Volume setting, gain and speaker level

rookster · « **on:** 11 Jul 2006, 10:01 am »

I hope this had not been discussed before, but is there a way to calculate what the volume setting would be for a given speaker SPL?

The reason I ask is I want to use a stepped attenuator for my GK-1 (unbuilt) which feeds my 55N+ (build underway) and my Aksonics (built).

If I know what SPL range I like to listen to and I know the output voltage from my CD player, can I confirm what dB settings of the volume control produce the SPL I want. If I know this I can confirm the dB steps that would be appropriate for me, prior to ordering the attenuator and resistors.

I know I can just build the GK-1 with a pot and measure the resistance at the different levels, then order the stepped attenuator later. However I want to order some other parts from Michael Percy to build my GK-1 and only want to order once, if I can help it, to save postage (to Australia).

Hugh, would a 22K or a 25K volume control be best? What is the sensitivity of the Aksonics?

I hope this does not sound too obsessed or retentive, but I only what to solder once and order parts from overseas once, if I can.

andyr · « **Reply #1 on:** 11 Jul 2006, 10:10 am »

Hi Rookster,

I'm wondering why you want to use a stepped attenuator (and pay all that money for one!) rather than using Hugh's supplied volume pot?

I seem to remember reading one or more posts on this Forum where Hugh explains that he carefully designed the way the vol pot is implemented, to make its "sonic quality" immaterial to the resulting sound?

Regards,

Andy

AKSA · « **Reply #2 on:** 11 Jul 2006, 12:42 pm »

Hi Michael,

No problem - I won't downplay the advantages, it's quite possible a stepped attenuator will sound slightly better.

10K, 22K, 25K or even 50K is fine for this pot - not critical - but the best compromise would be 22 or 25.

Sensitivity of the AKSonics is 87dB/watt/metre, principally determined by the drivers. Sadly I can't give you exact settings of the pot for db output - in any event, these will be impacted by room acoustics, material, preferred listening levels, but I can say that the present configuration will give you very nice listening levels at around 4 on a scale from 1 to 10.

Cheers,

Hugh

PSP · « **Reply #3 on:** 11 Jul 2006, 09:49 pm »

The best attenuator page that I know of is VoltSecond's, written for the Bottlehead Foreplay, but generally applicable, I think. There's a lot to read, but it's good stuff if you don't mind a little arithmetic.

http://www.siteswithstyle.com/VoltSecond/12_posistion_shunt/12_Position_Pure_Shunt.html

There is some good info on the Goldpoint page too: http://www.goldpt.com/how.html

Good luck,
Peter

jules · « **Reply #4 on:** 12 Jul 2006, 12:06 am »

Rookster,

there's been quite a bit of discussion on this circle about stepped attenuators so maybe a search would revive it.

I built one myself, mainly as a soldering exercise and it's been spot on as far as the choice of steps goes. A certain amount of juggling has to go on so that you get smaller [2db for a 24 step switch] steps where you want them and larger ones where it doesn't matter [particularly at the loud end but maybe also at the soft end]. Mine is 20k, currently in use on my 55N+, intended for use in my GK-1 and working with speakers of ~92db efficiency. Aksonics are about 88db efficient I think [could be wrong].

You'll need a spreadsheet to do calcs or maybe the info from the Goldpoint site. Your choice of brand of resistors and the values they have will have a bearing on what set you use to populate your switch. It can be hard to get things smooth so you don't have widely varied steps where you don't want them.

jules

stvnharr · « **Reply #5 on:** 12 Jul 2006, 02:21 am »

Quote from: rookster on 11 Jul 2006, 10:01 am

I hope this had not been discussed before, but is there a way to calculate what the volume setting would be for a given speaker SPL?

The reason I ask is I want to use a stepped attenuator for my GK-1 (unbuilt) which feeds my 55N+ (build underway) and my Aksonics (built).

If I know what SPL range I like to listen to and I know the output voltage from my CD player, can I confirm what dB settings of the volume control produce the SPL I want. If I know this I can confirm the dB steps that would be appropriate for me, prior to ordering the attenuator and resistors.

I know I can just build the GK-1 with a pot and measure the resistance at the different levels, then order the stepped attenuator later. However I want to order some other parts from Michael Percy to build my GK-1 and only want to order once, if I can help it, to save postage (to Australia).

Hugh, would a 22K or a 25K volume control be best? What is the sensitivity of the Aksonics?

I hope this does not sound too obsessed or retentive, but I only what to solder once and order parts from overseas once, if I can.

Rookster,
I use stepped attenuators and have made kits from Michael Percy. Goldpoint no longer offers kits, FWIW. What you want is a 25k attenuator. Michael will calculate anything you want, but there really is no reason to get fussy here. The kits with Elma switches have 23 steps, all but the lowest couple are 2 db. steps. The kits with the Shallco switches have 45 steps with 1 db. steps. Decide your budget, and if you want ladder or series. If you have any questions, Michael is usually pretty good with email replies on this.

I wouldn't be concerned about volume level setting. It makes no difference. There's lots of gain in the GK-1/Aksa combo, so you are mostly going to be somewhere in the lower half of settings. But there are just too many variables to calculate anything. And while your system numbers may be somewhat set in place, you have no control of the recording level of your discs. However, unless you listen to things classical, most discs are recorded with similar levels as the dynamic range is so small in popular musics.

Hope this helps.

Steve

rookster · « **Reply #6 on:** 12 Jul 2006, 10:13 am »

Andy,

I know I am going over the top with my GK-1, but I am spending a lot of time on the mechanical design of the case, internal layout, power cables and component selection. As such, while I believe a stepped attenuator is excessive, it will be in-line with my level of quality of the finished product I want to achieve

Hugh,

Thankyou for your reply. I was only trying to get an idea of where the volume control would be set. About 4 out of 10 "sounds" good to me. I am looking forward to finishing the GK-1. I think you will be impressed with my design.

PSP,

I have had a look at Voltsecond's page before and the Goldpoint page before. There is a lot of good information there. I will have another read.

Jules,

I have read posts on stepped attenuators on the Aspen circle, but not the other circles yet. I have generated a spreadsheet to calculate resistor values for a range of steps, so I am working on that to suit available resistor values.

Steve,

I will look at 22K or 25K depending on what resistors I calculate versus what is available. I will probably go through Michael percy and use Holco resistors. I will assume I will use somewhere between 1/4 and 3/4 setting for my listening and base my design on that.

All,

I know I sound very obsessed and pedantic, but want to build the best I can, within reason. However one person's reason might sound like madness to another. I think I am sane, but only just. I am an engineer, so quite creative anyway. Plus it is an exciting hobby.

Thanks for the input.

AKSA · « **Reply #7 on:** 12 Jul 2006, 12:04 pm »

Michael,

I applaud your approach; welcome to the madhouse

, where all present are dangerously sane......

It is very comforting to be surrounded by people with passion - heck, I almost feel like a real engineer in this company!!

Hugh

PSP · « **Reply #8 on:** 12 Jul 2006, 01:35 pm »

I must have diagramed my first 55w AKSA 1000 times before I drilled the first hole in the chassis. For months, every time the meeting got boring, every time I waited anywhere, I would pull out pencil and paper to work on the layout.

It took me a year from the time I recieved my GK-1R kit until I began construction.

Passion and a fierce desire to do your best is the heart and soul of this quest.

Peter

jules · « **Reply #9 on:** 12 Jul 2006, 11:26 pm »

Actually Rookster, having read Steve's post I have to agree his way is probably better than mine

unless you want to make a simple issue more complex.

jules

DSK · « **Reply #10 on:** 13 Jul 2006, 12:38 am »

Hi Rookster,
You may want to consider the TKD 2PC65S stepped attenuator. The late, great Bob Crump of CTC tested countless attenuators (including custom ladders) in his search for the best sounding attenuator and chose this one. Two of the mono version (PC65CS) are used in the cost-no-object CTC BlowTorch pre-amp (~US$12K+) and I believe also in one of the high-end Lamm pre-amps (L2 Reference?). Bob also applied a simple mod to this attenuator which further improved its performance.

Hugh and I installed the 2PC65CS in my GK-1 a couple of years back and heard an instant improvement. We then applied the mod and heard additional improvement. Before installing the attenuator, Hugh measured it and exclaimed "My God! It's like a scientific instrument, extraordinarily accurate!".

One of the benefits of this attenuator is that it has 40 steps, almost all of which are 1db increments.

I ordered mine from Michael Percy. They are not cheap at US$250 each and the mod was another US$120.

See link below for a picture of the stereo and mono versions. If you go this route, PM me for details of the mod.
http://www.thlaudio.com/indexE.htm

Like you, I spent countless hours drawing up the GK-1 layout. After listening to it for several months I decided that it was good enough that it deserved the very best attenuator I could find. I too was heading for a custom ladder attenuator until I came across the TKD. I have been very happy with it!

EDIT: Forgot to mention ... I used the 25k version as advised by Hugh.

andyr · « **Reply #11 on:** 13 Jul 2006, 08:36 am »

Quote from: rookster on 12 Jul 2006, 10:13 am

Andy,

I know I am going over the top with my GK-1, but I am spending a lot of time on the mechanical design of the case, internal layout, power cables and component selection. As such, while I believe a stepped attenuator is excessive, it will be in-line with my level of quality of the finished product I want to achieve

Hi rookster,

This thread of yours has opened my eyes ... I didn't realise using the non-standard volume control could deliver a much better result - as DSK has posted, the difference is not insignificant!!

I will now incorporate a stepped attenuator when I get around to taking apart my GK-1 to tweak its phono stage ... although I have the Remote GK-1, being able to change the volume without getting up from my seat holds so little attraction to me that the thought of being able to get better sound through a manual attenuator wins hands down!!

And I certainly don't think there's anything wrong with "going over the top" in terms of doing things to make the GK-1 sound better. With respect to this, you might like to try the following:
a) use Dynamat Xtreme (or equivalent) sound-deadening material on the inside of all case panels, wherever there's a section of case which is not covered with RCA sockets or LEDs or selector switches - including the top.
b) put a 6mm pad of Sorbothane underneath the two power transformers, to stop them vibrating the case.
c) likewise, mount the GK-1 PCBs on Sorbothane pads. I had some right-angle brackets screwed to the side of the case ... the PCBs sit on Sorbothane pads which rest on these right-angles and I used nylon bolts (not steel) to hold them in place.
d) put an internal mild-steel barrier to isolate the power transformers from the PCBs, inside the case.

Regards,

Andy

andyr · « **Reply #12 on:** 13 Jul 2006, 08:39 am »

Quote from: DSK on 13 Jul 2006, 12:38 am

You may want to consider the TKD 2PC65S stepped attenuator.

See link below for a picture of the stereo and mono versions.

Hi Darren,

Can you explain the advantages of going the dual-mono vs. going the stereo version and keeping my balance control?

Regards,

Andy

DSK · « **Reply #13 on:** 13 Jul 2006, 09:48 am »

Quote from: andyr on 13 Jul 2006, 08:39 am

Quote from: DSK on 13 Jul 2006, 12:38 am
You may want to consider the TKD 2PC65S stepped attenuator.

See link below for a picture of the stereo and mono versions.
Hi Darren,

Can you explain the advantages of going the dual-mono vs. going the stereo version and keeping my balance control?

Regards,

Andy

Hi Andy,
A technical person could probably give you a more detailed response. However, the basic advantages of the 2x mono attenuators are that they give you a balance control without actually introducing a balance control pot into the signal path, and that there is no chance of interference between channels. The downside is that you need to rotate 2 knobs instead of one and to keep them at the same setting (or a set number of detents different if using to adjust balance).

In my case, I don't lose remote control of the volume. I use a Bolder modded SqueezeBox to feed the GK-1 (the GK-1 was not hooked up when you were here) which feeds the AKSA 100N+. I manually set the GK-1's TKD attenuator to approx 12 o'clock which, in my system, enables me to set the SqueezeBox's remote volume control between 30 and 40 (max.) depending on recording. The higher an attenuator is set, the less impact it has on the sound. The SqueezeBox needs to be set to 16 or above to not have an audible impact. So, I retain remote control of the volume while virtually eliminating any sonic degredation from the attenuators. The sound was very good with the SqueezeBox direct to the AKSA 100N+ (volume was always between 8 and 20 depending on recording), but is better with the GK-1 in the system ...more dynamic and full bodied and seemingly quieter with no apparent loss of transparency or detail.

The magnitude of improvement provided by the modded TKD was probably a bit more than that provided by swapping the stock tubes to the NOS Siemens 7308 gold pins in the GK-1.

rookster · « **Reply #14 on:** 13 Jul 2006, 11:07 am »

DSK,

The TKD 2PC65S stepped attenuator "sounds" interesting, but the cost is a bit out of my range. Even 2 off Shallco 45 position switches are at my price limit. But I will have a look though. I have my 55N+ cases and GK-1 cases drawn on CAD and I keep making mods and changes as I go. Getting there though.

Andy,

I had not considered damping my case quite to the level you suggested. I have been thinking about damping the transformers, but not a lot else. However I have braced the cases very well. I would like to incorporate a mild-steel barrier as a shiled.

Still lots of things to order, design, change and make. very exciting, but time consuming. I bought my GK-1 15 months ago and only have the cases now. I have not made any part of the GK-1. Have only started on the cases for the 55N+, which may turn into a Lifeforce if I can swing it. I have 4 channels of 55N+.

andyr · « **Reply #15 on:** 13 Jul 2006, 11:20 am »

Quote from: rookster on 13 Jul 2006, 11:07 am

Andy,

I had not considered damping my case quite to the level you suggested. I have been thinking about damping the transformers, but not a lot else. However I have braced the cases very well. I would like to incorporate a mild-steel barrier as a shield.

Hi rookster,

Well, who knows whether Dynamat Xtreme actually delivers a sonic improvement or not ... it's kinda hard to do an A-B test!!

But theory says vibrrrration control is important - so I paid my $50!!

It's only a bit more work in addition to what you're planning on doing already.

And damping - including the underside of the power transformers - same applies to the AKSA 55, of course!!

Again, who knows whether the shield between the power transformers (I did this in my AKSA 55N+ as well as the GK-1) and the PCBs actually does anything but theory says it should so ...

Regards,

Andy

SamL · « **Reply #16 on:** 13 Jul 2006, 11:28 am »

Have a look at endler attenuators. They have good review and is reasonable in price.
http://www.positive-feedback.com/Issue19/endlerattenuators.htm

He even tell you what he uses and if you wanted, you can build one just like his.
http://mysite.verizon.net/vze4c5pt/id2.html

Have fun,
Sam

stvnharr · « **Reply #17 on:** 14 Jul 2006, 01:53 am »

Quote from: SamL on 13 Jul 2006, 11:28 am

Have a look at endler attenuators. They have good review and is reasonable in price.
http://www.positive-feedback.com/Issue19/endlerattenuators.htm

He even tell you what he uses and if you wanted, you can build one just like his.
http://mysite.verizon.net/vze4c5pt/id2.html

Have fun,
Sam

These, the Endlers, are a less expensive attenuator alternative that many like. However, a lesser number of steps tends to mean other kinds of compromises, with either larger steps or smaller volume range. The attenuators that plug in to the back of the amplifier are easy to implement, but you have your volume control on the back of the amp.
If you read the Percy page you will read mention of possible switch contact noise on the Elma 04 series switches. The BV series switches have larger contacts and are quiet. All BV series switches are quiet. Some 04 series switches are noisy, most aren't. Contact noise is irritable, to say the least. A good switch cannot be underestimated.

Also, dual mono switches or one stereo switch is no different in sound. The stereo attenuator just has both decks on one shaft. However, mono switches do allow for a bit of balance control, if so desired. I've come to rather like having 2 controls. And I used to think I couldn't live without a remote!

Steve

rookster · « **Reply #18 on:** 14 Jul 2006, 09:57 am »

There seem to be a lot of other stepped attenuators and pot options available.

I will do a little more research. I do want to order soon so I can confirm that they fit.

I will pay a bit more attention to damping of the transformers and case.

andyr · « **Reply #19 on:** 22 Jul 2006, 10:38 pm »

DSK said this:

"You may want to consider the TKD 2PC65S stepped attenuator.

Hugh and I installed the 2PC65CS in my GK-1 a couple of years back and heard an instant improvement. We then applied the (Bob Crump) mod and heard additional improvement.

I ordered mine from Michael Percy. They are not cheap at US$250 each and the mod was another US$120.

EDIT: Forgot to mention ... I used the 25k version as advised by Hugh."

Just for everybody's reference, M Percy no longer has mono 25K TKD attenuators in stock. He still has 25K stereo ... mine is on its way!!

Regards,

Andy