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FarnsAmp MkII ~ build thread ~ Going back and tidying the chassis after tweaking the circuit.

Guest Farnsbarns

By Guest Farnsbarns
in The Gibson Lounge

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Guest Farnsbarns

Guest Farnsbarns

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Yes, I have a couple of stumbling blocks. Due to a misunderstanding I don't have enough turrets, I also moved a decimal point in one of my calculations and had to order a handful of components because I had the wrong values. I realised as I was doing the layout for my reverb circuit which will go on a separate board. Found myself thinking "this is a very large cap".

 

Ho hum, since the last post I've drilled the main board and the reverb board is now staked with turrets although I might have to revise it once the components arrive and I can size them.

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Guest Farnsbarns

Guest Farnsbarns

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Here's the reverb board being done...

 

IMG_20140222_212612.jpg

 

IMG_20140222_213230.jpg

 

 

And here's the main board partially staked...

 

IMG_20140223_205401.jpg

 

More turrests and a few components arriving soon, by Wednesday I would guess.

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Guest Farnsbarns

Guest Farnsbarns

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I drilled some holes!...

 

RCA sockets for the reverb tank....

 

IMG_20140224_210222.jpg

 

IMG_20140224_210212.jpg

 

And for the reverb trany (this time it's as far as possible from the power trany)...

 

IMG_20140224_210349.jpg

 

I'm going to make the power supply board tonight, it's the only thing I can complete for now. Waiting on a couple of bits.

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Guest Farnsbarns

Guest Farnsbarns

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Hmmm, getting lots of views here but not many replies. I hope someone's interested.

 

The turrets and replacement components have arrived so I now have everything and should be pretty quick now, that said, I had a meeting today from 9.30am 'til 4.00pm and I feel so drained, similar meeting lined up for tomorrow and a possible guitar lesson to give in the evening so don't hold your collective breaths just yet.

 

Here's the power supply, ready for soldering....

 

IMG_20140225_205512.jpg

 

I'm gonna put all the boards together and then have a solderfest. I've realised some of the reverb components would be best placed off the board. Gonna put a couple of resistors between a reverb bypass switch and the reverb and dwell pots. There's a resister and cap that can simply be put across pos and gnd on the return rca socket for the tank so I'm going to cut some of the reverb board off and pop a couple of turrests out and use the holes for screws..

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Guest Farnsbarns

Guest Farnsbarns

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Here's the staked main board. Can't stay awake now...

 

IMG_20140225_223422.jpg

 

I have designed the cabinet, in detail, but only in my head. It's a bit different.

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surfpup

surfpup

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Hmmm, getting lots of views here but not many replies. I hope someone's interested.

 

Keep it coming. [thumbup] Build threads can be a little slow around here. It's not like an amp forum where people are gonna know what you are talking about - but I for one am interested and I am sure others are too. Where's the flux capacitor going?

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krock

krock

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How does an amp designer/builder know what it's going to sound like?

 

I think FarnsAmp MK 2 was going to be a modded amp based on an already designed amp. Its easier to know what something will sound like if tweaking than if designing from scratch. Many amp designs these days are built in this way which I imagine would save a lot of money in R & D costs.

 

A few years ago I asked my dad to help me build a point to point box of rock pedal. Half way through the build I started to wonder how Z Vex decided on certain resistor values. As a basic way of explaining how different resistor values would change the end result, he wired up a load of pots and bypassed a few resistors. On his oscilloscope he was able to show me the difference to waveforms

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Guest Farnsbarns

Guest Farnsbarns

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Yes me.

 

Stupid question time -

 

How does an amp designer/builder know what it's going to sound like?

 

Well, there's not really anything new that can be done with a bunch of resistors, caps and valves, unless someone designs a cometely new type of valve it's all been done. There are a number of possible valve configurations that can be miltiplied and multiplied. There could be any number of cascading gain stages etc. Different types of valve have different possible configurations but there is a basic set of "types" that each have their own sound. Ever noticed that the same wattages come up again and again in the amp world? There's a reason for that. Ever heard of people talking about the "British" sound? There's a reason for for that too. Pretty much all 5 watt amps will have a single power valve driving the output transformer for example. There are different valve options that each have their own sound. The finer points of sound, goverened by the minute details have to be developed by a combination of what experience one has, trial and error and plagiarism. Anyone building g an amp uses these tools to whatever extent they can. I'm largely using the plagurism root here.

 

I haven't here but I can design a circuit that dumps the guitar signal into a preamp valve, back through the other side of it, through a gain pot, then a volume pot, maybe a phase inverter valve, then on to the power tube and out again.

 

Creating the power supply for all this is really very simple. Turning AC into DC takes 4 (2 even) 50p diodes (or a valve) then we smooth it out with some caps and use various resistors to get the voltages we need.

 

When it comes to fine tuning the caps, tone stack, biasing, etc etc, I'm really just stealing from known good methods.

 

This exact circuit has never been done with reverb before so it's a bit of an unknown.

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Guest Farnsbarns

Guest Farnsbarns

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Well, I put the main board together in front of the telly this evening, never do that, I made a couple of mistakes, found myself bending component legs straight again several times...

 

IMG_20140227_004758.jpg

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Guest Farnsbarns

Guest Farnsbarns

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I should finish the chassis this weekend. I've built the boards and soldered the power supply board. Just got to solder the others and build up the chassis. Pix of that coming soon.

 

I've just ordered an 8 ohm Celestion Vintage 30, it's tight bottom end should compliment the amp nicely. I might order a greenback as well, just because I have no idea which will sound best until I've tried them and two 1x12 cabs would be cool, giving me options on sound and what to take when I leave the house. These cabs should work nicely with my 18w build too.

 

I had planned on going out to get some pine boards today but I had to go in to work and deal with some stuff so that's off 'til next weekend now.

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Guest Farnsbarns

Guest Farnsbarns

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All three boards done.

 

The reverb board is a bit of a mess. That's what you get for revising the design as your going. It's only aesthetics, it'll work fine.

 

IMG_20140301_213659.jpg

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Guest Farnsbarns

Guest Farnsbarns

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Started building up the chassis....

 

IMG_20140302_162823.jpg

 

Fitted the pots and switches to start working out wire lengths...

 

IMG_20140302_170855.jpg

 

Disaster!!! I've realised that 2x 1m pots I ordered seem to have been substituted with 420k. Bugger, email sent, awaiting reply.

 

This is where I am. I don't want to fit the heavy transformers until the last minute so I'm pretty much stuck without those pots. I s'pose I can do some wiring but I really wanted to power it up this evening and that's out the window now.

 

IMG_20140302_185045.jpg

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Guest Farnsbarns

Guest Farnsbarns

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Wow, reply received, more pots on way tomorrow! Not bad for a Sunday.... They said to keep the others as well.

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