Motown Direct Amplifier-inspired Preamp?

[untune]

Schematic looks basically OK to me. Nothing missing. I would be tempted to double the smoothing caps values. Heater elevation looks OK. It should sit at one third the HT voltage. I typically set mine at one quarter the HT voltage but one third is just as good.

Cheers

ian

Thanks Ian Noted on the caps, I put 100 as a minimum with the expectation of using a pair of 100+100 cans but it depends on what kind of chassis find, how much space there is etc. Currently looking for a decent shallow 2U aluminium rack enclosure that I can mount to the rear of for an old school approach

Also found an alternative power transformer here but I might see if they can do the same but with a higher rated heater tap—I was thinking about experimenting with the 6BX7GT at some point down the line but it's hungry on the current and wants 1.5A to itself. With the ECC83 it'll add up to 1.8A

 

[Perm0]

This seems to be local for you;

http://www.allmetalparts.co.uk/708-...ted-enclosure-chassis-case-5055726206378.html
No screws in the frontpanel 100mm depth

 

[ruffrecords]

Also found an alternative power transformer here but I might see if they can do the same but with a higher rated heater tap—I was thinking about experimenting with the 6BX7GT at some point down the line but it's hungry on the current and wants 1.5A to itself. With the ECC83 it'll add up to 1.8A

The 6BX7 is an interesting tube. I discovered it has already been used in a 4W audio amplifier design: 6BX7GT @ The Valve Museum
Note the 470uF smoothing caps.

Good to find another UK mains transformer manufacturer. There was another one, whose name escapes me right now, that I used to use years ago but the guy has now retired and shut up shop. You might also like to try Canterbury Windings but looking at his web site today I find he too is semi-retired and only making a couple a week for existing customers. Ho hum.

Cheers

Ian

 

[untune]

+20% VAT on the toal value (shipping included) + whatever toll fee. Ie, £180-200 total.

Sorry eskimo I skipped over this; quite pricey! Might be worth putting feelers out for a real Triad instead

This seems to be local for you;

http://www.allmetalparts.co.uk/708-...ted-enclosure-chassis-case-5055726206378.html
No screws in the frontpanel 100mm depth

Yes, thanks! I was looking over those last night, I may have even purchased some of these before when I built a modular synth a few years back. I had concerns over putting holes in back panel since I've never had to use punches before (I've always drilled metal) but it looks like some basic punches will handle 1.5mm mild steel. In the aforementioned synth project we had to trim down standard 19" black panels to fit a smaller case, and I was worried it'd either be too tough or the black coating would flake and shatter. We ended up doing it by hand with a jigsaw and a clamped guide, turned out fine, so maybe these are the best choice.

The alternative (and possibly very slightly cheaper) option would be to get either a Hammond or Bud unfinished aluminium chassis and then attach it to the back of a standard 2u rack panel. The aluminium would be easier to work with... either way there are options

The 6BX7 is an interesting tube. I discovered it has already been used in a 4W audio amplifier design: 6BX7GT @ The Valve Museum
Note the 470uF smoothing caps.

Good to find another UK mains transformer manufacturer. There was another one, whose name escapes me right now, that I used to use years ago but the guy has now retired and shut up shop. You might also like to try Canterbury Windings but looking at his web site today I find he too is semi-retired and only making a couple a week for existing customers. Ho hum.

It is, I have read around a lot and it seems like it is well suited for the cathode follower role, I guess that's why Mike chose it. No doubt they were much more abundant in the 1960s! I can't find much literature or many schematics, but plenty of discussion. Apparently the two triodes are very rarely well matched, and I think Morgan Jones tested a lot and found that distortion varied by a factor of four amongst his sample. Quite scarce in the UK too. I doubt it'd be a drop in in this circuit but maybe a paralleled CF like in the MB-1 output, unless there;'s some other cf arrangement it might have been utilised as. I'll attach a pdf I compiled of 6BX7 circuits from magazines, might be of interest!

And on the transformer front yes, it seems like primarywindings supplied AmpMaker with their non-Carnhill offering so I'm guessing the quality must be solid, and they're quite affordable - the one I linked even with the shroud is less than £40. And 40mA so not too overspecced - just that it could do with a bit more heater current for a second channel or the 6BX7 I had a look at Canterbury a couple of weeks back but if he's winding down then I guess it's best to stick to alternatives!

Cheers

 

[ruffrecords]

This seems to be local for you;

http://www.allmetalparts.co.uk/708-...ted-enclosure-chassis-case-5055726206378.html
No screws in the frontpanel 100mm depth

I was not aware of AllMetalParts either - handy range of stuff. 100mm should be plenty deep enough with the tubes mounted on the back panel.

Cheers

ian

 

[abbey road d enfer]

No screws in the frontpanel

Apparently, it's at the cost of having an ugly drop'out in the front panel...

 

[Perm0]

I recently found them when I googled for a 9.5" 1HE enclosure.
It was not in stock and not cheap, so I settled for a 28,- E Hammond box.

@Abbey ... I agree, it's not the most elegant enclosure.

 

[ruffrecords]

Apparently, it's at the cost of having an ugly drop'out in the front panel...

Looks like the front panel is meant to be some kind of U channel.

Cheers

Ian

 

[abbey road d enfer]

Looks like the front panel is meant to be some kind of U channel.

Yes, and it doesn't look as nice as a flat panel..

 

[untune]

I agree a flat panel would look better—on closer inspection, it appears as though the whole box has to be disassembled to get inside it, the lips of the front and back panels sit over the top and bottom pieces. What I'm inclined to do is get a Hammond 1444-20 (17" x 4" x 3") which is pretty much the standard size of a 2u enclosure, except in 1mm unfinished aluminium. The separate flat lid can be oriented to the top or bottom for easy access to the innards for modifications and maintenance, and flat 2u front panels are abundant - allmetalparts even do a 3mm or 1.5 mm flat front panel option in black or silver. Just a case of bolting the front on. Bit more metalwork, but you're going to be cutting and drilling anyway!

Or alternatively, you just buy the allmetalparts enclosure and get one of their flat panels (or see if they'll sub it for the folded one) but you'd be left with holes in the top and bottom front. It's cool that they do 50mm depth enclosures though, that's unusual and suits rear mounted hardware if you've nothing too hefty on your front panel, plus would keep your wiring runs shorter. I was finding it irritating that most places only do a minimum 8"/20cm depth—Hammond have 4"/10cm options but only in 1u.

 

[untune]

Just stumbled across this place , thought it could be of use since they have a few decent panel and case options and the prices seem very reasonable (bearing in mind they are ex. VAT). 3mm aluminium flat panels are a little dearer and are painted grey but it does say other options are available. If you can live with the extrusion they're cheaper, and you can also get them unfinished so you could paint them up yourself. Sounds like they do customisation too, though to what degree for one-offs I'm not sure. Oh and they offer 100mm depth for all cases!

 

[Perm0]

Oh, that's looking really good, love those EMC cases... UK broadcast stuff, classy !

I'm bookmarking this, thanks.

 

[ruffrecords]

Oh, that's looking really good, love those EMC cases... UK broadcast stuff, classy !

I'm bookmarking this, thanks.

Holt have been around for a long time and are much repsected.

Cheers

Ian

 

[Perm0]

For the quality I am seeing these are not super expensive, though for me in the Netherlands it will not be cheap, not the type of enclosore I would buy for messing around with an DIY build, but if I would commit to building something really classy with expensive parts this would the type of enclosure I would buy.

The broadcast guys have all the good stuff, really... I guess it's the government budgets they got in the past.
These guys went all out, spend it all !

I've got a lot of old Dutch broadcast stuff, saved from the scrapyard as I was the cable guy that had to pull it all out for the big digital HD conversion of the whole system.
The engineers liked that I was so passionate about this old stuff so they saved a lot of nice bits for me, transformers, transformers and transformers... and these nice huge solid EBE rotary switches.

 

[ruffrecords]

Schroff do a range of 19 inch enclosures and they are available in most European countries. Fischer do them too. There are quite a few manufacturers of this type of enclosure so it should be possible to find one more local to you.

Cheers

Ian

 

[Perm0]

Schroff do a range of 19 inch enclosures and they are available in most European countries. Fischer do them too. There are quite a few manufacturers of this type of enclosure so it should be possible to find one more local to you.

Cheers

Ian

Yeah I know these, never been a fan of the galvanicly plated ratteling lid that comes with these, but they are not expensive and have used them at work.
The Holt stuff is just the most appealing enclosures I have seen so far, I like that style, the paintjobs, the coating on the metal, this is craftsmanship, I'm a sucker for quality but it often comes at a price, that goes for all mechanical bits.

I have never had problems scoring cheap enclosures, many available, and I do my own frontpanels, I got a stack of nice Rittal 4mm anodized aluminium blindpanels that I got for free, I don't mind spending some quality time with these to save me a couple of hundred euros;

This has been hanging there for two weeks now, but I can still smell the paint so it's not fully cured yet and ready to handle.

I'm the "cheap front panel" guy

 

[untune]

Yeah I know these, never been a fan of the galvanicly plated ratteling lid that comes with these, but they are not expensive and have used them at work.
The Holt stuff is just the most appealing enclosures I have seen so far, I like that style, the paintjobs, the coating on the metal, this is craftsmanship, I'm a sucker for quality but it often comes at a price, that goes for all mechanical bits.

I have never had problems scoring cheap enclosures, many available, and I do my own frontpanels, I got a stack of nice Rittal 4mm anodized aluminium blindpanels that I got for free, I don't mind spending some quality time with these to save me a couple of hundred euros;

I know what you mean; they look crafted to a very high standard and like Ian says, if they've been around a while and they are well-respected then they're obviously doing it right.

Your front panel looks great, nothing cheap-looking about it! Takes a lot of patience to get things right with painting too, lot of time investment, but I think the satisfaction is worth it in the end.

With this project I wanted to try keeping that old-school look so I'm going to assemble it from pieces and bolt it all together, although I've had to order a steel front panel so that's going to be a challenge to put holes in, especially as I'm looking at putting a VU meter in which will probably need a hole of at least 55mm diameter, plus the punches I've found are only rated to 16 gauge and mine is 14.

I've also sent an enquiry to PrimaryWindings to see if they will do a variant on the 250v/40mA sec with more current on the heater tap, might grab a couple and keep one aside for future! Got to start gathering components now

 

[ruffrecords]

I wish someone would do a nice steel 19 inch case with aluminium front and back panels - they are so much easier to woodwork with than steel.

Of course Frank (frontpanels.de) does these but they are 300mm deep.

And I forgot about modushop.biz who do several different types of 170mm deep enclosures.

Cheers

ian

 

[untune]

I wish someone would do a nice steel 19 inch case with aluminium front and back panels - they are so much easier to woodwork with than steel.

Ian, I have used these from CPC in the past for an AML EZ1073 and an Oakley filter, case is 1.2mm steel and the front panel is 3mm aluminium... despite the rear panel being steel I have put XLRs, jacks and an IEC/switch in them and don't remember it being too much hassle.

CPC doesn't have any good technical documentation on them for some reason, but look at Penn Elcom's site here at the Q&As and they state that if you send them the necessary design, they will custom cut the rear panel for you, not sure on cost though. For some reason it's cheaper to buy them from CPC than PE directly but apprently they price match so, maybe worth enquiring

Only things I didn't like on these was: the venting in the top panel—not for any real reason other than aesthetic preference, but if you were doing anything with valves you might want them to breathe anyway! And minimum 220mm depth, they felt a bit oversized (for my needs at least) but if you like a lot of space then again, not really a concern.

Cheers

 

[MidnightArrakis]

Since I see that you fellows are discussing "rack-mount" chassis and enclosures, I thought I would share with you another potential supplier that sells their products in both the EU and the USA. They are called -- OKW Enclosures -- and they have a rather wide range of not only "rack-mount" enclosures, but also all manner of desktop, handheld, wall-mount and even wearable enclosures. Here are some links to their different "rack-mount" series of enclosures:

OKW Enclosures -- Combimet Series

OKW Enclosures -- Unimet Series

OKW Enclosures -- VersaMet Series

OKW Enclosures -- Mettec Series

And.....just for general enclosure browsing, you can visit their website at: okwenclosures.com

In addition, should you not be interested in drilling/filing/hacking your new enclosure for your project, OKW will also do the machining for you (at a cost).

I hope this helps everyone out!!!

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