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Input clip vs power section limits

Transverz

Transverz

May 3, 2004
1,041
87
#1
Does overdriving the preamp input have a similar sound as having aa SS power amp with not enough headroom?

In another thread I realized or rather feel that I was fooled into thinking my Walkabout was not able to put enough wattage (~150w) and volume into an 8 ohm 2x10 for my semi-loud rock band uses. With a Sansamp BDDI in the front end through the padded active jack, it sounded overtaxed playing regularly and was on the threshold of farting out when digging in. Definitely couldn't turn it past 11-12:00. Not much lows or headroom at all. Then I found I had the BDDI on LINE output rather than INST. So I put the BDDI to the return jack to use just the WA power section. Huge difference of sound. Night and day with it now having more than enough headroom and the way I imagined this gear should sound like. The WA preamp by itself should be at least the same, if not even better sounding than the BDDI "preamp" if I use it right.

So was the source of all the trouble too much input? If I run the bass straight to the input and I don't have the same great results, even with the gain turned up, do I not have enough input? What is the power section's role in all this? I just feel like I'm still not understanding the preamp and power section relationship in regards to input, clipping, and what is or isn't enough wattage.

Thanks for reading...
 
#3
fdeck said:
Preamp and power amp clipping can be a lot different. Power amps tend to clip the tops and bottoms of the waveform symmetrically. Preamps may clip symmetrically or asymmetrically, depending on the design.
Click to expand...

And these two types of clipping will sound quite different. Symmetrical clipping tends to produce only odd-order harmonics, which can sound somewhat harsh, depending on the audio signal going through.

Asymmetrical clipping tends to produce both even- and odd-order harmonics. Even-order harmonics can sound somewhat consonant, but again that is dependent on the audio.
 
#4
Looking at many bass and guitar signals in sound editors, of all the one's I've seen, including sounds off sample disks and basstasters.com - all the waveforms are asymmetrical. Top or bottom heavy. I suspect if a class-a preamp is asymmetrical in it's response that some basses or players may not get a good 'clip out of them. Or switching the phase 180 might give different results. I don't know why more preamps don't have a phase switch? it might help in some cases.

I ran across a great article on Universal Audio by Dr. Dave Berners that talks about the effects of symmetry and circuit topology.
[Invalid or Expired Link Removed]
 
#5
seamonkey said:
Looking at many bass and guitar signals in sound editors, of all the one's I've seen, including sounds off sample disks and basstasters.com - all the waveforms are asymmetrical. Top or bottom heavy. I suspect if a class-a preamp is asymmetrical in it's response that some basses or players may not get a good 'clip out of them. Or switching the phase 180 might give different results. I don't know why more preamps don't have a phase switch? it might help in some cases.

I ran across a great article on Universal Audio by Dr. Dave Berners that talks about the effects of symmetry and circuit topology.
[Invalid or Expired Link Removed]
Click to expand...

What software did you use to look at the waveforms? I am interested in looking at the same waveforms for a different reason.
 

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