Any problem with this Crown DC300A?

[pyonc]

Hi,

I tried Crown DC300A Series II, a vintage power amp that I bought on ebay, with lots of expectation. Preamp was Mcintosh C29, and Adcom GTP 500, and I tried both on my 4311 and 4343. The outcome was quite disappointing in terms of the quality and loudness of the reproduced sound, compared with Marantz (135 watts per channel) and Adcom 555 power amp (200 watts per channel).

With the preamp C29 volume at the same level (around 11 o'clock), I turned on the Crown, with its two channels set between 12 0'clock and 1pm. At the same time, I turned on the Marantz, with the same C29. The sound from the Marantz amp was at least five times as loud and clear as the Crown. I tried Adcom 500 preamp instead of C29, and the outcome was the same. So, this is my question: Is this Crown Professional Series II, an upgraded version of Crown DC300A, inherently weak in loudness? It's at least 155 watts per channel, as I understand. Is it because of a mismatch of Crown amp and C29, Adcom preamp, instead of Crown preamp? Or is there any problem with this vintage Crown amp? If so, what should I look into for possible improvement? Thanks a lot for your guidance in advance.

[JeffW]

Turn the knobs on the Crown fully clockwise and report back.

[HCSGuy]

If you are comparing for sound quality, you should first adjust the amplifiers to have equal loudness using the same preamp and speakers, then listen for differences. If you let the difference stay, you will be incorrectly tricked into thinking the louder one sounds better - sorry, human nature. Generally, for a simple home setup you should have the power amplifier's volume knobs most or all the way up - they don't boost, but attenuate signal only, so turning them up or down won't generally affect the power amplifier's sound quality, but if you have them way down and have to use your preamp for lots of gain, your preamp's distortion will be higher. Once you've equalized the amplifier's volume, take another listen and let us know what you think.

A little more:
THX standardizes on 29db gain through the power amplifier, so you can generally mix and match THX power amplifiers in a system without detriment or having to do lots of rebalancing. Everyone else is free to choose, but the gain structure has nothing to do with sound quality, it's just an outcome of the circuit design. Furthermore, the actual output power is not related to gain structure - if you compare a pair of 500w monoblocks that have 25db gain with a 45w/ch amp with 29db gain without adjusting their input attenuators, the little amp will be louder at the same preamp volume, which again may make you think it sounds better. Of course, when the amp runs out of power, the distortion should change your mind.

So, ignore the subjective impression left by wherever you had to put the Crown's input volume knobs - turn them up and match them to the other amp and don't read anything else into it. Listen, report, repeat...

[pyonc]

Turn the knobs on the Crown fully clockwise and report back.

Sure, let me try doing what you've suggested, and report back.
I just thought this might have something to do with the decay of
the parts of this vintage amp... Thanks!

[pyonc]

If you are comparing for sound quality, you should first adjust the amplifiers to have equal loudness using the same preamp and speakers, then listen for differences. If you let the difference stay, you will be incorrectly tricked into thinking the louder one sounds better - sorry, human nature. Generally, for a simple home setup you should be using keeping the power amplifier's volume knobs most or all the way up - they attenuate signal only, so turning them up or down won't generally affect the power amplifier's sound quality, but if you have them way down and have to use your preamp for lots of gain, your preamp's distortion will be higher. Once you've equalized the amplifier's volume, take another listen and let us know what you think.

A little more:
THX standardizes on 29db gain through the power amplifier, so you can generally mix and match THX power amplifiers in a system without detriment or having to do lots of rebalancing. Everyone else is free to choose, but the gain structure has nothing to do with sound quality, it's just an outcome of the circuit design. Furthermore, the actual output power is not related to gain structure - if you compare a pair of 500w monoblocks that have 25db gain with a 45w/ch amp with 29db gain without adjusting their input attenuators, the little amp will be louder at the same preamp volume, which again may make you think it sounds better. Of course, when the amp runs out of power, the distortion should change your mind.

So, ignore the subjective impression left by wherever you had to put the Crown's input volume knobs - turn them up and match them to the other amp and don't read anything else into it. Listen, report, repeat...

Thanks for your kind advice and explanation.
Just as you suggest, let me adjust this Crown amp to have the same loudness as Marantz, using the same preamp and speakers, and then listen for differences.
I'll report back tomorrow after trying this test. Hopefully my disappointment turns into a big job...

[JeffW]

Sure, let me try doing what you've suggested, and report back.
I just thought this might have something to do with the decay of
the parts of this vintage amp... Thanks!

I think it's more to do with the heavy attenuation you've imposed on the amp. A lot of amps have no attenuation control at all, they run always at "full clockwise" as it were. HCSGuy gave a much better explanation, but if you have a preamp already in the line, just turn the Crown all the way up and see how it does. If it still sounds bad, then it might have a problem.

[BMWCCA]

Crown suggests using the input attenuators to lower you system's noise floor by optimizing the gain structure. Used properly, the attenuators will be set to where you preamp volume control is at roughly half-way to 3/4 of the way up at the system sound level where you'd normally listen. This puts your pre-amp in its sweet-spot. Of course pro amps like Crowns are designed for fairly hot pre-amp outputs. The old Mac might not be up to the task, though it should still work fine. I've used an older C20 with my Crowns for over 40 years!

Pro sound runs unity gain to the amps. Without meters, your Mac can't tell you where that is but a safe bet is somewhere around 3/4 of the way up on the master volume control's range.

Similar discussion from the Crown forum:

am assuming that you mean the D-150 level controls have to be all the way up relative to the other amplifier. I checked the specs for the McIntosh C46 preamp and it will do 5Vrms output at the Balanced jacks and 2.5Vrms at the unbalanced jacks. So it has enough output to drive the D-150 which required a little over 1V for full output with the input attenuators all the way up.

The D-150 is only rated 20 to 20K rated for 80 watts. If it's not that the D-150 is just too small in power the only thing I can think of is that there is an input sensitivity difference between the two amps. Not knowing what the other amp is I will have to assume it is a consumer amp and not a pro audio amp like the D-150. Home consumer equipment usually runs on a much lower input level - meaning it needs a lower input voltage to get to full output than pro audio gear. If this is the case than the other amp is achieving full output before the D-150 can get to full output. To fix this you will probably have to turn the other amplifier's level controls down and turn the output of the Pre-amp up. In this configuration the D-150 would get more voltage and be able to produce full output.,

and this:

When working with a non-metered Preamp 3/4 of the way up, on the preamp output, is a good place to start as this is usually about the nominal output.

[scott fitlin]

With the front panel level attenuators wide open the Crown DC-300A has an input sensitivity of 1.75v. So, lowering the pot to the 12 o'clock position considerably lowers the input stage gain, and you could need well over 2v to drive the amp to full rated output.

The ADCOM 555SE has a 1.75v input sensitivity for full rated 8 ohm output, same as the crown DC-300A SERIES II.

You asked if the Series II generations are any different than the originals, and they say that by the time the Series II was in production, Crown was no longer using the same output transistor as they used with the older DC-300A.

Different generations of Crown amps did go through parts changes, and alterations of design, I can't say that this is what your hearing, though. But in any event, open the level attenuators then see what you hear and how it works. These things were talked about in the 1980,s though.

[pyonc]

I think it's more to do with the heavy attenuation you've imposed on the amp. A lot of amps have no attenuation control at all, they run always at "full clockwise" as it were. HCSGuy gave a much better explanation, but if you have a preamp already in the line, just turn the Crown all the way up and see how it does. If it still sounds bad, then it might have a problem.

Thanks a lot. If that's the case with Crown DC300A II, I'm going to turn the two channels all the way up as you suggest first, and see what happens.

[pyonc]

With the front panel level attenuators wide open the Crown DC-300A has an input sensitivity of 1.75v. So, lowering the pot to the 12 o'clock position considerably lowers the input stage gain, and you could need well over 2v to drive the amp to full rated output.

The ADCOM 555SE has a 1.75v input sensitivity for full rated 8 ohm output, same as the crown DC-300A SERIES II.

You asked if the Series II generations are any different than the originals, and they say that by the time the Series II was in production, Crown was no longer using the same output transistor as they used with the older DC-300A.

Different generations of Crown amps did go through parts changes, and alterations of design, I can't say that this is what your hearing, though. But in any event, open the level attenuators then see what you hear and how it works. These things were talked about in the 1980,s though.

Thanks for your kind explanation. Actually I didn't realize the co-relation of this input sensitivity and the input stage gain when I tried Crown. So, let me lower the two channels all the way down, instead of the current 12-1 o'clock set, and see what happens.

[pyonc]

Crown suggests using the input attenuators to lower you system's noise floor by optimizing the gain structure. Used properly, the attenuators will be set to where you preamp volume control is at roughly half-way to 3/4 of the way up at the system sound level where you'd normally listen. This puts your pre-amp in its sweet-spot. Of course pro amps like Crowns are designed for fairly hot pre-amp outputs. The old Mac might not be up to the task, though it should still work fine. I've used an older C20 with my Crowns for over 40 years!

Pro sound runs unity gain to the amps. Without meters, your Mac can't tell you where that is but a safe bet is somewhere around 3/4 of the way up on the master volume control's range.

Similar discussion from the Crown forum:
and this:

Thanks for your kind explanation and useful tip on the attenuation issue. As I'm accustomed to adjusting speaker loudness through preamp volume, the two channels on Crown DC300A II were sort of confusing. When they're set at the lowest, I can't hear anything even if the preamp volume's set at 1 or even 3pm o'oclock. Only when I turn them up, say 12 o'clock, could I hear the sound. So, for the good unity gain, I have to turn them up all the way down, above all.

[JeffW]

Thanks for your kind explanation. Actually I didn't realize the co-relation of this input sensitivity and the input stage gain when I tried Crown. So, let me lower the two channels all the way down, instead of the current 12-1 o'clock set, and see what happens.

You won't get any sound at all with them turned fully counter-clockwise.

I wouldn't worry about gain and all that just yet. Let's just see if the amp is working properly.

Turn the volume control on the preamp all the way down. Turn the controls on the amp all the way up. Start your music source. You should hear no sound. Slowly increase the volume control on the preamp. You should start to hear sound. Keep increasing the colume control on the preamp until the music is as loud as it was with the amps you said were louder than the Crown. Now adjust the knobs on the Crown until you get this same sound level with the volume control on the preamp in about the 12 O'Clock position. You're done!

[pyonc]

You won't get any sound at all with them turned fully counter-clockwise.

I wouldn't worry about gain and all that just yet. Let's just see if the amp is working properly.

Turn the volume control on the preamp all the way down. Turn the controls on the amp all the way up. Start your music source. You should hear no sound. Slowly increase the volume control on the preamp. You should start to hear sound. Keep increasing the colume control on the preamp until the music is as loud as it was with the amps you said were louder than the Crown. Now adjust the knobs on the amps until you get this same sound level with the volume control on the preamp in about the 12 O'Clock position. You're done!

Thanks so much for this step-by-step procedure!
Now I think I can understand more about this Crown issue.
Let me try this when I get home this evening, and report back.

[BMWCCA]

.

[JeffW]

.

I know you're an advocate of setting the gain structure, but when a guy says he can't get anything but weak sound out of a DC300A, and he has the levels set to 12 O'clock, my thought is that he simply needs to turn the dang thing up. It's not going to hurt anything to try, and if his amp still sounds weak, it's faulty.

But he was having wild, confusing swings that included trying it with the attenuators all the way down. That's not going to do much of anything.

On the other hand, if he can run the amp wide open and control the volume with the preamp just long enough to see that this amp should really rock his speakers if functioning properly, then he can go back and set the gain as he sees fit.

I just couldn't wrap my head around the "my amp won't get very loud, even though I'm running it at half mast" part.

I'll grab some popcorn if running it wide open doesn't get the volume level up.