Decibel Dungeon


This idea behind this page is to provide those with little knowledge of DIY hi-fi with the information they need to build their own hi-fi system. I will describe how to build a preamp, active crossovers, power amplifiers and matching loudspeakers. Although building CD players is not for beginners (but you could build a turntable, see the Turntable projects page for details), I will give full details of structurally modifying a Philips CD723 CD player which improves the sound quality considerably. This job is not too difficult and involves very little work on the electronics. Total cost of the system if you do all the work yourself should be around 700UKP (including buying the CD player).
I'll try and explain everything as carefully as I can and hopefully, you will learn some hi-fi and electronics theory along the way. If there is something I haven't explained to your satisfaction, you can email me and I will help you if I can. Before you contact me however, please refer to the relevant section of this site to see if it contains the information that you require.
The design of the preamp, active crossovers and loudspeakers is based on my own system so it is tried and tested, rather than just theoretical. As it would be difficult for everybody reading this to buy the same amplifiers that I use (modified Arcam A60's) I have chosen a design by Rod Elliott which should be relatively simple to build and not cost too much either. Rod supplies PCB's for this design so building the amplifiers involves soldering in the components, adding a power supply and then fitting everything into a case. I'm not trying to make this sound too easy but for anyone willing to try the DIY approach, this system will be about as easy as it gets.
You should remember that you don't have to do everything yourself. For instance you could find somebody qualified to build your power supplies and test your equipment for you. Or you may care to have a carpenter build the loudspeaker cabinets for you. Even if you had most of the construction work done for you, the finished system should still represent very good value for the outlay. Remember, this isn't a budget hi-fi, it's a top quality system using quality components. It has audiophile features like a separate psu, stepped attenuator and active crossover. It has been tried and tested, and sounds great.
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Setting it all up

Once you have built the Decibel Dungeon system, you will want to make sure that you get the best performance from it. This will entail using compatible interconnects and 'speaker cables, and installing the equipment correctly. You can find information on both these aspects by going to the relevent sections of this site. Despite saying that I had no intention of giving specific details about items like interconnects, I thought that I may as well describe those which appear to work well with the project system which I am using.


Taking the cables in some sort of order, I'll start with the interconnects between the CD player and the preamp. After a lot of experimenting with different cable configurations, I found the one which gave me the best all-round performance was a simple design based on the commercially available DNM Reson. To make this design, get some 0.6mm solid core wire, plain copper or silver-plated. Find some discarded plastic parcel strapping and tape two runs of wire to each edge (so that the strapping forms a spacer). Then solder plugs on either end. I prefer the plastic bodied type, they're cheap and seem to work very well. I did read an explanation of why plastic bodied plugs may sound better than metal ones. I think it was something to do with magnetic fields. One of these days I intend to move over to the XLR type plugs and sockets which are made entirely from plastic, apart from the conductors of course.
I prefer to use, and strongly recommend, long cables between the preamp and power amps which means a minimum length for the 'speaker cables. My 2.4 metre examples are made up as follows:
  1. Obtain the following wires, copper or silver-plated as you prefer (mine are silver-plated).
    • 0.6mm solid core
    • 19/0.12mm stranded
    • 19/0.25mm stranded
    To calculate how much you will need, take the length of the finished interconnect and multiply it by 5. (This is for a pair of interconnects)
  2. Cut lengths of each wire about one and a half times as long as the required interconnect length.
  3. Taking one length of each size, braid them together and then repeat the process three more times.
  4. Take two of the braids which will be the signal and return conductors. Get a length of polythene tubing (the sort used for tropical fish tanks and home-brewing) and carefully attach each conductor so that the tubing becomes a spacer between them. Some kind of sticky tape every 150mm should hold everything in place. Repeat for the other channel.
  5. Wrap the conductor assemblies in kitchen foil.
  6. Remove the insulation from some plain copper stranded wire the same length as the interconnect. Tape this in position over the foil.
  7. Slide a length of 19.1mm heatshrink tubing over each interconnect and shrink it.
  8. Trim the conductors to length and then attach suitable phono plugs (I find the types with larger cable entries easier to use here) to each end of each interconnect. Note that the drain wire over the foil is only connected to the return side of one plug. Mark which end it is connected and use that end to go to the power amp.

'Speaker cables

The 'speaker cables are probably the easiest as they are made from 'off-the-shelf' cable. You will need two types of RG58 coaxial cable, the solid core variety (RG58BU) and a stranded core version (RG58CU). The woofer leads are made from a length of each type of RG58 by joining the conductors together for the 'hot' lead and the shields together for the 'cold' lead. I prefer to use the solid core RG58 on its own for the tweeter connections.
And that completes the instructions for building the Decibel Dungeon project system. If there is anything which I have not explained clearly please email me for further advice. If you have read this section all the way through and are still wondering if you can actually replicate this project then let me say again that it really is feasible for you to do so, given the information on this site, perhaps some further guidance from someone qualified in electrical matters, and the help which you can find through the internet. And remember that you don't have to do everything yourself. You'll have a lot of fun along the way (and some frustrations no doubt) but when you have completed your system you will experience hi-fi at a new level of satisfaction. Good luck.
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