ERC-1 output impedance?

[jlafrenz]

I didn't really lose dynamics either.

Right now I am using the phono stage of the MMC-1 for my turn table. I am looking at upgrading the table and phono stage though. I can't decide between a Graham Slee or Jolida phono stage. It has come to these two because they are in my price range and will work with the passive preamp.

Do you happen to have the link to that article about the input and choosing the correct resistor? I remember reading it, but I would like to read it again and can't seem to find it.

[RPA-1 man]

I read so many articles but I didn't bookmark any of them. Duh!!

A lot of the articles I read were people debating the pro's and con's of using passive pre's and the types of pre's and resistor types they used. I've also learned that if you have a single resistor plus the attenuator the Vishay 1% precision resistor is the way to go.

Honestly, the Goldpoint info www.goldpt.com/info.html page pretty much sums up everything else I've read though. The first section "How To Choose the Correct Stepped Attenuator Value. General Rules and Considerations:" is a nice summation of what to look for.

[jlafrenz]

Mar 21, 2010 9:24:10 GMT -5 RPA-1 man said:

I read so many articles but I didn't bookmark any of them. Duh!!

Neither did I. That's why I was asking you for the link ;D

Even better, the info I was looking for is on the website from the manufacturer I purchased from

[RPA-1 man]

Well, so far I have to say that I like the passive approach. I've been listening every night and it's hard to turn the system off. The sound is smooth, dynamic and involving. Why do I have to work? I'd rather stay home and listen to the stereo. Oh well, reality has to set in sometime.

[sanjaygolf]

I'm not too knowledgeable with passive preamps. Are they just basically providing volume attenuation to a source? What would be the difference if I had a source with volume control connected directly to an amp vs having the source connected to a passive pre and then to the amp?

[jlafrenz]

Mar 25, 2010 17:55:01 GMT -5 sanjaygolf said:

I'm not too knowledgeable with passive preamps. Are they just basically providing volume attenuation to a source? What would be the difference if I had a source with volume control connected directly to an amp vs having the source connected to a passive pre and then to the amp?

Yes, they provide volume attenuation to a source. It is very similar to having a device connected to an amp. One benefit is that many passive preamps offer source switching.

[jlafrenz]

Hey RPA,

I have been doing some reading trying to educate myself further on this whole passive situation and have come across some good info that I thought I would share with you. You may have already read this (or something similar), but here are a couple of links that discuss input/output impedance and may be of value to you.

www.kpsec.freeuk.com/imped.htm

www.whirlwindusa.com/tech03.html

One other thing that I read is that when using a passive preamp, you have to combine the output impedance if both the source and the passive unit.

All this info just leads to more questions for me. Slowly, but surely, I am putting it all together though.

[rockguitar]

"One other thing that I read is that when using a passive preamp, you have to combine the output impedance if both the source and the passive unit."

Actually, to be more precise, my understanding is the most important criteria is the input impedance of the amp and that of the attenuator/passive pre as the output impedence of the source is usually very low. I use a DACT CT-2, the original version, and you can see how the frequency response varies here.
www.dact.com/html/ac_calculator.html

Here's a fine example of a passive preamp use DACT attenuators as a 6 channel attenuator. I just reread this today and thought I would post it as I just read this thread.

www.hometheaterhifi.com/volume_10_1/kimber-dact-volume-control-2-2003.html

I also give a thumbs up to my passive. It's the ultimate in simplicity and clarity. I Use two IC's soldered directly to the DACT CT-2. I can't remember the exact numbers, but I recall that you want a relatively high input impedence for the amp so that the frequency response of the attenuator does not change too significantly as the volume changes. I used to use it with a Pass Labs Aleph 30 with an input impedence of around 47 kOhms, if memory serves.

[RPA-1 man]

Rockguitar,

Thanks for the info and links. I will check them out. I like the idea of the DACT Attenuation Calculator.

Do you have any pics of your passive pre?

[Lonnie]

Sorry for jumping in here late but I just saw this thread.

The output impedance of hte ERC-1 is 620 for the balanced and 470 for the un-balanced.

Using a passive pre is certainly not an issue, the discrete output stage has more than enough current and voltage to over come the losses.

The only reason it match the imput impedance of the amp is to prevent the pre from affecting the broad band frequency response. If your using our amps, don't worry about it. They have a high impedance input and even if the pre did limit the band a little, it won't be audioble because the amps can play out well beyond 80Khz.

[rockguitar]

Jun 22, 2010 5:55:19 GMT -5 RPA-1 man said:

Rockguitar,

Thanks for the info and links. I will check them out. I like the idea of the DACT Attenuation Calculator.

Do you have any pics of your passive pre?

Sorry, I don't have any pics right now. In retrospect, I should not have called the DACT the ultimate, it's a bit of hyperbole. But it's darn good. Lately, with passive preamps on the mind, I've been looking into other DIY passive preamp arrangements. Right now I've been looking into the Lightspeed attenuator and other variations using an optocoupler design to change the resistance and volume.

Google Lightspeed attenuator or LDR attenuator and you'll see lots of feedback.

forum.audiogon.com/cgi-bin/fr.pl?aamps&1241550350
diyaudioprojects.com/Forum/viewtopic.php?f=12&t=388

The original Lightspeed attenuator has been recently reviewed in Stereophile by Sam Tellig. The designer, George, has shared a basic schematic on diyaudio.com and lots of people feel that that this is one of the most transparent ways to accomplish volume control. Feedback indicates that it is superior to using a DACT and comparable or superior to the best passive preamps out there. Nelson Pass himself has also contributed a design with the LDR and includes a buffer for better impedence matching if the amp has a low input impedence. Very interesting stuff.

[RPA-1 man]

Jun 22, 2010 8:36:34 GMT -5 Lonnie said:

Sorry for jumping in here late but I just saw this thread.

The output impedance of hte ERC-1 is 620 for the balanced and 470 for the un-balanced.

Using a passive pre is certainly not an issue, the discrete output stage has more than enough current and voltage to over come the losses.

The only reason it match the imput impedance of the amp is to prevent the pre from affecting the broad band frequency response. If your using our amps, don't worry about it. They have a high impedance input and even if the pre did limit the band a little, it won't be audioble because the amps can play out well beyond 80Khz.

Thanks for the input Lonnie. Your feedback is always appreciated.