Looking for passive volume regulator (passive preamp) recommendations - Page 2

I built one of the Pass B1s. Works pretty good using simple potentiometer controls.

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.


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.

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.


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.

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.

No.

Yes.

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.

The differences between passive parts, especially resistors is massively overstated.

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.

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.

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.

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.

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.

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.

http://www.sound4sale.com/products/MVC.php

Great engineering for $400. Linkwitz uses one: http://www.linkwitzlab.com/my_setup.htm

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!

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.

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.

A passive preamp cannot 'drive' any load. In the PP case that would be the source component supplying the current needed.

If you want transparency, stay away from typical tube design.

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.

Tubes generate both even and odd order harmonics.