Chassis dimensions and board dimensions?

[Chad]

NICE! Thank's for the link.

[Mark]

Thanks for all the photo's and info. I was looking at the silver Dumble that I have photo's of and I realise that just about every circuit I have has a master volume control in it. Thus I had to rethink the chassis.

I think it is important to be quite open about such things as chassis size and layout as the closer we come to having a standard size chassis and layout, the easily it will be to help each other as there will be less variables in the build to worry about.

I will have to do something about posting the pictures up of Gil Aran's D clones. He uses (overdrive) pots in both his Skyliner amp and the regular D amp that he uses.

P.S. Normster, that is an amazing build, please share more info with us about it!

[Mark]

I still haven't heard anything on the chassis dimensions from anyone.

As far as I can tell the chassis is 2.5" high, and probably around 19" long.

I was wondering if it is worth trying to come out with the dimensions of the silver Dumble chassis as most people seem to prefer the Skyliner of one of the hybrids with a master volume control.

Just out of curiouslity what are peoples thoughts on their favourite Dumble circuit?

[jelle]

Hi Mark,

I found a data sheet for the ODS combo:
http://homepage.mac.com/bill_jpn_morgan ... le/od.html

19'' will be about right.

On this site there's a lot of information, but most of you probably will have seen it already...

Being a SRV fan, my fav Dumble would be a SSS.

Normster, now you've succesfully built the jFet, would you like to share some details with us?:
How did you do the jFet circuitry? How did you blend it into the signal path and how is the power supply connected to the jFet?

Does anybody know how to add a jFet volume knob?

Thanks,

Jelle
The Netherlands

[Normster]

Normster, now you've succesfully built the jFet, would you like to share some details with us?:
How did you do the jFet circuitry? How did you blend it into the signal path and how is the power supply connected to the jFet?

Does anybody know how to add a jFet volume knob?

Thanks,

Jelle
The Netherlands

I'll draw up a schematic this weekend. Basically, the FET output is wired to the switching jack of the NOR input. Input for the FET is handled with a stereo switching jack. Power comes from B5 via a wire connected to the plate resistor B+ for V1. To add a volume knob, just connect flying leads in place of the 10k trimmer and run them to wherever you want to install the pot. I saw a picture of a modded Dumble that had the pot mounted on the bottom of the chassis. Looked awkward to me.

FWIW, the FET input on my amp sounds like crap. Even with the trimmer turned down, it boosts the signal in a very unpleasant way. I suppose if I still had my old accoustic (piezo and no preamp) it might be useful. I included it because I wanted to try building a "replica" as a baseline for other builds. On future builds, I'll probably use the two inputs for impedence matching of single coils and humbuckers...more practical for me.

Edit: Here's the schematic. Kinda rough but you should be able to figure it out from this.

[Mark]

Dear Normster

Can you give me a few tips about your chassis?

[jelle]

Hi Normster,
Thanks for the explanation!
It looks great in your amp, it's a pity it doesn't sound good.
I have a number of questions ever since I got the pictures from acplink...

What is the 20uF (?) 500v e-cap in the left corner of your built for? Is it for the jfet?

Did you use the NTE 452? Can this be done with another jfet? The electronics shop in the town I live in doesnt have the NTE 452 but will probably have some european equivalent. Does anybody know which one to pick?

Does anybody know of a dumble-amp user that actually used the jfet input? I understood it has a purpose for ancient effects that need a high impedance and also for acoustic passive piezo guitars.
Why are the built into every dumble amp if it sounds like crap?

Dazed and confused..

Jelle
The Netherlands

[Normster]

Dear Normster

Can you give me a few tips about your chassis?

Glad to. In fact, since there are some first time builders on this forum, I'll go into excessive detail.

I got the chassis from Natchanis Srivarakom [natchakom@hotmail.com] in Bangkok, Thailand. I believe there are a few others on this forum that have ordered this chassis as well. The chassis is .080" brushed aluminum with screen printed lettering. Natchanis used to sell these on ebay, but was issued a cease and desist. Cost was $105 plus $35 shipping. He also had an Overdrive Reverb chassis for $135. You can try contacting him via email. (I'm surprised he's not a forum member.)

Note that there are some layout issues with the Bangkok chassis. Tube spacing is about 3" instead of 2.5". Not a big deal. The chassis is punched for a 100W PT so you'll have to use big flat-washers or an adaptor plate if you're using a 50W tranny. Choke and OPT holes are drilled in the wrong place so you'll have to redrill if you're as detail-obsessed as I was. Then you've got those nasty extra holes. Lastly, the end caps are only inset by about 1/8" so you have to run your chassis mount screws inside the chassis rather than outside. This requires mounting the FET/bias/relay boards slightly off from the Dumble pics of #40. There's just enough room if you mount them with 1" clearance from either front or rear of the chassis.

The boards that come with the chassis are not useable. They're drilled wrong and have cheezy brass eyelets (not tinned). However, building an eyelet board is easy anyway. I used 1/16" Garolite G10/FR4 from McMaster-Carr. Eyelets are Keystone 1/8" x .093" from Mouser. I used 3/8" spacing on the eyelets when laying out the preamp board.

As you've already noted, this is an early pre "ratio control" style chassis. Although the last control knob is labelled "Level" it is actually a Master Volume. To compensate, I installed a 100k trimmer on my relay board that functions as an OD level. I just set it for where I typically run the OD and do any tweaks using the clean volume pot. It also doesn't use a Presence control, but has an "Accent" switch instead. The amp is very bright and articulate so I don't miss it and usually keep the Accent switch OFF.

The cab was built by my friend Loren, including all tolex work. My chassis was 1/4" wider than a real Dumble so my combo dimensions are 21"H x 21"W x 10 1/4"D. I didn't have the actual dimensions before building the cab so it's about 1" too tall. No biggie. It's built from 3/4" pine with 3/4" birch ply for the baffle.

Like many builders here, I used the Hybrid-A as the basis for my circuit. Also, like many builders here, I've swapped out a few values here and there to shape the tone to my liking. In the tone-shaping department, many thanks to Dogears for his knowledge, guidance, and generousity!

Trannys have already been discussed in another thread, but for the record, I used Bassman PT, OPT, and choke replacements from Hoffman Amps. The speaker is a Tonespotter. Hmmm...I think that about covers it.

While I really like the retro look of this amp, I think the chassis from BWilliamson and Funkalicious are far more practical foundations for a Dumble build. The holes are all in the right places, and they're punched for 8 control pots so you get an OD level and presence. Of note, Funk's chassis are already screen printed.

Hopefully this has been more than a long boring read. One of these days I'll get off my lazy duff and document the details of all of my builds.

[Normster]

Hi Normster,
Thanks for the explanation!
It looks great in your amp, it's a pity it doesn't sound good.
I have a number of questions ever since I got the pictures from acplink...

What is the 20uF (?) 500v e-cap in the left corner of your built for? Is it for the jfet?

Did you use the NTE 452? Can this be done with another jfet? The electronics shop in the town I live in doesnt have the NTE 452 but will probably have some european equivalent. Does anybody know which one to pick?

Does anybody know of a dumble-amp user that actually used the jfet input? I understood it has a purpose for ancient effects that need a high impedance and also for acoustic passive piezo guitars.
Why are the built into every dumble amp if it sounds like crap?

Dazed and confused..

Jelle
The Netherlands

The 20uF cap is filtering for V1. It's an odd place for it, but I guess it helps keep the PS board shorter.

Yes, I used the NTE452. Not sure about the Euro equivalent. Overall, I'd say that the FET is poorly understood, especially by me. I'm going to eliminate it from my next build.

[jelle]

Normster,

Thanks for the information.
The odd place for the cap looks like a way to keep the B+ supply for V1a/b cleaner ( less hum picked up because the leads are shorter) and perhaps more direct.

I 'll ask a local studio technician about the jfets. Maybe he knows..

Thanks,

Jelle

[Mark]

Dear Normster

Thanks for your reply, I hadn't heard of anyone other than Brent Williamson doing a run of Dumble chassis's thanks for the tip. I will have to shoot these individuals an email when I'm ready to build an amp.

I surprised that Nik at Ceriatone doesn't also build these chassis's?

Normster I hope you don't mind the questions, but I like to ask all the questions and try and think the amp through prior to building rather than building something that is vastly inferior.

After all it is all about building something that is special.

[Normster]

Dear Normster

Thanks for your reply, I hadn't heard of anyone other than Brent Williamson doing a run of Dumble chassis's thanks for the tip. I will have to shoot these individuals an email when I'm ready to build an amp.

I surprised that Nik at Ceriatone doesn't also build these chassis's?

Normster I hope you don't mind the questions, but I like to ask all the questions and try and think the amp through prior to building rather than building something that is vastly inferior.

After all it is all about building something that is special.

My pleasure, Mark.

[tonelab2]

The common garden replacement for the nte452 is the 2N5484.
I love the Fet layout. Tried it in a pedal form and found it great. Heaps of gain, adds sparkle with the 100pf cap(also good without), transparent , very slight compression which helps evens out an uneven guitar infact it gives a cheap guitar/amp setup abit more class with only spending a couple of bucks. Adds a little sustain to a dull guitar. I think it has a tube quality about it and think thats why HAD used it ( could be my tin ears as well). It's a nice little toy to play with. sub a trimmer for the bias resistor helps to tune it depending on voltages. 9v or 2x 9v in series. Don't know about the tone of the 2N5484, it's easily more available cheaper but haven't tried it. tweaking is the key.