$175 Class D amp--120 wpc

luckyrolls · « **Reply #580 on:** 2 Mar 2010, 06:32 pm »

Quote from: steve k on 2 Mar 2010, 06:24 pm

No I mean the interconnects your using between your preamp and the D amp. Are they shielded cables?

I think they are some generic cheap cables I had lying around. So I assume not. Let me try getting some shielded cables.

steve k · « **Reply #581 on:** 2 Mar 2010, 06:34 pm »

www.bluejeancables.com is a good source for low cost good quality cables. This may or may not solve your problem but at least at blue jeans prices, you won't be out a lot of money.

pumpkinman · « **Reply #582 on:** 2 Mar 2010, 08:33 pm »

Well here's my tale. I hooked up the amp to a Mcintosh C712 preamp and Vandersteen 3A speakers. I right off the bat noticed there was a hum coming out of the speakers, the amp didn't stay in the system long. I then moved the amp out
by my computer using a Adcom GTP-400 pre and Missiom bookshelf speakers NO HUM and high end which was not really present before appeared. I've been told input impedance my be a issue as this amp has a low value and maybe the Adcom
was just a better match for this amp. Thoughts on this please ........Pumpkins just don't know

mfsoa · « **Reply #583 on:** 2 Mar 2010, 09:28 pm »

Hey Mr. Pumpkin,

Any comments to make about our listening session at Shadowlights?

Pleasure meeting your wife, for sure!

-Mike

pumpkinman · « **Reply #584 on:** 2 Mar 2010, 09:46 pm »

Quote from: mfsoa on 2 Mar 2010, 09:28 pm

Hey Mr. Pumpkin,

Any comments to make about our listening session at Shadowlights?

Pleasure meeting your wife, for sure!

-Mike

We were listening to I believe a Cherry Class D amp $2000.00(?) Brought by someone on Sunday.
The big diff. that I noticed was that bass was much tighter in the Cherry. The Cherry was very very nice amp
Shadowlight was using a tubed pre his Class D sounded much better than mine hooked up to the Mcintosh
......................................P umpkins just want to have fun
If anyone is interested I found a link to the Cherry http://www.digitalamp.com/ Of course this is not CHEAP and cheerful

roymail · « **Reply #585 on:** 2 Mar 2010, 10:06 pm »

I've been told input impedance my be a issue as this amp has a low value and maybe the Adcom was just a better match for this amp. Thoughts on this please...

Well, Tom told me that the amp's input impedance is 45K. That doesn't sound low to me.

We need to clear up this hum issue so others can avoid it.

pumpkinman · « **Reply #586 on:** 2 Mar 2010, 10:10 pm »

Quote from: roymail on 2 Mar 2010, 10:06 pm

I've been told input impedance my be a issue as this amp has a low value and maybe the Adcom was just a better match for this amp. Thoughts on this please...

Well, Tom told me that the amp's input impedance is 45K. That doesn't sound low to me.

We need to clear up this hum issue so others can avoid it.

I was told it's value was 3000 which would be low by someone on line..............Bill

roymail · « **Reply #587 on:** 2 Mar 2010, 10:13 pm »

Here's the email.

Hi Roy,
Yes, the impedance is 45K. Please let me know if I can be more help.
Thanks,
Tom

wushuliu · « **Reply #588 on:** 2 Mar 2010, 10:16 pm »

Quote from: roymail on 2 Mar 2010, 10:13 pm

Here's the email.

Hi Roy,
Yes, the impedance is 45K. Please let me know if I can be more help.
Thanks,
Tom

Which amps are we talking about, the IR based amps or the TI...

roymail · « **Reply #589 on:** 2 Mar 2010, 10:19 pm »

I asked about this one...

http://classdaudio.com/index.php/class-d-power-amplifier-250w-x-2-500w-x-1.html

steve k · « **Reply #590 on:** 2 Mar 2010, 10:22 pm »

Quote

We were listening to I believe a Cherry Class D amp $2000.00(?) Brought by someone on Sunday.

What Class D Audio amp were you comparing to what Cherry amp?
steve

pumpkinman · « **Reply #591 on:** 2 Mar 2010, 10:29 pm »

Quote from: steve k on 2 Mar 2010, 10:22 pm

What Class D Audio amp were you comparing to what Cherry amp?
steve

Shadowlight's which is the same one I did, but to me this is not apples to apples.
Price point says that all buy itself.

roymail · « **Reply #592 on:** 2 Mar 2010, 10:54 pm »

I just looked over the website, and the Cherry Jr. and DAC 4800A appear to be nearly the same and the price, too. Very, very nice... would love to hear one, but I'd love to hear a lot of stuff.

etcarroll · « **Reply #593 on:** 3 Mar 2010, 12:25 am »

Pumpkinman -

Don't forget, Shadowlight showed us that when he toggled a switch in back of the Bella the hum was noticable, then not noticable, and he thought the toggle was matching the impedance, or at least changing the value to something more agreeable to the classD amp, thus diminishing the hum.

Gene

shadowlight · « **Reply #594 on:** 3 Mar 2010, 12:42 am »

Quote from: etcarroll on 3 Mar 2010, 12:25 am

Pumpkinman -

Don't forget, Shadowlight showed us that when he toggled a switch in back of the Bella the hum was noticable, then not noticable, and he thought the toggle was matching the impedance, or at least changing the value to something more agreeable to the classD amp, thus diminishing the hum.

Gene

The Bella Pre has a -6db switch in the back which made the hum go away on the amp. When I hooked up the amp directly to the squeezebox or to yamaha htr receiver I do not hear any hum. Most likely what we were hearing was tube hum or one of the tube is not functioning correctly because I get that hum with the Butler, Threshold or VAC amp.

I liked the sound of the Cherry also but currently the price is out of my range/budget. If I had the coins would I spring for the Cherry amp and the answer would have to be yes.

What I will most likely end up doing is purchase a second amp board and run the two together in bridge mode to get 250wpc @ 8ohms.

mfsoa · « **Reply #595 on:** 3 Mar 2010, 01:38 am »

I think we may have been hearing an impedance mis-match with Shadow's pre and his ClassD kit. The difference between his Bella (900 ohm IIRC) and ClassD kit vs. the the VAC preamp and Cherry Jr was so striking as to make me think something was not matched up right. Perhaps the switch on the Bella was coming into play? If I'm right about the 900 ohm output of the Bella and the 3Kohm input of the kit, that's quite a way from the oft-cited 10:1 ratio.

Sure cheap and cheerful is great, but it's gotta be hi-fi too

This has really gotten me thinking about the importance of impedance matching.

Is the Pass B1 kit supposed to be used in between a preamp and the kit? Sound like a lot of doing to be able to drive a 3K input impedance.

Just trying to be honest so people can get the most from their kits.

-Mike

mfsoa · « **Reply #596 on:** 3 Mar 2010, 01:40 am »

I don't recall where I heard the 3Kohm input impedance value from - If mistaken I apologize for the misinformation.

-Mike

shadowlight · « **Reply #597 on:** 3 Mar 2010, 01:44 am »

Quote from: mfsoa on 3 Mar 2010, 01:40 am

I don't recall where I heard the 3Kohm input impedance value from - If mistaken I apologize for the misinformation.

-Mike

One of the earlier post had mentioned 3kohm but post 173 (quoted email from Tom) says 45k ohms.

wushuliu · « **Reply #598 on:** 3 Mar 2010, 02:05 am »

Quote from: shadowlight on 3 Mar 2010, 01:44 am

One of the earlier post had mentioned 3kohm but post 173 (quoted email from Tom) says 45k ohms.

a 900 ohm output impedance from the Bella should be fine for the IR based Classd amps. I've read 3k input impedance from several places, and the pdf for the IR chip actually states to use a source with no more than 600 ohms. But clearly good performance is being had at higher values. So it's hard to say what works best. If Tom says its 45k, though, I'll defer to him.

I will say that from all the playing around I've done with my amp, I believe it is very, very transparent. Any changes upstream are noticeable straight away. Whether or not a buffer like the B1 is *necessary* to get the most out of the amp is uncertain. People certainly seem to be enjoying them without it!

Maybe once my build is done we can do what Audiokarma (aptly) does for some gear and send it around to different people to try out w/ their own classdaudio amps and pres and report back (it's light and should easily fit in a Priority medium flat rate box).

gitarretyp · « **Reply #599 on:** 3 Mar 2010, 02:54 am »

I'm the one that originally mentioned the 3k input impedance in this thread. The measurements from which I derived that input impedance are on page 13, and I'm quite certain the input impedance of my amp is ~3k ohm. Also, as wushuliu stated, 3k is the value given in the spec sheet for the amp (also posted by me on page 13), and others on diyaudio have stated the input impedance is 3k. I would be very curious to see Tom's measurements demonstrating an input impedance of 45 k or to know if he's made changes to the amp since I ordered mine.