Bottlehead Forum
General Category => General Discussion => Topic started by: Frederick Petersen on May 31, 2013, 11:30:44 AM
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Gentlemen:
This is my first post to the Bottlehead Forum. So I want to apologize in advance to those who disagree with what I'm about say.
To begin with I sent the following e-mail to Doc B. the other day and got no response. It then occurred to me "that was not the proper way to broach a new subject to the Bottlehead community." What actually prompted me to send the e-mail was reading about the passive volume control on the site. It occurred to me that a Baxandal (bass, mid, treble) circuit might work & if mounted in a box similiar to the Submissive it would look cool. If enough of us are interested maybe a kit could be in the future. You might even want to call it the B&D because it is after all about control. Anyway here's the e-mail I sent. So please read it and let's see what happens.
Hello Doc B:
I know that in most hi/end circles tone controls are frowned upon. However they can be useful for example when listening
at low levels so as not to wake family members. I have been searching for a quality unit but just can't seem to find one.
For me a simple Bass Treble unit isn't sophisticated enough, yet a parametric or octave eq is too much. Would some thing like the parasound unit below be something BottleHead's future. If so I know of at least four audio friends who would be interested.
FYI: There are a few hi/end manufacturers who've gone on the record lamenting the loss of tone adjustment, one example is the ceo of Harbeth. link ( http://www.harbeth.co.uk/usergroup/showthread.php?466-Tone-controls-equaliser-or-tilt-controls-at-home )
Parasound made one which I admired in the mid nineties. link(http://www.parasound.com/pdfs/vintage/req150om.pdf )
Quad also used a type of tone control tilt circuit.
............................. thanks Doc
........................... Fred Petersen
( www.audiofyle.com )
p.s. I know there are going to be people who disagree with tone control use. Respectfully this post isn't for you.
I'm interested in responses from people who would like to see this kind of kit offered, I know I want one.
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"The moral ambiguity of pseudo/science as a marketing tool".
On your website you have a photo of my products as a link to the aforementioned article.
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My Apology Doc:
It was supposed to link to your website. It now does, hopefully no harm done.
I am playing guitar again & love the image of the Tode & will be ordering one soon.
I'd appreciate your thoughts on my post. I was quite impressed with your tone cntrl
solution on the Tode. This was another reason why I am enquiring about a tone cntrl solution
for home audio.
.......................... Fred Petersen
p.s. I read on your site that perhaps Blumenstein Audio will be doing the new cabinets for the Tode?
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Thanks for fixing it Fred. The tone control idea is interesting. Let me take a look at the Parasound you mentioned and see what we might cook up. One potential issue that pops into my head is that doing this as a passive stand alone unit might make its response curve influenced by the load it runs into. I'll kick the idea around with the guys and see what they think.
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I'd be interested. If nothing else, it would be fun to play with...
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One of the things I admire about Bottlehead products is the retro design & especially the wooden enclosures.
If a power supply is needed would that make the cost prohibitive. Again to me a small high quality tone control
or eq ( I believe the Parasound is an EQ ) is for me a necsessity. My fingers & toes are crossed.
............................ Fred Petersen
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I don't miss tone controls, generally...but sometimes I do miss that "Loudness" button...not so much at home, but in the office it would be pretty handy...
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The thing about passive tone controls is, they can only be subtractive. The standard circuits (the ones without opamps and feedback) lose about 20dB of signal voltage.
There is only one approach suitable for passive implementation that I am aware of. It's actually a close relative of the "scoop" in the Tode. We'll kick the idea around and see if it squeals. :^)
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I like the idea of a passive design. I do not care for the Parasound device. Too much going on. Yamaha had a great idea for a loudness control. It simply lowered part of the midrange instead of boosting the hi's n lo's. I think that a Bass Mid Treble unit would suffice, as long as there were turnover frequency adjustments for each control, especially the bass.
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FWIW, the best tone controls I've heard are the kind that are cut-only -- as in Sam Kim's modified Scott and Heathkit integrateds. But those aren't exactly passive either.
Greg, I used to have one of those mid-70s Yamaha integrateds -- CR 820 -- it , as I recall, had both a mid control and variable loudness, though it was a long time ago and maybe it was just one but not both.
-- Jim
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I think that a Bass Mid Treble unit would suffice, as long as there were turnover frequency adjustments for each control, especially the bass.
[/quote] Paul Joppa
The thing about passive tone controls is, they can only be subtractive.
[/quote]
In my original post I referred to the Passive volume control (the SUBMISSIVE). I like it's aesthetic design. The initial question wasn't about a passive tone control, just a tone control that would match the appearance of the submissive. I want an active tone control not a passive. (4KROW Greg Peyton) hit the nail on the head a Bass/Mid/Treble unit with turnover frequency adjustments for each control, and for my 2 cents "separate controls for each channel in other words left ch bass/mid/treble and turnover. Right ch. Same as left.
thanks guys ........................... fastfred (Fred Petersen)
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Here's an interesting idea:
* A tone control that attenuates the midrange with variable bass and treble turnover frequencies; possibly a variable treble level level as well. *
This is exactly what a "baffle step correction" or BSC circuit does - there is an example in the SEXy Speaker page. Thus it could serve either or both functions. The basic circuit is extremely simple.
It should be much more affordable than the old White Instruments passive RLC notch filters, which were available with up to 24 bands on 1/3 octave centers!
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FastFred was posting at the same time I was, so this post addresses the "active" notion.
Old-style tone controls are a lossy passive control followed by an amplifier to restore the signal level. The more modern designs, which became common about the time that tubes disappeared and transistors or opamps took over, use feedback with equalization inside the loop. Both are called "active" but to my ear the passive eq approach sounds better.
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Here's an interesting idea:
* A tone control that attenuates the midrange with variable bass and treble turnover frequencies; possibly a variable treble level level as well. *
This is exactly what a "baffle step correction" or BSC circuit does - there is an example in the SEXy Speaker page. Thus it could serve either or both functions. The basic circuit is extremely simple.
It should be much more affordable than the old White Instruments passive RLC notch filters, which were available with up to 24 bands on 1/3 octave centers!
I like the idea of a tone control that attenuates the midrange with variable bass and treble turnover frequencies; and I vote for a variable treble level level as well. * Aother addition I would want to see & that is a complete bypass circuit for those recordings that don't need help. I think we're getting close, although it's my post its you guys are the ones who are designing it.
I have 2 main reasons for asking for tone controls I'm sure there are more.
1. to maintain some sense of contrast while listening at low levels.
2. I have a lot of cd's that aren't audiophile grade recordings some are downright terrible, to the point of being unlistenable to be able to give them some sparkle would be a wonderful thing. One more thing Paul I really appreciate your attention to this issue. I'm sure there are others out there as well who can see the value of an intelligently designed tone control.
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I would add that while tone controls are sometimes an invasion into perfection, the real world may suggest otherwise. That is to say, as mentioned above, there are those recordings that need help, either in an addition or subtraction of frequency balance. Also, I don't like to admit it, but my ears hear a little different from one another these days. Lastly, my room has few issues that could be diminished a bit with a little help. Other times, it is just fine to bypass the tone control altogether.
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I have an Audio Research SP3a. I don't use in my current setup but it has a "contour" control, an adjustable loudness, which was nice for low level listening.
Never found the tone controls very useful. If I needed them all was pretty much lost to begin with.
I like Paul's idea of using a BSC as a loudness control...John
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My reading of the history is that tone controls appeared when tubes got cheap enough that the extra gain was affordable, and were (in the thirties and forties for example) useful because speakers were very far from flat. Even the best home-audio speakers had serious deficits in both bass and treble. Remember, back then "transient smearing" referred to the treble coming out of a bass horn 5-10 milliseconds before the bass, or the bass ringing for a similar time after the signal stopped. The term was "bass overhang" IIRC.
These days it is a reasonable expectation to look for a speaker with a fairly flat response. But between bad recordings and room acoustics (not to mention esoteric speaker designs with oddball response curves) a bit of equalization can come in mighty handy.
There was an important paper that came out, maybe early seventies(?) that suggested "loudness" controls did not accurately reflect human hearing - this was because the ancient Fletcher-Munson curves were updated around then. But that was also when tone controls were disappearing, and I think this improvement never actually made it into commercial production - they just kept on using the old designs. That would be another interesting thing to revive.
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4KROW (Greg Peyton)
(QUOTE)
I would add that while tone controls are sometimes an invasion into perfection, the real world may suggest otherwise. That is to say, as mentioned above, there are those recordings that need help, either in an addition or subtraction of frequency balance. Also, I don't like to admit it, but my ears hear a little different from one another these days. Lastly, my room has few issues that could be diminished a bit with a little help. Other times, it is just fine to bypass the tone control altogether.
(QUOTE) 2WO (John Scanlon)
I have an Audio Research SP3a. I don't use in my current setup but it has a "contour" control, an adjustable loudness, which was
nice for low level listening. Never found the tone controls very useful. If I needed them all was pretty much lost to begin with.
I like Paul's idea of using a BSC as a loudness control...John
(QUOTE) Paul Joppa
My reading of the history is that tone controls appeared when tubes got cheap enough that the extra gain was affordable, and were (in the thirties and forties for example) useful because speakers were very far from flat. Even the best home-audio speakers had serious deficits in both bass and treble. Remember, back then "transient smearing" referred to the treble coming out of a bass horn 5-10 milliseconds before the bass, or the bass ringing for a similar time after the signal stopped. The term was "bass overhang" IIRC.
These days it is a reasonable expectation to look for a speaker with a fairly flat response. But between bad recordings and room acoustics (not to mention esoteric speaker designs with oddball response curves) a bit of equalization can come in mighty handy.
There was an important paper that came out, maybe early seventies(?) that suggested "loudness" controls did not accurately reflect human hearing - this was because the ancient Fletcher-Munson curves were updated around then. But that was also when tone controls were disappearing, and I think this improvement never actually made it into commercial production - they just kept on using the old designs. That would be another interesting thing to revive.
(QUOTE) fastfred (Fred Petersen)
I like the reference to the paper about loudness controls and the improvement which never got to market (thanks Paul)
I'm hoping that Doc B and the guys will weigh in soon. One last observation from me. To be honest as long as I can improve the sound of those old thin sounding moldie oldies that I have so many of it doesn't matter to me whether the design decided upon is passive or active. I know Doc B & the guys wouldn't bring a below par product to market.
Another reason for a tone control, back in the day if a record sounded bad you just tweeked the tone controls. It's still a valid reason for having them today. I was culling my cd collection last week, by just quickly listening to each cut what amazed me was how poorly recorded some of those cd's were. I pulled out some box sets & recordings I never listen to any more and made myself about $250 for 6 box sets & 30 CD's 60's & 70's rock mostly. The plan was to use the money to download hi res files of those recordings. Then I remembered the change from vinyl to cd, the the release of the remastered cd's, set aside the audiophile versions, example I have Exile on Mainstreet the latest box set, & found a 2 disc version of Exile, as well as a version with both albums on 1 disc. How many times do I have to buy a recording in a new format to keep up with the Jones's. Thats actually when I had the "aha" moment. I'm not going to repurchase a 1200 cd record collection. I'm going to find a tone control. I'm sick of lining record company pockets.
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Whoa... another Winnipegger...
/back on topic
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At this point in the conversation I will mention that it could be some time before we can get to this. Off the top of my head there is the Reduction manual to finish and those kits to get shipping, Mainline to finish and get shipping, The DAC to finish, the experiments with an active step up to finish, The AC motor controller and several other things we are working on. So if it seems at some point that nothing is moving on this idea understand that it's probably just because we always have many projects going at once.
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Don't forget the SR45 v2! Two years and counting :)
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I've never used them, but I know that many feel that the tone controls on the Quad preamps are very useful for helping with different recordings. They have a tilt control, which sounds intuitively right to me for correcting some recordings. This page has an interesting discussion of the tone controls: http://kenrockwell.com/audio/quad/34-preamplifier.htm (disclaimer - I don't know the author or anything about him.)
I've never used a Quad preamp, but I do have an Apt Holman, which also has unusual and less-intrusive-than-normal tone controls. The same guy has a page on this preamp too: http://kenrockwell.com/audio/apt/holman-preamplifier.htm
Food for thought for tone control designers.
Pete
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Take anything Ken Rockwell says with a grain of salt. He is often deliberately provocative, and he isn't shy about spouting opinions, including on things he isn't terribly knowledgable about (he reviews all kinds of stuff). It isn't that he doesn't know anything, and he sometimes has a valid point when he is being provocative, but you just need to bring your own knowledge and experience to bear when evaluating what he says. Again, he's not a bad guy, but I never start out assuming he is right.
Regards,
Adam
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AC Motor Controller? Sounds like you've got a veritable Skunk Works going over there! Awesome :)
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AC Motor Controller? Sounds like you've got a veritable Skunk Works going over there! Awesome :)
Yeah, next project is an AC flying saucer controller.
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I'll beta test for you, I already have my tin foil hat ;D...John
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The tone controls on the Quad 22 pre-amp. are subtle but really do make a difference. I'm a fan of both tone and loudness controls, they have their uses when used in moderation.
A few years ago I designed and built my own loudness control using two poles of an Electroswitch 4-pole 23-way switch from Parts Connexion. The inspiration for this project was in an article from Audio Engineering, August 1951, page 15 by William O. Brooks. I use it as the volume control for a line-level preamp. feeding a couple of 76 triodes. I've found that loudness controls really do restore the 'body' to music when listening at low levels.
If anyone's interested I could post more information on this site.
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I just moved the independent volume controls to the top of my amps to be able to adjust "by ear" and "on the fly". My crossover points are 100, 500 and 7khz. It is a fun new toy.
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I'll just mention that a passive EQ with a gain stage to restore the lost level is very similar in operation to a phono preamp with passive equalization. (I'm just mentioning this since arguments were made that this is a violation of some type of unspoken audiophile code)
-PB
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The tone controls on the Quad 22 pre-amp. are subtle but really do make a difference. I'm a fan of both tone and loudness controls, they have their uses when used in moderation.
A few years ago I designed and built my own loudness control using two poles of an Electroswitch 4-pole 23-way switch from Parts Connexion. The inspiration for this project was in an article from Audio Engineering, August 1951, page 15 by William O. Brooks. I use it as the volume control for a line-level preamp. feeding a couple of 76 triodes. I've found that loudness controls really do restore the 'body' to music when listening at low levels.
If anyone's interested I could post more information on this site.
Yes please!
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A few years ago I designed and built my own loudness control using two poles of an Electroswitch 4-pole 23-way switch from Parts Connexion. The inspiration for this project was in an article from Audio Engineering, August 1951, page 15 by William O. Brooks. I use it as the volume control for a line-level preamp. feeding a couple of 76 triodes. I've found that loudness controls really do restore the 'body' to music when listening at low levels....
That design (from 1951) was I believe derived from the Fletcher-Munson equal loudness contours, which are somewhat obsolete. A much improved set of contours became an ISO standard, I think in the early seventies, and shortly thereafter a better compensation control was developed. Unfortunately the AES, like other technical societies, supports their activities by selling technical papers. So they are not available on the web except at $20 per paper. (This is a 4-page "project note"!) I believe this is the reference:
JAES Volume 24 Issue 1 pp. 32-35; February 1976
There was a thread on DIY audio here:
http://www.diyaudio.com/forums/solid-state/30290-loudness-control-print.html
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What? :o After all that work building my own control! Oh well, back to the drawing board as they say. ::) Currently I'm using a Nad 1240 preamp. which has a loudness control and hopefully conforms to the 70's revised Fletcher-Munson curves.
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Here are the details of my home-made loudness control as requested by pboser.
The article in Audio Engineering, August 1951, page 15 requires the use of a tapped potentiometer, which nowadays are almost impossible to get. I can't reproduce the article here as I do not have permission of the copyright holders but give the values I calculated for a working loudness control. Note, these are from the 1950's Fletcher-Munson curves.
To create an equivalent potentiometer you can get a superior quality component by using a multi-way rotary switch and good quality resistors, tapping at any point along the chain. The switch I used is an Electroswitch 4-pole 23-way rotary switch from the C7 series. I found the method for calculating the volume control values on page 794 of 'The Radio Designer's Handbook' by F. Langford-Smith, 4th edition, 4th impression 1957.
The picture "Attenuator" shows the attenuator network. The values given are for a total resistance of 100K ohms with 2dB difference between switch positions. The picture "Circuit" shows the resistor and capacitor networks that give the bass and treble boost. The small monochrome picture is copied from the original article and the values given are for a 1 Megohm control. Tapping points are at one sixth total resistance (measured from the ground rail) and one third. The values calculated (in ohms) are as follows for a 100 Ohm attenuator.
Switch position
23 R0 = 20567 no attenuation
22 R1 = 16337
21 R2 = 12977
20 R3 = 10308
19 R4 = 8187
18 R5 = 6503 - One third tapping point here
17 R6 = 5166
16 R7 = 4103 -| One sixth tapping between these points
15 R8 = 3259 _|
14 R9 = 2589
13 R10 = 2056
12 R11 = 1633
11 R12 = 1297
10 R13 = 1030
9 R14 = 818
8 R15 = 650
7 R16 = 516
6 R17 = 410
5 R18 = 325
4 R19 = 258
3 R20 = 205
2 Rf = 794
1 0 (tied to ground rail) infinite attenuation
C1 & C3=33nF
C2=679pF
C4=1953pF
R4 & R5 = 12K ohms
The one sixth tapping point is between switch positions 15 & 16 (counting clockwise). With a 100Kohm control one sixth of the resistance is 16666 ohms. At step 15 the total measured resistance of the chain is around 15770 ohms (using 1% metal film nearest value resistors) so to get the correct tapping point I connected an 820 ohms resistor at step 15 in series with a 3300 ohm one connected to position 16. The tap is taken from the junction of the series connected resistors. The one third tapping point is 33333 ohms which is at position 18. The chain resistance here was around 31400 ohms and in this instance I decided not to add any more resistors.
The bass boost is given by C1, R4 and C3, R5. These remain fixed and do not need altering for different potentiometer resistances. The frequency around which C1 and C3 work is 400Hz (the turnover frequency). When the reactance (resistance to a.c current) of C1 equals the resistance of R4 the turnover frequency is 400Hz. Above 400Hz the reactance decreases thus pulling down the voltage at the junction of R4, C2 and C4 and attenuating the treble. Below 400Hz the reactance of C1 increases effectively boosting the bass. R4 helps to limit the effects of C1 which on its own would have too big an effect on treble frequencies. C3 and R5 perform the same bass boost function on the lower tap of the control. The turnover frequencies for treble compensation are 3500Hz for C2 and 5000Hz for C4.
The picture "Finished Control" shows the loudness control in situ in my line level preamp using 76 triodes. The control's effect is pleasant and subtle with music retaining "body" at low volume levels.
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Yowser! That is some pretty scary looking stuff.