risingjay Posted June 8, 2007 Share Posted June 8, 2007 If my pre has a output voltage of 1 V and my amp has an input of 1.9 V, do these match well? Quote Link to comment Share on other sites More sharing options...
Deang Posted June 9, 2007 Share Posted June 9, 2007 A good discussion topic. Quote Link to comment Share on other sites More sharing options...
PrestonTom Posted June 9, 2007 Share Posted June 9, 2007 If my pre has a output voltage of 1 V and my amp has an input of 1.9 V, do these match well? Your amp has three specifications that are intertwined. The first is wattage, but this assumes what the input level is. In this case, 1.9V is the input required to achieve that wattage. The more informative number is called gain. This is in units of dB and makes no assumption about the "expected" input level. It is typically the increase in power of the signal. Not all 100 watt amps will have the same gain (they may "expect" different input levels or sensitivities). I have ignored some details (i.e., input impedance), but this is the quick answer. Good Luck, -Tom Quote Link to comment Share on other sites More sharing options...
risingjay Posted June 9, 2007 Author Share Posted June 9, 2007 Amp= 700 watts RMS @ 8ohms, 1.9 V input sensitivity, input impedence of 12k ohms with balanced inputs and 6k ohms with unbalenced inpputs and a voltage gain of 40x( 32db). Pre= Output sensitivity of 1.0 V and a input impedence of 1k ohm. I understand that the output impedence to input impedence macth good when used with balanced inputs. Is the gain on the amp used just to boost the input sensitivity coming from the preamp? If not, shouldn't the output sensitivity at least match the input sensitivity of the amp? Am I missing quality of sound due to this? Is this what you just described to me Tom? Just trying to understand why sensitivity is important in my situation. Quote Link to comment Share on other sites More sharing options...
risingjay Posted June 9, 2007 Author Share Posted June 9, 2007 If my pre has a output voltage of 1 V and my amp has an input of 1.9 V, do these match well? ============ No. But, you have an Xtreme, and the output is not 1V, it is as high as 30V. You must be referring to some other preamp. I am unaware of any preamp with a 1V output. If your amp needs 1.9V in to deliver full output, you obviously will need more than 1V from a preamp. I'm using a Outlaw audio Pre model 990. http://outlawaudio.com/products/990.html It says in the specs 1V and a max output of 9V. Does this mean the Pre puts out what the amp requires when called upon? Another forum member bought my Extreme. I just wish I could have kept it along with my Outlaw. Quote Link to comment Share on other sites More sharing options...
risingjay Posted June 9, 2007 Author Share Posted June 9, 2007 I'm sorry, wrote that wrong. The Output sensitivity of the Preamp is 1 V to 9 V max. The Output Impedence is 1k ohm. But if I use the balanced concections, the input impedence changes to 12k ohms on the amp. This would give me a decent ratio for the Preamp/Amp combo, right? I thought the raito was 10x the impedence of the Preamp. Quote Link to comment Share on other sites More sharing options...
stormin Posted June 9, 2007 Share Posted June 9, 2007 Your preamp still has way to high of an output impedance. Good gosh that looks like my Audible Illusions preamp impedance which is a horrible pre to match with many ss amps. Like Mark has stated you really need 600 ohms or less but i would say you need to be down around 200. You haven't even begun to hear the qualities of that QSC. Quote Link to comment Share on other sites More sharing options...
djk Posted June 10, 2007 Share Posted June 10, 2007 The Outlaw has a voltage gain of 5X from the CD input to the preamp output, far more than what you need. At full output it can drive 9V, far more than you need. The QSC has a voltage gain of 40X, far more than you need. The input impedance can be either 6K or 12K, a good match with the Outlaw. Since the Outlaw has XLR connectors on it, just hook them up to the XLR connectors on the QSC. Fifty years ago professional equipment had an output impedance of 600 ohms, and was in turn connected to an input impedance of 600 ohms. We don't do it that way today. If your Outlaw really has an output impedance of 1K (which I doubt, despite what the spec sheet says), then it would be fine driving anything above 1K input impedance (which is what I think they meant to say on the spec sheet). Just hook the two pieces together. Quote Link to comment Share on other sites More sharing options...
stormin Posted June 10, 2007 Share Posted June 10, 2007 The basic rule of thumb is to have input impedance of the amp be at least 10x the output impedance of the preamp. However, many consider this ratio too low and would be more comfortable with numbers of 20x or better. Also, preamp mfgs sometimes do not disclose that the output impedance can sometimes vary significantly with frequency, although the larger variations are more common to tube preamps. If your ratio is low, such variations can result in frequency roll off, most common in the bass causing the system to sound thin and/or bright. You obviously have enough voltage gain but I'm not sure I understand what the previous poster is suggesting at all in regards to impedance. My Audible Illusions L-1 has an output impedance of 1.2k ohms and my QSC SRA 2422 has an input impedance of 10k ohms. These two are a horrific match. The bass is extemely rolled. The system sounds very bright and thin with the combination. I do find it hard to believe that the Outlaw would have such a high output impedance. SS is usually very low while tube pres are usually high except for some designs such as the JM Peach. Quote Link to comment Share on other sites More sharing options...
djk Posted June 10, 2007 Share Posted June 10, 2007 "The basic rule of thumb is to have input impedance of the amp be at least 10x the output impedance of the preamp" Something made up, and not always applicable (that's why it's called rule-of-thumb). As I explained above, impedances used to be matched. "The bass is extemely rolled. " Most likely the L-1 output coupling cap is too small, in any case the Outlaw is not a tube unit. I remember when The Absolute Sound reviewed th HK Citation Sixteen, they said it had poor bass. They were driving it with an ARC tube preamp with a small output coupling cap. Obviously the magazine reviewers were not up-to-speed on technical issues. Just hook it up and see how it sounds. If you think it needs to be some magic ratio, then by all means change the input impedance to what ever you want it to be. http://www.qsc.com/support/library/schems/Discontinued/PLX%20Series/plx3402.pdf R8, 9, 12, and 13 can be changed to any reasonable value (should be changed as a set of four). While you're in there, do something with C7 and C11. A film bypass will improve the sound quite a bit. Quote Link to comment Share on other sites More sharing options...
stormin Posted June 10, 2007 Share Posted June 10, 2007 "The basic rule of thumb is to have input impedance of the amp be at least 10x the output impedance of the preamp" Something made up, and not always applicable (that's why it's called rule-of-thumb). As I explained above, impedances used to be matched. "The bass is extemely rolled. " Most likely the L-1 output coupling cap is too small. Did not know that. I become more educated everyday. Thanks! Jay, just realized Arky has the same preamp and loved the combo with his QSC PLX. Quote Link to comment Share on other sites More sharing options...
risingjay Posted June 10, 2007 Author Share Posted June 10, 2007 The Outlaw has a voltage gain of 5X from the CD input to the preamp output, far more than what you need. At full output it can drive 9V, far more than you need. The QSC has a voltage gain of 40X, far more than you need. The input impedance can be either 6K or 12K, a good match with the Outlaw. Since the Outlaw has XLR connectors on it, just hook them up to the XLR connectors on the QSC. Fifty years ago professional equipment had an output impedance of 600 ohms, and was in turn connected to an input impedance of 600 ohms. We don't do it that way today. If your Outlaw really has an output impedance of 1K (which I doubt, despite what the spec sheet says), then it would be fine driving anything above 1K input impedance (which is what I think they meant to say on the spec sheet). Just hook the two pieces together. I think you are right about the misprint that Outlaw has written. Yesterday I borrowed my brother-in-laws preamp (Acurus LS-11) which has an output inpedence of 47 Ohms. There wasn't that much difference in sound and felt I wasn't missing anything compaired to the Outlaw. I've been running the Ootlaw/QSC combo ever since my dynaco's took a crap. They sound alright together but not as good as the dynaco's (which will shortly be moded by Craig). I really want to use the QSC to run a couple of subs. The resistor chages look intresting. Quote Link to comment Share on other sites More sharing options...
tigerwoodKhorns Posted June 10, 2007 Share Posted June 10, 2007 "The basic rule of thumb is to have input impedance of the amp be at least 10x the output impedance of the preamp" Something made up, and not always applicable (that's why it's called rule-of-thumb). As I explained above, impedances used to be matched. "The bass is extemely rolled. " Most likely the L-1 output coupling cap is too small, in any case the Outlaw is not a tube unit. I remember when The Absolute Sound reviewed th HK Citation Sixteen, they said it had poor bass. They were driving it with an ARC tube preamp with a small output coupling cap. Obviously the magazine reviewers were not up-to-speed on technical issues. Just hook it up and see how it sounds. If you think it needs to be some magic ratio, then by all means change the input impedance to what ever you want it to be. http://www.qsc.com/support/library/schems/Discontinued/PLX%20Series/plx3402.pdf R8, 9, 12, and 13 can be changed to any reasonable value (should be changed as a set of four). While you're in there, do something with C7 and C11. A film bypass will improve the sound quite a bit. Thanks for the info. Looking at the output and wattage I assumed it was a QSC that we were talking about. I have a few questions about the resistor change. I learned about it on Basstalk and spoke to the guy in Denver who figured it out. It looks like the value of the resistor is what you want the input impedence to be on Balanced, or 1/2 of what you want the unbalanced input impedence to be. Am I correct? I may have the balanced and unbalanced reversed but I am more concerned with the values. Next question, are these regular curcuit boards that are easy to solder on or are we talking about microelectronics like the Teac L700 amps boards? Thanks again. I have a PLX 1202 that I have already changed the fan on to a low flow Paniflow and I have wanted to change the input impedence to get it closer to the other amps in my tri-amp setup. Quote Link to comment Share on other sites More sharing options...
risingjay Posted June 10, 2007 Author Share Posted June 10, 2007 "The basic rule of thumb is to have input impedance of the amp be at least 10x the output impedance of the preamp" Something made up, and not always applicable (that's why it's called rule-of-thumb). As I explained above, impedances used to be matched. "The bass is extemely rolled. " Most likely the L-1 output coupling cap is too small, in any case the Outlaw is not a tube unit. I remember when The Absolute Sound reviewed th HK Citation Sixteen, they said it had poor bass. They were driving it with an ARC tube preamp with a small output coupling cap. Obviously the magazine reviewers were not up-to-speed on technical issues. Just hook it up and see how it sounds. If you think it needs to be some magic ratio, then by all means change the input impedance to what ever you want it to be. http://www.qsc.com/support/library/schems/Discontinued/PLX%20Series/plx3402.pdf R8, 9, 12, and 13 can be changed to any reasonable value (should be changed as a set of four). While you're in there, do something with C7 and C11. A film bypass will improve the sound quite a bit. What is a Film Bypass and what would you suggest? Quote Link to comment Share on other sites More sharing options...
djk Posted June 11, 2007 Share Posted June 11, 2007 "Next question, are these regular curcuit boards that are easy to solder on or are we talking about microelectronics like the Teac L700 amps boards?" Surface mount, tweezer stuff. "It looks like the value of the resistor is what you want the input impedence to be on Balanced, or 1/2 of what you want the unbalanced input impedence to be." The value of the resistor becomes the unbalanced input impedance, the balanced will be twice that. "What is a Film Bypass and what would you suggest?" A polypropylene as big as you can fit (probably between 0.01µ~0.1µF at 50V). These may be tricky for some people with not much soldering experience. "I have wanted to change the input impedence to get it closer to the other amps in my tri-amp setup. " Shouldn't matter as your crossover probably has a low enough output impedance to drive the thing. One last point: The unbalanced input for the QSC uses the tip and sleeve, or pin 2 hot on the XLR. If you wire the ring as hot, or pin 3 on the XLR, the input impedance will double (to 12K). Remember to reverse the speaker connections to preserve absolute polarity. Quote Link to comment Share on other sites More sharing options...
stormin Posted October 13, 2007 Share Posted October 13, 2007 "The basic rule of thumb is to have input impedance of the amp be at least 10x the output impedance of the preamp" Something made up, and not always applicable (that's why it's called rule-of-thumb). As I explained above, impedances used to be matched. "The bass is extemely rolled. " Most likely the L-1 output coupling cap is too small, in any case the Outlaw is not a tube unit. I remember when The Absolute Sound reviewed th HK Citation Sixteen, they said it had poor bass. They were driving it with an ARC tube preamp with a small output coupling cap. Obviously the magazine reviewers were not up-to-speed on technical issues. Just hook it up and see how it sounds. If you think it needs to be some magic ratio, then by all means change the input impedance to what ever you want it to be. http://www.qsc.com/support/library/schems/Discontinued/PLX%20Series/plx3402.pdf R8, 9, 12, and 13 can be changed to any reasonable value (should be changed as a set of four). While you're in there, do something with C7 and C11. A film bypass will improve the sound quite a bit. djk [] diyAudio Member Offline Registered: Feb 2001 Location: USA Post #16 Hi Jens, I will use your nomenclature for consistency. The saturated rail switch will be referred to as class H, and the linear follower (modulated rail voltage) as class G. Prior art on class G (3772606): http://patimg1.uspto.gov/.piw?Docid...ey=637608C562C2 An earlier example for CRT deflection (3622899): http://patimg2.uspto.gov/.piw?Docid...ey=2E6E84FB42ED Early class H (3319175): http://patimg2.uspto.gov/.piw?docid...26RS=PN/3319175 'Commutation' was Bob Carver's nomeclature for a rail switching design. I believe he coined this term for the diode on the lower rails, also refered to as an ORing diode (as it allows the output stage to use power from either the lower, or the higher supply, as needed). These diodes switch, or commutate as needed. The fast switching, soft recovery types, or newer high voltage Schottky type are best here. The theoretical class B efficiency is 78.8%, a three rail design like the M1.0 is 87% (after Pol HSU). When you consider bias in a class AB design, 60% is more in line. Pol HSU found that the rail switcher showed even higher efficiency driving reactive loads vs resistive. At full power, class G and H are slightly less efficient than class AB. However, the majority of the time we are not at full power. Worst case for the class AB would be at about 50% voltage out, where the rail switchers are king. Most Carver are three rail designs, most Crest are two rail designs. AB International has an interesting two-and-a-half rail design. Instead of a third set of transformer windings, associated rectifiers, and filter caps, they use 0V as a rail in class H. No improvement on a resistive load line, but much better into a reactive load line, and a reduction in the Vce required for the outputs. IMO class G sounds better than class H. One example of this is the QSC MX2000, a 1KW per channel design. The original was class G, the 'A' version class 'H'. The original sounds better, and the used market value is higher for that very reason. Why do any class H? Cost, it is much lower for class H. The later Carver M1.0 is an interesting hybrid, being class G on the lower rail, and class H on the higher rail. Good sonics at a reasonable cost. The Early Effect doesn't seem to be a real issue. An early example of the 'Tracking Down Converter' or 'BASH' type (3426290): http://patimg2.uspto.gov/.piw?docid...26RS=PN/3426290 I believe its possible for Class H to sound great. I believe it was accomplished with the Studio Reference Series from QSC designed for both home and the studio. I think alot of folks especially those running around Audiogon do not accept class D, H or G. When I've played the same recording at home compared to a McIntosh MC 402 at my dealers with his high end Mac pre and SACD cd player I could not tell a difference. I listened to Patricia Barber there for about 2 hours then came home and listened to the same music with tones out of the circut. Now he was using the top of the line BMW's and I just have a lonely ole pair of Chorus II's but to these ears of 43 years I couldnt see any benefit of spending the big bucks. I have a 6,000 dollar system and that was a 35,000 dollar system. So for there to be something apparently wrong with class H design I just dont see it or hear it. Maybe they've come along ways and fine tuned it. Or maybe you hear something that I dont. But I cant believe that good smooth sound with alot of slam is considered bad. A question I do have is has QSC changed the design that Bob Carver started. Has the switching become undetectable with the oscilloscope when looking at the output waveform? Am I missing something here? Exactly what am I suppose to be hearing during the switch? It switches 230,000 times a second. Another viewpoint: http://mixonline.com/products/review/audio_qsc_audio_sra/ Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted October 13, 2007 Share Posted October 13, 2007 "If your Outlaw really has an output impedance of 1K (which I doubt, despite what the spec sheet says), then it would be fine driving anything above 1K input impedance (which is what I think they meant to say on the spec sheet)." I disagree about the general "rule of thumb" aspect of the 1:10 ratio. It's an important figure, and have found that even higher ratios between stages are an improvement. 1:10 is often described as a minimum allowable ratio of output z to input z. I remember a time when I misread the resistor color code on a grid-leak resistor of an output stage, where the interstage impedance relationship, after I tracked down the problem to the value of resistance I used between grid and ground, resulted in exactly the case mentioned above. The sound was miserable. Erik Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted October 13, 2007 Share Posted October 13, 2007 Too: The majority of vintage equipment I've seen or worked on generally had rather higher input impedances than more modern counterparts. One example that comes to mind is the commonly seen Dynaco preamps, which had output impedances in the range of 1k ohm. On the other hand, the amps they were designed to be used with, such as the Mark III and ST- 70, had input impedance figures in the range of 500k ohms. The same is true for the vast majority of vintage hi fi schematics I've looked at elswhere. In the case of power amps or integrated amplifiers, the input impedance, established either by a volume control or fixed resistor (power amp) was in the range of 470k to 500kohm. If you take, in particular, the instance of the 'so-called' passive preamp, the same thing applies. The interstage impedance issue is all the more critical for exactly the same reason. What's ideal is a very high input impedance, which couples to a significantly lower output z to the amplifier. With the majority of either fixed resistor or carbon comp/strip potentiometers there is always a compromise because of this problem. That's where transformer-based attenuation has been found to be far more suitable: The primary of the transformer, which is connected to the input, will have not just slightly but a considerably higher impedance than that of the output, so that the lowest output impedance possible is what is driving the amplifier. High output impedances have difficulty driving capacitive loads, which in turn is where the shortest possible length of IC is suggested to offset related capacitance effects that result in roll-off. There are many factors that come into play, Miller capacitance effects being one of those, which Mark also mentioned. Erik Quote Link to comment Share on other sites More sharing options...
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