|
New member Username: Simple_smithLapeer, Michigan United States Post Number: 8 Registered: Dec-08 | I just picked up 2 Crown DC300A 2 channel amps. I have no idea how old they are, but i want to try using them. They're in good condition. Are they worth keeping? |
|
Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13374 Registered: May-04 | . When was the last time they were used? (Some kinda good sentence construction there, eh?) . |
|
Platinum Member Username: NuckPost Number: 11653 Registered: Dec-04 | Smith, if they have not been powered up in a while, like over 2 years, you do not want to just plug them in and go. |
|
New member Username: Simple_smithLapeer, Michigan United States Post Number: 9 Registered: Dec-08 | I'm pretty sure they have been used fairly recently. I got them from a house that was going to be torn down and it looked like they had been used to run some kind of multi-room intercom system. The two amps were all that was left so i don't know the specifics. |
|
Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13377 Registered: May-04 | . Crown at one time - the days of the DC300's - had a decent reputation among American amplifier manufacturers. They also had a reputation for a specific sound. Crown has stayed true to its road tested - dropped down a flight of stairs by a roadie and run over by a truck but ready for tonight's show - reputation. This doesn't make for the most refined sound in existence but you might find it appealing since it projects the feel of "high power" quite well. Do some research before you make your decision. Refurbishing, or even repairing, a decades old amplifier is not cheap or easy. O.E.M. transistors are very likely no longer available. You might find it is better to sell the amps to someone who can appreciate them for what they are. . |
|
New member Username: Simple_smithLapeer, Michigan United States Post Number: 10 Registered: Dec-08 | Alright I'll look into that. Thanks for the help Jan |
|
New member Username: ToobsessedwithbassPost Number: 4 Registered: Mar-09 | I just picked up a couple Crown 300aMk2s. One for my subs, and one because I just got obsessed on Ebay one night. I run the 2nd off my Onkyo 805 preamp and the sound thru my Magnepan MG12s are as clean thr the Crown as they are thru my Onkyo directly. Im sure I can find cleaner amps like adcom or accurus in the same $$$ range, but the crowns definetely have power. Easy to get zapped with the crazy rear face plate!Unfortunately, the Onkyo starts to limit output well before I get to max power |
|
Platinum Member Username: NuckPost Number: 11807 Registered: Dec-04 | RF, how do you know that you are limited in power? What is the first issue? The difference between 100w and 200w is barely noticeable in volume. |
|
New member Username: ToobsessedwithbassPost Number: 5 Registered: Mar-09 | The Crown have a very large and heavy power supply, generating higher current than my Home theater amp trying to drive 7 channels with one power supply. The higher current drives the Maggies easier, giving a more open sound and more punch in the bass. It can also drive a difficult 4 ohm load. More can be said from the experts on this forum but its not always about total watts. I was told a godd amp can double power output at 4 ohms. As for my Onkyo, I have not figured out why I cant get the gain up high enough to get to clipping as I can with my smaller Yamaha receiver but maybe its something to do with my Intelligence Volume feature in the 805s. Does my Onkyo 805s have a good quality preamp for driving my Crown 300A Mk2s |
|
Platinum Member Username: NuckPost Number: 11820 Registered: Dec-04 | Both may be OK, but if the Onkyo has an output that is too low for the crown input, then you will never reach full power. If clipping is the ultimate goal,know that the Crown amp will clip very very hard, and oscillate enough to fry tweeters and XO's. Keep in mind that the last doubling of wattage is only worth 3db, barely audible. |
|
New member Username: ToobsessedwithbassPost Number: 6 Registered: Mar-09 | Got it! saty away from clipping. I dint really plan on it but its nice to know where full power is, especially in the bass. Im not camplaining too much as it gets plenty loud enough. I wondered if preamps such as mine begin to limit ( bad word) prior to reaching full output to avoid clipping the preamp. |
|
Platinum Member Username: NuckPost Number: 11822 Registered: Dec-04 | If your pre was delivering the required input to the amp to reach max amp out, then you would be free to drive the amp into oscillation. Depending on the load of the speakers, you may already be able to do that, or overpower the speakers. You should be able to hear that quite readily. The specs you need to google are preamp output voltage from the pre and input voltage for the amp. Along with those, you will find output/input impedence, also note those values and cmon back. |
|
Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13408 Registered: May-04 | . Invert these two sentences and you'll clear up some of your thinking; "I was told a godd amp can double power output at 4 ohms." "More can be said from the experts on this forum but its not always about total watts." In a strict sense the on paper wattage from an amplifier will double when the load is halved. That's Ohm's Law. However, when dealing with audio what occurs on paper isn't always what we find in reality. Not everyone agrees that a "good" amplifier should double its wattage when the load is halved since this tends to reflect a less than ideally regulated or a sufficiently stiff power supply. And since "power" or "wattage", whichever term you choose, is a function of both voltage and current into a load, what the amplifier does on a test bench is somewhat irrelevant to how it responds to the real world, reactive load of a speaker. The magnetic planar design is recognized as a moderately to highly reactive load for any amplifier with its primary load being a rising inductance/impedance in the high frequencies. It's not surprising an amplifier with a more robust power supply than the one in your HT receiver has less trouble driving such a load. "I wondered if preamps such as mine begin to limit ( bad word) prior to reaching full output to avoid clipping the preamp." Pre amplifiers do not tend to "clip" in the same manner as power amplifiers. They can be overdriven at their input which will result in high levels of distortion but since the load on a pre amp is typically quite high in comparison to its output impedance, and current demand is negligible in most preamps, the voltage output of a pre amp doesn't respond in the same fashion you would expect from a power amp driving a load of a few ohms. It's not too difficult to provide a power supply that can handle the demands of a pre amp. That's not to say a better ps cannot improve a pre amp's performance, it certainly can. However, a pre amp tends to just peter out and dynamically compress the signal rather than clip the signal. By the point pre amp compression occurs the pre amp will be providing sufficient voltage to drive most power amps to full power and then some. I doubt your pre amp has any sort of limiter or compression function since it provides output jacks to feed an unknown input on an unnamed power amplifier. It's more likely you are just hearing the limitations of your HT receiver's design. Whatever the case, don't intentionally clip the amp. When you hear distortion, turn down the volume. . |
|
Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13409 Registered: May-04 | . "If your pre was delivering the required input to the amp to reach max amp out, then you would be free to drive the amp into oscillation." Oscillation? I understand what oscillation is but I don't understand why you are using that term in that sentence. . |
|
Platinum Member Username: NuckPost Number: 11824 Registered: Dec-04 | I subbed it for clipping, it didnt seem to matter for this discourse. Expand at will, folks, I love these threads, especially if anything is new to RF or me. |
|
Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13410 Registered: May-04 | . Oscillation and clipping are quite different things to an amplifier though both might destroy a speaker attached to an amplifier that is allowed to clip or oscillate for more than a few seconds. Otherwise, an amplifier that is mildly clipping the signal output might remain in that state of operation for long periods. An amplifier that begins to oscillate will typically build upon itself and, if left unattended, will eventually destroy itself. Oscillation occurs when the amp becomes unstable, a tube amplifier might become unstable and begin to oscillate when there is no load present on its outputs. A solid state amplifier with zero feedback is a prime caniditate for oscillation since most output transistors require some small amount of local feedback at minimum to keep them from imploding. Clipping is the result of the amp being asked to perform beyond its limitations. When the power supply can no longer provide enough "watts" to allow the output to accurately reflect the input, the output waveform becomes "clipped" as it reaches its highest voltage swing, rather than being a continuouos sinusoidal wave the top and bottom of the waveform are missing or "clipped" off in appearance. . |
|
New member Username: ToobsessedwithbassPost Number: 7 Registered: Mar-09 | Man, this is good stuff. Im new to this site and "treading" audio stuff. Its nice to get advice from some one other than my high end audio store who always tells me my stuff isnt good enough! Thanks guys!Ill check the specs online to see if my HT preamp is enough to drive the amp to full power |
|
Platinum Member Username: NuckPost Number: 11826 Registered: Dec-04 | Does the feedback circuit affect the input or output circuit of the last device JV? It would seem input, also negating much heavier circuitry. Does it differ from bi-polar and mosfet outputs or others? |
|
Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13411 Registered: May-04 | . Common ol' negative feedback is tied to the speaker outputs which makes it affect the input. In other words, the back EMF and return signal from the amplifier's "+" output is received on the return trip at the amplifier's "-" terminal completing the circuit of amplifier/speaker/amplifier. Where it goes from there is up to the designer and whether the amp will employ global feedback or local feedback or both. Global fedback is just what the name implies and there is a small/medium/large (depending on the designer's desired result) amount of the signal taken from the "-" terminal and fed back to the input of the amplifier. This signal has now been inverted in phase by the round trip and when the inverted output signal is placed against the incoming input signal the idea is the out of phase output of the amplifier meets the in phase input of the amplifier (or the other way around if you care to get technical). What amounts to an "error" circuit determines "what is the same" (signal) vs. "what is not the same" (distortion). Ideally the distortion is then eliminated by the error gain circuit. If the feedback is global in nature, the signal is fed from the speaker outputs to the amplifier inputs. If the feedback is local, the signal is fed through a small portion of the amplifier only. In many cases an amplifier that uses global feedback will also employ local feedback to keep things tidy though the reverse is not always true. Most high end components will use some degree of local feedback around specific circuits. The higher the "dB's" of global NFB the higher the gain of the amplifier circuit overall since more signal voltage is present at its inputs. NFB is meant to lower distorion and lower output impedance while making the amplifier more stable. Any audio amplifier must have some amount of feedback to extend its bandwidth beyond a too narrow range for high fidelity. Some types of output devices, however, particularly triode type vacuum tubes, have inherent local feedback in their circuit design and so "zero NFB" can be stated without being an outright lie. In a push-pull amplifier with any type of output device or most esecially with bipolar transistors, "zero NFB" can typically be taken as no additional feedback has been designed into the circuit. That is a very simple explanation of feedback and only applies to negative feedback (the most common and most commonly abused type). Time for a search engine if you want to know more; http://search.yahoo.com/search?ei=utf-8&fr=slv8-hptb5&p=negative%20feedback%20in %20audio%20amplifiers&type= Because the feedback loop is tied to the amplifier's "-" terminal it also affect the damping factor of the amplifier. . |
|
Platinum Member Username: NuckPost Number: 11827 Registered: Dec-04 | I love this stuff. Thanks JV, it even works for rookies. Cut n paste |
|
Silver Member Username: Simple_smithLapeer, Michigan United States Post Number: 122 Registered: Dec-08 | Okay so i've been messing around with those amps and the both work well. However, i am mostly into car audio, so i just have subs sitting around. So my question is, could/should i bi-amp these to a sub? the sub would need anywhere from 800-1500rms. Also if i just run one of these to a JL 10w6, how would i go about getting a low pass filter? I've heard its possible to make them yourself, but i could be woefully wrong. Forgive my home audio ignorance lol -Smith |