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New Tube Amp Use EQ or not

I've been using my new amp for about 2 weeks now and have been very happy with the more "rounded" edges and richness in the mids. My main reason for the switch away from SS is my age related sensitivity to certain frequencies, especially if they have a percussive source. I used to think these offending frequencies were in the high frequency range and experimented with several types of tweeters to no avail. After using test equipment I discovered that the problem actually occurred in the 1000 to 1400 KHz range. I bought a decent EQ (Behringer DEQ2496) in an attempt to tame these and, to some extent, it worked.

Switching to the Cary Audio Design 808R (Rocket 88R) amp made a difference that even I could tell. The sound was richer with no loss of detail that I could discern. I just received a new Ralph Towner CD, though, with Xylophone accompaniment that brought back the discomfort at approx 1000Hz. I'm not looking for perfection but the idea of putting the Equalizer back in service to tame this frequency range crosses my mind. I know I can selectively attenuate these frequencies but my concern is that by doing so to selectively diminish these frequencies that are so uncomfortable as a percussive source, will result in some loss of the richness or fullness that those frequencies contribute otherwise. My gut says it would have to but I'd like to hear from the experts.

FYI, I switched from Peachtree Audio Nova Pre, Peachtree Audio 220, Martin Logan Ethos TO Peachtree Nova pre, Cary Rocket 88R amp, Reference 3A MMC Serie Speakers. The EQ has not been in the system for months.
128x128broadstone
lowrider57's avatar
lowrider57
5,417 posts
 
Hi Broadstone, good move trying the EL34's. They'll give a different colour to the sound of your system.
But, if there is still a problem with annoying frequencies, ask your tube dealer if a change in one of the small input tubes, such as the driver will help. If so, go with a classic sounding NOS tube.

Keep us informed of how it sounds.
atmasphere's avatar
atmasphere
11,841 posts
 
Broadstone, I think you do indeed have an opinion about tubes vs transistors based on your experience. Tubes do indeed have a more 'rounded' quality as you pointed out in your initial post.

This is because they tend to have less higher-ordered harmonic distortion than transistors tend to have. The ear is very sensitive to these harmonics (5th and above) and uses them to determine how loud a sound actually is (rather than trying to get that information from the fundamental frequency).

It may interest you to know that you can take this a step further. Amplifiers that employ loop negative feedback will also have increased amounts of higher ordered harmonics as a result of the feedback itself. I know this sounds counterintuitive but this has been well-known for the better part of 60 years! The amount of additional harmonic content is slight (in trace amounts and hard to measure on test equipment) but since our ears are tuned to detect these harmonics (which, when feedback is added, can go up as high as the 81st harmonic), we can hear them with ease.

If you can find an amplifier that does not employ loop feedback and will also work correctly on your loudspeakers (feedback is often used to get flatter frequency response) then the distortion components will be lower orders and generally are considerably less annoying. Tubes, triodes in particular, can be quite linear so feedback is not a requirement for low distortion. As a result there are a good number of low or zero feedback tube amps on the market. Something to think about...

 
broadstone's avatar
broadstone OP
310 posts
 
OK, I installed the EL34's, biased them to 165 mA and started listening. With only about 15 hrs on them, though, I didn't expect much and, sure enough, they sounded pretty bad and the only way to get them to sound nearly as good as the 88's was to switch from triode mode to UL. A friend, though, traded me a set of 34's that he had in his PrimaLuna for mine and, what a difference. This amp, then, is definitely a keeper and the EL34 tubes will remain at least until I try the 6L6's that also came with the amp. 

Lowrider, in regard to your suggestion that I look into the front end tubes,  I spoke with Mark at Cary who suggested that I try 12AX7 in place of the BZ7's.  I haven't tried it yet but I do have some spare ones that I keep for the DACs that I have so will try it later. I don't, though, like making multiple changes at the same time for obvious reasons. 

Atmasphere, re your last comment, you ALWAYS give me plenty to think about especially as regards the importance of feedback and harmonics and how they influence sound quality. I'm using the Cary Rocket 88R which I thought did not incorporate loop feedback. I don't know where I got that info or if it's even true.  

Anyway the progress I'm making is very satisfying and even fun. 
atmasphere's avatar
atmasphere
11,841 posts
 
Fun is number one!
n5yey
6 posts
 
Behringer also sold a parametric Equalizer that you may benefit from in your situation. It has adjustable notch filters that could be adjusted to the offending frequency. Also the Parametrics are not locked into a set number of frequencies that are adjustable, it is variable from top to bottom broken up into bands. The frequency and bandwidth of the frequency are adjustable as well as the gain or attenuation for the frequency. I have a pair of these and found them more useful than the DEQ2496.
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