[Wyloch]

Sick of the CMOY, not enough cash for a PIMETA, so going with the A47. I'm following the plans here:

http://www.feistworks.com/ben/a47/default.asp

Questions:
1. The diagram says to use a OPA2227 for each channel - is that interchangable (same pinout) with the OPA2134 (which I hear is superior)?
2. I'm somewhat new to the three-pin TLE device. In the power supply circuit diagram, it seems to have four connections, not three: 1, 2, 3, and 8 which goes to cap C5. What's the story on that?
3. I assume D1 is a diode - what's it for?
4. And perhaps most important: I am going to be using this with my Senn HD270s, which an impedance of 64 ohms. This is speced for 32-50 ohms. Which resistors can I adjust to make it more suitable to my headphones, and what values?
5. Are R3 and R4 on the audio circuit diagram 47 ohms or 47 kohms?

Also, regarding the basic idea of the amp: from what I see, it uses two dual amps, and basically amplifies each signal twice by running through both channels in the opamps, correct?

Thanks all for your time.

 

[Jazper]

yes you could use the 2134 opamp - will leave the other questions for other people.

 

[BlazerFRS]

The A47 should drive 64ohm phones fine with no changes.

If you felt comfortable with modifiing the layout you could use one opa4134 instead of 2x opa2134

the TLE2426 come in several different packages. From the sound of it you have the three pin LP package. The schematic on that page you cite uses the 8 pin DIP package, which has a niose reduction pin. The three pin will work fine; just omit the extra connection. Also notice that his layout uses the three pin, not the DIP8.

R3 and R4 are 47 ohms.

D1 is a 'crowbar' protection diode. If you hook up the battery backwards it will short it, probably damaging or destroying the battery, but protecting the rest of the amp.

hope this helps

 

[Wyloch]

Thanks so much for the responses!

How necessary are the two .1 uF input capacitors? I will be running off of two 9V exclusively, with no plans to ever mod it with a wallwart (form what I understand, the input caps are only necessary in such a case - is this correct?)

R3 and R4 are 47 ohms, right? That's not a typo or missing "k"? (obvious circuitry newb here)

Also, sorry to pile on the questions, but I want to be my magnum opus/finishing line amp for the next year or so, and don't want to compromise any of it. The power capacitors: should they be electrolytic?

 

[Garbz]

"crowbar" diodes are zener diodes. Just to clarify.

The 8pin package has a noise reduction pin, so use it. Throw a cap in according to the datasheets, it yields only benefits.

Also only the first stage amplifies the signal, the second amps buffer them and don't actually raise volumes at all.

 

[BlazerFRS]

Quote:

Originally Posted by Garbz "crowbar" diodes are zener diodes. Just to clarify.

My bad; must have misread something.

Yes R3 and R4 are both 47 ohm; really.

The input caps strip dc offset from your source. If you can be sure all sources the amp may be used with have 0 mV DC offset, and will always have 0mV DC offset, thenthey are not needed. However, most sources have some minor dc offset, and even those that don't could develop a problem without you realizing it. Therefore it's good design to include it. I would, however increase the value of C1 as much as space and $$ allows to minimize it's effect on sq.

.47 is reasonable, i've seen A47 designs that suggest a value as high as 1uf.

 

[Wyloch]

Thanks all - placing the order - will update soon!

 

[Wyloch]

Well, looks I got the BUF634P instead of the BUF634T, so I've got an 8-pin device here.

Can I use it? I assume so, because at the bottom of the layout page, in the circuit diagram, the BUF634P is used - okay to just follow those four pin assignments (1,3,4, and 7)?