[pumpkinman]

I just picked a Mod Squad Line Drive passive that I plan to try it with

[wushuliu]

I've been lurking here since the beginning of this thread. Now, I feel compelled to buy one of these amps. So, I've got to find a suitable pre (tubed?) to drive it. Does anyone have a specific recommendation? I mean, is there some particuar electronic characteristic of the "dBop" that causes it to sound better with some particular kind of pre.   

I've already been told by a well-informed person that using my passive pre is possible, but it would entail more futzing than I want to do.

I'm sure there are a zillion recommendations for preamps but I still recommend the Nelson Pass B1 Buffer. It's extremely easy to build, others report performance easily surpassing their >$1k pre's (Enjoy the Music had it more or less tied w/ an $18k pre. http://www.enjoythemusic.com/Magazine/equipment/0708/first_watt_b1_preamplifier.htm   Sheesh, not bad for $80 in parts.

http://www.passdiy.com/order.htm

Most importantly you can make the output impedance extremely low to match the Class D Audio amps. After A/Bing with and without the buffer, you'd have to pry the Pass out of my cold dead hands.

 

[earplay]

I just picked a Mod Squad Line Drive passive that I plan to try it with

Well, you might want to make sure it will work. It's all beyond me, but someone who knows, I think it was gitarretyp, told me there would be some special electronic considerations if one were to use a passive pre.

Maybe it was the low impedance issue he mentioned. Now that I think of it, his reply to me is probably in this thread... I hope everyone is enjoying my stream of consciousness. Forgive me, I'm tired!

Yes, it was gitarretyp. It's on page 13 of this thread.

[atroder]

I hope driving one of these kits from the preamp output of a regular AVR (Pioneer VSX-21) is ok without have to mod the kit.

[earplay]

I'm sure there are a zillion recommendations for preamps but I still recommend the Nelson Pass B1 Buffer. It's extremely easy to build, others report performance easily surpassing their >$1k pre's (Enjoy the Music had it more or less tied w/ an $18k pre. http://www.enjoythemusic.com/Magazine/equipment/0708/first_watt_b1_preamplifier.htm   Sheesh, not bad for $80 in parts.

http://www.passdiy.com/order.htm

Most importantly you can make the output impedance extremely low to match the Class D Audio amps. After A/Bing with and without the buffer, you'd have to pry the Pass out of my cold dead hands.

 

Wow, thanks, Wushuliu. I'll look into it.

[wushuliu]

I hope driving one of these kits from the preamp output of a regular AVR (Pioneer VSX-21) is ok without have to mod the kit.

It should work fine. I was using something similar before building the B1 Buffer. The amp sounded great, but the buffer takes it up several notches.

[steve k]

I hope driving one of these kits from the preamp output of a regular AVR (Pioneer VSX-21) is ok without have to mod the kit.

I could be wrong (Lord knows it happens a lot) but I think the impedance matching with these amps is less and issue than a lot of people think. I've seen these amps fed with a VTL preamp, a Conrad Johnson preamp, an AMC tube pre, a Yamamoto pre, a Musical Design SP1, a Dodd tube pre and the front end of a Wyred4Sound Integrated. I imagine the output impedances of all these preamps are all over the map and haven't made any difference in the quality of the sound.

I could also be lucky to not have run into a problem. 
steve

[atroder]

wushuliu - thanks for the quick response. Pardon my ignorance, but I presume that connecting the preamp output from the AVR to the B1 buffer, and then connecting that to the amp is not an option for improving SQ. In other words, using the AVR preamp output precludes the use of the B1 buffer?

[pumpkinman]

Well, you might want to make sure it will work. It's all beyond me, but someone who knows, I think it was gitarretyp, told me there would be some special electronic considerations if one were to use a passive pre.

Maybe it was the low impedance issue he mentioned. Now that I think of it, his reply to me is probably in this thread... I hope everyone is enjoying my stream of consciousness. Forgive me, I'm tired!

Yes, it was gitarretyp. It's on page 13 of this thread.

Well I have a Mcintosh C712   Adcom GTP-400   and a Marantz 1060 intergrated that I can remove the jumpers and use that as well so I have a few options but I do appreciate you keeping an eye on me Thanks.....Bill

[wushuliu]

wushuliu - thanks for the quick response. Pardon my ignorance, but I presume that connecting the preamp output from the AVR to the B1 buffer, and then connecting that to the amp is not an option for improving SQ. In other words, using the AVR preamp output precludes the use of the B1 buffer?

Right now the AVR output is indeed going through the B1, which is being setup as a pre for the AVR, a gamma1 dac, and a Hagerman bugle Yes the SQ is hugely improved from the AVR output pre of my Marantz SR4002.

[Nick77]

I hope driving one of these kits from the preamp output of a regular AVR (Pioneer VSX-21) is ok without have to mod the kit.

Im driving my 120 wpc with HK AVR and its actually working really well. I tried direct from my Paradisea with SB3 volume and was maybe a little more refined but lost alot of bass.

[gitarretyp]

The low input impedance of these Class D amps is something to keep in mind, but I wouldn't be that concerned with it, overall. I'm using the Class D amp in a passive system myself and am quite happy with it.

There are two issues with the amp having a low input impedance:
1) If your preamp (or other device immediately preceding the amp) has coupling caps at its output and they aren't larger than 6 uF, you will be losing a couple of dB of output below ~40 Hz. Whether this will be noticeable will depend on your system. In my case, I have pretty flat response to below 20 Hz and found the high pass filter created by the interaction of the amp and my DAC very noticeable. This is the problem Keith (Nick77) had using the Paradisea as his source rather than his receiver.

2) If your preamp has a high output impedance (above 400 Ohms), your preamp will be required to supply more current than it would otherwise need to supply into a higher impedance load. This will lead to increased levels of distortion relative to a larger load. I don't think this problem would be noticeable in most cases.

[steve k]

Dude,
You're smart! 

[santacore]

Here's a sweet deal for someone who hasn't already purchased one of these.
http://www.head-fi.org/forums/f42/class-d-audio-300-wpc-amplifier-473760/

I already have the 120wpc kit, or I'd be all over this.

[pumpkinman]

Well I'm all in now I just ordered my kit now to ebay and other sources

http://classdaudio.com/index.php/class-d-amplifier-kits/home-kits/250w-x2-500w-x1-amp-large-power-supply-transformer.html
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=350207584020&ssPageName=STRK:MEWAX:IT
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200435755054&ssPageName=STRK:MEWAX:IT
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110469293757&ssPageName=STRK:MEWAX:IT

[earplay]

Dude,
You're smart! 

 

You said it! Told ya he was well informed.

And, yeah, what he said!

So, what I'm left wondering, among other things, is if I should try to get my hands on a PassDIY buffer.

I see that there are plans posted on the Pass site, but I can't read a schematic. If they had a complete kit and instructions, I'd like to make one to go with the dBop.

[wushuliu]

If it's of any help, here's my BOM for the Pass. Everything should be available from Mouser or Digikey. It's fairly straightforward, just solder according to the values on the board. And Alps pot matches directly with the inputs, etc. It's a nice sized board too, so no squinting or tight spaces to sweat about.

BOM

Resistors
(6) 1Mohm
(4) 1k
(2) 221K
(2) 10k
(1) 15k
(1) 1 ohm / 3 watts

Capacitors
(2) 10uF - high quality. Signal caps.
(1) 1uF - polyester or better. PS bypass cap
(2) 15000uf 25v

JFETs.
(4) JFET - 2SK170's, LSK170's or 2SK370
(available from Pass w/ his PCB)

(1) 1N914 type diode

(1) 18v-24v wall transformer power and jack
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=T987-P5P-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CP-037A-ND

(1) 25k Potentiometer

(1) Switch / Selector

[earplay]

Wushuliu, thanks. Appreciate it. I'll take your word for building it and order the parts. I didn't realize the board contained part values. Now, we'll see if I can read the board. Here goes....

This should make a great partner for the dBop.

[atroder]

Hey - providing that BOM is really cool. Do you think the B1 buffer board could fit in the same standard sized chassis along with the class D amp boards?

[wushuliu]

Hey - providing that BOM is really cool. Do you think the B1 buffer board could fit in the same standard sized chassis along with the class D amp boards?

I use a wood enclosure for the amp, so dunno. but the dimensions for the B1 are here:

http://www.passdiy.com/order.htm