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Topics - darwindeathcat

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Amplifier Discussion / Battery power for street amp....
« on: January 07, 2012, 08:11:02 PM »
About a month or two ago, there was some discussion ( about building 12 volt battery powered amps with more power than the typical 1-5 watts you get with the typical 9volt designs. The discussion mainly centered around battery technology, and which one would give you the most output for the buck, as well as the one that would be the lightest (important for a battery amp). Well, I found the former (best bang for your buck), and bought one for a little combo amp I built for street busking. It's a 12v 7aH Gel-Cell marine battery meant for fish finder:

The battery weighs in at about 6 lbs, so it ain't light! But, for a little less than $30, you get the battery and a charger (not a smart charger, but not a totally dumb charger either. An "average intellegence" charger, if you will). The amp is 20 watts, class AB, discreet transistors (I didn't build the amp, it's a PA head I integrated into a cab). I've played it on battery power at a few busking sessions now, the longest was about 2 hours, with no sign of power loss. My math tells me I ought to get about 4 hours playing on full, but since I don't turn it up past 4, I'm not sure how long could actually go for (maybe 5-6 hours?).

Here's my review that I posted on Amazon:

There are a few other 12v 7AH SLA batteries in this price range that also come with chargers. It's hard to tell the difference between them from the info posted here on Amazon, but this one has the most reviews, all positive, even though it's a couple of dollars more expensive than the other ones. So why buy this one instead of those others? Well, partly because this one is sold directly from That's a big plus because if you live in an Amazon hub city (like Phoenix, where I live), you can get your package very quickly even with the free super saver option. In fact, I ordered this battery at about 4pm on a thursday, and the package was delivered to me at 9am the next day! This is with the free super-saver shipping! Secondly, this one comes with a slightly nicer charger than the others do (at least judging from the pictures of the other chargers). The charger that comes with this one has a nice LED status light that changes color when the battery is charged (from yellow to green), and also has cross polarity protection that will keep the battery from shorting (and light a red warning light) if you hook it up backwards (VERY nice thing to have).

I am using this little 6lb battery to power a small 20watt amplifier I built for busking on the street. I get several hours of play time from it, and it holds a charge very well. Like all SLA batteries, you have to maintain it properly, and be sure that it never drops below 11.5 volts, or sulfation will occur, and the battery will be permanently damaged. But if you keep it charged up, and don't store it for too long, it should last for many years!

In sum, this is a great deal on a very good battery.

Amplifier Discussion / Anyone own a Pyp PB-1 battery amp?
« on: October 05, 2011, 02:13:44 PM »
Hi all! I just picked up a Pyp PB-1 ( for cheap ($40) in a craigslist deal, but the only catch was that the guy had lost the wall wart adapter needed to charge the damn thing! So, I was hoping one of you lovely people might own one and could tell me the specs on the charger? I looked on the website and in the manual, and it seems they don't list the specs anywhere. I also sent an e-mail to the Pyp Bomb people, but haven't gotten a response. So, you guys are my only hope!

FWIW, I've got an adapter that charges my spotlight, which is also powered by a 12v sealed lead acid battery. The specs on that wall wart are 12v, 300 Ma, center negative. The barrel plug fits the power jack on the back of the PB-1, but I'd like to confirm that the specs match before giving it a try!

Thanks for any help you can give!

Amplifier Discussion / lm386-powered amplifed porch-board bass drum idea
« on: February 24, 2010, 10:48:09 PM »
Hi guys,

   It's been a while since I've posted anything here, but I've definitely been lurking around and reading posts... Not to worry, I'm still doing crazy DIY audio electronics stuff in my mad scientist workshop here in Arizona!

That brings me to my latest project idea: an "self-amplified" porchboard (also sometimes known as a "stompbox", not to be confused with "stompboxes" in the pedal effects sense). If you want to understand what I mean better, see these links:
Basically, it's a thinish wooden box with a pickup glued inside, and 1/4" jack that you run out to a bass amp or a powered subwoofer. When you stomp your foot on it, it sounds like a bass drum. It's for solo people to self-accompany themselves with a but of rhythm...

Okay, so my "big idea" to improve the idea is to incorporate the bass amplifier into the porchboard itself. I've built a small one from a wooden cigar box with a piezo pickup, but I'll go much bigger with this one. I've got a subwoofer speaker (taken from a defunct, but high end, computer speaker set), a range of pickups to try out (piezo, dynamic, etc.), and the heart of the matter: an lm386 chip. The idea is to have the pickup fed right to a simple lm386 circuit that's house IN the porchboard itself. The lm386 will drive the subwoofer, which will also be housed IN the poarchboard.

So, I wonder if anyone has any advice about building an lm386 circuit that will sound good in this application (ie heavy, thuddy, bass tones). I want to avoid as many problems with feedback, muddyness, fartyness, etc. that I can. Can anyone point me to a good lm386 circuit that sounds good with bass tones? I'm worried that using a stock ruby/little gem/noisy cricket circuit will be too trebly for this application?  I'd like something with a simple but effective one knob tone control that I can use to change the timbre of the kickdrum sound a little bit, but the minimum control will just be an on/off switch and volume (I've got plenty of pots with integral switches, so I'm good there)

Any advice would be appreciated!



Amplifier Discussion / Battery-powered "Busking" amp.
« on: October 19, 2009, 01:59:26 PM »
Hi all, This is something I've been thinking about for a good while now, and I thought I'd poll the knowledgeable crowd here to see if anyone has any words of wisdom for me before I start in on it.
So here's the idea:

I want to build me a small battery powered busking amp for playing amplified blues harp on the street. I have a little pignose that I use now, but I'd like an amp with bit more bottom-end and that can actually clean up a little if I want (the piggy is all dirt, all the time). I've built a couple of lm386 chip amps, and I'm not really enamored with them either.
So, what I've got now to work with is a Hitachi HA 13001 single supply chip amp that I've built from a kit. It was way too noisy when powered from a wall supply (even with a well-filtered PS), but  I think it have WAY less hum on battery power, which should be doable since it requires only +8 to +18 V at ~1amp. The pignose is powered with 6 rechargeable AA's (9volts) and lasts quite a while. The current draw is nowhere near as high as 1 amp though (I think it's ~300mA), so I don't know if this battery configuration will work well for the Hitachi chip, or not. I can get a 4-5 AH 12 volt sealed lead acid battery for about $15 at Fry's Electronics. I'm assuming that if the amplifier circuit is pulling 1 Amp (on average) that means that a 4-5 AH lead acid battery will give me 4-5 hours of continuous play time. Is that a safe assumption? Following this logic, if I'm using 2100 mAH double A's in series, I would only get ~2 hours if the circuit is drawing 1 amp? Does that make sense?
   Oh, I'll be using a modified ROG peppermill for a preamp, which let's me dial in clean or go to some pretty nice overdrive if I want.

Pros and cons of battery type:

 To go the AA route, I would not have to buy anything (I have battery holders already and an external charger too), but I'm not sure how quickly the batteries would drain. For the 12volt I'd be spending ~25 bucks for the battery and charger, but it *should* give longer play time. If I go with the AA's I'm cool for the preamp supply too (9volts), but I'd have to use a regulator if I went with the 12volt. I know that the 12 volt will get me louder output (data sheet says it'll put somewhere in the realm of 15 watts into 4 ohms at 12volts/1.5-2 amps, so i'll prob get 10watts), but I'm cool with lower output (it'll prob be more like 5-6 watts running on 9v using a bunch of in series 2100 mAH AA batts) if it's easier/cheaper for me to build. It will still be PLENTY loud enough. I'll run this amp through 2 vintage 8" speakers as well (in parallel for 4 ohm load), so that should help get more of the low end out (the piggy I use now only has one 6" speaker).


What about other battery-powered amp designs (beyond lm386)? Anyone experiment with 12volt single supply chips meant for car audio? These could be very cool if paired with 12 volt "space charged" tube preamps... Thoughts?

Tubes and Hybrids / Low voltage "space charge" tube designs
« on: September 22, 2009, 09:37:56 PM »
I was just perusing the internet and came across this site about certain types of tubes that were meant to be run at low voltages (both on the heaters AND the plates). 20v or less. Most of the info at that site is about building low voltage tube radios radios, but there is no reason on can't build instrument amplifaction stages with these tubes. The sopht amp uses common space charge tubes (12u7 in the preamp and I forget what the power tube is). AFAI understand space charge tubes will sound  different than "starved cathode" designs that use regular tubes in a low voltage mode. Anyone know of any other designs, specifically preamps or overdrives, that use space charge tubes. I searched google, but got a lot of useless repsponses. The idea is to use a space charged tube circuit as the preamp to a chip amp. I've got one chipamp that runs at +-24, and another at +18 that I'm fooling with the preamp sections on. Of course I can use a regulator to get whatever voltage I need for the space charged tube preamp design.



Schematics and Layouts / 25W lm1875 Harp Amp with Professor tweed preamp
« on: October 26, 2008, 06:23:36 PM »
Hi all, These are the schematics I used to build my solid state Harp Amp. I should say a couple things about it:
1) I used mainly scavenged parts for the power supply (except the 10000uf 35V filtering caps and the 12v regulator for the preamp power), so that's the reason you see two transformers. You should note that the trannies are wired in series such that there are +, -, and ct taps on the secondaries. It's vital to get the proper phasing here, so you must test the output with a multimeter before permanently wiring here, or you will get phase cancellation (effectively producing 0v out either tap). Figure 1
2) The prof tweed was tweaked with some info I gained from the DIY stompbox forum. The following changes were made and are shown as notes on my schematic: I changed all the DC coupling caps to 0.1uf. I changed the caps in the speaker sim section to 5n8. I changed the cap in the feedback loop to 0.01uf. The first two mods allow for more bass, a mod that is normally done to guitar amps to help "voice" them for harp. The last mod actually increases the gain a bit, which I found necessary to make this circuit work properly as a preamp. Also you should note that I am powering the thing at 12v, which means the fets should be biased at around 6v (it was originally powered by 9v). Of course, I biased the fets "by ear", which I always find more satisfactory. Figure 2
3) The lm1875 poweramp board is a kit obtained from I won;t paste the schematic here, but this is the link to where you can purchase it from qkits: The kit is high quality: I found the board to be really well designed, and the components to be of good quality. If you think it is necessary, you could always use higher quality components (1% metal film resistors instead of the stock 5% carbon ones, tantalium caps instead of the stock electrolitics), but who knows how much difference that would make. I really appreciated the on boarde fuse protection. You will need to provide your own heatsink, and make sure you isolate it from the rest of the chassis (the chip is not insulated). Also, there is an on board zobel network, which is prevents oscillation when driving difficult speakers or when pushing signal over long lengths of cable. No schem

Finally, please note that this amp was designed and intended for amplified Harmonica tone. That means it's really quite dirty, although I plan to add a clean channel in the near future. It may work for guitar or bass, but I don;t play either, so I can neither confirm nor deny it's efficacy in either case. Also, I decline to show schematics of the jacks and switching, as I did not make any, and these are often a matter of personal choice anyway. I wired a true bypass switch to the preamp as a place saver for a clean channel switch, and I made a effects send/return loop before the master volume control, but these are not requirements for a working circuit.

The amp can be seen and heard here:

Amplifier Discussion / preamp to poweramp ground loop question.
« on: July 07, 2008, 06:07:21 PM »
Hi all, I am 50% finished with my lm3886 amp build. I am designing the power supply for the preamp portion, which will be a "proffessor tweed" from ROG, and I have a question about the way I am proposing to derive the lower voltage rails for the preamp. I have done the calcualtions to get +/- 6v supplies from my +/-23.4v poweramp rails. The design uses a basic resitive divider from the +23.4v to ground to get the +6v rail, and the same thing from the -23.4v to ground. The idea is to use the -6v rail as the ground point for the preamp, effectively making it a +12v design.
   My question is this: will running the premap with a ground point that is offset -6v relative to the ground of the poweramp create an awful groundloop/hum problem? Would it be better to derive a non symetrical single +12v supply rail from the +23.4v rail instead? I thought of this, but did not want to create an uneven current draw from one rail that might cause some sort of oscillation issues... Any advice would be helpful and greatly appreciated!

Amplifier Discussion / The mother-load of affordable transformers...
« on: June 03, 2008, 07:46:06 PM »
Hi all, I just came across this page:

  As you will see they stock MANY very affordable transformers, of varying voltages and amps. Many of them are right for building chipamp dual-rail powersupplies with (right VA rating, and also center tapped). None are toroidal, however... I just thought I might pass on the news!

I found a schematic for a ridiculously simple FET-based power amp on this site:
The schematic I'm looking at is the UCLA3 (I can't figure out how to attach a picture to this post). The site says it's capable of 17w with a single +60v DC supply! Does this seem right? If so, this could be a ridiculously cheap and EASY power amp project for ANYONE! Combine this sucker with any of the ROG preamps (the ROG "distortion" pedals are actually preamps) and you'd have a killer small amp that would sound really tubey!

Thoughts anyone?

Preamps and Effects / "Solid State Tube Sound" preamp video clip!
« on: March 13, 2008, 06:28:52 PM »
Hi All,

   I built this "Solid State Tube Sounding" preamp from a schematic found here:, and I reported it earlier in a thread over in the newbies forum.
   Well... I finally got around to recording how is sounds! I posted a video on you-tube of me playing through it with a couple of different effects. You can check it out via the following link:
   I'd really like to hear your feed back as to how it sounds. Although *basically* know what a tube amp is supposed to sound like, I have never owned one, so I am not sure how close this preamp gets. I do think that it sounds really good, and definately sounds *better* to my ears than a standard solid state preamp... Now, the question of it sounding "tubey"? Well, I'll let you decide!

I was just perusing Syndromet's transistor pinout encyclopedia that he just posted on anther thread, and I noticed that the Jfet's used in most of the ROG circuits (mpf102/j201) have the same pinout as all the MosFets he listed. I know the main differenced between the BJT type of transistors preclude them from being used when a FET type is called for, but what is the difference between Jfet and Mosfet in terms of functionality? Could one stick, say a BS170 mosfet in the place of a mpf102 in a circuit? What would be the result of such a swap (ie. smoke and flames, or just different sound, or nothing?).
  The reason is that I have a bunch of BS170's I got cheap in a bulk purchase, but I only have one mpf102 left in my parts box... I already finished the project that required the BS170's (the solid state tube sounding preamp. See the newbie forum for that thread), and want to start fooling with some of the ROG designs for my multichannel combo amp (see the "preamp for lm3886" thread in this forum)...
  Any sage advice would be greatly appreciated!

Hi All,

    I've been looking for an amp build that was: 1)easy, 2)in the 30-40 watt range, and 3)used a single rail power supply so that it was 4)cheap. After untold hours of searching, I seem to have found the solution in two schematics that use the TDA2030 in conjunction with two power transistors. The first schematic comes from a kit offered by quasar electronics (UK) ( (schematic is a pdf listed at the bottom of the description, and the other is listed on (
Power Amplifier : Power Amplifier OTL 30W by IC TDA2030 +Transistor).
   My questions for the list are as follows:
   1) I would prefer to build from the schematic from the quasar kit because I know it is proven, and it puts out more power. However, they (of course) do not list any component values other than the IC and Transistor types, and the input voltages. I'm more of a "follow instructions guy" when it comes to amp building, so I have no idea how to calculate these values. Can I use similar values from the other schematic (the elecfree one)? That schematic is very similar except that it uses different transistors and has a lower input voltage (and is missing the equivalent of C2, R1, and R3 in the quasar schematic).
    2) As the TDA2030 seems to be hard to find here in the states, I have looked up the NTE replacement for it, which is the NTE1380. Looking over the datasheet, it *seems* to be an exact duplicate. Is anyone aware of any deviations from the TDA2030 pinout?
   3) As far as the transistor types: I was unable to find the exact types from the schematics. Can I uses some sort of generic equivalents? Any suggestions on which ones?
   4) Any other suggestions about these schematics?

Any help would be greatly appreciated!!!

The Newcomer's Forum / building the "Solid State Tube Sound" preamp...
« on: January 06, 2008, 12:12:42 AM »
Hi all, I'm new to the list, and am about to embark on my first major "from scratch" amp project (i've built a few general purpose amp kits, and modified several existing amps). Instead of starting with the de rigour noisy cricket or little gem, I came across a schematic at this site: for what seems to be a very cool and easily built "tube clone" preamp circuit. Before I place my smallbear and electronics goldmine orders for parts, however, I wanted to ask the list if anyone knows or has built this circuit? Does it work? Does it sound good? Is it worth my time? Are there any known flaws in the design or any essential mods I need to know? Any help I could get would be greatly appreciated...

BTW I play blues harp, and plan to use this to get good tube style blues tone to feed into my vintage 20watt pa amp...

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