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#1
Hey, having recently regained some income (yay) and beginning to get some stock in to get my wife's 30th birthday present guitar built I figured I'd look at building her a little amp to go with it.

EDIT: updated the details from here based on my recent decisions.

I have an empty Fender FM15 box with a Celestion Super 8 speaker in that will be my enclosure. As such space is a little bit of an issue so I'm going single tube (combination triode and power pentode) and no filter choke. Also got the parts layout figured out and will hopefully be getting the parts ordered in the next week.

Here's the schematic, if anyone fancies double checking my work for me feel free.

Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
Last edited by GABarrie at Feb 26, 2012,
#2
Made some decision and done up the turret board layout, yay.

Stay tuned for some real updates
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
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#4
Actually they're not, the data sheet says 300v typical operation for both plates and 200v max for g2

Do I need the coupling cap in front of the volume/tone control? Wasn't aware it was affected by DC
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#5
My bad, finally tracked down a copy of the datasheet from the manufacturer I'll be buying and the values are miles different. Will update schematic soon
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#6
Revision 1.8 updated
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#8
which resistor? and you mean the coupling caps? I only had one and you complained :p
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#10
but but... I like filter caps on my preamp tubes
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#11
You don't need that filter cap if that node isn't supplying anything.

You have more than enough filtering for the little amount of current you will be drawing.
#12
right, hopefully my last update before ordering parts

Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#14
My supplier doesn't do 4k4 resistors :p

I guess I could go down to 3k9, increase headroom a little. EDIT: or I might go down to 2k2 or 2k7, and replace the filter for B+2 with 15k or 22k, I'm still well below maximum ratings and would definately increase my headroom and push the output to about 4W

Having the grid leak after the grid stopper produces a voltage divider that produces a small drop, helping to reduce power tube distortion, which as my wife is not really the crunch type will help, will be having enough issues that are inherent in a low watt amp and headroom, can't really afford to build bigger though >.<

The 3W plate resistor was originally for aesthetics on the turret board but I've since tweaked the design and can probably drop it back down again
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
Last edited by GABarrie at Mar 1, 2012,
#15
OK... (hopefully) final lot of tweaks unless you complain again kurt :p

Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#18
nah man, I appreciate the help, I'll take all the help I can get!

Was mostly being playful, I was a little annoyed at the sheer number of times I had to twiddle the PSU design which I'm still not sure about because Sovtek datasheets for the EHX tubes don't have any bloody graphs on to get better plate current values and I don't know how to draw my own load lines and stuff, but the annoyance wasn't aimed at you.
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#19
Well, I've ordered the components based on the last sketch. Can manage layout changes and some minor changes, like resistor values and stuff as I can probably get them shipped out on a basic stamp rather than as a packet.
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#20
For the 1K dropper will 3W be enough?

What's this amp drawing in current?
I'd guess maybe 50mA total at idle. It's probably around there 40mA-80mA.

Anyways (1K)(50mA)^2 = 2.5W
2.5W is cutting it pretty close to the 3W mark. I'd be using 5W or more for that resistor.


Also for the tone control you might find you will prefer an audio taper. The Tweed control (that your using) is implemented with an audio taper pot generally.
#21
Hrmm, you're right, I'll see how it goes. If it gets hot I'll get a 5W.

I use the tweed tone control in a few of my pedal designs using a linear on the tone, if it doesn't work well I'll swap it.
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#23
Well... I ordered screw mount turrets (for ease) but forgot to get the nuts to go with them do I tagged a 5W resistor on the order.

Here's a few pics to keep you going though


Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#24
screw mount turrets? where?
Jumping on dat gear sig train.
PRS Hollowbody II / BKP Warpigs
Strandberg OS6T / BKP Aftermath
Strandberg OS7 / Lace Poopsticks
Skervesen Raptor 7FF / BKP Warpigs
Skervesen Raptor 6 NTB / BKP Juggernauts
Hapas Sludge 7 FF / Hapas Leviathan
Anderson Baritom / Motorcity Nuke BKP Sinner Anderson H2+
Warmoth Baritone / BKP Piledriver
Ibanez Rg2120x / BKP Nailbomb

Blackstar ID:Core Beam
#26
nuts still not arrived yet Getting impatient
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#28
a) they're M2.5, they are by no means common, nowhere local have them I'd have to go all the way into town which I'm doing today but they're due in the post today too so no point really.

b) OMG! Jared! long time no speak! lol, hey man :p
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#30
That's alright, I'll stick with it as is unless I run into any problems.

Stuck at my mother's house... wish I could get home and get on with the amp build, my light duty planer blew up planing down my ash and took a chunk out of it on the guitar build, should have waited and used my boss's one, but ordering myself a heavy duty trade one now, need it anyway training as a chippy

But now I'm stuck doing nothing until 7 :/ so bored
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#31
An evening's work:


Got the day to myself tomorrow so hope to have the control plate cut and drilled, and the rest of the wiring soldered to the board, and if my punch arrives the wiring finished and the tube socket fitted
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#32
I promised updates, but then my daughter got sick, consequently I didn't sleep, wedding anniversary, work, and now mother's day tomorrow so I've been kinda swamped, and to top it off one of the handle brackets has disappeared so I may need to order a whole new handle should hopefully get some more work done on Monday
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#33
ok, I got the whole thing put together, and I got some very annoying and weird feedback/hum/squeal kind of stuff going on now that oscillates when I use the volume control and sounds like trying to tune a radio with the variable whistle and stuff, I'll try get some sound samples later tonight before I start debugging, got it narrowed down to several possibilities to check for in order of (my guessed) likelihood:

Layout issue - ground loop
Layout issue - wire dress
Microphonic tube
SS recto forming an AM antennae

will be debugging tonight as I said so will see how things go
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#35
tube* there's only one

and all the ground connections were checked prior to first powerup


here's a sound clip:
http://www.unquenchable.co.uk/images/ampsamp.wav

the small squeal is the basic issue, the wavey oscillating stuff is when I move the tone control
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#36
ok, think I've narrowed down the issue to a lead dress issue, had the (unshielded) signal wire between the triode grid stopper and the actual pin on the tube running basically right under the OT, so I think I was getting RF feedback from the transformer, gonna replace it for a shielded cable tomorrow night and try that
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#37
Definitely sounds like lead-dress problem to me. It's strange that it would be so intense in what should be a rather low gain amp. Is there any chance you can get some pictures up of the inside of the amp?

Also, never neglect the old chopstick trick. Move the wires around with a chopstick and see which ones affect the squeal.
#38
the chopstick is how I found the wire (and the other wire to try after)

the amp is really REALLY tiny, it's built into a FM15 enclosure so everything is built into a measly 12"x5" floorspace, and unlike normal amp enclosures it's all on the same level not with an earthed chassis between the transformers and the components

I actually have photos, let me see if I can find a link...



If I can't work the issues out I'll have to get a new chassis and build a new enclosure for it, I've got some 1/2" ply hanging around
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#39
Two things:

1. The transformer on the far left in that picture (looks like the power transformer) - its endbell can be pushing some its magnetic field into the output section of the amp. I doubt it's your problem, but it can't be helping.

2. This one is more likely your problem. The way you have your tube makes it so that all your wires must past next to each other to get to the tube. The grids are very sensitive to any stray signals. So you're plate and heater wires are feeding stray signals into the grids which are most likely giving you troubles. If you must run the tube that way, run the two grid wires in their own separate holes away from the rest of the wires. The grid wires should be as short as possible and not be anywhere near the other wires - except maybe the cathode wire. Cathodes don't tend to give much in the way of stray signals.
#40
if I shield both the grid wires and run them separately will that help? it is both my grid wires that are the possible issues (identified via chopstick) so I'll go ahead and separate them and replace them with shielded cable and ground the shield straight to earth.

If I can't solve it like that I'll have to rebuild the damn thing as I'll need more space for a better layout

EDIT: pretty much no way I can fit the trannies in anywhere else without making the floorspace bigger so hopefully that isn't gonna be the issue
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
Last edited by GABarrie at Apr 16, 2012,
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