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

[capmaster]

You see that's why id never even try to build an amp.. I can do basic electrics but most of this goes way over my head...

 

So.. good on you man...

 

Maybe I can build you a nice tru oil finished cabinet ? :)

Thanks for the offer, maybe I'll need one some day.

 

I think that due to being an educated safety expert, I may have the notion to think about such things...

 

Moreover, they nearly killed me at a TV recording studio of a public radio station here in Germany on 29th September 1982. They operated a balanced power line not referred to ground, and the circuit ground voltage difference between my guitar amp and the vocal amp was about electrocuting me between vocal mic and my 1978 Gibson S-G. Having survived this changed my life forever.

[Rabs]

Thanks for the offer, maybe I'll need one some day.

 

I think that due to being an educated safety expert, I may have the notion to think about such things...

 

Moreover, they nearly killed me at a TV recording studio of a public radio station here in Germany on 29th September 1982. They operated a balanced power line not referred to ground, and the circuit ground voltage difference between my guitar amp and the vocal amp was about electrocuting me between vocal mic and my 1978 Gibson S-G. Having survived this changed my life forever.

Well I was talking to Farns as he lives not to far from me..

 

But ok.. if you want one we can talk too :) (not that ive ever built one before, but how hard can it be after what I have just done ;))

[capmaster]

Well I was talking to Farns as he lives not to far from me..

 

But ok.. if you want one we can talk too :) (not that ive ever built one before, but how hard can it be after what I have just done ;))

Sorry, my fault, no offense intended, I just referred your reply without quotations to my previous posts

[Rabs]

Sorry, my fault, no offense intended, I just referred your reply without quotations to my previous posts

Lol.. no problems at all... no offense taken.. :)

[Guest Farnsbarns]

Just asking because it isn't obvious to me: Did you refer the heater voltage to ground? Connecting each leg to circuit ground with a 100 Ohms resistor rated 1/2 watt is very useful. 1/4 watt would be sufficient but I'd go for safety.

 

Ungrounded heaters may invite trouble for the heater/cathode isolations due to static voltage buildup. Therefore voltages for indirect valve heaters are usually referred to ground.

 

No, but I could easily. I haven't on previous amp builds and not had an issue but that doesn't mean this won't be the time. We'll see...

[Guest Farnsbarns]

You see that's why id never even try to build an amp.. I can do basic electrics but most of this goes way over my head...

 

So.. good on you man...

 

Maybe I can build you a nice tru oil finished cabinet ? :)

 

Rabs, I had plans for a cabinet but I kinda like the idea you present. Have a think about how much you'd need and PM me.

[Rabs]

Rabs, I had plans for a cabinet but I kinda like the idea you present. Have a think about how much you'd need and PM me.

:) Lol...

 

Hmm... in just having a think I would have to see about what the effects of heat will do to any finish.. As I assume at least the amp part would get fairly hot....

 

I will have a look around if you really want too and do some research...

 

What were your plans for the cabinets ?

[Guest Farnsbarns]

:) Lol...

 

Hmm... in just having a think I would have to see about what the effects of heat will do to any finish.. As I assume at least the amp part would get fairly hot....

 

I will have a look around if you really want too and do some research...

 

What were your plans for the cabinets ?

 

I doubt the heat would be anywhere near enough to worry about.

[capmaster]

No, but I could easily. I haven't on previous amp builds and not had an issue but that doesn't mean this won't be the time. We'll see...

Many Fenders have a trim-pot connected to the heater lines, with the tap connected to ground. They often are user-accessible on the chassis back and named "Hum Balance."

[Guest Farnsbarns]

Good news, it works, except the reverb. every knob and switch functions as it should and it sounds great, however, there's no reverb send. Bashing the tank yields a nice, wet sounding badoiyoiyoiyoiyoingggg so the send is the issue. I've tried a few simple things and can't locate the problem. It's 11pm and I'm knackered but it must be fairly simple and I'm sure the issue will be obvious with fresh eyes tomorrow.

[capmaster]

Good news, it works, except the reverb. every knob and switch functions as it should and it sounds great, however, there's no reverb send. Bashing the tank yields a nice, wet sounding badoiyoiyoiyoiyoingggg so the send is the issue. I've tried a few simple things and can't locate the problem. It's 11pm and I'm knackered but it must be fairly simple and I'm sure the issue will be obvious with fresh eyes tomorrow.

I know how bad it can be to have to sleep over something like that, but I'm sure you'll get it fixed tomorrow. I cross my fingers for you!

[quapman]

You're doing a beautiful job here man.

Very nice work.

Can't wait to hear it.

[Guest Farnsbarns]

You're doing a beautiful job here man.

Very nice work.

Can't wait to hear it.

 

Thanks QM.

[Guest Farnsbarns]

I was examining my circuit in my minds eye as I fell asleep last night (like you do) and I realised I've wired the reverb pot backwayds so 0 is 10 and vice versa. I'm wondering if it's possible I only ever tried with the pot on 10. It may be fixed by a simple wire swap.

[pippy]

...I realised I've wired the reverb pot backwayds...

Idiot...

 

 

 

 

 

 

 

 

 

 

P.

[pippy]

I just re-read the whole thread.

I can understand slightly more of the logic second-time around but it's still, pretty much without exception, way way over my head.

 

A few questions, if I may?

You say the circuit is, barring your mods, 'someone else's intellectual property'. Is this someone whose designs would already be familiar to us?

For some reason I was thinking it was going to be a 25W but if I read it correctly it's 0W - 5W stepless? Switchable?

What is the length of the chassis, Farns? How big is the cabinet going to be?

And up to what point does the size of the cabinet affect the final sound?

Does 'ported', 'enclosed' or 'semi-enclosed' (or whatever) make a huge difference?

What difference - if any - would there be if you chose to use a pair of speakers instead of a single 12"?

How much (ball-park) would the reverb circuit cost on it's own and could one be built up to be installed in an existing combo easily enough?

 

As Manuel was wont to say; "I know naathing..."

 

P.

[capmaster]

I was examining my circuit in my minds eye as I fell asleep last night (like you do) and I realised I've wired the reverb pot backwayds so 0 is 10 and vice versa. I'm wondering if it's possible I only ever tried with the pot on 10. It may be fixed by a simple wire swap.

Glad you found out which way to fix it.

 

I know it isn't always easy to bear in mind that the pot rotation is the other way round when seen from the back side. When rewiring guitars using new components, I sometimes turn the pickguard respectively the whole instrument around to check before soldering.

 

Rather funny is working on a left-handed instrument's pots with inverse sense of rotation, apart from the fact that reversely audio tapered pots are hard to locate.

[Guest Farnsbarns]

I just re-read the whole thread.

I can understand slightly more of the logic second-time around but it's still, pretty much without exception, way way over my head.

 

A few questions, if I may?

You say the circuit is, barring your mods, 'someone else's intellectual property'. Is this someone whose designs would already be familiar to us?

For some reason I was thinking it was going to be a 25W but if I read it correctly it's 0W - 5W stepless? Switchable?

What is the length of the chassis, Farns? How big is the cabinet going to be?

And up to what point does the size of the cabinet affect the final sound?

Does 'ported', 'enclosed' or 'semi-enclosed' (or whatever) make a huge difference?

What difference - if any - would there be if you chose to use a pair of speakers instead of a single 12"?

How much (ball-park) would the reverb circuit cost on it's own and could one be built up to be installed in an existing combo easily enough?

 

As Manuel was wont to say; "I know naathing..."

 

P.

 

All very good questions....

 

Doubtful you'd know the designer, Barry at AmpMaker.com. lovely bloke, always willing to sell me a "kit" with loads of stuff deleted/substituted, loads of extra components, unstaked boards etc etc. He is also very open to discussing possibilies with mods. Absolutely top man. Can't speak highly enough. If you want to look at the circuit this was based in it's his new N5X, supplied with main board unstaked which made the integration of reverb/effects loop much easier as I could change the layout to suit (no reverb/effects loop in his design), also supplied with no face plates (I'd have had to have drilled straight through the logo), loads of extra components for the reverb and effects loop and extra board and hardware.

 

The chassis is about 18" but could have been an inch or two shorter I guess.

 

Cab size and venting is important but is generally governed by the speaker choice. A pair would generally sound bigger, if that's a reasonable description of a sound? Must remember though, that speaker efficiency will drop of fast as we reach the extremes of under powering.

 

This will be a head and cab arrangement.

 

The reverb could potentially be added to most amps, cost about £70, but let's wait and see if I actually get it working.

[Guest Farnsbarns]

Just got home and tried it. Sure enough, reverb pot wired backwards so turned it to 0. I can now hear the faintest reverb. Looking deeper, I am running the front half of the 12ax7/ecc83 reverb valve from the same voltage as the back end but because of the reverb tranny I needed to tap it off before the plate voltage control resistor. I'm just going to reverse the pot now and then I'll tap a higher voltage from further back in the power supply. I think I'm on the home straight with this.... Update coming soon. (Once my cap voltages have dropped a bit).

[Guest Farnsbarns]

WORKING!!! Got it! not perfect, it's quite capable of falling into a feedback hole but if I'm careful with the knobs it sounds great. perhaps a little bright/harsh but that's no big issue to resolve.

 

I did record a short clip but it sounds dreadful recorded on my phone so I'll make a nice recording soon.

[pippy]

...I am running the front half of the 12ax7/ecc83 reverb valve from the same voltage as the back end but because of the reverb tranny I needed to tap it off before the plate voltage control resistor. I'm just going to reverse the pot now and then I'll tap a higher voltage from further back in the power supply...

You just beat me to it, Farns.

 

P.

[Rabs]

Sweet... looking forward to the sound clip..

[capmaster]

Congrats, Farns! Looking forward to your sound clip here, too.

[Guest Farnsbarns]

Well, here's an embarrassingly bad video. Funny how your mental approach changes when your listening to an amp you built, playing goes out the window.

 

Forgive me for being upside down... Downright rude of me I know!

 

http://www.youtube.com/watch?v=MeMtjY6NySk

[Rabs]

Well, here's an embarrassingly bad video. Funny how your mental approach changes when your listening to an amp you built, playing goes out the window.

 

Forgive me for being upside down... Downright rude of me I know!

 

I didn't know you are currently in Australia :P

 

The amp sounds pretty frikken awesome... and some nice BB type subtle blues licks there at the beginning

 

Will have to try one of my builds through it :)