Howdy! I'm new here, and found the forum while researching an idea for a bigger portable amp. I have been an electronics tech for a grass roots company for the last 14 years, and I've been fixing pedals and amplifiers for a few of my musicain friends for what seems like forever...
There's a group of guys that I've hung out with for years that have been bitten by the cigar box guitar bug. They have built several 2, 3, and 4 string CBG's that sound awesome! They commonly play in the smoking area at work, which doesn't have access to power. Several have bought small 9V powered mini amps, but most of them have horrible tone and very small output. I built a couple of Noisy Crickets that were converted to cigar box amps, but the tone of those amps is horrible and not what anyone considers usefull. I built a MKII with the bridged LM386 chips and it was a flop with the group as well.
My goal has been to design and build a small portable amp that's battery powered and has clean headroom with enough volume that they can play for at least an hour without recharge. I'd like to add in a SLA battery with a charging circuit that would allow the amp to be played off of the charging circuit without loss from the battery, yet keep the battery charged and ready for any excursion. The ability to charge the battery from a cigarette lighter in a car would also be very usefull.
The enclosure would be similar to a 10" x 10" x 5" cigar box built from 1/4" western red cedar, and I'd like to have the option of using 5", 6", or 8" speakers.
I've been paging through the portable amplifiers that grace the pages here, and I'm sure there's a chip amp that will be perfect for this, but I'd like to get a few opinions on what would be the better route for this set up. I have a umble preamp that I built as a pedal that I'd like to use for the preamp section on this, but it's not a design requirement.
Anyways, nice to meet everyone, and I'm interested in any ideas that may come up.
Thanks,
Baja
Hello there, welcome to the forum!
The whole cigar box guitar thing is just amazing! I never heard of this kind of diy guitars and it's very interesting! When I got some time I'll definitely go to my local flea market and look for a nice cigar box to do one myself! :D
By the way, maybe I got something for you: I got a Marshall M2-S which is a mini Marshall amp, powered by a 9 volt battery, with clean and distorted channel, and that thing ROCKS! It's very small, but powerful, and when the battery is at the end of its life, the distortion channel degenerates to a very cool fuzz tone!
I was going to tell you that there's no schematic of it, but I just found it!
http://guitar-dreamer.blogspot.it/2010/06/modding-marshall-ms-4ms-2-micro.html
This guy talks about a little mod he has made to its mini marshall, and was kind enough to add the whole schematic of the mini amp too! Hope you'll like it ;)
edit: just found out this topic on the forum: http://www.ssguitar.com/index.php?topic=1596.0 with schematic, give it a look because there is an alternate version of that amp with a different op amp, the original op amp used in it is very hard to find
The big problem in such amps is the battery itself.
6 to 9 V, no matter what they say, is not loud enough.
Chips designed for such low voltages are meant for radios or cassette players or portable Nintendo/GameBoy/PSP, etc.
Now if you get 12V, whether Lithium/Lead Gel/NiMh/etc. the horizon opens immensely because we enter Car Amp territory.
You can easily get from 4W RMS to almost 20W which is *loud*.
But usually it's not light, unless you invest in highest technology batteries.
Your choice.
PS: and LM386 is crummy, it's the *worst* 6 to 9V amplifier.
It's so popular only because it's *so* simple.
Welcome!
Acoustic bass guitar uses water jug and two strings
http://hackaday.com/2013/04/07/acoustic-bass-guitar-uses-water-jug-and-two-strings/#more-97413 (http://hackaday.com/2013/04/07/acoustic-bass-guitar-uses-water-jug-and-two-strings/#more-97413)
In a world populated by multi-thousand dollar guitars and amps I love this back-to-the-roots stuff. I built a few "hobo instruments" called monochords from garbage scrounge, tin can, lump of wood, bit of wire, even a giant bass one, and even had one of them used on stage too - kind of slide-banjo-dobro sound.
As I'm sure you are aware running or recharging from a suitable wall wart wouldn't be a problem, but recharging batteries like SLA's from a car system can be a bit of a challenge because the voltages are so similar. Overall I think the electronics are the least of your problems, particularly as you are experienced in the art.
IMO the most serious limitation of small low powered amps is the speaker. I have often amazed people by hooking up some flea powered crud box to a big cab to demonstrate just how compromised "practice" class amps are by the small case and speaker, so I would consider an 8-inch unit absolutely the smallest speaker to consider, and a 10 would be much better, but really, the physics is against you in a small enclosure and you are never going to get good sound in a tiny cabinet.
You might be able to get away with a small driver if you can add something like fold out wings that form a bigger baffle or horn-like structure around it.
Running from batteries also means that speaker efficiency is very important and high dB/W is vital - the better the speaker is the less power you have to generate and store.
I've seen a small amp built using a car door speaker in the side of a plastic jerry can with a couple of 6 volt gel cells in the bottom, and being enclosed sounded fairly reasonable (but I'm sure could be improved). Very easy to carry.
I hope you will keep us posted on your progress. :dbtu:
Thanks guys, I'm tickled that I found a forum like this!
That mini marshall is cool, and it one of the ones they play out there alot, along with the mini Orange. They just don't make enough noise is the big problem, but they have tones of cool tones.
I'm thinking more of something in the 10 - 20 watt range that runs a 6" or an 8", with a umble tone control and a clean boost circuit for those days that ya just gotta be clean and loud. It's also got to be able to handle a pedal if they need it. I spent a bunch of hours last night going over some of the chip amps availible, and there's a ton that will run on 12V. I really don't want to build a differential supply if I don't have to, but I'm not afraid of it either. Anyone got a preference or a suggestion?
Baja
10 AA NiMh batteries will give you *very good* 12V , and 2700mAH (2.7 AH) at very low weight and reasonable price.
There are more modern options (Lithium, LiPo, etc.) being discussed in other Forums but they run U$ 100/125 a pack, *plus* have very expensive shipping, on safety concerns.
A plane was almost brought down when one of those exploded and a cargo compartment caught fire, and it already happened quite a few times, so .... getting a pack f them would border U$200 , I think it's too much.
If you can carry more weight, a gelled lead 12V 4.5AH costs around U$20/25 .
This battery thing has been discussed in:
http://www.ssguitar.com/index.php?topic=2780.msg20357#msg20357
FWIW you'll see there my biamplified 30W "Callejero", run from a 12V 7AH "Alarm" type battery.
I read that thread, your amps are very nice! Are you running the tweetr and 10 on separate controls? It's an interesting concept, and very close indeed to what I'm looking for in this design.
I'm looking at both of those chips now, thanks for the leg up!
Baja
:cheesy: Thanks.
Yes, I had to add a separate (unabelled) volume control for the TDA2003 teweter amplifier, because it was louder than the 10".
Since I was using an active crossover, it was easier than adding the typical L-Pad .
And in a huge, cavernous hall (many of my customers play at Tube Stations), you just put it on 10 and cut through the noise.
Incoming/outgoing trains are *very* noisy, plus all the door hissing (compressed air), etc., you need every dB possible to fight that.
Twenty watts! Holy Himmel. How big a venue/crowd are you serving here? Do these guys work in a barbed wire factory that runs during lunch time? Lot's of guys here play clubs and pubs, noisy venues, with 15 watt amps and they are plenty loud enough.
Loudspeaker parameters and loudness
http://www.ssguitar.com/index.php?topic=707.msg4933#msg4933 (http://www.ssguitar.com/index.php?topic=707.msg4933#msg4933)
And...
| Speaker sens. (1dB/W@1m) | Required power (watts) |
| 104db | 1 |
| 101db | 2 |
| 98db | 3 |
| 95db | 6 |
| 92db | 12 |
| 89db | 24 |
| 86db | 48 |
| 83db | 96 |
| 80db | 191 |
| 77db | 382 |
Listener range 8 feet, desired listener SPL 80dB, amp headroom 15dB
Quote from: Roly on April 10, 2013, 10:18:11 AM
Twenty watts! Holy Himmel. How big a venue/crowd are you serving here? Do these guys work in a barbed wire factory that runs during lunch time? Lot's of guys here play clubs and pubs, noisy venues, with 15 watt amps and they are plenty loud enough.
Loudspeaker parameters and loudness
http://www.ssguitar.com/index.php?topic=707.msg4933#msg4933 (http://www.ssguitar.com/index.php?topic=707.msg4933#msg4933)
And...
| Speaker sens. (1dB/W@1m) | Required power (watts) |
| 104db | 1 |
| 101db | 2 |
| 98db | 3 |
| 95db | 6 |
| 92db | 12 |
| 89db | 24 |
| 86db | 48 |
| 83db | 96 |
| 80db | 191 |
| 77db | 382 |
Listener range 8 feet, desired listener SPL 80dB, amp headroom 15dB
Great chart! I amp going to share this on the Watts vs Volume thread.
I look at it like the horsepower rating in your car. You don't NEED 400 horsepower to drive back and forth to work, but you'd be glad to have it if you take your car to the dragstrip :dbtu:
I always have a tendency to overbuild, not saying that I couldn't get the job done with something way smaller. Still, the idea of having a clean 20 Watts through a nice fat 8 in a portable amp that looks like a cigar box would rank right up there high on the cool scale :tu:
I looked through a few amplifier kits online the last few days to see if I could buy the building blocks cheap enough, rather than having to proto them. I'm looking seriously at a bridged TDA2050 or TDA2030 to get the job done, but i'm not sold until I've rocked one in the box to see if it's the right fit.
Baja
Quote from: joecool85Great chart! I amp going to share this on the Watts vs Volume thread.
Fine, but look around first
Joe, there are better.
@Bajaguy - my point, to continue your parallel, is that you need less (average) power if you don't drive around with the handbrake on. The difference between an 89dB/W speaker and a 98dB/W is the difference between the battery going flat before lunch is over, and going for hours with awesome SPL reserve - using the same battery and chip.
Quotebridged TDA2050 or TDA2030 to get the job done,
If you have only 12V, these are not a good choice, original TDA2003 (or 2005, which is 2 x 2003 in the same chip) or all other "car amps" are better.
Quote from: Roly on April 11, 2013, 12:57:02 AM
@Bajaguy - my point, to continue your parallel, is that you need less (average) power if you don't drive around with the handbrake on. The difference between an 89dB/W speaker and a 98dB/W is the difference between the battery going flat before lunch is over, and going for hours with awesome SPL reserve - using the same battery and chip.
I understand your point completely.
Baja
Quote from: J M Fahey on April 11, 2013, 02:45:16 AM
Quotebridged TDA2050 or TDA2030 to get the job done,
If you have only 12V, these are not a good choice, original TDA2003 (or 2005, which is 2 x 2003 in the same chip) or all other "car amps" are better.
You are completely right, sometimes I think that without dislexia I'd have no fun.... :duh
Thanks for the correction, those are the two chips I looked into.
Baja
So I decided to purse the TDA2005 chip in bridged mode, which should give me about 12 watts into an 8ohm load. I found this schematic (which is right out of the datasheet) that looks like it will work. It even has a nifty veroboard layout which should help with the prototyping:
(http://i210.photobucket.com/albums/bb79/TheJester357/tda2005schem_zps223a34c8.gif) (http://s210.photobucket.com/user/TheJester357/media/tda2005schem_zps223a34c8.gif.html)
I'm looking to pair it up with the umble schematic from runoffgrove. It should give me a great little preamp with good adjustability and I hope play well with the input impedance of the TDA2005.
(http://i210.photobucket.com/albums/bb79/TheJester357/umble_zps2b8c88a5.png) (http://s210.photobucket.com/user/TheJester357/media/umble_zps2b8c88a5.png.html)
I'm not seeing any giant issues, but I'm not a designer by trade. I figured I'd post up the two and see if the designers of the group had any comments before I started running it all together into a single schematic.
Thanks for looking!
Baja
Hey there, nice to see that you finally found something that could suit your needs :)
I'm kinda new to preamp designing, but I think that this setup should work; the things I'd do is to check that the preamp signal that goes into the final amp doesn't exceed the maximum input values of the TDA2005, and lay down the two sections on separate board so that you could plug them together later, just to rest assured that if they do not fit well together, like you are not happy with the way they sound together, you can easily separate them, and maybe reuse 'em; like, you could keep the preamp if you like it, and plug it on a more powerful final amp, for example. :)
Yea, the umble circuit is really cool, but the big question is do I run a LM7809 to bring the 12V down to 9VDC, or refigure all of the resistances so I don't feed the J201's more than they can handle? From the protoyping end, I'd be better off using the regulator in case I don't end up using the two togther, but I can't see leaving it that way in the end.
Baja
Run the Umble from 12V, it will work much better.
FWIWit would work even better with around +24V power, go figure.
JFETS don't like low voltages, such as 9V.
Only precaution would be to separate the Umble power from the TDA2005 (to avoid motorboating instability and such) with an rcrc filter, with, say, 2 220 ohms resistors and 2 470 to 1000uF x16V (or 25V) caps.
So you'll end with somewhat less than 12V, no problem.
But your proposed combination looks fine. :dbtu:
Now why do I look at that preamp with all those bloody trimpots and have a strange feeling of deja vu? :-\
Quote from: Roly on April 13, 2013, 02:12:43 PM
Now why do I look at that preamp with all those bloody trimpots and have a strange feeling of deja vu? :-\
Let me guess, something you've worked on?
Nah, something we've previously discussed here as a "design fail".
When I see every Drain load made adjustable between zero and 100k, accounting for the fact that this changes both the DC and AC conditions at the same time, then I suspect that the "designer" didn't actually know what he was doing. These will not only adjust the Drain voltages to half the supply, they will also change the gain of each stage.
Just now I have spotted that four inverting stages in a row run off a single power supply rail with no decoupling between stages having the same phase, a really basic error.
At the time I was moved to sketch out something;
(http://i1341.photobucket.com/albums/o743/Roly49/Solid%20State%20Guitar%20Amps/FETPreamp121003_zpsc44f4831.gif) (http://s1341.photobucket.com/user/Roly49/media/Solid%20State%20Guitar%20Amps/FETPreamp121003_zpsc44f4831.gif.html)
Look Ma, no trimpots at all!
Running the Umble from more than 9V should have no issues as JM says, but the power supply decoupling certainly needs to be fixed up.
Congratulations, GRoper !!
This is exactly how my own preamps are designed - and they run on +24V.
That's cool! I just have one question, do the fets have to be the MPF102 or can they be the J201?
Baja
You'll actually have to try them, there's a wide variation in FET parameters, even is same brand and model ones.
That's why poor designs need trimpots everywhere, by the way ;)
Well I got the schematic all rolled into Eagle this morning, and I thought I'd run it by everyone before I went any further. I stuck in the J201's hoping they will work in the circuit, but I'm going to run this on a protoboard before I PCB it anyways.
(http://i210.photobucket.com/albums/bb79/TheJester357/9070939e-c789-48de-bb72-bd7545935499_zpscda2fbc0.jpg) (http://s210.photobucket.com/user/TheJester357/media/9070939e-c789-48de-bb72-bd7545935499_zpscda2fbc0.jpg.html)
Anyone see anything I missed?
Baja
I'll have a guess, Maybe try Power feed at other end. :)
Phil.
Quote from: balabooCongratulations, GRoper !!
This is exactly how my own preamps are designed - and they run on +24V.
Original, but quite conventional. The idea was to create a gain module that has very high input impedance and low output impedance, and was hopefully tolerant of devices and spreads.
{I'm just trying to remember why the 10M's from Gate to +ve rail ... I'm sure I had a reason at the time but it just plumb evades me ATM}.
FET's generally have a fair bit of spread, but I've been using quite a few MPF102's lately and it hasn't been a problem (yet). I imagine J201's should work okay, but if you do need to tweek anything it should be the value of the Source resistor, not the Drain as in the Umble. As long as the Drain voltages wind up somewhere arounf half the supply it should be okay. Need more gain? Just replicate the stage again after the Master volume.
Quote from: phattMaybe try Power feed at other end.
Phil beat me to it.
Quote from: phatt on April 16, 2013, 03:12:42 AM
I'll have a guess, Maybe try Power feed at other end. :)
Phil.
Ok, I'm lost with this one....
On a good note, I found a source for the MPF102's :dbtu:
I'm going to finish up the schematic for the amplifier portion today and get my parts order squared up. I'd love to get this thing runing next week, the weather is starting to get nice out here and we've been having a ball playing outside lately.
@ Roly - Thanks so much for the help on the preamp! I've spent a few hours with the old elctronics book from college and the calculator out trying to figure it all out. I did have one question, is the third leg of the preamp gain pot ok just hanging in the breeze, or should it be attached to something?
Baja
Power feed: +12V, R1, C2, Collector of Q4, then otherwise how it's drawn. That way the power to the most sensitive stage (Q1 & Q2) gets the most power filtering.
What would you like to connect the free end to? You could try your wife/girlfriend but she might have a bit too much hum. If you really want to prevent electrons jumping off the end like Lemmings you could connect the free end to the pot wiper. 'course if you do that then some of them will be able to go around in a circle and might get dizzy and confused, so I guess it's a choice between some electrons freelancing or going around in circles - your call really. 8|
Ok, I suppose I walked right into that one. No lemmings around here, but I might be able to scare up a oppossum or something. The last time I attached something to the wife I ended up with another mouth to feed, so hanging in the breeze works well enough for me :duh
As fdor the power feed, I understand what your getting at now, and I'll correct it and repost the schematic tomorrow. Thanks again for the help and the laughs :lmao:
Baja
I finally had a few spare hours and got the preamp and amp tied together. I figured I'd throw the schematic up and see if anyone found holes in it before I took to breadboarding it.
(http://i210.photobucket.com/albums/bb79/TheJester357/jifamp_zpsc4e167e5.png) (http://s210.photobucket.com/user/TheJester357/media/jifamp_zpsc4e167e5.png.html)
The more I look at the preamp circuit, the happier I am with it :tu:
Baja
Yeah, well I'm thrilled to bits with it as well 8) , but the real points are A) does it actually WORK?, and B) what does it SOUND like? It doesn't matter if it looks wonderful on paper if it fails either of these tests.
So what I'm interested in hearing is A & B.
{um ... shouldn't the south end of the Zobel networks be grounded?}
Re Pwr Amp?
Not sure about this but my understanding is that the + input of those black blobs (opamps) should have a ground ref or bias voltage ref. Head scratch?
Or maybe I've missed something?
Phil.
Quote from: Roly on April 26, 2013, 09:58:05 PM
um ... shouldn't the south end of the Zobel networks be grounded?
Yep, cleaned up one too many line on the schematic. Thanks for the catch.
Quote from: phatt on April 26, 2013, 11:30:03 PM
Re Pwr Amp?
Not sure about this but my understanding is that the + input of those black blobs (opamps) should have a ground ref or bias voltage ref. Head scratch?
Or maybe I've missed something?
Phil.
Man, I'm not saying I don't have it wrong, but I took the front end of that circuit right out of the spec sheet. I looked back through it and I can't find any of the circuits that aren't this way?
Although drawn as Op Amps , TDA2003/2005/LM383 are "different" ones.
Meant for car radios and such they were designed by a Italian Genius , Bruno Murari :dbtu: who invented the concept of a 5 leg Power Amp chip with minimum parts count.
He succeeded immensely of course.
Part of the trick(s) was to internally design it so the speaker output always stays at 1/2 the +V voltage.
With no need for resistive voltage dividers, neither external nor internal. :o
http://www.idea2ic.com/LM383/
Arrh,,, thankyou Jaun, Now I see da tricky bit.
As you say,, Very clever. :tu:
Sorry to Bajaguy,, carry on all is well. 8)
Phil.
Just got back from 14 days on the road stuck in a hotel without internet >:(
Had some time to do some screwing around while sitting in the hotel, so I changed up my preamp a bit to try to give the whole 1 knob tone stack thing a try. I used the stack out of a Matchless Lightning and tried my best to fold it in with what I already had. I ordered up some MPF102 and some BC549C, but found out this morning that they won't be here for another week. I had a couple of questions about this one:
I left the gain from the first circuit alone and added the matchless stack in behind it, do I need that second FET behind the circuit to buffer the impedance for the input of the TDA2005, or will it work fine the way it is drawn? I really like the way this tone control works on my buddy's tube amp (lots of fat tone), but I'm not sure if it will sound the same with the 2005?
Here's the circuit:
(http://i210.photobucket.com/albums/bb79/TheJester357/JIFPAII_zps9385c7ed.png) (http://s210.photobucket.com/user/TheJester357/media/JIFPAII_zps9385c7ed.png.html)
Thanks ahead for the input, man am I glad to be back in touch with the web!
Baja
Quote14 days on the road stuck in a hotel without internet
Well, if you got stuck in this unconnected middle-of-nowhere crappy hotel.
(http://cdn.cnwimg.com/galleryThumb/07ab8e4be78b56acdb79e3de4a11611b.jpg?a=61bcab)
in this crappy room
(http://cdn.cnwimg.com/galleryThumb/b99942e2dc3bc6441bc87fa2a9b09169.jpg?a=fc74c4)
and with only your Company's *boring* Financial Manager to share it (we all know how dull Accountants are ;) )
(http://1photos.com/wp-content/uploads/2010/10/wpid-web_thinking_manager_s32_11_part.jpg)
yes, I would also have felt depressed, very depressed :lmao:
Man, I want your job!
I was stuck in a hotel downwind of the dairy, with a train that came through every night at 2:30 am.
Your idea sounds way better.... :dbtu:
Baja
QuoteI was stuck in a hotel downwind of the dairy,
Ouch!!
I live in Buenos Aires but I'm from an agricultural town in the middle of the Pampas.
*Many* times I was stuck driving for many miles in a narrow 2 lane highway behind a "cage" truck full of cows being carried to the slaughterhouse.
Man, did I have to "breath nature" !!! xP xP xP
Man JM, where do I sign up? I could use a coupla weeks months years of that.
{ahem} returning to more mundane matters...
Tone controls don't come much simpler than the ol' Top Cut, but all tone controls like to to be fed from a low impedance and work into a high impedance. Is the input impedance of this chip amp high enough? Dunno, would have to look at the data sheet; but given that the drive impedance is very low there is no reason to use such high values for the volume and tone pots (and is C10 really 1uF? Seems very large to me). As drawn the tone control will interact with the volume control having its greatest effect at mid volume and none at maximum.
I'd suggest if you want to stick with a single knob control you have a look at the Big Muff circuit;
(http://www.ozvalveamps.org/ava100/ava100graphics/ava100eqcct.gif)
...and place it ahead of the volume control so it is less dependent on the volume setting.
And again, the resistances can be scaled down and capacitances scaled up to get a lower impedance.
See Duncan's TSC (http://www.duncanamps.com/tsc/download.html?).
I like the big muff stack, but I read that it was lossy and needed a recovery stage before the power amp. I like the way it looks on the stack calc, but will I need another gain stage to compensate?
Baja
The simple top cut is about the only (partial) exception to the rule that passive networks can't boost anything, they can only cut less, so any passive control that has "boost" must have insertion loss as a starting feature, generally about 20dB, and it "boosts" by attenuating less; so normally some make up gain is required somewhere, generally following as in my original circuit.
However, if the following chip amp itself has a lot of gain then a make up stage might not be required.
One of the attractive things about the Big Muff over a simple top cut is that there is a lot more scope for tweeking the resistance and capacitance values to get more or less mid-band scoop or to move it up or down.
That makes sense. I'm on my way out for another few days, so I'll take the datasheet for the 2005 and play with the ducan calculator while im gone. I'm sure I'll have a bunch more questions by the time I get back... :cheesy:
Baja
Just a quick update:
I've been building a few different preamps to play with, but I ordered some J201's from overseas and I'm still waiting.....
I'll be sure to throw an update when I get all my parts and get topluggin the modules together.
Baja
I have made some changes; 3-pin regulator instead of zeners for lower hum; experimental "quasi-parametric" tonestack, and lowered the tail resistor fo the last emitter follower to produce soft clipping.
(http://i1341.photobucket.com/albums/o743/Roly49/Solid%20State%20Guitar%20Amps/FETPreamp130522_zpsed803c67.gif) (http://s1341.photobucket.com/user/Roly49/media/Solid%20State%20Guitar%20Amps/FETPreamp130522_zpsed803c67.gif.html)
Importing FET's? MPF102's should be locally available just about everywhere.
I have the MPF102's, but I was waiting on the J201's I ordered. I think I have enough parts to breadboard up your new shematic so I'll get back whern I have it up and running.
Baja
Hey Roly,
Will 2n3904 be ok to replace the BC549C? I'm having trouble sourcing them locally, but I have a hand full of 3904's at my disposal and a weekend off to play with this! :dbtu:
Baja
Well I chose the BC549C because that was what I noticed in the LTSpice transistor list. Being an emitter follower in a pretty undemanding situation just about anything worthy of the title "transistor" should work. 8|
(if you recall this started as a response to that trimpot horror as a preamp circuit that was component tolerant without trimpots, so substituting devices to hand is exactly what I had in mind)
For a long while Elektor rationalised their transistor and diode types with terms like TUN and DUS, "Transistor Universal NPN" and "Diode Universal Silicon", and had huge lists of compliant types. Jaycar here still sell packs of PN100's which are intended to replace a large range of transistors in most applications. As long as the transistor has a voltage withstand greater than the supply and a current rating a bit higher than the peak expected current, and an hfe of at least 50 (100 is better) then it should work. From the datasheet the 2N3904 looks quite suitable.
I'm still hanging out to hear how you get on with this, if you find it satisfactory, or if it has shortcomings that need tweeks, or ...
That's great, I'll get to bread boarding it while I have some down time in the shop this week. I'm really excited to see if this works out! Stay Tuned...
Baja
Quote from: Roly on August 17, 2013, 04:00:52 AM
Well I chose the BC549C because that was what I noticed in the LTSpice transistor list. Being an emitter follower in a pretty undemanding situation just about anything worthy of the title "transistor" should work. 8|
(if you recall this started as a response to that trimpot horror as a preamp circuit that was component tolerant without trimpots, so substituting devices to hand is exactly what I had in mind)
For a long while Elektor rationalised their transistor and diode types with terms like TUN and DUS, "Transistor Universal NPN" and "Diode Universal Silicon", and had huge lists of compliant types. Jaycar here still sell packs of PN100's which are intended to replace a large range of transistors in most applications. As long as the transistor has a voltage withstand greater than the supply and a current rating a bit higher than the peak expected current, and an hfe of at least 50 (100 is better) then it should work. From the datasheet the 2N3904 looks quite suitable.
You know, I always kind of suspected this was the case 99% of the time, but it's good to hear that I was right. Thanks for the helpful information.
There are exceptions where you have to tread carefully but they tend to be pretty obvious, low noise such as mic preamps, VHF applications, high voltage, and high power. But audio preamps for guitar are not a demanding application and many common devices will do just fine. The MPF102 for example is actually designed for VHF signal amplification so it does just fine for audio and even down to infrasonic tremolo frequencies, or as an audio path switch.
These days as long as a transistor (or IC) has "enough" of everything a particular stage needs, then the main problem is the physical one of "will it fit"? The main reason certain devices become very well known like the 2N3055, LM555, 4558, BC109 and so on, is that the one device will work in all sorts of situations and this allows everybody to narrow their inventory of device types.