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modenar1's picture
Last seen: Never ago
Joined: Feb 6 2007 - 4:27pm
CD player direct to amp?

i was wondering if its possible to connect a CD player direct to a amplifier, without going through a Pre-amp stage? is there an separate volume controller i can get?. will going directly to the amp give it better sound, since it will be a much more simple connection? i am asking this because i am thinking about getting the Onkyo DX-7555 cd player, but since i am a student and work part time, i dont want to spend too much money at once, and since i already have a 2 channel amplifier. i was wondering if this setup would be able to work, ofcourse with a external volume controller, if there actually is such a product. all your feedback would be appreciated.

Monty's picture
Last seen: Never ago
Joined: Sep 16 2005 - 6:55pm
Re: CD player direct to amp?

What you are proposing has been steadily gaining in popularity over the last few years and is being done quite a lot. If your CD player has a variable output, you don't even need a volume controller.

Several companies are making volume contolling devices that even come with a remote control. The first to come to my mind is the Creek OBH devices.

Most CD players have no problem driving the cables and amp through the controller. Still, there are a few amps that aren't particularly sensitive and that could present a problem.

I've tried it with two tube amps and liked it in both cases. I tried it with one of my solid state amps and didn't like it. I'm not talking night and day performance issues, but noticeable to a nut like me.

If CD is your primary source, it's certainly worth a try and usually presents no compatability issues. Unless you are set on getting the Onkyo, why not look for a player that has a variable output and avoid the controller all together? I'm not familiar with the Onkyo and it may have one as well. Just make sure the player doesn't default back to full output when powered down and back up again or unplugged...or at least don't forget that you will be getting maximum volume from your discs the second it starts to play and you'll have to remember to turn down the CD output level, which you won't always remember, which means you will be buying new speakers.

Jan Vigne
Jan Vigne's picture
Last seen: Never ago
Joined: Mar 18 2006 - 12:57pm
Re: CD player direct to amp?

You don't state what amplifier you are considering in this system. Many people refer to a receiver as an "amplifier". I'll assume you mean a separate power amplifier since you understand what a pre amp does.

What you are asking about is referred to generically as a "passive pre amp". As usual, I would suggest you put "passive pre amp" into a search engine and get a good feel for the benefits and the limitations of running such a system. If you'll place "DIY" in front of that, you'll find a few suggestions for building a passive pre amp that can be as simple as nothing more than a high quality pot or as elaborate as a transformer coupled device. The transformer coupled method of construction will mitigate many of the negatives of the passive system but will cost considerably more to do well.

The negatives you should be aware of in your proposed set up are output/input impedance problems and the effect of cables on such a system. Additionally, you should make certain the CD player you choose will provide sufficient voltage to drive your amplifier to full power. The last item is typically not a problem as most CD players can manage enough output voltage. Check the numbers just to make sure before you buy.

Dealing with the cable issue first means you typically cannot drive long interconnects between the passive device's outputs and the power amp. This will require replacing long interconnects with long speaker cables. Consider the cost of cables when making the decision to use a passive control. Also the cables will affect the sound of the system in a more obvious fashion when using passive controls than when an active device with output buffering is in the system. Whoever you buy cables from should be made aware of your plans before you invest in any purchase and make certain you know the shop's return policies before you hand over any money. You do not want interconnects with high capacitance or high inductance. To get truly good cables (and a quality volume control) for a passive pre amp will often offset the cost savings of such a set up.

When you use a passive pre amp, there obviously is no "pre amp" included in the system. For the most part a "pre amp" can be more correctly referred to as a "control amp" when no phono input is required. This means you will have to provide switching for more than one input as your system grows unless you don't mind plugging and unplugging cables. Since you have no gain stages in the passive device, the issue of output voltage from the CD player is one issue to address. The other important issue is the output impedance of the player and of the volume control. The CD player will more than likely have an output impedance that is sufficiently low to drive the system but the pot's output impedance will vary with its position. In other words, as you turn down the voltage coming from the player, whether with a variable output from the player or through a passive pre amp's potentiometer, you will be increasing the impedance of the passive pre amp's output. Obviously, the inverse is true and as you raise the level of the pot, you will be decreasing the output impedance. One function of most active pre amps is input/output buffering, which provides a constant output impedance for the power amp to work against. Without this buffer stage in the passive device you will typically find the system will sound its best in a very small portion of the passive unit's control range where voltage and current requirements are met by an output impedance that the power amp finds likeable. Depending on the pot you choose, the power amp you run it into and the sensivity of your speakers, the "correct" level may be too high or too low for your desires or those of your neighbors.

One reason tube amplifiers typically do well with passive systems is their often times higher input impedance sees less effect of this constantly changing output impedance from the passive pot. Solid state amplifiers more often than not have a slightly lower input impedance than tube amps and therefore will often have more problems with where on the dial's range the correct point for sound quality will fall. For the most part, all of this is a "suck it and see what happens" sort of arrangement since each case must be taken on its own values according to which pot, which cables, which amplifier and which speakers you choose.

Finally, the quality of the volume control, whatever type you choose, will determine the quality of the sound. With little other than a pot typically in line from the player to the amp, the pot becomes very important and cheating on the pot will leave you unimpressed by passive pre amps. Most CD players have very poor quality variable outputs due to the poor quality of the trim pot they use. So, while the most economical option is to buy a player with variable outputs, it will also result in some of the worst choices you can make in terms of sound quality. A power amp with variable gain controls will probably do better than a CD player with a pot. The best choice is a simple, high quality pot (or two for dual mono) which you can buy from a supplier such as Michael Percy or any of the DIY suppliers you find on line. Do not skimp on the quality of the pot and you will have your best chance for good sound from a simple system.

The trend today is toward passive pre amps with transformer coupling to provide some form of output buffering. If you've placed "passive pre amp" in a search engine, you'll surely find a few of these mentioned. Transformers are a good solution to the problems of passive devices but they are costly and cheap transformers are worse than no transformer at all.

Read a few of the past reviews of passive devices that have run in Stereohile over the years to find more thoughts on the benefits and limitations of the set up. If you don't come across it, here's a link to a DIY passive unit with buffering that was run more than a decade ago and written by Corey Greenberg. If you're not familar with CG, the article should be quite enlightening.

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