Help On Building A47/CHA47

[danlaix]

I've just finish building myself another cmoy amp. But this time with a 470uF/25V , 1UF/63V , 2x9V batt. The result on my SR-80, i didnt really like what i listen. Its too much on the treble and not enought bass. Also when i tried to crank up the volumn, it starts to distort. I'm so scared that it might blow my Grado.

So maybe i should build myself an A47, where i get lots of feedback that this amp fits best with Grados. But i found lots of threads on this forum with different specs building the amp.
So can anyone help me with the right specs? WHat opamp tp use?
For the loopback part, should i use anothe opamp or a buffer in stead??
If using a buffer, should i use a DIP8 or TO220?? A bit confusing though.

Can anyone be kind enough to provide me a clear and complete schematic for the amp??

Millions of thanks in advance.

 

[sTaTIx]

Quote:

Originally posted by danlaix The result on my SR-80, i didnt really like what i listen. Its too much on the treble and not enought bass. Also when i tried to crank up the volumn, it starts to distort. I'm so scared that it might blow my Grado.

I think you should disclose what opamp you're currently using in your Cmoy.

 

[da_burl]

Apheared did do a lot of experimenting, and did have many designs, however, the CHA47 is pretty straightforward. There are not really a lot of variations.

Over the years, the regulars have adopted a little code system to identify these amps, in the CHA47, the C-H-A stands for Cmoy, whose Cmoy amp kind of started everything (and who started the forum, I believe), Hansen, who used to make some PC Boards for it, and Apheared, who sort of designed it, ("adapted" it from an application note that somebody else pointed him to, actually). Nothing against Apheared, I really miss his regular posting, help, and general enthusiasm!! I really hope he's allright, and that's all I've got to say about that.

Here's a link to the article

I would just use the good old OPA2134 to for starters, unless for some reason you have trouble getting them. Make sure your layout and construction is sound

, then you could possible look at upgrading the chip, but I can testify that even the OPA2134 can sound great with Grado's. The "ultimate" 47 would probably have AD823s for portable or AD843's for permanent home use. Although there are those who like the Higher end chips, if you haven't already, take a look at Tangent's Opamp Article
In a pinch, you could use the NE5532, or even TLO82's, if you have trouble ordering from Digikey.

You also might want to consider if you absolutely need portability. My other testimony is that it sounds much better with a decent "home" Dual DC Power Supply. I am just speculating that some of your distortion and lack of bass "could" be from your power supply. If you absolutely need batteries, you might look at "lifting" the PS section from the META42, with the rail splitter and buffer.

 

[danlaix]

Opps...forgot to disclose the opamp i'm using for my cmoy.

OPA2134PA
2x 470uF/25V
2x 1uF/63V
2x 9V Batt
Gain 11

The resistors are the standards used in CMOY amp.

 

[danlaix]

Thanks da_burl for the advise.
I too suspect it would be the power supply that is at the lack of bass. But somehow i'm comparing my cmoy with my X-Cans. The mid in the cmoy seems lack too.

As for the schematic given up there, as i understand it, that schematic is only for 1 channel right? Meaning, i would have to use 2 OPA2132, or 2 OPA2134 for building the CHA47. Confirm this? Also in another thread in HeadWize, bdx uses OPA2134 and BUF634.
(here's the link http://headwize.com/ubb/Forum3/HTML/000661.html)
Does it mean that bdx is using 1 OPA2134, and 2 BUF634??

Sorry to ask this but it really confuses me. But i need to confirm all this before i make the purchase from RS Components or Farnell. The prices for these opamps and buffers are really expensive.

Also, what about the power supply for CHA47?? I would really like to build it portable. Maybe an extra DC point would be considered, but how much power do i need to make it optimum?? And also the caps for the PS.
Phew!! Lots of questions to ask. But i'm excited and cant wait to build one.

 

[Voodoochile]

Quote:

...Since I am willing to tote around a headphone amp weighing up to a pound, I used two 8-cell AA battery holders (Radio Shack 270-407) to get ±12V .

From the Apheared Scrapbook.

Yeah, you need to look at the power supply when pushing low-z cans like Grados, as they are current hungry. Higher voltage seems to help most OPAs, but a high-current design, like the META42 or A47/CHA47 provides the most benefit.

I have to second the notion of doing up a nice little +/- supply, or even a wall-wart. To make the amp really shine, and still have a decent battery life, you may have to insert your name at the end of the quote above. That's about $12 worth of batteries, and heavy.

Quote:

As for the schematic given up there, as i understand it, that schematic is only for 1 channel right? Meaning, i would have to use 2 OPA2132, or 2 OPA2134 for building the CHA47. Confirm this?

True.

Also, BDX's power supply works very well, but you should really go with a railsplitter, AKA the META42 ps. You can sub a buf634 easily if you like. It's basically the BDX psu with the resistor divider pair replaced with the railsplitter ($1.50) The railsplitter is notably more conservative in it's consumption of power. Do a search, as Tangent has provided much pertinent info relating to this.

Based on all this, you now have 1 buffer in the PS section, and one dual OPA for stage 1, with another OPA for the follower stage. It's still not too bad for the three chips. You'll save the money in batteries if you go with the railsplitter, in not many months.

 

[da_burl]

Quote:

Originally posted by danlaix Thanks da_burl for the advise. I too suspect it would be the power supply that is at the lack of bass. But somehow i'm comparing my cmoy with my X-Cans. The mid in the cmoy seems lack too. As for the schematic given up there, as i understand it, that schematic is only for 1 channel right? Meaning, i would have to use 2 OPA2132, or 2 OPA2134 for building the CHA47. Confirm this? Also in another thread in HeadWize, bdx uses OPA2134 and BUF634. (here's the link http://headwize.com/ubb/Forum3/HTML/000661.html) Does it mean that bdx is using 1 OPA2134, and 2 BUF634??]

Yes, this is one channel, so it would take 2 OPA213x each, most people can't seem to tell much difference between the 2134's and 2132's, so you could save some there.
Again, the buffered output amp is a different animal, tangent covers this very well in his article on the META42, in the section about different topologies. When this all started, I think most people were not using multiloop, but now most (but not all) are using multiloop, thanks to ppl, and of course Jung and the META team
Personally, I would try the CHA47 first, then move up to a buffered output. The META42 is so flexible, that it can get a little confusing at first trying to figure out resistor values and such. It might not hurt to order the parts for a META42 (don't get confused here, the META42 refers to the PC board, the actual circuit should be called something like Multiloop buffered output amp, and you could add some names or initials if you like

or The Space Oddity, if you prefer. Quote:

Sorry to ask this but it really confuses me. But i need to confirm all this before i make the purchase from RS Components or Farnell. The prices for these opamps and buffers are really expensive. Also, what about the power supply for CHA47?? I would really like to build it portable. Maybe an extra DC point would be considered, but how much power do i need to make it optimum?? And also the caps for the PS. Phew!! Lots of questions to ask. But i'm excited and cant wait to build one.

I am exactly the opposite, to paraphrase Apeared "I live in Texas, we all have cars, and don't walk anywhere (its either too wet or too hot most of the time). So we don't need portability. I work in an office cube, and spend about half my day on the phone, so I live without headphones at work. So all I need is a home unit (well, sometimes a hotel room unit, too). So I use external Dual DC Power Supplies exclusively"

Basic rules, the higher the voltage, the better, up to +/- 15V (30v when split with the voltage divider/virtual ground). Mine was set to +/- 12V and it sounds very nice. With batteries, you could probably get away with +/- 6 to 9 volts, or 12-18 before the split. So 8 AA's, or two 9V's, in a series parallel combo. Some people are using rechargeables. Cmoy talks about this in the CMOY article. You can get a higher voltage wallwart for non-portable use, going to the splitter. There are lots of threads around talking about different options here.
Also, the bigger the capacitors the better, 470 to 1000 x2 here. It doesn't use a lot of current, so even .5 amps is plenty for both channels, you do always want a little extra just in case.