Decibel Dungeon


In the dark and distant past, DIY hi-fi was either limited to knocking up a pair of loudspeakers, or confined to those lucky enough to have the skills and knowledge to design and build their own electronics. The Internet has changed all that and since I started Decibel Dungeon, the hobby has become more popular than I could have imagined ten years ago. With the advent of the Gainclone, and more recently, the class-T amps, more and more of us have been building our own amplifiers, either from scratch, from kits or by housing completed modules. One of the hurdles that potential builders have to over come, and arguably the biggest one, is finding a worthy housing for their amp, pre-amp or DAC. Here is one attractive solution to that problem.

A pair of propods
Ladies and gentlemen - The Propods.

OK, if you are familiar with this site, you will notice some similarity to the DIY Pods that I have described here. A friend of mine who is also a local businessman decided to take the idea and offer some ready-made pods with a more professional finish.
Aluminium was chosen as the material for the casing as many builders prefer some sort of shielding but do not want a magnetic material like steel. I had always wondered why such cases were not more widely available and my answer came when my friend tried to source some suitably sized tubing. The only option was to have it specially manufactured. This in turn meant a minimum order quantity and therefore a substantial financial commitment to the project. And it was the same with most of the other parts that go to make up the Propods. So we DIYers should be very grateful that somebody has been prepared to outlay such a large sum to make these cases available.
I can't start to tell you how much work has gone into producing the Propods. Because of the way the aluminium tubes are produced, they require an enormous amount of work to polish them up to an acceptable finish. The wooden fronts and feet require sanding and finishing too. But at last the Propods are ready!
For now, the pods are available in a natural polished aluminium finish with wooden front plates and matching feet. Wood options are Oak, Cherry, Walnut, Ash, and Maple. If there is enough interest in them, it is planned to offer a black anodised finish and possibly resin front plates/feet perhaps in an translucent blue finish.
Each Propod comes as shown in the picture below. Apart from the front plate and feet, there is a matching wooden knob. The knob is drilled to accept a 6 mm diameter spindle and there is a corresponding hole in the centre of the front plate. If you don't use the knob, the hole will accommodate an LED.

A Propod with oak trim
A Propod with oak trim.

Inside the Propod is a metal tray that is attached between the front plate and back plate. This makes it relatively straight forward to attach a PCB using your choice of stand-offs. The tray has been designed so that you can fit electronics both above and below and it's surprising how much you can fit in to them!

A Propod tray
A Propod 'tray'.
The tray is 92 mm wide and 190 mm long. The internal diameter of the tube is 99 mm.

The back plate is ready for drilling to accept any necessary sockets. It is attached to the tray using allen bolts and nuts and can be quickly removed to facilitate drilling. It may also be removed from the front plate if necessary by unscrewing two screws.

A Propod with cherry trim
A Propod with cherry trim.

A Propod with ash trim
A Propod with ash trim.

The Propods will easily accept class-T amplifier modules such as the DiyParadise Charlize and Autocostriure class-T amps. DAC's also fit in very well. One, or even a pair of chip amps could be accommodated subject to the cooling being adequate. It is also possible to fit a pre amp into one of the pods with a little planning and depending on how many sources you need to connect. I have fitted one of the Skynet modules inside a Propod. So you can see that these cases are quite versatile!

A Propod system
A Propod system.

Here is a system that I built for a customer who wanted a compact, aesthetically pleasing, and bespoke system that used compact SMPS modules and used the DiyParadise Monica2 DAC and Charlize amplifier.

In order to match the DAC and amp, it was necessary to add an active stage between them and this was accomplished with an opamp buffer using OPA134 opamps. I had originally intended to use OPA627 opamps but they do not work very well with lower (12 volt in this case) voltage rails. I tried several opamps before settling on the OPA134, and then set about tuning the circuit until I got the best possible sound. A gain of 8 works very well in this system. I must give thanks to Carlos Machado for his advice on this part of the job.

Circuit of pre-amp used in the Propod system
The pre-amp circuit. IMPORTANT - please note: The supply rails for the above circuit are +/-12v. If you use higher voltage rails, the chip (as biased here) will dissipate too much heat!

Because this will be used as a 'system', and because there are DC blocking caps on the output of the DAC , and input of the amplifier, there was no need to add more DC blocking caps in the pre-amp. If you use this circuit in other applications, please be aware that you may need to add DC blocking caps.

The capacitor across the feedback resistor lowers the gain at higher frequencies. The impedance of a capacitor is 1/(2*pi*freq*C), so as frequency increases the impedance of the cap decreases. This in turn decreases the feedback impedance because the cap is in parallel with the resistor. 33pF will start to gradually reduce the gain around 50kHz and will reduce the gain to about half around 2MHz.

The pre-amp has two inputs and a stepped attenuator. There is also a delay circuit that shorts the output until the circuit has 'settled' after power up. Another delay circiut in the amp is used to apply the power gradually, thus reducing power up noise to a minimum.

The whole system is turned on and off by one switch as it will be used by other members of the customer's family.

This is a good example of what can be achieved using the Propods. I won't tell you how much all this cost but if I tell you that you can almost have two of these systems for the price of say a 47 Labs Gaincard, if gives you some idea. I'm not knocking commercial hi-fi here, I fully understand their overheads, but it does show that there is a viable alternative to good-looking, and good-sounding commercial hi-fi! Believe me, this system sings and you can judge the looks for yourself.

But don't just take my word for this. Here is what the person who owns this system says:

Dear Nick,

I just had to write and thank you for putting the propod system together for me. I have had it running for several weeks now and I am discovering new things about my existing music every day. I have to agree with your dungeon opinion that the propod system combining a diyparadise Monica2 DAC, the preamp design on the propod page on your site and the diyparadise charlize T-power amp with the fostex fe207e MLTLs that I put together is a real winner.

Your professionalism, rigour and real investment in the project were impressive throughout the process of decision assembly, testing and delivery.

I could have taken my budget and put it into something that looked more "ordinary" sounded worse but came with loads of marketing and brand image. Admittedly the finish on my homegrown speakers is certainly not up to par compared with your work or factory built items but, satisfaction from having researched and listened and waited apart, I am conviced that there is no way that I could have the sound I have today for the same money any other way.

So, thanks to you specifically for all your help and thanks to the rest of the DIY HiFi community in general for putting so much real intellectual capital into the public domain.



So now we come to the business part of the page. The price for a Propod as described above will be 59 UK pounds. The initial aim was to have produced something for a bit less, but this is as low as it can go and not loose any money on the project. And remember, if the money comes back in, it will be used to develop some more options. I can assure you that I have seen the material costs for the pods, and seen the amount of man hours that go into making them. Considering that, the price is more than fair. Please keep in mind these are currently being made in smallish numbers by hand!
Because this product is aimed at the DIY market, and because it can be quite labour intensive to finish the Propods, it has been decided to offer them either 'finished', or in 'kit' form. That means that you could purchase all the parts needed to complete a pod but you would have to polish up the aluminium tube and finish the wood parts with varnish, wax or oil as you prefer. In this case, the purchase price would be 49 UK pounds. The Propods are currently polished on a polishing machine using a variety of polishing wheels. But you can achieve excellent results using a fine grade wet and dry abrasive paper, followed by a metal polish. Full instructions will be posted here soon.
We would also like to point out that it is impossible to achieve a totally blemish free finish on this type of curved aluminium surface but any blemishes are only noticeable on very close inspection and the Propods look great under normal viewing. The 'finished' Propods are protected with a special clear wax to prevent them tarnishing.
Other options being considered include a full build service for certain commercial products like the Charlize amplifier and Monica2 DAC. In this case we would suggest having the modules sent to us so that they can be built into a Propod with the appropriate sockets. It may also be possible to carry out other bespoke work to the customer's instructions (see the above system).

A Propod with walnut trim
A Propod with walnut trim.

Purchasing Propods.

The total cost for a single Propod including the shipping charges depends on where you want them delivered to:

Delivery toFinished *Kit **
All UK destinations 65 UK pounds 55 UK pounds
All Europian destinations 67 UK pounds 57 UK pounds
All other destinations 72 UK pounds 62 UK pounds
If you require currency conversion click here.

* Finished means that the Propods have been polished and sealed and the woodwork sanded and sealed.
** Kit means that the components (aluminium tube and wooden front plate, feet and knob) are supplied for the buyer to finish.

If you would like to purchase one or more Propods, please write to me by clicking on the contact button below. Please state exactly what you want to buy, ie number of Propods, finished or kit, and choice of wood. Please also state where you live and make sure that you supply the correct email address.
Contact me

Please note that I always reply to all enquiries so if you don't hear from me, it is because your account is bouncing or the email addresss you supplied is invalid!

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