A Stereo Instrument Preamp/Headphone Amp (formerly "a JISBOS-with-gain Headamp")
Nov 18, 2009 at 4:35 PM Post #46 of 109

Steve Eddy

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Quote:

Originally Posted by mugdecoffee /img/forum/go_quote.gif
One thing you might want to think about for the unbalanced input is just grounding the negative input so you'd basically have two active ground channels. You'd "lose" half the signal voltage compared to a balancing scheme (such as the input transformer) but the upside is that its practically free, just add a DPDT switch. You'd still get the channel separation and more current output.


Yes, that can work. Though you won't get more current output. With the negative input grounded, there will be no signal at the negative output. Which means no doubling of the voltage swing which means no more current output.

se
 
Nov 18, 2009 at 5:41 PM Post #47 of 109

Zaubertuba

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Quote:

Originally Posted by mugdecoffee /img/forum/go_quote.gif
One thing you might want to think about for the unbalanced input is just grounding the negative input so you'd basically have two active ground channels. You'd "lose" half the signal voltage compared to a balancing scheme (such as the input transformer) but the upside is that its practically free, just add a DPDT switch. You'd still get the channel separation and more current output.


Quote:

Originally Posted by Koyaan I. Sqatsi /img/forum/go_quote.gif
Yes, that can work. Though you won't get more current output. With the negative input grounded, there will be no signal at the negative output. Which means no doubling of the voltage swing which means no more current output.


Well, I don't do that much critical listening from my receiver (my wife listens to the tuner during the days she's not working), so that could work, except it would be nice/fun to be able to A-B other sources like my wife's Fuze or other unbalanced sources down the road.

Going balanced (I know Steve, "bridged" would be the preferable term, but very few would understand my use of that term in common parlance
wink.gif
) has made a huge enough difference to my ears that I'd want to keep that architecture as much as possible for headphone listening. Also, not having the negative signal prevents the use of two different unbalanced headphones.

Quote:

BTW I've ordered 4 JISBOS's for a very similar amp which I'll hopefully integrate with my proto LCDuino. This thread is definitely giving me ideas.


Cool! Will you be running them at unity or will you be adding a little gain?

I've looked at all the Arduino projects and I have to say I'm intrigued. You could do a killer preamp interface with such a thing, but unfortunately I'm short on project build time and money. It may be January before I'm able to start ordering parts for this project.
rolleyes.gif
 
Nov 18, 2009 at 5:48 PM Post #48 of 109

Zaubertuba

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Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif
a square wave generator and oscilloscope. Also, my guess is you'll need a RC circuit across the secondary.


Quote:

Originally Posted by Koyaan I. Sqatsi /img/forum/go_quote.gif
Go with either the 10k/10k or the 15k/15k model....(etc. etc..)


All incredibly useful info. Thanks guys!

Quote:

I certainly wouldn't use the Edcors for anything I was serious about.


So, in your opinion, would using the Edcors be better or worse than using a DRV134 opamp?

I also noticed some Xicon matching transformers in my Mouser catalog but I'm not positive they'd spec. any better than the Edcors.
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Nov 18, 2009 at 6:02 PM Post #49 of 109

Steve Eddy

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Quote:

Originally Posted by Zaubertuba /img/forum/go_quote.gif
Going balanced has made a huge enough difference to my ears that I'd want to keep that architecture as much as possible for headphone listening.


Fair 'nuff. Though when you get right down to it, grounding the negative input doesn't really change the overall architecture at all.

Quote:

(I know Steve, "bridged" would be the preferable term, but very few would understand my use of that term in common parlance
wink.gif
)


Yeah. Unfortunately it appears to be another lost cause.

Quote:

Also, not having the negative signal prevents the use of two different unbalanced headphones.


True enough. I'd forgot about that requirement.

se
 
Nov 18, 2009 at 6:20 PM Post #50 of 109

Steve Eddy

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Quote:

Originally Posted by Zaubertuba /img/forum/go_quote.gif
So, in your opinion, would using the Edcors be better or worse than using a DRV134 opamp?


Well, the DRV134 would likely be better in absolute terms. But then you previously stated that your unbalanced sources were rather low fi anyway. So dunno. Could be a wash.

Quote:

I also noticed some Xicon matching transformers in my Mouser catalog but I'm not positive they'd spec. any better than the Edcors.
rolleyes.gif


Not likely.
atsmile.gif


se
 
Nov 23, 2009 at 8:32 AM Post #51 of 109

Zaubertuba

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So, barring less-than-stellar transformers, I found something a little different for a converter: Balanced Line Driver & Receiver

Someone on diyaudio seemed to think it sounds better than a simple drv134 circuit, and it's still relatively simple, so why not?

New schematic--could somebody be so good as to give me a sanity check on my power/grounding paths?

odysseyblockdiagramd2.jpg
 
Nov 23, 2009 at 4:32 PM Post #52 of 109

Steve Eddy

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Quote:

Originally Posted by Zaubertuba /img/forum/go_quote.gif
So, barring less-than-stellar transformers, I found something a little different for a converter: Balanced Line Driver & Receiver

Someone on diyaudio seemed to think it sounds better than a simple drv134 circuit, and it's still relatively simple, so why not?



Go for it. It's a bit messier as it needs to be fed power, but ultimately it'll work.

Quote:

New schematic--could somebody be so good as to give me a sanity check on my power/grounding paths?


XLR pin 1's should tie to chassis ground. The ground at "MAINS" (the safety ground) should be tied to the chassis at the closest point to its entry and be indicated with a chassis ground symbol (three vertical lines). Signal grounds should star or bus/star to the power supply ground. That point ties to chassis ground through your ground loop isolator.

se
 
Nov 23, 2009 at 7:34 PM Post #53 of 109

Zaubertuba

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Quote:

Originally Posted by Koyaan I. Sqatsi /img/forum/go_quote.gif
Go for it. It's a bit messier as it needs to be fed power, but ultimately it'll work.


It does need power, but it requires the same +15V/-15V that I was planning on using for the JISBOS boards. Is there any problem with sourcing them from the same supply?

Quote:

XLR pin 1's should tie to chassis ground.


DOH! Duh! I was equating the XLR ground pin as a signal ground. As the signal is only present on pins 2 and 3, what was I thinking? Guess that's what I get for working on this in the wee hours of the morning.
rolleyes.gif


Quote:

The ground at "MAINS" (the safety ground) should be tied to the chassis at the closest point to its entry and be indicated with a chassis ground symbol (three vertical lines). Signal grounds should star or bus/star to the power supply ground. That point ties to chassis ground through your ground loop isolator.


Domo Arigato! I'll re-vamp this when I get home tonight.
biggrin.gif


Oh...I suppose I should probably add a fuze to the mains power?
redface.gif
 
Nov 23, 2009 at 9:47 PM Post #54 of 109

Steve Eddy

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Quote:

Originally Posted by Zaubertuba /img/forum/go_quote.gif
It does need power, but it requires the same +15V/-15V that I was planning on using for the JISBOS boards. Is there any problem with sourcing them from the same supply?


Nope.

Quote:

DOH! Duh! I was equating the XLR ground pin as a signal ground. As the signal is only present on pins 2 and 3, what was I thinking? Guess that's what I get for working on this in the wee hours of the morning.
rolleyes.gif


atsmile.gif


Quote:

Oh...I suppose I should probably add a fuze to the mains power?
redface.gif


Naaah. Ain't no fun unless there's at least SOME chance of injury, bloodshed, or worse.
very_evil_smiley.gif


se
 
Nov 24, 2009 at 6:34 AM Post #55 of 109

Zaubertuba

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Quote:

Originally Posted by Koyaan I. Sqatsi /img/forum/go_quote.gif
Ain't no fun unless there's at least SOME chance of injury, bloodshed, or worse.
very_evil_smiley.gif



LOL - There's more than one reason I'm waiting on my first tube amp build.
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Nov 25, 2009 at 4:23 AM Post #57 of 109

mugdecoffee

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Just finished stuffing and wiring (oh the wiring) four jisbos boards. They took me something like three hours to stuff and another two or three them all together. There are certainly a fair number of parts crammed onto the board which is quite small. Right now I'm running them off of a 2*9V unregulated wallwart which is supplying about +/- 10V while the whole mess is running. I'm using the balanced output from my Opus without any output stage/filtering. Also instead of using output caps I made a new signal ground with a resistor divider that gives the midpoint of the positive and negative channel. The divider is smoothed with a couple of small caps. It seems to work just fine. I may experiment later to see if it impacts the sound at all. For now instead of an expensive balanced pot or stepped attenuator, I'm using the volume control in foobar. Altogether the setup is a little hacked together.

So how does it sound? With k240 sextetts, it sounds really thick. The bass and lower mids seem to drown out the highs. With my k701s everything sounds much better, or maybe just more like what I'm used to. The bass has nice impact but is perfectly balanced, not overwhelming at all. The bass seems better than with my bijou for sure which always sounded a little muffled and indistinct to me. The jisbos lacks the soundstage, detailed highs, and warmth of the bijou though.

The bijou is clearly better to me but it should as it cost three or four times as much. Also the unregulated power supply is far from ideal. I think after the power and wiring is cleaned up it'll shine a little more. Now onto the casework...
 
Nov 25, 2009 at 5:33 AM Post #58 of 109

Zaubertuba

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Quote:

Originally Posted by mugdecoffee /img/forum/go_quote.gif
Just finished stuffing and wiring (oh the wiring) four jisbos boards. They took me something like three hours to stuff and another two or three them all together. There are certainly a fair number of parts crammed onto the board which is quite small. Right now I'm running them off of a 2*9V unregulated wallwart which is supplying about +/- 10V while the whole mess is running. I'm using the balanced output from my Opus without any output stage/filtering. Also instead of using output caps I made a new signal ground with a resistor divider that gives the midpoint of the positive and negative channel. The divider is smoothed with a couple of small caps. It seems to work just fine. I may experiment later to see if it impacts the sound at all. For now instead of an expensive balanced pot or stepped attenuator, I'm using the volume control in foobar. Altogether the setup is a little hacked together.


Awesome! Are you running the boards as-is or with a little feedback added? How was it biasing the boards?

Quote:

So how does it sound? With k240 sextetts, it sounds really thick. The bass and lower mids seem to drown out the highs. With my k701s everything sounds much better, or maybe just more like what I'm used to. The bass has nice impact but is perfectly balanced, not overwhelming at all. The bass seems better than with my bijou for sure which always sounded a little muffled and indistinct to me. The jisbos lacks the soundstage, detailed highs, and warmth of the bijou though.


Thanks for the mini-review!
biggrin.gif
It's interesting: The JISBOS was designed to complement the SOHA. With better bass but less performance in other areas I wonder how it would perform integrated with the Bijou?
very_evil_smiley.gif


Quote:

The bijou is clearly better to me but it should as it cost three or four times as much. Also the unregulated power supply is far from ideal. I think after the power and wiring is cleaned up it'll shine a little more. Now onto the casework...


Very useful info. Makes me think the LCBPS may be a good choice for a power supply after all.
wink.gif


I'm jealous--I've been thinking the Opus might be a good option for my next build, and yes I was also thinking of the Bijou as well down the road (when my wallet gets heavy enough).

All this, and I haven't even started this build yet.
rolleyes.gif
 
Nov 25, 2009 at 7:00 AM Post #59 of 109

Steve Eddy

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Quote:

Originally Posted by Zaubertuba /img/forum/go_quote.gif
I think I'm closer...


****. Sorry. I got the EMail notification for this but had something else going on at the time and forgot to get back over here to reply.

Looks fine, but you still need to change the ground symbols on the XLR pin 1's and the ground loop breaker to chassis grounds.

se
 
Nov 25, 2009 at 12:45 PM Post #60 of 109

mugdecoffee

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Quote:

Originally Posted by Zaubertuba /img/forum/go_quote.gif
Awesome! Are you running the boards as-is or with a little feedback added? How was it biasing the boards?



Thanks for the mini-review!
biggrin.gif
It's interesting: The JISBOS was designed to complement the SOHA. With better bass but less performance in other areas I wonder how it would perform integrated with the Bijou?
very_evil_smiley.gif




Very useful info. Makes me think the LCBPS may be a good choice for a power supply after all.
wink.gif


I'm jealous--I've been thinking the Opus might be a good option for my next build, and yes I was also thinking of the Bijou as well down the road (when my wallet gets heavy enough).

All this, and I haven't even started this build yet.
rolleyes.gif



My original plans were to add 2x gain with the feedback resistor hack but I started out with just the default buffer configuration. It drives my k240s (600ohms) to a louder listening level for most things and a normal listening level for quieter thigns. My k701s got very loud, beyond listening levels for sure but not absolutely painful. I think when I get this cased up I'll end up adding some gain for headroom and also in case I run single ended headphones out of it.

For the PSU regulator, I was going to use a couple of 7815 regulators on a piece of perfboard which shouldn't cost more than about $5 all together.

You seem like a pretty thrifty diyer which I like to think of myself as. The Opus I have only cost around $100 with only USB input. I saved money by buying the bare boards and parts separately and by making a simple 317 regulator on perfboard. My bijou cost well under $250 before I started upgrading it by just repurposing an old tape player enclosure. Basically, there are plenty of ways to cut corners.
 

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