hi all ive got way to much gain from my cd player to pre and poweramp which means i can only use the first qaurter of my volume control on my pre is there an easy way i can reduce the gain from my cd player into my preamp to make my volume control more usable maybe with some resistors in my cd to pre interconnects or something .i dont want to do anything that will degrade the signal
hi all the pre is a metaxas opulence and i cant find any info on the gain.. the cd player is a opera audio reference 2.2 linear and its output is 2.35 v .im using anthony e holtons nx400 synergy modules that i have made into monoblocks ill get some info on the gain from him today thankyou to all for any help /advice .also the speakers are troels gravesen ekta grande and i would say there sensitivity is 90+
I'm sure.
Advice from Andrew T is on the money but I'm willing to bet that changes to compensation values will not be recommended by the designer. There are various parameters to consider such as 20KHz OL voltage gain, noise figure, and slew limiting. A voltage gain of 40 is actually about 6dB above the average and your metaxas preamp is probably designed to drive a wide range of power amps, and may have a voltage gain of about 5. This assumes 15V rails and 2Vrms as a designed input signal. This means that your total av is near 200 which is probably 20dB too much. Padding the output of the preamp seems sensible but you may unavoidably load the preamp with a lower than intended load resistance or feed the power amplifier from a higher than intended source impedance, and actually it's likely to be a combination of the two, so although the voltage gain will be corrected there may be some bandwidth limiting at one or both ends of the audio spectrum. This is because the power amplifier will have an input filter with pole f calculated from approx 100 ohms source impedance (very typical) and the preamp will expect to be seeing 10k ohms or greater at the PA input so if there's an output capacitor it will not be sufficiently large to prevent LF roll-off. However, if your Metaxas preamp can really drive 1K ohm without problems then the simple solution is an L pad with starting values of 1K in series and 200 ohms to ground. This will keep the output impedance low (150 ohms) without overloading the preamp and the gain will be reduced by about 16dB.
Hope this makes sense.
Hope this makes sense.
hi all i spoke to anthony the amp designer and he said the amp gain could be reduced but he does not recciomend it as it may affect the sound .im very interested in your solution vhf man can you explain firther about how i would make your changes to my pre like where do the connect to and maybe a simple schematic any further help you could give me would be very much appreciated . for the meantime ive purchased some rothwell attentuaters which i should recieve next week but im worried they may affect my sound quality and would prefer to use another way if possible
slr 5000 said:
"hi all i've got way to much gain from my cd player to pre and poweramp which means i can only use the first quarter of my volume control on my pre. Is there an easy way i can reduce the gain from my cd player into my preamp to make my volume control more usable?"
Joe said: Hi SLR, The easiest way I have found to do this is I bought a 50K ohm passive preamp? from eBay and vary the CD player output level. I have noticed that different CD's have varying levels and the step attenuator works well.
"Maybe with some resistors in my cd to pre interconnects or something .i dont want to do anything that will degrade the signal."
I tried fixed attenuators that I made myself with Metal Oxide resistors and the attenuators sounded great but the level always seemed to be not right. Variable attenuator fixed this problem.
I usually use between 6 and 9 db of attenuation. Sometimes less depending on the CD. A fixed attenuation of 12 db kills the music, flat and lifeless. Hope you did not order this level of attenuator.
Joe
"hi all i've got way to much gain from my cd player to pre and poweramp which means i can only use the first quarter of my volume control on my pre. Is there an easy way i can reduce the gain from my cd player into my preamp to make my volume control more usable?"
Joe said: Hi SLR, The easiest way I have found to do this is I bought a 50K ohm passive preamp? from eBay and vary the CD player output level. I have noticed that different CD's have varying levels and the step attenuator works well.
"Maybe with some resistors in my cd to pre interconnects or something .i dont want to do anything that will degrade the signal."
I tried fixed attenuators that I made myself with Metal Oxide resistors and the attenuators sounded great but the level always seemed to be not right. Variable attenuator fixed this problem.
I usually use between 6 and 9 db of attenuation. Sometimes less depending on the CD. A fixed attenuation of 12 db kills the music, flat and lifeless. Hope you did not order this level of attenuator.
Joe
slr 5000 said:
Unless you havea turntable, and it's a phono pre.
A simple fix:
1: to improve your sound
2: get rid of the excess gain
3: and make money in the process.
If you have that much gain, that's rediculous, get rid of the pre (make some money). Then make or get a passive pre, and improve your sound at the same time.
Cheers George
hi all the attentuaters i ordered are a fixed 10db .i might open them up if its to much and play around with it ,better quality resisters of varying resistence . i dont want to change my pre as its the most dynamic pre ive ever heard and apart from my gain issues it really gells with the rest of my system
slr 5000 said:
Don't change or get rid of the preamp. Passive preamps may seem like a perfect solution with no active elements to generate distortion but they cannot avoid failing the most important (real world) role of a preamp, that being an impedance transformer.
Before you install a signal attenuator you need to know if your preamp can drive 1k ohm load resistance. Have a look through the manual and see if there's any mention of its drive capability or output impedance. If the output impedance is in the order of 150 or 200 ohms or higher then it's likely that the output stage is simply an op-amp with 100% vfb. On the other hand an output impedance of 50 ohms will probably mean that the output stage is discrete which is good news. If possible you should take the lid off and look inside and visually check it out. Placing a 15dB pad between the preamp and power amp may seem big but from my experience it does not flatten or degrade the sound. Let's face it, your existing volume control is simply a variable attenuator and in normal operation you will have upwards of 20dB. Does this flatten the sound ?? Fixed resistors are also far better than potentiometers because it's difficult to get 1% tolerance in a dual pot. And then you have other considerations such as crosstalk and contact resistance. The purpose of this proposed attenuator is to reduce your overall voltage gain to a sensible amount and at the same time improve system noise figure. If your preamp can drive low impedances then you achieve these objectives without adding distortion or compromising other parameters.
If you would like a drawing of what's required I can create one.
Cheers.
Hi,
1K / 200R IMO is overkill on the low impedance side and unecessary.
Placed at the output of a pre-amplifier it wil give ~ 150ohms.
But this is not the best place to put it. The best place is at the input
to the power amplifier where 4.7k/1k or 10k/ 2.2k will be fine, the
preamplifier still driving the cable capacitance directly.
/sreten.
1K / 200R IMO is overkill on the low impedance side and unecessary.
Placed at the output of a pre-amplifier it wil give ~ 150ohms.
But this is not the best place to put it. The best place is at the input
to the power amplifier where 4.7k/1k or 10k/ 2.2k will be fine, the
preamplifier still driving the cable capacitance directly.
/sreten.sreten said:Hi,
1K / 200R IMO is overkill on the low impedance side and unecessary.
Placed at the output of a pre-amplifier it wil give ~ 150ohms.
But this is not the best place to put it. The best place is at the input
to the power amplifier where 4.7k/1k or 10k/ 2.2k will be fine, the
preamplifier still driving the cable capacitance directly.
I see your point but I figured 150 ohms is fine for many many metres of cable. You would need perhaps 6m of cable before hf rolloff approached 250KHz and the preamp is driving a pure resistor. The low values were to ensure that the dreaded input filter in the power amp did not roll off the hf prematurely. Since I don't know what's in there the values recommended were as low as I dared. However, any pre worth it's weight in salt should be able to drive IK without an issue. - IMO.
The benefits of DIY are now all too clear.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.