CD output voltage too high for preamp: what to do?
I have an Audible Illusions preamp which is designed for a 1.5v input signal. I am told that this is standard. My Ayre CX-7e puts out 2.25v. They play beautifully together but I have too little control over volume: I cannot use the preamp vol controls beyond 9 o'clock because it is way too loud. Likewise it is hard to get just the right volume in the limited range available. This is worse with some CDs for reasons I do not know. Audible Illusions will change the preamp attenuation board for $275, but before I do so I wonder how others have dealt with the problem of newer CD players with higher outputs than their preamps were designed for.
Hi there, a set of Rothwell attenuators will solve your problem. I think these can be had in differnt values and cost about £35 over here - sure I've seen them advertised on Gon. Russ Andrews (the Kimber distributor in the UK) does attenuated i/c's for this very reason, not sure if Kimber do likewise. Rgds Si
Your only other option is to use an in-line attenuator between the cd and pre. They come in various values and are modest in costs. You can try an inexpensive set from Parts Connexion and then if it works out, get a more expensive set like the Rothwells.
BTW, 2V (at 0dB level) is the output standard for CD players although, as you already know, it is often ignored. In crude A/B tests, the louder player will always sound more impressive.
That said, another major factor in your problem is the input sensitivity of the power amp which may be a bit high as well. After all, 2.25V is only 6dB more than 1.5 and should be within the ambit of the volume adjustment.
I have a similar situation with a high gain amp (.8v for full output, 30 db gain) and was having the same issue with the volume control, both for digital (1.5v) and analog playback. I just bought the Rothwell attenuators and they work for me. Now I can go to about 12 o'clock before the level begins to get too loud (previously between 9 and 10 was the norm). I don't notice additional noise and used on the inputs of the amp I've lowered the gain from the preamp about 10db. Since this seems to be an issue with the CDP, I would first try these on the CD input of the preamp so as not to interfere with an other sources you may be using.
The fancy term "Attenuator" disguises the fact that we are talking about a couple of resistors. It's just a voltage divider. I would simply build it into the input jacks of the preamp. Do it with ordinary resistors, and when you get the volume right you can replace them with "audiophile" resistors if that makes you feel good.
This is a bit of a curiosity for me. If the output of a DAC is 1.5V, is there a minimum input impedance the preamp should have to accomodate the DACs output? Does the preamps gain play into this equation? My preamp has 4 gain settings, 11db, 14db, 17db, and 20db. I have always used the preamp with the 11db setting, but since I am now using the Rothwell attenuators it would appear that only 1bd of gain is getting passed into the amp. That seems pretty low to me. It's been suggested by others to go to a passive, but I researched this and don't want to risk giving anything up in dynamics. The preamp is a Joule Electra LA-100 MkIII (20k input impedance, 300 ohn output impedance).
If your AI preamp is out of warranty and you have the schematics, you can probably get a good tech (if you know one) to change a couple of resistors on the premap attentuation board....come to think of it, AI should do this for you at a very low cost.
Endler attenuators r the best and easily crap on the Rothwell's. I have both and the Endlers are transparent and flexible as you can set the exact attenuation you need.
I have similar problems: A tube preamp with 23 db gain, a fairly high output CDP with 2.3V, a very sensitive amp. Overall this results in about 10db too much gain.
As for solutions:I also read about mixed results with the Rothwell attenuators and therefore ended up looking at the following attenuators:
In looking at the Endler attenuators they appear to be a replacement to the active preamp, not used with it. Am I understanding this correctly? If they indeed can be used with an active preamp to reduce the gain, these might be worth a try.
Ive owned the audible illusions M3A 3 of them. the stepped attens are not a good thing for CD. I say sell the M3A, I switched the a eastern electric mini-max (used 500.00 and dont miss the m3A at all. The Add on attn units ive tryed also roll off frequency extremes. You just cant win with that m3a's curve. even when you can get it matched the steps are still too far apart. I had a Tjoeb 4000 and reduced the level to .75 volts and still wasnt heppy...
I trust you did flip the gain switches to their lowest position (setting) in the M3A. They're 3 dip switches per channel. Two for bypassing the output caps and one for lowering the gain.
Best solution would be to have Ayre, or someone with the schematic to reduce the output of the CD player. I have no idea of the topology of the output circuit, be it discrete or op-amp based. I am assuming its solid state, maybe not. If it's tube, it should be quite simple. Barring that, I agree with Eldartford. A pair of high quality series/shunt metal film (or carbon comp.,if you want to go retro) resistors right across the solder tags of the CD input RCAs on your preamp will beat the snot out of adding another attenuator in series with your preamp volume control. Another attenuator adds increased capacitance; switch or slider contacts; and in most cases a reduction in the impedance your CD player has to drive. If you're interested I'll post the equation to determine the values.
The endler variable attenuators can be used as a volume control or with an active pre amp. That is what I used them for. Put them at your amp inputs or pre inputs if you only want CD volume reduced.
As I said they work extremely well. They look a little ungainly but are totally transparent.
I noticed you have a premier 350, I do as well and since installing it in my system, I too have a gain issue. Do the Endlers have any effect on the sound other than attenuation and I assume by your comment that the Rothwells do effect the quality of sound.
Hi Chuck. I use the attenuators plugged into the amp inputs and on about 8db attenuation.That got rid of the gain noise I was experiencig between the pre and power. The Endlers are truely transparent, no real difference between the attenuators attached and not attached, except for the gain. I was sceptical as well, but decided to try them and I am very pleased., The Rothwell attenuators are quite coloured and change the sound of the amp too much.
BTW, I don't use them anymore as I sold my VTL 7.5 and using a cj pre amp. The cj has the same amount of gain as the VTL, however there is no noise.
Thanks to everyone for their suggestions. I did set the Audible Illusions dip switches to minimum gain without enough of a change in volume. I will look into attenuators both at the pre inputs and inside the AI directly on the CD RCA plugs. Hifi57audio, I'd appreciate it if you'd let me know the formula to calculate the resistor values. I contacted Ayre: they won't adjust the CDP. Illenema2 thought that the AI pre doesn't do well with attenuators at all. Does anyone have more thoughts on a change in preamp, although that solution is the most expensive!
Just for information, the CD inputs on the AI are not the most transparent. Try the aux. inputs. They're resistors on the inputs of the cd that are not on the other inputs. Art put them there to reduce glare on "Cheaper" CD players. Also, the output #2 has resistors also that, to me, degrade the sound. Always use output #1 for best sound. He did away with these in the L-2. He may have also done that with newer M3a's but I don't know that is the case. It did say in the owners manual. I would locate the resistors on the main circuit board (I think they are near the dip switch) instead of the input resistors and replace them with the appropriate value. You do not want more in the signal path than absolutely required. Since these resistors are allready there, these would be the ones I personally would adjust. Call Art Ferris at AI, he's a good guy and would probably help you or at least tell you if it's a bad idea. The outboard controls would probably be the way to go honestly unless you returned it to him for adjustment.
The equation for voltage dividers is: (shunt/(series+shunt))=voltage reduction factor. VRF x Vin=Vout... (Vin/Vout)log20= db attenuation Put simply in your case, dropping from 2.25 to 1.5 is a voltage reduction of exactly 1/3. So, Series R would equal 1/3 of R total, and Shunt R would equal 2/3 of R total. R total =Series R + Shunt R. As concerns attenuation, R total may be any value you want. Obviously, if there are in fact resistors on the circuit board allowing further attenuation or gain reduction, use those. Hope this helps.
Almost forgot, as concerns input impedance; R total should be selected as to maintain yours. For instance if it's 50k and you plug a 50k attenuator into the inputs, your CD player will see a 37k load.( when set for 1/3 attenuation) and will vary over the range of the attenuator. And yes, if your source impedance is high enough, the upper frequences will be rolled off. Finding Rtotal is way too easy, it equals 150% of input impedance.(are you seeing that 1/3 relationship again?). Input impedance at audio frequences is almost purely resistive, so this can be measured with an ohm-meter. Alternatively, you could simply add a series resistor,to the CD input, of a value of 50% of input resistance and achieve the same voltage reduction. This of course would raise the input resistance by a third. All the above advice assumes a standard circuit design pratice used in almost all high end products. Mock it up first, with a set of male and female RCAs and resistors from Rat Shack, plug it in and listen, before taking the hammer and tongs to your preamp. O.K., now I'm done.
Hifi57audio, I was wondering about exactly the same point concerning imput impedances, when inserting external shunt type attenuators:
Why do the EVS or Endler attenuators typically use a much lower impedance attenuator?
For example from the Endler website:
These are 4k or 20k shunt type attenuators which place only one resistor in series with the signal. Series resitance values of 1k, 2k, 4k and 20k were evaluated with 4k sounding the best. I use a proprietary technique on the switched side of the circuit to eliminate the possibility of an open circuit in case the contacts bounce. This helps keep things ultra quiet even in the presence of dc.
And from the EVS site:
Attenuators are available in a low impedance (1K) and a high impedance (10K) version.
Hifi57audio, any clarification on these low impedances for external stepped attenuator would great!
I ordered the Endler attenuators in the 4k 24 step version. I am going to use them on the amp with my preamp in the chain feeding them. I did read in the PF review that used alone with a source feeding it, while the attenuators were very musical and transparent, there was a tradeoff in reduced soundtage and imaging (more 2 dimensional sound is what the end result was). Has anyone experienced this? Might this be different using the preamp in the chain?
My preamp is a Joule Electra LA-100 MkIII, with input impedance of 20k ohms and output impedance of 300 ohms. Currently it is set at 11db of gain.
Restock- Beats me, unless they are designed for pro use. Sound reinforcement/studio equipment often employ a matched impedance interface to optimize power transfer. If thats the case it would almost certainly be offered with a balanced connection only.
Depends on how much the gain is reduced. My preamp has switches with plus or minus 3db increments. Even at the lowest level of 11db I am experiencing too much gain.
I purchased a pair of the Rothwell 10db attenuators and installed them between my pre-amp and amp and did not notice or perceive any degredation in sound quality........they did solve my gain issue.
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