What is a preamp?

[miklorsmith]

Welcome!

[mgalusha]

Just to muddle it up a little more, I took and connected a gold point stepped attenuator up to my buddies Burson Buffer (6dB of gain) and put it between my phono stage, a Hagerman cornet and the electronic crossover. This was in place of my UltraVerve clone. I can say that it worked very well and I didn't miss my tubes, which I was sure I would. Just another path on the way to audio nirvana (which I'm sure doesn't exist )

mike

[richidoo]

Thanks Dave, welcome to AN. Glad to know more AR fans onboard!

Mike, your post is very timely as I just sat down to force myself to make a decision.
Thanks
Rich

[WEEZ]

Mike, you put the buffer after the attenuator, right? or before?

WEEZ

[mgalusha]

Weez, I put the attenuator on the input of the buffer (before). The chain looked like this:

TT -> Cornet -> attenuator -> buffer -> XO => power amps => speakers. The only downside (in my admittedly short audition) was the attenuator caused small pops when the level was changed. However, this is an older "mini shunt" attenuator. Series mode attenuators don't have this problem but they also cause more impedance mismatches than do shunt mode attenuators.

A very interesting but also very DIY attenuator option is the "Joshua Tree" ladder attenuator that Twisted Pear Audio makes. http://www.twistedpearaudio.com/joshuatree/jt.aspx

It doesn't cost much and the few reviews I've read pretty much rave about the sound in comparison to pots and ordinary stepped attenuators. Of course the downside is one has to build it (an upside for me) and that it currently doesn't support remote control (natively) but that appears to be coming soon. I believe they have a prototype up and running.

Mike

[WEEZ]

Right.... (on all counts )

Curious what attenuator value you use....25K? 50K?  Thanks..

[mgalusha]

I'll have to look at it. I literally pulled it out of a box and wired it up just to play with.

[WEEZ]

I understand.

...but if you get a chance to check, I'd appreciate it.

WEEZ

[mgalusha]

...but if you get a chance to check, I'd appreciate it.

Weez,

This particular attenuator came from a deHavilland Ultraverve where the owner wanted a remote control and it is wired differently from my other gold point "Mini H" attenuator. It measures about 43-50K on the input for most of the range, increasing to 143K on the next to the last position and 1M when wide open. Zout runs from about 20R to 3.3K at 12:00 o'clock to 100K at the next to last position. It's 1M wide open, obviously somewhere you wouldn't want to go. In my system I never went above about 9:30 or 10:00, so the Zout was still reasonably low. If I was doing this for a keeper project I'd definitely choose something else but it worked surprisingly well.

mike

[mgalusha]

Just came across this article on switched ladder networks. Lots of good info here.

http://jos.vaneijndhoven.net/switchr/index.html

[WEEZ]

Thank you very much, Mike. Useful info....

WEEZ

[steve]

" The only downside (in my admittedly short audition) was the attenuator caused small pops when the level was changed."

Hi MG,

     Quick question. Is the switch a make before break contact switch? If break before make, popping can occur. Or the possibility, any chance that a little DC voltage might be present at the switch, from the source? Doesn't take much voltage.

Take care and hope this helps.
Steve

[mgalusha]

Steve, It's not, the switch is an ELMA of the type used in the DACT attenuators, many of these are shorting but this one is not. It's what Gold Point used to sell as a "Mini H", which is a shunt attenuator but not a full ladder.

I fully understand about having small amounts of DC on the inputs. In this case the source was capacitively coupled and it didn't have any DC. One of the reasons Gold Pt doesn't sell these anymore is that they were noisy, at least I believe that's what I read. In any event, connecting it up to the Burson buffer was just an experiment.

mike

[WEEZ]

Mike, just fwiw...my pre uses a DACT/ELMA series type. Dead quiet and the best volume control I've ever used.

Steve, welcome! (SAS Steve?)

WEEZ

[mgalusha]

Weez, I have a DACT as well and they are quiet and sound excellent. This is because they have a continuous string of resistors (series attenuator) and that the circuit is never broken. When the level is changed the wiper simply selects the next resistor in the string. With a shunt or ladder attenuator there are only two resistors in the circuit at any one time. While there are some potential noise advantages (resistor noise) to this, the downside is that the circuit must be broken and reconnected each time the level is changed.

Steve refers to a make before break switch. This means that it makes contact with the next element before disconnecting from the previous one. In the case of my test attenuator it's not using this type of switch and it's a shunt attenuator, so it makes a little noise. Some folks put a high value resistor across the shunt attenuators so that the circuit is never truly broken and this reduces the switching noise. This is the case with the one I have (and older Gold Point). While quieter, it's not completely silent.

There is a lot of information on stepped attenuators on the Gold Point web site if you want more info. http://www.goldpt.com/index.html (no, I'm not affiliated with them except as a customer)



Mike