Practice Amp?

[E]

Okay, i've managed to source pretty much everything apart from two, being the BZY88 4v7 Zener Diode and a 2A 100V in-line bridge rectifier. For the latter i can find either a 2A 200V one or a 3A 100V, which would be better? As for the Zener Diode... does it even exist? I can't find it anywhere, is there something that would work in its place?

Comes to about £80 now for all the innards and speaker, not including enclosure or PCB. That is with a new soldering iron but does that not strike you as a bit much? I mean, i could get a Peavey Vypyr 15 for £85 which would probably be cheaper than the total project cost.

[J M Fahey]

the BZY88 4v7 Zener Diode is just any 4V7 (4.7V) 1/2W or 500 mW Zener Diode.
The rectifier diode is an 1N5402 or better (meaning higher voltage) 3A 200PIV "200V" or better (1N5404, etc.)
You *may* use an 1N4002 there (many do) but it will be marginal at best.
Now the million dollar question: HOW did you manage to spend 80 British Pounds on it? Only for the "innards" ? How much's that in US$/dollars?
Please post a detailed item list, with prices.
It will be very useful/educational for us.
Good luck.

[E]

I haven't pressed 'buy' yet, i smell something amiss somewhere... £80 is about $125 by today's exchange rate, but that's including tax. I found a 1N5408, will that be aright? I was talking about the in-line bridge rectifier though, not the diode but thanks for the catch.

Sorry about the large images, just me being lazy.

www.rapidonline.com:



www.maplin.co.uk:


cpc.farnell.com:

EDIT: Replaced with thumbnails, probably a good idea.

[E]

Okay, well evaluating the whole cost of it i think i'm going to have to put this project on the backburner for a bit and do what i probably should have done to begin with an make a Noisy Cricket.

I've got two old computer speaker drivers here, 4 Ohm 3W with a 70mm diameter. I assume they'd be up for the job? Would they be in series or parallel? Is it a choice between a speaker or the output jack? I could make two i guess, one with speakers and one to feed into a cab... one thing that's been bugging me about this is that in a 'sealed' enclosure, what is the earth? Is it just a bit of aluminium or something? Is there a way of working out how big it has to be? And the Radioshack wiring diagram doesn't show anything connecting to the earth, but the circuit diagram clearly shows 11 different ones. Thanks.

Again, sorry for the large number of newbie questions. Don't know who else to ask...

[J M Fahey]

Hi E.
I hadn't answered yet because I was trying to assemble a cost list, which here in Argentina *should* be higher than in USA or UK, yet often it's the opposite.
I'm not taking Australia as a reference because I know prices there fly high.
I still want to do it as I find that comparison interesting.
Please post here a simple text  list with all components, including the PCB .
Don't be *too* detailed, just group all same price components together, such as 1/4 W resistors, small ceramics, etc.
I'll add what I can get parts for.
Maybe somebody else does the same in a different country, it will be interesting to compare.
It's good that you start with an intermediate project first.
The earth is connected to the metal chassis, unless it's a very basic plastic case project, *and* either to the negative of the single power supply or center tap of a dual/split one.
On the schematics often you find "many" grounds, but they are all the same, joined by a PCB track, a piece of wire, or sometimes simply by the metal chassis itself, although that last uncontrolled connection system can give you some nasty surprises, such as oscillations, motorboating, etc.
If your computer speakers are 8 ohm each, you can use them in parallel; if 4 ohms, only in series, unless you build a TDA2003/LM383 which is happy with 2 ohms.
Beep! Beep! Beep! Beep! , we're sorry to inform that your credit is over, please reload it with your credit card.
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[E]

I was going to go for a wooden case.These are all at Rapid where possible. Price is 'each' and i've listed below where there is more than one.

• 0.25W 5% Carbon Film Resistor 100 pack - £0.50 (0.5W is twice as much)
  I count 8 of these so £4
• 500k Miniature Carbon Preset Pot, Lin, 30% tolerance, 0.03W rated - £0.08
• 10k Rotary Carbon Pot, Log, 0.1W - £0.80
• 4u7 50V Low Impedance Radial Electrolytic Capacitor - £0.05
  Sheet sais 6 of these but i could get 10 for exactly the same price of £0.30 (they're £0.03 if you buy 10 or more)
• 100pF Ceramic Disk Capacitor - £0.01
• 100nF Ceramic Disk Capacitor - £0.02
  3 of these so £0.06
• 470pF Cermic Disk Capacitor - £0.01
• 2200u 25V Axial Electrolytic Capacitor - £0.59
  2 so £1.18
• 4.7v 500mW Zener Diode - £0.02
• 1N5408 Rectifier Diode - £0.07
  2 so £0.14
• 5mm Green Recessed Chrome LED - £0.87
  Just thought i'd treat myself to a fancy one
• GBU8J SIL Bridge Rectifier 8A 600V - £0.44
  Going by as much 'overkill' on that one as possible.
• Preamps i'm not to sure about, TL071 is £0.26, a TL081 is £0.34 and there's one called a TL081CD for £0.20. What would be better?
• TDA2050V - £2.27
• 6.35mm Mono PCB Mounting Jack Socket (2 switched)- £0.33
• 3.5mm Stereo PCB Socket  (2 switched) - £0.10
• Subminiature Omni Directional Electret Microphone Insert - £0.50
  Do i need solder pad or PCB mounting?
• SPST High Current Toggle Switch - £0.99
• 100mA 20mm Slow Blow Fuse - £0.15
• Chassis Mains Transformer 50VA 0-15V 0-15V - £9.15
  Would that be okay? Just that other site turned out to be wholesale...
• EPE PCB 336 - £5.47
• 8 pin DIL Socket - £0.14
• 20mm panel mounted fuseholder - £0.27
• Black Pointer Knob - £0.28
• 11x2m Stranded Equipment Wire - £1.25
• 13A Standard Mains Plug - £1.10
• 3-Core 13A Mains Cable - £1.69/m
  Say 3m? £5.07.
  

I make that to be £35.32. Which is fair enough, £10 more than in 2002. Add onto that VAT (keep forgetting to show it on that site) and it's roughly £42. Delivery at two separate places is £4.95 and £2.99 making the total £50. Then i'll need a new soldering iron and solder, so that's £15 (for a 30W Antex) bringing it to £65. The Celestion Super 8 is £13.23 with £6 delivery so lets say £20 bringing the total to £85. The enclosure will probably cost at least another £20, which is a bit much for me really at the minute. £85 is the price of a Peavy VYPR 15w, which will be a hell of a lot better than this however you look at it. Hence i'm still thinking about just making a Noisy Cricket (which i make to be about £35 total including soldering iron) or something for the time being, i'd come back to it since i've got the PCB already and i would have the tools already. Not only that but i've been playing without an amp and i've kinda got used to it.

Incidentally, i found this:

http://www.diystompboxes.com/smfforum/index.php?topic=66623.0

[J M Fahey]

Very interesting post.
Now I'm falling asleep, besides being Saturday night, but I'll check some prices on Monday.
Anyway on first sight most look reasonable.
Your Celestion speaker costs about 8 or 10 times what Peavey puts in their VYPYR, thta's for sure, and it's *much* better, it's the real thing.
You should not consider the price of tools , multimeter, etc. into your costs, or if you want to be very conservative, charge, say , 5% of the cost, no more.
The same goes for your 1/2 pound roll of solder, your 100 yard wire spool, and so on.
Thanks.

No, nothing, just checking emoticons, I missed them 

[E]

By that measure i shouldn't really factor in delivery either so 40+15 brings it to £55. Which is okay, i guess. It's just that it's all very well not factoring in these costs for the sake of comparison but i've still got to pay them. The soldering iron would probably pay for itself mind you, the amount of things i've broken and said 'i need to buy a soldering iron' for... i digress, if i can salvage a bit more wood then i shouldn't have to spend so much on the enclosure, say £60 in total? I dunno, i'm at two ends about it now.

Doing a quick list compilation (as you do) it looks like making that Tube Cricket would be more expensive than continuing with this. And there are a lot of things i don't understand about Valves just yet... or indeed betray the forum  8|

[E]

I still don't know... part of me wants to say:

• Bah, just go through with it. You've got the PCB already, and more than enough money kicking around. At the end of it you'd have a pretty decent amp that (if you make the enclosure correctly) will be fairly portable, and you'll have learnt a fair bit by the experience.
  

and another part of me wants to say:

• Whatever, just build a Noisy Cricket for the sake of having an amp. It will be easier, cheaper and you'll have the tools to make it a lot cheaper to come back to this project at a later date. With a decent pair of drivers (which you have) it should sound quite good and will be far more portable.
  

I just don't know which one is right...

[joecool85]

I would start with the noisy cricket myself.  Its always fun and rewarding starting small then building larger stuff later.  Plus, I've found I don't need a large amp, most of the times 20 watts is my max requirement.