[Graz]

Has anybody tried taking a simple opamp-based amp & configured it for "balanced" or "dual mono"?

Just wondering how hard it might be...could it be done with, say, two cmoys or two mints...something like that?

Anybody care to take a stab at some schematics for something like this? I'd sure be game to try building one...a battery-powered, balanced, pocket amp! Sounds kinda cool...providing it's even possible...

Peace,

Graz

 

[blip]

Sorry I'm a bit unclear what you are looking for? Are you asking for an amp with balanced inputs, balanced outputs and/or dual mono design?

If you just want a balanced input check appendix 3: http://headwize.com/projects/showfil...=cmoy2_prj.htm

If you just want true dual mono then that should be pretty simple to obtain in a CMOY design.... Just use single-channel chips and seperate batteris for each channel.

 

[bg4533]

For balanced or dual mono operation you will need to rewire your headphones to use seperate grounds for left and right. One tricky thing about building a balanced amp is that there are no cheap 4 channel pots. You need either a 4 channel stepped attenuator or 2 attenuators (1 for each channel).

If you have a balanced source than you basically just build 2 amps. Pretty much any amp will work. If you don't have a balanced source than you need to invert the signal. There are are a number of ways this can be accomplished and each has its positives and negatives.

 

[DigiPete]

Quote:

Originally Posted by bg4533 For balanced or dual mono operation ...there are no cheap 4 channel pots. .

There are some decently priced 4 channel pots, SFT sells one on his website.

 

[bg4533]

Quote:

Originally Posted by DigiPete There are some decently priced 4 channel pots, SFT sells one on his website.

Thanks, that is the first I have seen for a decent price.

 

[Graz]

Would a pimeta design make sense as a foundation for this? Or maybe take a mint design & add pimeta-style ground channels to each side?

Please tell me if I'm way off base here, but I was thinking that part of the magic of the balanced output-style amp was in keeping the grounds from each side isolated from each other.

I'd really like to try this (even if it ends up not really being portable or even not battery powered), but I need a little guidance first...if somebody could tweak a pimeta or mint schematic with some ideas, that would be awesome.

Thanks for any input & ideas!

Peace,

Graz

 

[Graz]

Quote:

Originally Posted by blip Sorry I'm a bit unclear what you are looking for? Are you asking for an amp with balanced inputs, balanced outputs and/or dual mono design?

Hi, thanks...yea, I guess I'm definitely talking about balanced outputs/dual mono design.

Peace,

Graz

 

[bg4533]

The Pimeta has an active ground channel that sinks the return current from the headphones. In a balanced configuration the Pimeta will be better than the Mint, but it the difference will be less than an unbalanced config since the active ground channel is unused. The buffered PS in the Pimeta still provides more power and with the Pimeta you have more room for capacitance and better parts. The Pimeta will also allow you more opamp choices.

If I was building this amp I would just hand wire it. Neither the Pimeta or Mint board really fits my vision of it.

 

[bg4533]

Quote:

Originally Posted by Graz Hi, thanks...yea, I guess I'm definitely talking about balanced outputs/dual mono design. Peace, Graz

Balanced amps are ofter dual mono, but dual mono doesn't mean balanced.

In dual mono the left and right grounds are seperate and in a true dual mono setup each channel will have its own power supply. The headphones will have connections for L, L ground, R and R ground.

In a balanced setup there are 2 extra active channels, L inverted and R inverted. Grounds may be connected or the amp may be dual mono and have separate grounds. The headphones will have connections for L normal, L inverted, R normal and R inverted. Ground is not connected to the headphones, it serves only as a reference within the amp.

The only advantage dual mono has in well designed equipment is to decrease crosstalk and in well designed equipment crosstalk is usually minimal anyway.

 

[Graz]

OK, hand-wiring is no problem for me...I have fairly mad soldering & wiring skills...and better still, I've got a craving for a new project & have some cash to pretty much use only top-notch parts...

So, since....
Quote:

Neither the Pimeta or Mint board really fits my vision of it.

...what is your vision of it?

The only criteria is that it be fairly simple (say, pimeta at the high end of the complexity scale)...something I can hand-wire reasonably & preferably opamp-based.

I've hand-wired Mints/Pimetas before...no problemo

http://www6.head-fi.org/forums/showthread.php?t=113971

Peace,

Graz

 

[00940]

Why not simply using a fully dfferential opamp such as the ths4130 or the OPA1632 ? Single ended or balanced input, balanced output, works on relatively low voltages, 85ma output.

 

[Graz]

Quote:

Originally Posted by 00940 Why not simply using a fully dfferential opamp such as the ths4130 or the OPA1632 ? Single ended or balanced input, balanced output, works on relatively low voltages, 85ma output.

Can you please elaborate? I sure don't mind trying it, but I lack the audio EE expertise to envision it. I can read schematics, and have the mechanical ability (soldering & wiring). Maybe a block diagram would be helpful, if you have time?

I'm envisioning something like this:
- Qty. 2 dedicated Elpac power supplies, one for each channel
- Qty. 2 matched, stepped attenuators, one for each channel
- Qty. 2 "to be determined" opamp-based amp sections, one for each channel...this is where I'm looking for some help.
- Top quality components throughout

Peace,

Graz

 

[00940]

See the fig.38 in this datasheet : http://focus.ti.com/lit/ds/symlink/ths4130.pdf

Consider also fig.33 and the layout considerations at the bottom of the datasheet.

 

[bg4533]

Graz,
Are you looking for a portable amp or a home amp? The designs will likely end up very different. If you want both you should probably start a separate thread for each.

Do you have a balanced source? Your design will depend on this a bit.

I have been wanting to build a balanced amp similar to what 00940 posted here.

 

[00940]

bg4553 : beware that the PS was a bit stupid on that schematic. I had finally to use the same PS for opamps and buffers.