final version of my IMPRO REVERB (+Casino pron)

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sookwinder
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final version of my IMPRO REVERB (+Casino pron)

Post by sookwinder » Sat Jun 16, 2012 11:49 pm

As I mentioned previously, last year I develop/designed/stole ideas for my Princeton sized IMPRO REVERB (IR01)
IR01: 2xEL34 / GZ34 / reverb / bassman OT /Champ style trem / vintage Jensen C10N/ mids switch / bright switch /NFB switch / somewhere around 30 - 35W

Got it working sufficiently well (read: stable and not likely to melt into a giant white ball of flames) that I have been recording with it and I felt the design was robust enough so my nephew could build one. I did, over the xmas break' make some layout and component changes (moving locations of cathode caps/resistors to be close to the particular star earth point they needed to be near) and Daniel and I started building his amp.

In parallel I started building my second IR01 because really the first one was and can only be called a prototype.

I decided not to use the vintage style cloth covered wire, even though it is a dream to use, as I wanted to utilise the teflon covered wire I had used on the first version of this amp's heater wires, throughout this entire second build. I had secured enough white teflon covered wire (ex 1970s US Navy) and red teflon wire (ex USSR military from Czech Republic) and jumped right in.

I have come to the conclusion that the best way to build amps is when you actually do not need the amp. That way you build it more slowly, more carefully and there is not the need or desire to just keep going for another 30 minutes into the small hours of the morning. If you are tired or are rushing mistakes occur, you wire it up incorrectly, you give yourself electrical shocks ... it just isn't an enjoyable process.

However with this build because (as you can see by the photos) the solid core teflon wire behaves a little differently than the solid core cloth coverd wire, you need to or maybe you just can look at the layout, the lead dress and work out the exact shape, the exact locations of bends the wire needs and then pre-form the wire to fit ... rather than soldering one end and moving/bending the wire as you go to the other solder point .

Some evenings I just soldered 3 or 4 wires (in fact one evening it was just one wire ... the one bewteen the NFB switch and the NFB resistor ... but it did take 45 minutes to determine the best path and exact shape the wire needed to be)

The end result using the teflon covered wire is superb.
Yes it takes more thought and overview of the layout to determine the routing of the wires. I know I could have just done what I normally do with cloth wire ... cut a piece and if it's too long just push it "somehwere" ... but given this amp is like shoe horning a V8 into a Mini Cooper, I wanted to have the best lead dress I could.

Another advantage of this teflon covered wire is that because the teflon is quite thin compared to say plastic coated wire you can do a small radius bend with no trouble. Further the lead dress and layout can be almost 3-D if that makes sense... Plus there is the obvious advantage of safety and the build itself looks cleaner and not as cluttered.

All future amp builds I do will be using teflon covered wire.

The only "stuff up" I did was not triming the "legs" of one of the main line filter capacitors. I had placed the caps into the Doghouse fibreboard and bent the legs so the caps wouldn't fall out. Soldered them all except for the filter cap for the preamp section as it has a separate earth from the other line filter caps. But when I came to solder that final filter cap I had forgotton that I had not trimmed the legs. When I turned on the amp I had no volts at all in the preamp section because the legs were shoring out and the voltage was leaking directly to earth.

It took me about 40 minutes (with the amp being turned on and then off) to finally realise what I had done. Amazingly no damage occured to anything.

Using my scope (a Hantek Digital Storage Oscilloscope DSO5102B 100M 1Gs/S), a signal generator and an 8 ohm dummy load resistor, I measured 22 watts of clean and about 30 watts of distorted power. Basically what I wanted.
The distortion cuts in about 6.8 - 7 on the volume dial and the output valves go into distortion before the PI. The PI doesn't distort until somewhere between 7.5 - 8 and given that the PI is cathodynePI, the distortion is second order anyway .. a postitive in my book.


The amp is much quieter than the prototype build, but with the same cut through that a BF style amp has. The NFB switch, MIDS switch and BRIGHT switch are great at tonal changes. The VibroChamp style trem is wonderful... but as Brad mentioned some years back, always keep a shorting plug in the trem pedal RCA (if the pedal isn't fitted). The slight changes I made to the reverb circuit from the prototype set up worked and the reverb is how it should be. The earth is back on its axis.

Vintage NOS Mullard EL34s & a GZ34, RCA 1950s 12AX7s and a Telefunken 12AT7 all do their stuff as we expect. The 60s Jensen smooth cone C10N cannot be beaten.

I had intended to fit this amp into a SURF GREEN coloured tolex cab (from Mojotone) which I had ordered and received. But while I was building the amp I noticed MOJO had a new colour tolex available: TEAL ....awesome... so I ordered a TEAL tolex covered cab. When it arrived the colour was even better than the photos they had sent me... it was a cross between TEAL and a Fender FOAM GREEN ..wwoooooooooooowwww. Plus the quality of the cabinets from MOJO is second to none. I love their product.

I don't know what it is or why, but the digital cameras I have access to do not seem to be able to capture the real colour or the real hue of the tolex. The following pic shows what the colour really looks like compared to what the camera thinks it looks like:
Image

For those interested below are the schematic,layout and fibreboard drawings:
IR01 layout
IR01 schematic
IR01 main fibreboard
IR01 DOGHOUSE fibreboard
IR01 DOGHOUSE layout

Thanks to all that have commented (on Daniel's amp) and especially thanks to James (Jimboyogi)

I took some shots of the completed amp by itself and with my 65 Casino. they look good together and sound great as well.

As they say ... it's been a blast !

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The actual lead dress looked amazingly like the layout drawing I developed
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Once you understand the theory behind "star earths" it makes so much sense and allows a clean build
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The legs of the final line filter capacitor shorting the voltage to earth!
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===========
Edit September 2012
for what ever reason no matter what camera I use to take a photo of this TEAL coloured tolex from MOJO it always comes out bluey teal not greeny teal like it actually is. So just to show what the colour of the tolex really looks like I have done some rough graphics manipulation and this is pretty much spot on.

Image
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Re: final version of my IMPRO REVERB (+Casino pron)

Post by jimboyogi » Sun Jun 17, 2012 1:50 am

Congratulations David, a true work of art :?

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by andersthode » Sun Jun 17, 2012 5:18 am

This amp looks so cool! I want so bad to build my own Priceton or Deluxe Reverb clone, but I'm sure I'll electrocute my self in the process.

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by øøøøøøø » Sun Jun 17, 2012 5:48 am

what is the second slide switch? the one between the 2 tone controls?

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by sookwinder » Sun Jun 17, 2012 6:47 am

øøøøøøø wrote:what is the second slide switch? the one between the 2 tone controls?
The slider is a MIDS switch.

While working on the design I decided to add a switch that would re-gain the mids that are normally lost to earth in a standard BF tone stack circuit.

Checked out lots and lots of schematics of amps that are known for and known as "amps with lots of mids" . Both vintage designs and modern designs. Where Fender BF amps usually have a 6.8k resistor to earth in the tone stack,
these other types of (non BF) amps have anywhere from 18 - 35k resistor.

Now my logic was if I wanted a full on amp that had more mids than you can poke a stick at then I might as well get one of those amps and be done with it. But this slider "MIDS" would be for when you want a noticable increase in those mid frequencies, adding thickness and body to the sound but still retaining a SC pups feel.

So I decided to have a switch which allows (1) the standard 6.8k dropping resistor as per BF design and (2) a 22k combined resistor (6.8 + 15) to recover the mids.

It works just as I hoped. Also when coupled with the NFB switch turned off there is a wildness not seen often in a BF style amp

The wiring was pretty simple.
The common tab (left one) on the bass pot normally has the 6.8k resistor to earth.
Rather than connecting the 6.8k resistor, the slider switch is connected to the bass pot common tab.
The bottom half of the slider switch then is connected to the 6.8k resistor and then the resistor in turn to the earth rail.
All this will produce the standard BF set up.
When the slider switch is slid up, it connects in the 15k resistor in series prior to the 6.8k resistor making a total of 22k

Here's some pics that may help...
Image
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Re: final version of my IMPRO REVERB (+Casino pron)

Post by tribi9 » Sun Jun 17, 2012 8:09 am

A work of art. Beautiful. Congrats.

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by matt22 » Sun Jun 17, 2012 11:19 am

I'm very impressed! Nicely done!
Matt tha Kat Lentz

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by øøøøøøø » Sun Jun 17, 2012 2:09 pm

interesting mids control. And all without adding any extra (appreciable) length of wire to the tone stack. Smart!

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by s_mcsleazy » Sun Jun 17, 2012 3:09 pm

clips?
offset guitars resident bass player.
'Are you trying to seduce me Mrs Robinson? Or do you just want me to solder a couple of resistors into your Muff?'

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by sookwinder » Sun Jun 17, 2012 3:22 pm

s_mcsleazy wrote:clips?
at the moment we are in vocal tracking mode... but when we get back to laying down more guitar tracks, I'll put something up...
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Re: final version of my IMPRO REVERB (+Casino pron)

Post by StevenO » Sun Jun 17, 2012 4:03 pm

s_mcsleazy wrote:clips?
With that Casino, please. ;)

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by 46346 » Sun Jun 17, 2012 6:18 pm

fantastic wiring job! an inspiring build for sure.

hey sook - what's model is that Hantek scope? my old analog scope has bitten the dust. i really only need something affordable that can cover amp and pedal circuits, but that one looks rad. is it nicer than i need or would that be a candidate?

thanks for you help on my Bassman!

-eric
Dream Apes, ACME, Malcolm Mooney, Cat Museum, Cooling Time

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by sookwinder » Sun Jun 17, 2012 7:07 pm

46346 wrote:hey sook - what's model is that Hantek scope? my old analog scope has bitten the dust. i really only need something affordable that can cover amp and pedal circuits, but that one looks rad. is it nicer than i need or would that be a candidate?
-eric
Hantek Digital Storage Oscilloscope DSO5102B 100M 1Gs/S

check them out on ebay
http://www.ebay.com/sch/i.html?_nkw=Han ... &_osacat=0
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Re: final version of my IMPRO REVERB (+Casino pron)

Post by korey-craft » Sun Jun 17, 2012 7:44 pm

a run down of that Casino would be nice too. The finish looks different than most, and also the rotary switching explantion would be cool as well. Looks great!

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Re: final version of my IMPRO REVERB (+Casino pron)

Post by sookwinder » Sun Jun 17, 2012 8:32 pm

korey-craft wrote:a run down of that Casino would be nice too. The finish looks different than most, and also the rotary switching explantion would be cool as well. Looks great!
The rotary switch is a "varitone" system that Gibson used on their 345 and 355 models.
The varitone system being fitted to a Casino is extremely rare.
It is a 6 poistion rotary switch which adds into the circuit an additional capacitor (on top of the caps already there on the tone pots).

The variation in cap sizes allow for a dramatic change in voicing... for example position 4 makes the guitar sound like a strat.

the positions are as follows:
Pos.1 no additional cap in circuit
Pos.2 0.001uF cap added to circuit
Pos.3 0.003uF cap added to circuit
Pos.4 0.01uF cap added to circuit
Pos.5 0.03uF cap added to circuit
Pos.6 0.22uF cap added to circuit

This thread has more info
http://www.offsetguitars.com/forums/vie ... =9&t=56062

I had the stereo output jack changed to a mono jack... in my scenario using a "Y" cable was just stupid and so the guitar is now totally usable.
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