Looking for passive volume regulator (passive preamp) recommendations - Page 2 - AVS Forum
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post #31 of 63 Old 04-03-2012, 07:55 AM - Thread Starter
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It is getting closer.
It is clear and final no LDRs. Only simple resistive based VC.
Next step to find out the right, resistance changing mechanical approach, which guaranties nice and smooth motion/rotation feeling and good electrical performance. One of two options: Potentiometer based (TKD, Vishay and etc.) or a rotary multi-postion switch, factory made or custom (PCB based with SMD or through hole resistors mounted on it and the viper).
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post #32 of 63 Old 04-07-2012, 07:09 AM
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I built one of the Pass B1s. Works pretty good using simple potentiometer controls.

Just because there is a knob doesn't mean you should turn it.
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post #33 of 63 Old 04-07-2012, 01:24 PM - Thread Starter
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I actually looking (as a possibility) in to build by me self, from DIYAudio forum.
The DCB1 unit, technically same as Pass's B1 except it is no bypass caps. Will use group buy option.

The problem is that need to find a decent case/chassis and time to build it.
The Luminous Axiom is a very sweat deal, as a passive approach, and I may till go for it.

About the potentiometer/multiposition switch:
Does it really have to be a shunt topology based or a more conventional standard potentiometer divider approach would work as well?

I never understood what is the big deal about this shunt regulator connection.
I do not buys so much an idea for shunt regulator that "signal does not go through the potentiometer or switch, only through the series resistor".
If it as a problem with potentiometer, all its behaviour will be 100% reflected to then output signal (in any case).
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post #34 of 63 Old 04-07-2012, 02:01 PM
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Quote:
Originally Posted by bordo32 View Post

I actually looking (as a possibility) in to build by me self, from DIYAudio forum.
The DCB1 unit, technically same as Pass's B1 except it is no bypass caps. Will use group buy option.

Make sure you use the relay to mute at switch on/off as it will thump otherwise. Worrying about the caps is really a waste of effort though - Pass does not consider them an issue, and he is no fool.

I have a squillion BF862 to match to make 12 buffers with the same topology as the original B1 (with caps) maybe later in the week.

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Originally Posted by bordo32 View Post

The problem is that need to find a decent case/chassis and time to build it.

Plenty on ebay or use a rack mounting unit and you can custom design the front through frontpanelexpress. There are lots and lots of options here.
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The Luminous Axiom is a very sweat deal, as a passive approach, and I may till go for it.

Much better deal than the Placette as at least they try to optimise for your system, rather than giving no data at all. One sixth the price too.

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Originally Posted by bordo32 View Post

About the potentiometer/multiposition switch:
Does it really have to be a shunt topology based or a more conventional standard potentiometer divider approach would work as well?

I never understood what is the big deal about this shunt regulator connection.
I do not buys so much an idea for shunt regulator that "signal does not go through the potentiometer or switch, only through the series resistor".
If it as a problem with potentiometer, all its behaviour will be 100% reflected to then output signal (in any case).

You can do a series ladder with only two resistors in the signal path if you use 2 (or 3 if you're really OCD) decks/channel This is 'theoretically' the most direct. But you will most likely need to custom make it. Works just like a pot, with it's pros/cons.
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post #35 of 63 Old 04-08-2012, 04:37 AM
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I used a Par-Metal 10-series case. You're not going to mistake it for a something from, say, Klyne or Ayre, but it's not bad.

Just because there is a knob doesn't mean you should turn it.
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post #36 of 63 Old 04-09-2012, 09:19 AM - Thread Starter
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Thanks for your comments and recommendations.

Speaking about the volume regulator itself.
Is it really necessary to have a shunt regulator topology or the conventional potentiometer, used a resistor divider topology would be sufficient enough? In case of multiposition switch the signal would go through all series resistors, but at those signal levels I do not see any possibility to have an elevated noise generated by those resistors.
Even by using a shunt approach, when between input and output only one series resistor, I still believe that resistors used in the shunting to ground switch would affect the signal quality. I am wrong here?
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post #37 of 63 Old 04-09-2012, 01:54 PM
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Quote:
Originally Posted by bordo32 View Post

Is it really necessary to have a shunt regulator topology

No.
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Originally Posted by bordo32 View Post

or the conventional potentiometer, used a resistor divider topology would be sufficient enough?

Yes.
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Originally Posted by bordo32 View Post

In case of multiposition switch the signal would go through all series resistors, but at those signal levels I do not see any possibility to have an elevated noise generated by those resistors.

20 resistors in series that sum to 1kR have the same noise as a single 1kR resistor.
I already told you how to do a traditional series attenuator with only two resistors in the path at any given time. Think about it and it's obvious, but I don't have a diagram to hand.
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Originally Posted by bordo32 View Post

Even by using a shunt approach, when between input and output only one series resistor, I still believe that resistors used in the shunting to ground switch would affect the signal quality. I am wrong here?

The differences between passive parts, especially resistors is massively overstated.
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post #38 of 63 Old 04-09-2012, 03:07 PM - Thread Starter
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A9X-308, thanks, I agree. It all makes sense.
Does it mean that the shunt volume regulator topology approach (instead of regular resistor divider), Luminous Axiom uses for example, is all about the marketing, does not provide actual benefits?
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post #39 of 63 Old 04-09-2012, 04:51 PM
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Quote:
Originally Posted by bordo32 View Post

Does it mean that the shunt volume regulator topology approach (instead of regular resistor divider), Luminous Axiom uses for example, is all about the marketing, does not provide actual benefits?

No benefits that I see.

Looking at their customisation page, why ask for speaker sensitivity, but not amp power (or gain)? Let alone source Zout, both interconnect capacitances or what the source actually is - see previous 12AU7 CF example.
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post #40 of 63 Old 04-09-2012, 04:55 PM
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If you want to try something simple and inexpensive:
http://www.nhthifi.com/passive_volume_control_PVC_PC

It has a quality ALPS volume pot.

$99 wow.
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post #41 of 63 Old 04-09-2012, 05:45 PM
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wow.

It's good to see that some people are still able to be easily impressed.
It's also not what the OP is looking for.
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post #42 of 63 Old 04-09-2012, 07:50 PM - Thread Starter
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Simba, thanks for your advise, but I am looking for a bit different approach.
Well, after A9X-308 wa clearing up some basic things, it appears that only a few simple basic things need to get to build it: the unity gain stage helping to match in-out resistances, also helping drive cable load (B1 or DCB1 type), the nice looking case and the multipostion switch or potentiometer. Potentiomerter looks an attractive idea since provides smooth and nicee rotation feeling, where the switch based is way more expensive but keeeps good balance between chennels. I am not sure which multiposition switch (mechanics it self) would have a nice and smooth (potentiomer like) rotational feeeling. I found Goldpoint, DACT, DALE, SHALLCO, not sure which one to try.
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post #43 of 63 Old 04-10-2012, 04:53 AM
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Quote:
Originally Posted by bordo32 View Post

I am not sure which multiposition switch (mechanics it self) would have a nice and smooth (potentiomer like) rotational feeeling. I found Goldpoint, DACT, DALE, SHALLCO, not sure which one to try.

None of them. A mechanical switch is a mechanical switch and that is that.

If you want a switch that feels like a nice smooth potentiometer, you have to enter the digital domain.
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post #44 of 63 Old 04-10-2012, 05:04 AM
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None of the switches will be as smooth as a pot. Even those pots that have 'detents' will be smoother than the switches.

Alps Blue Velvet are a better than usual conventional carbon pot, and there are even motorised version - I have one of these you can have, but I'll have to find it and check it's a suitable value.

TKD also make very good units, but they're about $100.
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post #45 of 63 Old 04-10-2012, 05:47 AM
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Quote:
Originally Posted by arnyk View Post


If you want a switch that feels like a nice smooth potentiometer, you have to enter the digital domain.

Not necessary. You may have a resistor array switched by relays, all controlled by totary encoder. Encoder itself can be as smoith as you want, and volume change step is only limited by number of relays used there. That way you have fully passive volume regulator without disadvantages of mechanical switch.
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post #46 of 63 Old 04-10-2012, 06:06 AM
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Not necessary. You may have a resistor array switched by relays, all controlled by totary encoder. Encoder itself can be as smoith as you want, and volume change step is only limited by number of relays used there. That way you have fully passive volume regulator without disadvantages of mechanical switch.

Yes, I guess. I've even had such things.

Discrete resistor arrays and mechanical switches are so retro-tech.
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post #47 of 63 Old 04-10-2012, 08:00 AM - Thread Starter
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Sorry that I was not cleare here describing what I am looking for.
I am ot seeking a switch with the same rotation feeling as a pot.
I actually need a switch, with the goal to have a most smooth performance.
Or just in general a good switch.
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post #48 of 63 Old 04-19-2012, 12:05 PM
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post #49 of 63 Old 04-19-2012, 09:11 PM - Thread Starter
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Thanks to all for your recommendations and adivises.
I am still in the process to decide which approach would fit the best.
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post #50 of 63 Old 04-20-2012, 06:00 AM
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Hi Bordo32,
I'm Wes from Tisbury Audio. I've tried and tested most attenuators on the market, so I thought I could offer a bit of helpful insight.

All stepped attenuators will have a detended rotation as this is required to ensure the wiper settles correctly on each step. However some are smoother than others.

DACT & Goldpoint: These both use the same Elma switch, so both feel the same. The rotation is noticeably stepped, but switching between steps is smooth and effortless. These are both serial types (I'll cover different types and their impedances below).

Dale attenuators: These have a much stiffer rotation. They offer brilliant sound quality, channel matching and price, but the stiffness is a real downer. You can get them in serial, ladder or shunt configuration. I'd only ever recommend ladder for these.

Chinese SMD attenuators: These are available on eBay from gigawork and lasercollection for about $10.
I actually really like these. They have by far the smoothest rotation of all the attenuators. You can feel the steps, but they're very smooth.
They're serial surface mount resistor types, the same as DACT & Goldpt. They sound great and have good channel matching.
Because of the price, there have been concerns on other forums about build quality, but I've not personally had any problems. Plus they're so cheap you can just buy 2 or 3.

Seiden/Shallco: These use a spring loaded ball against a cog to step the rotation, so as you can imagine the rotation goes 'clunk, clunk'. They're very expensive, and the main advantage over DACT/Goldpt is that they can be made in any configuration and with any resistors.

Different types and their impedances:

Ladder: These can give the most consistent input and output impedance if the resistor values are chosen correctly. They can sound fantastic, too. However, they are usually the most expensive, and obviously the resistor values need to be correct.

Serial: Although 'serial' means passing the signal through multiple resistors, as A9X-308 said this does not effect distortion and these are some of the best sounding attenuators you can get.
These will have the same impedance behaviour as a pot. Input impedance is fixed at the value of the attenuator. Output impedance will vary slightly, with the worst case scenario being approximately 1/4 the attenuator's value.

Shunt: You are quite right, the shunt resistor does indeed affect the signal. In fact, it's quite plausible that the shunt resistor is more critical than the series, as the signal seen by the amplifier is effectively the voltage across the shunt resistor. This was very well covered over on diyAudio (search "shunt attenuator myth").
They are basically a gimmick. The reason they've caught on is that they can be constructed fairly cheaply, while appearing to have high performance. But the companies that use them conveniently don't mention this comes at the expense of impedance. Output impedance will vary from 0 to the value of the series resistor + source output impedance. Even input impedance will vary, although this is usually less of a problem.

Also I think you mentioned your amp is 25k in. In which case you'll be wanting a 10k attenuator.
And if you do go down the DIY route, for the love of God don't over tighten the fixing nut on an attenuator/pot! It can be an expensive lesson to learn. They have a little nub to stop them from rotating, so use that and keep the nut tension fairly light.

Hope that helps!
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post #51 of 63 Old 04-22-2012, 08:57 AM
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I've been using a Channel Island passive preamp for a few years now, nice inexpensive way to see if you like going that route. As a general rule, passives like a low impedance source and an amp with an input impedance of 50-100kOhms.

I'm currently building a tube buffeted volume control that will use a Dodds tube buffer and a Goldpoint Mini V. Same principle as using the B1 kit. The buffer has an input impedance of 100kOhms, and an output impedance of around 100ohms, using a 6H30-DR tube.

If you are interested in diy, Dodds also makes a full buffer kit (I went with the cheaper basic one).

http://doddaudio.com/diy.aspx

PS, I also entertained going the LDR route, talked myself out of it, for numerous reasons. Maybe try one later.
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post #52 of 63 Old 04-23-2012, 09:13 PM - Thread Starter
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jkhome, thanks for pointing out Dodds buffer kit, looks interesting.

Tisbury Audio, wow wow wow, that is information evey DIYselfer would be looking for.
Thanks for sharing your experience!

I will follow your advice and stick with Elma switch based attenuator.
The whole unit on your web looks attractive, even a small DCB1 or B1 type of preamp board my fit in it. I my still think about preamp, since 5k or 10K passive attenuator would not be able to "drive" properly cables to the power amp.

Would you also have available chassis with XLR sockets for two pair of inputs. The quad version of DACT attenuator would be nice option.
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post #53 of 63 Old 04-24-2012, 02:21 AM
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Not sure how big the standard B1 board is, but the B1DC should definitely fit. The internal dimensions of our enclosures are 160mm x 114mm x 44mm.

Sure, we could do a balanced model for you. I'll send you a PM and we can talk through the details.


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Originally Posted by bordo32 View Post

jkhome, thanks for pointing out Dodds buffer kit, looks interesting.

Tisbury Audio, wow wow wow, that is information evey DIYselfer would be looking for.
Thanks for sharing your experience!

I will follow your advice and stick with Elma switch based attenuator.
The whole unit on your web looks attractive, even a small DCB1 or B1 type of preamp board my fit in it. I my still think about preamp, since 5k or 10K passive attenuator would not be able to "drive" properly cables to the power amp.

Would you also have available chassis with XLR sockets for two pair of inputs. The quad version of DACT attenuator would be nice option.

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post #54 of 63 Old 04-24-2012, 02:44 AM
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Quote:
Originally Posted by bordo32 View Post

I my still think about preamp, since 5k or 10K passive attenuator would not be able to "drive" properly cables to the power amp.

A passive preamp cannot 'drive' any load. In the PP case that would be the source component supplying the current needed.
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post #55 of 63 Old 04-24-2012, 06:43 AM - Thread Starter
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A9X-308, I understand your pint, this is why word drive is in "", I may need to use a buffer stage. I will make an experiment, will order any suitable potentiometer from DigiKey, play with cables, potentiometer values, and findout if a passive volume reguilator would work. If not - definetely a buffer stage will be needed.
Tisbury Audio, thanks for your comments, I got your PM, I will take a look. Need to findout the inputs-outputs requirements. I will make a few experiemnts first.
Just an idea, can you just think about upgrading your products line offering as an optional buffer stage.
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post #56 of 63 Old 04-24-2012, 07:35 AM
 
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Quote:
Originally Posted by bordo32 View Post

If not - definetely a buffer stage will be needed.

If you want transparency, stay away from typical tube design.
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post #57 of 63 Old 04-24-2012, 12:10 PM - Thread Starter
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Diomania, thanks, I know-I know, those tubes generated even number harmonics will put a special "coloring" to the sound. I am using tubes based an external DAC (as an option for my vocals containt music records). Those tubes work as a harmonizer, injecting harmonics which are interfearing with the high ends and not good for some others music containts.

I am looking for J-FET transistor based DCB1 type of buffer. Again, first I need to experiment finding if the passive attentuator approach would not be good enough.
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post #58 of 63 Old 04-24-2012, 01:05 PM
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Quote:
Originally Posted by bordo32 View Post

Just an idea, can you just think about upgrading your products line offering as an optional buffer stage.

We do actually have a buffer stage in the works. We're putting together a few prototypes at the moment, so hopefully should have something finished in a couple of weeks.
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post #59 of 63 Old 04-24-2012, 01:53 PM - Thread Starter
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Tisbury Audio, it is called "market orriented" approach/decision, excellent idea!
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post #60 of 63 Old 04-24-2012, 02:37 PM
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Quote:
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those tubes generated even number harmonics will put a special "coloring" to the sound.

Tubes generate both even and odd order harmonics.
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