To tone control or not to...

[dagerman]

Hi,
while waiting for the last parts needed to complete my first amp build based on the Tubelab Simple SE, I have been pondering whether it would be desirable/needed/possible to introduce a tone control (bass&treble) circuit into the amp. I have found plenty of good info for potential circuits and a myriad of options on where it is best placed, i.e. between audio source and amp, before/after volume control, between driver stage and final stage, etc., so the 'possible' question - however rhetorical that may have been to begin with - is answered.
What I am curious to find out is whether having tone control is a matter of personal taste or whether many members here find it to be a desirable part of the audio path. Do you find yourself frequently adjusting tone and do you do it to compensate for different tubes reproducing frequencies differently, or because of how your speakers reproduce bass/treble, or just because you like more bass?
I know, this is an oddball question and there are probably as many answers as there are members on here, but I'd appreciate your experienced thoughts for a tube newbie anyway.
And yes, I will certainly finish my first build first and see (pardon: hear) what it sounds like before venturing into preamp/tone control territory. Just trying to get a read, maybe the next step is to just build a better amp...!?
Thanks for any thoughts you may have,
Stefan

 

[Richard Ellis]

Tone or no tone?

Introducing a so-called tone control into an amp really changes the character of the amp....it is now considered an "Integrated amp". One needs to consider what is going onto the front-end of your amp...Are you going to have multiple inputs?...with their own designations? outputs?
Leave the amp..a pure amp & cook up a separate 'Pre-amp'....Most tone controls are very complex, frequencies, multiple, bandwidth adjustable..plus consider how it would integrate into a "loudness button".......too much to cram into your 'purist' amp.

_________________________________________________Rick.........

 

[Eli Duttman]

Stefan,

It's a fact that very few recordings benefit from the presence of tone controls. AAMOF, tone controls mess the sound of good recordings up. If you are not prepared to make the tone controls totally defeatable, as in switched out of the signal path when not in use, don't bother building them.

Good tone controls are not at all simple. Refer to the Max Robinson's Baxendal implementation that I've uploaded. That circuitry is "unity" gain, unlike most (all?) of the examples you've looked at, which incur an insertion loss. Now, 4X 12AX7s are a bit OTT for a stereo setup. The bottle count can be reduced to 1/channel and the signal path cleaned up by using DC coupled ZVN0545A source followers, instead of cap. coupled cathode followers.

 

[elliottstudioarts]

I wonder if anyone knows what kind of tone control circuit went into the Cello Audio Palette? From first sight years ago in a clients system I've wondered how hard it would be to build?

 

[Jeff Yourison]

I agree with Richard and Eli. Well designed speakers and amps should not need dedicated tone controls. If your speakers are consistently to bright on top with various sources and recordings, you can use an L pad on the tweeter or rework the crossover. If you need more bass, consider an active subwoofer with adjustable gain and highpass settings. Once integrated into your room, you won't constantly have to fiddle with it all, and you'll find that good recordings are fine in a "flat" EQ situation. Plus, your signal path remains cleaner.

If you listen frequently on a very quiet volume setting, a loudness control might provide some benefit by boosting bass at low settings. You can get a pot with a loudness tap or use a button or switch to drop in the boost when needed.

--Jeff

 

[dagerman]

Thanks to all who took the time to respond. Your answers are in line with what I expected and I personally always have my SS amp on linear/flat settings.
The friend who will receive the SimpleSE (if it works and he likes the sound) said that "[...] I always increase the treble setting and then turn up the bass to match it[...]", which made me scratch my head, because he is a semi-pro musician and SHOULD know better.
I am sure the tube sound will peel him out of his socks as it is; I just hope the SimpleSE Is beefy enough for his less-than-ideal 91dB speakers. Then again, he wants to continue to live in his apartment complex, I believe...
Thanks again for your time, much appreciated!
Stefan, waiting for his power transformer (would you believe I forgot to order THAT out of all parts needed...?!)

 

[dovla]

A relatively cheap 'trick' I use is a mini-mixer (the cheapest Behringer of $20-30 would do) between the source and tube amps (PP EL84 & SE EL34). Your semi-professional musician friend may have one already.
Mixers' Low/High EQ usually works by boosting all frequencies below 80Hz/above 12.5kHz rather than making a bell-shape around 100Hz and 10K as with 'normal' tone controls.
One of the amps has two inputs and I've switched between EQ-ed and direct signal trying to hear the difference and/or added noise and there is nothing audible (to me) with 96dB speakers (other than the EQ changes I did want). I was a but skeptical in the beginning and expected some 'metalized' sound as the mixers use op-amps but none of that showed up (but then, most CD players would also have op-amp output)
I found out that the most useful control is actually cutting the mids (@2.5K) by some 3-5 dB and the bass then just needs up to 3dB boost. All of this with CDs, SAT radio and vinyl usually do not require any adjustment.

 

[Miniwatt]

A relatively cheap 'trick' I use is a mini-mixer (the cheapest Behringer of $20-30 would do) between the source and tube amps

 

[evavdv]

I second that MiniWatt, my humble opinion Less (components) is better.
If you do want to put in a tone control make sure you can bypass it with a simple switch of a button, the switch won't do much harm compared to the RC networks you want to add.

 

[dovla]

You'd be surprised - sounds much better (that is, more natural) with the mixer than with the SW EQ applied on the digital source.
Bypass is just the flip of the amp input selector to the other position (on which the same source is connected sans mixer)

 

[Miniwatt]

I second that MiniWatt, my humble opinion Less (components) is better.

Especially with disposable mixers. Please, it's junk..

 

[Bob Richards]

I consider tone controls a must, but they have to be done a certain way. I prefer a four section baxandall or equivalent, which is optimized to be able to give you a loudness comp curve that is right when the acoustics of your listening room and absolute level is taken into account. At lower levels you'll want to increase the lower mid and bass, and the high treble. Listening room acoustics usually create significant damage to the frequency response at any listening position. All rooms are different so you want to have better than normal flexibility. I also use a 31 band EQ to deal with lower mid and bass peaks, and flanking drivers to fill in cancellations due to room reflections causing a delayed signal to add at your ear with the direct signal, thereby forming a comb filter effect. To be honest, I probably don't need the 31 band digital EQ at all if I do the flanking drivers right. When it's about enjoying the music, tone adjustment should be an option. If it's more about comparing preamps or monitoring while mixing at a recording studio, there may be times when you'd like to bypass the tone circuit. Flat coming out the speakers is never flat at your ears in most typical living/listening rooms. If turning up the bass makes it sound boomy, the problem isn't the tone circuit, it's the room acoustics. Uneven low frequency response at your ear sounds boomy.

 

[Wavebourn]

If to speak of control listening environment, or listening for music enjoyment, 31-band, or even 512-band EQ is needed to be touched once, to equalize frequency response. After that it must be locked firmly. If after that "bass makes it sound boomy" such a record does not pass QA and should be discarded.