looks like I might need a passive preamp

dvenardos · « **Reply #20 on:** 30 Jul 2010, 07:10 am »

If you are also looking at replacing your amp you might want to take a look at the Virtue Sensation with Dodd Buffer. They are 20% off right now. Not sure if that fits into your ultimate plan but the virtue amps are really very good.

Rclark · « **Reply #21 on:** 30 Jul 2010, 07:41 am »

It's certainly a possibility. I'll have to get a feel for my speakers first. I think I'll need a bit more headroom than the Virtue offers. But that stage is way way down the line after I build my subs and have my treatments done and everything just right and working properly. Hopefully that will be the last thing I do for this system (other than add an AVR and tv). It will be come after power conditioning, which is like, dead last. Maybe like five or six months.

The more I read about the Dodd the more impressed I am. When I'm at that stage I'll just give Gary a call and ask him about my application. Still curious as to the whole 100K attenuator being a problem issue... what was that guy on about.

edit - it says the output impedance with the stock 6N1P tube is 133. So that's not a low impedance, that's high, right, compared the the 25k input impedance of my UPA-2 amp.

Help me out guys. I'm not following you.

HAL · « **Reply #22 on:** 30 Jul 2010, 11:18 am »

You want a low output impedance from the (i.e Dodd buffer 133 ohms) preamp to feed your power amp input impedance of 25K ohms. The input impedance of the Dodd is 100K ohms that loads the front end device like a CD player, DAC or other source. You want the low output impedance to drive interconnect cables.

This is not a passive preamp. The tube gives current gain so that the output impedance is low, but keeps the input impedance high.

Passive preamps have no buffer stage to give the current gain. This makes them more sensitive to cable capacitance loading. The higher the capacitance and higher the output impedance, the more high frequency rolloff is in the system.

Hope this helps.

Rclark · « **Reply #23 on:** 30 Jul 2010, 08:35 pm »

Ok.. But I was under the impression that the unit is supposed to match the impedance of the amplifier?

But anyway, if you guys think it will work. It was Danny's first and only recommendation. I'll be plugging my cd player into the DAC, the DAC into this preamp, and this preamp into the amp. AVR also into the preamp.

It looks to be an absolute no brainer. I just can't find anything as neat looking in the price range. Reviews and user reports are great. So at this point I'm sticking it into the chain and it will be my preamp. Buffer.

I wonder why if a buffer works so well why anyone would want gain, as in a preamp?

srb · « **Reply #24 on:** 30 Jul 2010, 08:55 pm »

Quote from: Rclark on 30 Jul 2010, 08:35 pm

I wonder why if a buffer works so well why anyone would want gain, as in a preamp?

Some source + amplifier + lower efficiency speaker combinations need the extra gain that a preamplifier would provide.

Steve

corndog71 · « **Reply #25 on:** 30 Jul 2010, 09:21 pm »

Why would you plug your AVR into the preamp? That doesn't sound right.

I keep my AVR seperate from my high-end gear. Receivers are all about compromising maximum sound quality for convenience and multichannel.

Rclark · « **Reply #26 on:** 30 Jul 2010, 09:49 pm »

Where else would I put it? It's not active until I switch over to it.

HAL · « **Reply #27 on:** 30 Jul 2010, 10:00 pm »

Quote from: Rclark on 30 Jul 2010, 08:35 pm

Ok.. But I was under the impression that the unit is supposed to match the impedance of the amplifier?

But anyway, if you guys think it will work. It was Danny's first and only recommendation. I'll be plugging my cd player into the DAC, the DAC into this preamp, and this preamp into the amp. AVR also into the preamp.

It looks to be an absolute no brainer. I just can't find anything as neat looking in the price range. Reviews and user reports are great. So at this point I'm sticking it into the chain and it will be my preamp. Buffer.

I wonder why if a buffer works so well why anyone would want gain, as in a preamp?

The impedance matching term should not be used in this case. This is used in RF connections like 50 ohm or 75 ohm transmission lines or video interface cables. This is truly buffering.

Danny Richie · « **Reply #28 on:** 30 Jul 2010, 10:02 pm »

Ask Gary Dodd about adding a home theater by-pass.

He has added them in the past to where the by-pass is engaged when the pre-amp is not on and dis-engaged when it is turned on.

face · « **Reply #29 on:** 30 Jul 2010, 11:10 pm »

Quote from: Rclark on 30 Jul 2010, 06:20 am

I'm actually pretty pumped. I was just going to be using a nice AVR as a stereo preamp but then I read on Emotiva's site they are coming out with this uber DAC in October and that if you pair it with the ERC-1 cd player (which I own) it takes it up a whole new level. However now I'll need a passive preamp to connect all these devices since the new uber DAC doesn't have HT bypass.

I don't understand why you need a passive preamp. I'd look into the Dodd unit and inquire about HT bypass, it should be easy to add to the unit. As long as you have an amp that's easy to drive, there are also a few DAC's out there with a built in volume control and even HT Bypass.

jtwrace · « **Reply #30 on:** 30 Jul 2010, 11:20 pm »

Gary did a tape loop for me..

johnnycopy · « **Reply #31 on:** 30 Jul 2010, 11:21 pm »

http://thehornshoppe.websitetoolbox.com/post?id=4363445&trail=15

dvenardos · « **Reply #32 on:** 31 Jul 2010, 06:02 am »

Did you get all this stuff figured out?

Quote from: Rclark on 30 Jul 2010, 07:41 am

Still curious as to the whole 100K attenuator being a problem issue... what was that guy on about.

If the Dodd didn't have the buffer and only had a 100K pot that would be an issue because your output impedance would be much to high. You want your output impedance to be lower than the input impedance of your amp and the input impedance to be higher than your source.

Quote from: Rclark on 30 Jul 2010, 07:41 am

edit - it says the output impedance with the stock 6N1P tube is 133. So that's not a low impedance, that's high, right, compared the the 25k input impedance of my UPA-2 amp.

133 versus 25,000 is pretty low.

I have to share two-channel and home theater also. A six channel passive preamp is the solution that I came up with. I plan get an Oppo BD player and use the analog outs to the six channel preamp. Almost finished with it. I use an Outlaw ICBM for bass management which basically will give me a solid state buffer after the passive preamp. You could also order from Gary the buffer he puts in the Virtue Sensation and put three of those at the outputs, or I am sure he could rig something up for six channel.
http://www.tweakcityaudio.com/forum/showthread.php?t=545

Rclark · « **Reply #33 on:** 31 Jul 2010, 08:43 am »

That sounds like the ticket:

Quote from: Danny on 30 Jul 2010, 10:02 pm

Ask Gary Dodd about adding a home theater by-pass.

He has added them in the past to where the by-pass is engaged when the pre-amp is not on and dis-engaged when it is turned on.

Hey Dvenardos, the only thing I know is that you guys think this will work great and is a great unit. The technical aspects of preamps are new territory for me so I'm learning something new here. But as long as you're SURE

that it will work with my gear I think I'm in there. I've started reading up on impedance, actually the other night I was reading the wiki pages on capacitors, inductors, and potentiometers, so hopefully I can have soon the minimal sort of crude knowledge base to really begin understanding what I really want out of pre-amp and amplification.

Anyway, a little over 650+ for this unit I get to build or, somewhere over 400+ for a GoldPoint is pretty much what I'm looking at. Actually, I'll probably order it without a remote and just do that sometime down the line. Save $200 for a while and put that money elsewhere in the system.

Rclark · « **Reply #34 on:** 1 Aug 2010, 05:50 am »

Ok so another guy (who I absolutely love right about now) tells me I don't even need an AVR at all, since I'm going stereo.

Tell me if this is correct: I'm using a PS3 as my source for games, bluray. If connected stereo the PS3 handles all the processing (DD, DTS, etc) and downmixes to stereo on its own. So all I need is the preamp, I don't need an AVR. I'd go PS3 HDMI to the tv, then PS3 AV/RCA out to the preamp, or maybe even into the DAC then into the preamp.

He says the only reason to get an AVR is if I wanted surrounds.

Anyway, if that's correct I just saved a ton of money and can go even fancier on some other parts.

So I can go cd player/ PS3 av/Rca to DAC, to preamp, to amp and done. No other hardware needed.

srb · « **Reply #35 on:** 1 Aug 2010, 06:19 am »

Quote from: Rclark on 1 Aug 2010, 05:50 am

So I can go cd player/ PS3 av/Rca to DAC, to preamp, to amp and done. No other hardware needed.

Yes, if you are going 2 channel you wouldn't need an AVR. An AVR would facilitate in connecting a subwoofer, so if you are going to use a sub without an AVR, if the preamp doesn't have two sets of variable outputs you would need to either use a Y-splitter on the preamp output to send the signal to the sub, or use speaker-level inputs on the sub (if the sub is equipped with them).

The PS3 can either output analog stereo through the supplied AV breakout cable and connecting the analog L & R RCA's to your preamp, or if you want an external DAC to perform the digital to analog conversion, you would use the PS3 optical digital audio output (with a Toslink optical cable, not RCA) to connect to a DAC with an optical input.

Steve

Rclark · « **Reply #36 on:** 1 Aug 2010, 08:47 am »

I was wondering about that. What is the best way to connect subs? is it to come from amp to subs to speakers, high level, as you say? Or the other way around, amp to speakers to subs? Or possibly amp, split to both?

chlorofille · « **Reply #37 on:** 1 Aug 2010, 11:46 am »

I prefer to use the speaker level inputs on the sub. If you have some fullrange main speakers, you can set the cutoff to 30Hz or less on the woofer's plate amp. So my way of connection is from speakers to amp, then take a parallel set of wires from my amp's output and hook it to the woofer's speaker level inputs.

HAL · « **Reply #38 on:** 1 Aug 2010, 11:54 am »

The stock Dodd Buffer has two sets of variable outputs.

In my stereo setup I run one set to the main drivers and the other set to the servo subs. They are both controlled by the volume control. Works well here!

Rclark · « **Reply #39 on:** 2 Aug 2010, 02:30 am »

Perfect. Thanks Hal. Ok, well, good enough for me. Before the end of the month I'll be learning how to use a soldering iron. Actually, by the end of the month I hope to have my basic, raw system up and burning in.

Thanks Danny, thanks everyone.