designing headphone amp

[JohnRoberts]

For Wavebourn et all.. my suggestion to add caps is not for the dynamic impedance of LEDs or large signal source impedance, the opamp loop gain will take care of all that, but to allow the bases of output devices to be driven above/below supply for some extra signal swing. Not a huge deal.

The last time I researched headphone amps, I found cans as low as 3.2 ohm, while not common, they were out there. I suspect part of the popular build out resistors on published headphone amp applications notes were to make those 3.2 ohms cans a little more manageable for cheesy IC drivers. The last headphone amp I made sounded OK with speakers too (TL07x opamp with some to-220 bipolars hung on the output), but I ended up power limiting the PS because driving speakers would take out the thermal fuse in the walwart PS after several minutes, if I didn't.

Regarding the popularity of using real amps on studio headphone distribution systems. IIRC it was also common to use couple hundred ohm build out resistors at each headphone jack so one low Z can wouldn't load down the whole string, and it would work with a wide range of brands/models, while not releasing their smoke.

JR

 

[Guest]

[quote author="JohnRoberts"]For Wavebourn et all.. my suggestion to add caps is not for the dynamic impedance of LEDs or large signal source impedance, the opamp loop gain will take care of all that, but to allow the bases of output devices to be driven above/below supply for some extra signal swing. Not a huge deal.
[/quote]

Further step: resistors R5 and R6 should be split for bootstrapping (from output to points of splitting).

 

[JohnRoberts]

Indeed breaking up that resistor string accomplishes the same thing only better and with smaller bootstrap caps (but even more added parts). At some point we are surely over engineering this. Headphone amps can be thought of like scaled down power amps so there's all kinds of extra circuitry that could be added but with marginal utility.

If we add the capability to clip the outputs the next thing to consider are anti-sat diodes to keep outputs from saturating and having longer recover time. This may be moot since opamp will surely have a recovery time to wait for also. Simpler to just let bias string starve out if happy with peak output level.

Micromanaging this extra volt or so of swing is clearly less important on 18V rails than 12V like another poster asked about. IMO this is lower on the list of considerations than things like DC errors, etc.

JR

 

[Guest]

[quote author="JohnRoberts"]

Micromanaging this extra volt or so of swing is clearly less important on 18V rails than 12V like another poster asked about. IMO this is lower on the list of considerations than things like DC errors, etc.
[/quote]

Ok, one more option: double JFET instead of that resistors.

 

[tv]

Warning: NOT for the purists!

I have had very good results with tweaked cheapo "TDA" (2003 and 2004) based HP amps, running off 15V single supply and a little harder biased to Acls with pulldowns than from datasheet schems (from memory it was 110E/1,1E; gotta be 1W ones, they do heat up actually). I was surprised at it's sound ...

With added simple passive "contour" in front, it doesn't fatigue and it can wake up the most dead headphones. (rude awakening)

Units can be made to be screwed to the rack backplates trough holes in TDA chips' heatsink (or what's that metal thingie called ... ).

Def. good for guitarists and drummers.

 

[bcarso]

One caveat about STMicro amps of that vintage: they require a high closed-loop gain, or at least a high noise gain, and sometimes quite considerable care with grounding details, if you want to avoid oscillation.

I used a lot of the smaller TDA2007A in powered speakers, and although capable of some very good numbers at least, it was always a new experience with each new layout. A lot of the problem is their practice of combining a fairly straightforward current-feedback stage with additional voltage gain.

 

[JohnRoberts]

[quote author="mediatechnology"]

In some Soundcraft designs they simply parallel a couple of IC's (use both halves of an NE5532 for one channel for example) - to give more drive current.

Doug Self writes about doing that on his website. I've tried it and it does work but I'm not sure how, with the emitter resistors acting as ballasting inside the feedback loop how current hogging is prevented.

Here's an inefficient (Class A) but clean amp I did recently:

http://headwize.com/ubb/showpage.php?fnum=3&tid=7162&fpage=1[/quote]

I have paralleled opamps before to double drive current capability. Oddly enough I did it in a mic preamp where I wanted to make the feedback network resistor values lower than a single opamp could drive comfortably to full swing. It was easier for me to just turn a quad opamp (TL074) into a high current dual than bring in a new part number for that one socket.

They will play nice together if you use reasonable value current sharing resistors and connect the feedback appropriately.

JR

 

[JohnRoberts]

The opamps probably have some resistance internally so if say internal compensation nodes were shorted together that could share OK.. in general with the huge DC open loop gain, just shorting inputs and outputs seems like asking for trouble as typical offset voltage means they would fight each other and perhaps release smoke.

JR

 

[JohnRoberts]

Interesting in an "its only money" kind of way. I guess it will clean up the grounds, Perhaps useful for single supply operation without big blocking caps.

I've talked about this before, as long as your adding an amp for ground lead, I made a headphone amp where I drove the common headphone ground with a combined opposite polarity signal to get roughly 2x signal swing. Of course normal L and R feeds had to also carry opposite channel info to cancel out common mode.

That one would melt the wax in your ears.

JR

 

[Samuel Groner]

www.amb.org/audio/mmm/mmm_sch.pdf

Seen that before and I wondered how that capacitur multiplier in the supply line works--to what are the bases of the pass transistors referenced to? Seems relatively ill-defined depending on JFET parameters.

Samuel

 

[JohnRoberts]

While perhaps it's a subtle difference, when I parallel opamps for more drive current, I use only one opamp as a gain stage, and configure the others as unity followers. In the case of the LT1397 example, I'd connect the + input of the 3 added opamps to the junction of Rf and first Rs. The three added opamps still use individual Rs build outs.

In the first example the DC errors will be input error multiplied by closed loop gain, so several times higher than my approach. I suspect there may be other arguments in favor of either approach.

JR

 

[Guest]

[quote author="mediatechnology"]
Note to Wavebourn: This is not a headphone amplifier but a general concept and the LT1397 not necessarily a good device for this. Thought it might be a good idea to state the obvious twice to prevent sharp-shooting drive-by snipers.
[/quote]

I understand. But I have to warn you that to get 100W output power you'll probably need some special measures to make all wires of equal lengths. Also, some caps near cases will be needed. :green:

 

[Guest]

[quote author="mediatechnology"]Wavebourn - Here's the high wattage solution:

44 NE5534's per channel[/quote]

I would not call 1 Amper output "High Wattage". More sand is needed! :grin:

 

[rodabod]

Has anyone here tried the OPA132 / OPA2132 opamps as single-opamp headphone amps?

I know it's not ideal, but I've been using off-the-shelf cheap headphone amps recently which sound like ass. They distort quite heavily at louder levels. I opened them up to find single NJR4560 opamps in one and NJR4580 opamps in the other. I know these are preferred in cheap gear for headphone amps as they have better current drive than the other cheap alternatives, but I wondered if the OPA might be worth a shot as a replacement seeing as it's popular with some DIYers.

 

[Guest]

[quote author="rodabod"]Has anyone here tried the OPA132 / OPA2132 opamps as single-opamp headphone amps?

I know it's not ideal, but I've been using off-the-shelf cheap headphone amps recently which sound like ass. They distort quite heavily at louder levels. I opened them up to find single NJR4560 opamps in one and NJR4580 opamps in the other. I know these are preferred in cheap gear for headphone amps as they have better current drive than the other cheap alternatives, but I wondered if the OPA might be worth a shot as a replacement seeing as it's popular with some DIYers.[/quote]

4560 sound nice in my modified 31 band Altec EQ (LC-filters inside)
In my todo list I have a headphone distribution amp using cheap chips D2822.

 

[MartyMart]

I made a CMoy headphone amp about 18 months ago for use with my new
but WAY underpowered Ipod Photo: http://tangentsoft.net/audio/cmoy-tutorial/misc/cmoy-tangent-sch.pdf

I used something slightly better than the OPA2134 but can't remember what
right now ... sounds fantastic though, much better with full .wav tracks or from
a CD player .... I hate mp3's under 320kbps !!

MM.

 

[peranders]

This guy here seems to have put quite some effort into his headphone amps: http://sjostromaudio.com/joomla/index.php?option=com_content&task=section&id=4&Itemid=27

Michael

Old thread, I know, but it's true that I have put some effort into my designs and as info, which model do you think is number one and two? A bit surprising, QRV07 = no. 1 and QRV08 = no. 2, surface mounted designs where QRV08 is a major overkill but was fun to design.

 

[dagoose]

We have a simple, good headphone DIY-project coming up sometime soon - it's under final testing by a couple of select local diy'ers:

all info, including layout as .pdf - http://www.gyraf.dk/gy_pd/hpamp/

image - http://www.gyraf.dk/gy_pd/hpamp/sch_small.GIF

Jakob E.

digging up an old thread because i was looking for a decent headphone amp.
I think this will run on +/- 15v as well? maybe a little less headroom but for the rest ok doesn't it?
I'm also wondering if anyone has a board left, would help me a lot

 

[abechap024]

I'm thinking about making a good headphone amp too....anyone think about using opa 552 opamps in a headphone amp? they are high current....

 

[JohnRoberts]

http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=23

Wayne seemed pretty happy with this one...

based on a THAT chip...

JR