie something together? Leave two of them unconnected?
Not wanting to die, set my house on fire, or kill a $20 transformer, I have not touched them yet. Also there should probably be a fuse wired in there somewhere as well I assume.
Edit: Actually, looking at that diagram again, I notice those two connections crossed to opposite coils. So I am assuming this means I tie something together... but still not sure how. Do I tie the black from one coil to the red from the other, on both sets?
Hi toptop,
It looks like you have dropped the extra diodes as per advice on the other thread?
In which case I have a hunch it won't work.
That PSU is insane and is overkill in the extreme and only serves to confuse a hobby person with little understanding of what is needed.
Yes the complex PSU design makes sense if the PSU was for a 400 Watt Monster Bass Amp
but for a 40 watt chip amp? *Then NO*.
The LM3886 chip is worlds away from serious hi-end power amps but just perfect for what you need.
Just Go find a simple split supply and build that instead.
You need a Transformer that has clearly marked windings printed on it,, or data for such.
Two mains wires for primary input.
3 wires for secondary,,called 50VAC CT (Or 25-0-25VAC)
VA rating is not super critical (again unless you want full power at 10hZ you won't hear
anymore watts at guitar freq that will make the extra expense worthwhile.
If you can't fully understand the PSU board I'd stop now.
Go work out some PSU basics and learn to understand them before you embark on the harder ones.
It is perfectly feasible to rewire the Board you have to work as a simple supply BUT as it's
a double sided affair it could turn out to be more trouble than it's worth. :loco
One more thing,, The Case is PLASTIC!! Bad move chum :trouble Try a Steel case instead.
I'm all for making things cheap but not that cheap.
The steel case becomes the ground plane which helps to reduce unwanted hums and buzzes.
The CT of your PSU secondary is often tied to a grounded metal chassis and the EARTH wire
from the *Primary Mains plug* is/Should be well connected to same via a bolt on the chassis in case
of a major meltdown/failure the short runs to ground Not Through YOU 0:)
Remember your guitar has steel strings and is connected to the electrical circuit so if something
goes really wrong the *Grounded metal Case* will help to save you from getting the full jolt back to ground.
It may just save your life. winky. 0:) 0:) 8|
Go learn first; http://sound.westhost.com/project27b.htm
halfway down that page is *Figure 3* That is all you would ever need for the Amp you wish to build.
Without knowing the voltages on your transformer and as no voltages are given on the schematic
it's near impossible to help you.
Phil.
ok... need to step back a second here.
The board was assembled by JoeCool and was tested by him as well to be working (hope he can jump in here and throw down a word about how he connected it).
My problem is that I do not know how to hook up a power transformer to it. It was my impression that all I needed was a power transformer.
Several people have suggested the power transformer I have bought (see earlier posts in this thread), so I am wondering why that is the case if it will not work.
Thanks for the tip about the chasis. I may install large metal plates inside of it to act as a ground plane.
The board does work the way it is and does only need a transformer, not sure why anyone would think otherwise. I know it works because I played my guitar through it for a few hours before sending it out.
I used a 18 - 0 - 18 transformer and it worked fine. A center tapped transformer will have 3 output wires and two input wires. The two input wires go to the ac line as expected. 2 of the output wires will be "hot" and one will be center tapped. Put one hot one on AC1, one of AC2 and the center tap on the ground. Done.
Not sure about your transformer since it has all these extra leads.
That said, there is NO REASON to build a PSU for this amp when this works just fine the way it is.
Ok, you did wire it wrong, but it's no big deal. 8)
Your transformer is different because it is a toroidal and setup to take 110 or 220 on the primary - this gives you "extra" wires.
Here is the spec sheet for your transformer: http://www.antekinc.com/pdf/AN-1225.pdf
**edit**
Ok, you will need to connect the two black wires together and the two red wires together. This is how you hook it up to 110v primary. Connect the red and black to neutral and hot on your mains voltage. Make sure you connect your chassis to ground for safety reasons. Also connect your board's ground to chassis ground, same reason.
For the secondaries you will want to connect a blue and a green together - this will be your center tap and you will connect this to ground on the board. Then connect the remaining blue to AC1 and the remaining green to AC2 (or vice versa, doesn't matter since it's still AC at this point). That should do it for you. :tu:
The other option would be to have me send you some more MUR860 diodes so you can have all 8 in there and then wire in all four of the secondary wires to the board. Either way will work but this last way is overkill and more of a pain in the butt.
So let me make sure I have this correct -- few questions:
1. the "AC1" & "AC2" with the line over them on the board stay unconnected? (the ones that currently have the green wires going to them)
2. I would want to take a blue and a green from separate secondaries (one from output 1 and one from output 2) to connect together, right? I assume so otherwise I am shorting the transformer, if I understand correctly. And they connect to that middle "GND" connection on the PSU side of the board?
3. The grounds can all go to the same chassis ground connection? (ie: Mains ground (prong 3 on 3 prong power plug), AC secondary ground (the green and blue tied together) and DC/audio/speaker ground)? Will it be the same for when I add a small preamp/mixer running at a lower DC voltage? (tapped/stepped down with a regulator off the DC voltage going to the amp chip)
I think that's all for now, I am sure I will have more questions later.
1. As depicted in your picture, you need to remove the top left blue wire and the bottom right green wire.
2. Correct you want to take a blue and a green from separate secondaries to connect. Tie these two together and put those in the ground hole (labeled GND in the middle of the board).
I should have said that before :P You should also have a fuse on the primary/mains voltage hot line. This would blow if you accidentally shorted the secondaries.
3. Grounds all to the same location regardless of voltage or function, this is called star grounding and I recommend it.
Glad you ask a lot of questions or you might have smoked your transformer if you connected the blue and green from the same section of the secondaries...not so much dangerous, but frustrating. Always best to ask for clarification ;)
Arrh tiss all good, it sounds like you have it sorted, wink.
@Joecool, Sorry if I come across as a cranky old sod but If these boards
had a simple straight forward supply setup the maker would likely sell many more units
because the most likely customer would be the home hobby builder who (more often than not)
is not up to speed on complex PSU design.
As has happened here,, Without your help toptop would be stuck with nowhere to turn. :'(
My guess is you could fit the whole thing on a SS board if you used a simple PSU.
I'd bet he would double his sales in a month,, 8).
Another point,
Unless I'm wrong the board layout has a common ground rail but is drawn on the schematic
as two separate rails. Again more confusion.
The owner would wise to correct that slight oversight as it would make life easier
for the end user.
Of course *Not having the board in front of me* I can't be certain but the Filter caps
seem like they all attach to a common ground rail.
See my schematic suggestions.
One could argue that a schematic does not have to represent the board layout exactly
but given such a simple circuit it is not hard to draw it as it is connected on the board.
Cheers, Phil.
Phil, no problem. And I think you are right about the common ground rail on this board. That schematic was from his other PSU boards which are similar but much larger in physical size. Actually, the PSU boards he normally uses are twice the size of this entire PCB I sent to TopTop!
As far as sales go, he doesn't sell this board, it was a prototype. This is what he sells: http://chipamp.com/lm3886.shtml
Ok got all this so far.
I am on the fuse now. the 3 prong power cord that I am using has black white and green wires. I know the green is ground (it goes to the center ground prong). I looked up online and it says black is usually hot and white is neutral. Does that mean I should hook the black wire from my plug to the fuse terminal?
And then from the fuse to the input of the transformer - do I hook the black or red wires to it? Or perhaps it doesn't really matter because ultimately it is just rectified to DC anyway?
EDIT: did a little research and found info that says you should connect hot to the fuse... so I did.
The main question then is from there into the transformer - does it matter if the "hot" from the wall goes to the red or black wires into the transformer? I would think the only difference will be that the AC is 180° out of phase one way vs the other, but shouldn't matter if it is being made into DC anyway, right?
Here I go again,,, whinger me! >:(
This one bugs me because in the old days it was RED=Hot, Black=Neg and Green was EARTH.
Really simple and really obvious but these days it's seems anything goes.
It would be great if the international bodies got together and made up there mind and settled on a standard.
In Australia it's now Brown for Hot Blue for Neg and green/yellow stripe for earth
but some OS gear comes with black and white power cords %^&*
Re fuse;
Normally the fuse is on the HOT wire as this is the one the wall switch disconnects when switched off (most power point switches only switch the HOT)
but in the case of a power cord wired out of phase then it makes little diff. (can get confusing ay?)
In all the books I've read the power cord runs,, Hot to Fuse > then to main switch of Amp > then to transformer.
That makes perfect sense to me but I've seen some kit builds showing the switch before Fuse,,, go figure??
I do like the IEC power connectors that have the input cord connector/fuse/powerswitch all in one unit.
The fuse can only be removed after the power cord is removed,, very clever and very safe.
You are correct in thinking the mains input phase is of no concern BUT in your case
the dual primaries should be wired *IN Phase*
i.e. The two reds tied and then the two blacks tied,,,(though I would double check the specs).
A simple single primary would of course be so much easier to wire up,, winky.
Phil
Phil's got it right. Connect the black wire to the fuse, then that fused lead to the power switch. Connect the switch from the wire as well as the white neutral from the power cord to your red and black on the transformer. Doesn't matter which goes to red or black. In fact, a lot of times on the primaries it will be just two wires, both the same color - that's how much it doesn't matter. I think they only did colors due to the 4 wire setup that allows this to be wired for 110v or 220v input.
Ok, so far so good. Why they excluded the color red for hot is beyond me.
Is there any major safety concern that I am not thinking of for not having a power switch? My rig is all in a rack/shelf thing with a main power switch anyway, so I was actually just going to exclude it to have one less place where 120V AC needs to be exposed/soldered.
Also, how do you know what the calculation of the fuse rating should be? I bought a holder and a fuse, but I think the fuse I got is rated extremely high.
Quote from: Top Top on June 10, 2011, 12:04:15 PM
Ok, so far so good. Why they excluded the color red for hot is beyond me.
Is there any major safety concern that I am not thinking of for not having a power switch? My rig is all in a rack/shelf thing with a main power switch anyway, so I was actually just going to exclude it to have one less place where 120V AC needs to be exposed/soldered.
Also, how do you know what the calculation of the fuse rating should be? I bought a holder and a fuse, but I think the fuse I got is rated extremely high.
2 amp slow blow fuse would be ideal. I always figure go 1.5 times what the amp can put out in power.
LM3886 puts out a max of 120w PEAK. 120w/110v means it would draw peak 1.09 amps. However, due to thermal inefficiencies etc I multiply by 1.5 to make sure it won't blow. This puts you at 1.6, round up to the next available fuse size and you're at 2 amp. I recommended a slow blow fuse because that's what Brian at chipamp normally recommends, but to tell you the truth, I'm sure a regular 2 amp fuse is fine.
Safety wise no reason to not include a power switch. I like having one because it's handy, but thats up to you entirely.
**Also, I didn't mean to edit your post TopTop, hit the button by accident lol.
Try to fit a power switch anyway, so if necessary you can turn it off independently of the rest of the racked devices.
The power fuse is not there to "protect" your amp from harm, (they are too slow for that) but to avoid the damage spreading too much and specially to prevent it catching fire and burning your house down, loss of life, etc., and I'm not kidding or exagerating.
That said, you need a fuse that's *somewhat* larger than the maximum "normal" power consumption, so it neither blows needlessly (and annoyingly) at turn-on, nor "never" blows letting your transformer melt or catch fire.
SS amps need around 50% more than rated power output, so a 100W amp needs around 150W, divide that by wall voltage to get Amperes.
150/120=1.25A ; next higher value is 1.5 or 1.6A .
2 A might be used if the only available, but not higher or it may not do its job.
OOPS !!! Looks like we simulposted !! 0:)
Juan is right. You don't want to have the amp burn your house down, or worse. A regular 2 amp fuse should do nicely. Just watch and listen very closely when you turn the power on. When I fixed my old amp, The first few times I used it, I mostly watched for any signs of smoke or odd smells. Sometimes you'll be able to tell if something's going wrong, and if you're lucky, you may get to kill the power before it kills your amp, or you. I came close to killing an amp once, the speaker wire had shorted out, and it got really hot, then it shut down. I'm not sure what saved it, but it still works. I got lucky, though, It's a peavey. I don't think Juan, or Joe will tell you the wrong thing. They seem to know what they're talking about. Their advice has helped me with a few things. I hope the amp works for you, and I hope what I've said helps you out.
Alright. Got heatsink and all ins and outs set up and first plug in!
It works, no smoke, no sparks, I am still alive!
Generally impressed at how little hiss/hum this amp puts off!
Now, I have no preamp yet and no input vol control, and just plugged a guitar straight in. I expected more volume, but I am assuming the input is looking for a much hotter signal than I am giving it.
Looking at the 3886 datasheet, I think I don't know the proper term to look for for the spec on what is the upper limit of input signal voltage before distortion.
I am thinking of tacking a simple mixer on the front of the amp -- probably the GGG mini mixer, which you can see the schem for here:
http://www.generalguitargadgets.com/diagrams/mixer_sc.gif?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
(sorry says not to post schem, so I am just linking)
Thinking I might have to up the gain on the last opamp stage in order to get the most volume out of the amp. Maybe just replace that 100K feedback resistor with a pot for a master vol control?
Yes.
As shown, that mini mixer has no gain (or rather, gain=1).
You can replace either R9 or R13 with an Audio (Logarithmic) 1M pot, which becomes a gain control.
Or you can build a TubeScreamer clone (I guess GGG has a board and layout ) and use it as a preamp, if you add a small switch in series with the clipping diodes, so it can be either a distortion pedal or a clean preamp.
This project will be of the same complexity as the mini mixer but far more useful to you, not to mention it will sound better.
Quote from: J M Fahey on June 14, 2011, 04:51:58 AM
Yes.
As shown, that mini mixer has no gain (or rather, gain=1).
You can replace either R9 or R13 with an Audio (Logarithmic) 1M pot, which becomes a gain control.
Or you can build a TubeScreamer clone (I guess GGG has a board and layout ) and use it as a preamp, if you add a small switch in series with the clipping diodes, so it can be either a distortion pedal or a clean preamp.
This project will be of the same complexity as the mini mixer but far more useful to you, not to mention it will sound better.
This isn't strictly a guitar amp and having a mixer built in would be handy for handling the multiple sources I would be plugging into it, which is why I was going for the mixer idea. I recall from the past that the mini mixer is unity.
I'll probably go with a gain pot on the mixer as built in distortion is not what I am looking for.
If I recall correctly it wants something like +/-2v. I remember that my LM3886 (same circuit as this but different PCB) was pretty quiet without the preamp and then when I hooked it up to my K-20X lineout it just about blew my head off because I had the volume pretty high and wasn't expecting much. I also had it hooked up to a fairly efficient 10" Dean Markley cab and as we all know, the more efficient the speaker - the louder the amp!
Hi Top top, Not sure where to direct you but the mixer is going to be a potetial problem.
It will work with powered units (i.e. a drum machine or synth as these have onboard preamps already built in)
BUT the 10k pots on the inputs will just kill any guitar plugged in direct.
Quite honestly a small 4 or 6 input mixer can be picked up cheap and that would save a big headache trying to build a mixer that will give good results.
Hint! if you are not up to speed on electronics,,, stay well away from mixers .
Phil.
Quote from: phatt on June 15, 2011, 08:33:52 AM
Hi Top top, Not sure where to direct you but the mixer is going to be a potetial problem.
It will work with powered units (i.e. a drum machine or synth as these have onboard preamps already built in)
BUT the 10k pots on the inputs will just kill any guitar plugged in direct.
Quite honestly a small 4 or 6 input mixer can be picked up cheap and that would save a big headache trying to build a mixer that will give good results.
Hint! if you are not up to speed on electronics,,, stay well away from mixers .
Phil.
I'm actually fine with regular audio electronics. It is the power supply/120V AC stuff that is new to me (and much more dangerous hence all the questions). I've built several mixers before and a lot of other audio circuits, even designed some basic audio and synth circuits.
I will not likely be plugging a guitar straight into this amp/mixer, though I do have a mixer design that combines basic JFET pre-amps with the mini mixer I linked there (and 100K pots). I could throw one of those on one of the input channels, but I do not have a huge front panel, so I can't have too many pots.
Any proper mic/guitar pre-amping will probably be done outside of the amp (right now my guitar runs through a rangemaster clone before my current amp).
Finished it!
(http://oi51.tinypic.com/292rvxj.jpg)
It has a two input op-amp based mixer with a gain control on one of the op amp stages as mentioned earlier... I put an LM317 on the mixer board and regulated the DC off the amp board down to 15V for the mixer.
Works well, minimal buzz. It even sounds decent with a guitar plugged straight in, though that is definitely not the aim here.
I had thought about doing more than 2 inputs, but I was running out of room as the enclosure is pretty tight with the transformer, amp board, and mixer in there now. 2 inputs is actually fine and is what is on the amp that I currently use.
The enclosure is plastic, yes, but the bottom is lined with a metal mesh which acts as a ground plane.
I haven't been able to turn it up all the way yet (it's the middle of the night), but it definitely gets much much louder with the mixer.
Thanks everyone for being patient with my questions.
Looks good. Is that a power button all the way to the right? If so, does it turn or push in?
Oh, no, it's a power indicator lamp. (LED off the regulated 15V)
Nice. Congratulations.
Any gut shots?
Quote from: Top Top on June 22, 2011, 04:21:24 PM
Oh, no, it's a power indicator lamp. (LED off the regulated 15V)
Ah, good idea. Not sure I've seen one quite like it before.
The yellow lamp lens I got from an electronics surplus store. I have no idea what it's really supposed to be, but it works well as a lamp lens.
Behind it I just have a normal yellow LED to light it up.
Quote from: J M Fahey on June 23, 2011, 07:38:46 AM
Nice. Congratulations.
Any gut shots?
Sorry, missed your post somehow.
Should have snapped one before closing it up. I'm sure I'll find some reason to open it up again and take one then... Pretty much looks like the pics I posted before but with more wires running around and a small perf board with the mixer op-amp on it.
Nice looking amp, Top Top. :tu: