Bravo / Indeed Headphone amplifiers

[oohms]

Guess what i replaced the IRF630 with? An LM317... yep a voltage regulator

It required a little pin bending but it works fine. The sound signature has changed a bit, the bass is more defined, but i think the highs have rolled off a little. I'll have to listen to it some more to see if i like it or not, and then try the IRF510

[Deleted]

?

[robertkd]

Feb 15, 2010 8:20:54 GMT oohms said:

Guess what i replaced the IRF630 with? An LM317... yep a voltage regulator

It required a little pin bending but it works fine. The sound signature has changed a bit, the bass is more defined, but i think the highs have rolled off a little. I'll have to listen to it some more to see if i like it or not, and then try the IRF510

What, and you say it sounds fine??

[oohms]

Feb 15, 2010 9:36:47 GMT robertkd said:

What, and you say it sounds fine??

Yeah it sounds pretty good... so good that i have to listen fairly carefully for any differences from the stock IRF630

I did add a 10nF cap between "gate" and positive inspired from another lm317 design, but i think this may have attenuated the highs a little..

edit: here's one of the threads about this
gilmore2.chem.northwestern.edu/ubb/showpage.php?fnum=3&tid=5153

[Deleted]

Feb 15, 2010 9:21:17 GMT @solderdude said:

?

I didn't reply, because I was lost for words !
P.S.
I have heard of this previously,along with using a LM3909 Flasher I.C. as a radio, but not to connect to the anode of a valve which has only .4mA current flow .

[Deleted]

You know what...

I amma gonna build me one... just for fun.
have lots of LM317's lying around and do some measurements on it.
In fact they are sort off a darlington transistor arrangement with lots of transistors around it for regulating/overcurrent and temp protection.
The coupling of the input with the basis of the darlington output stage is somewhat suspect though.. ;D>

don't know when I have the time for it ..

[Deleted]

Hi Mike,
Thanks for your help. Given that the TX has 2 x 25v outputs, would it be better to link them together, (+ve to +ve and -ve to -ve obviously), or safely seal (isolate) one outlet and just use the other. Sorry if this is a numptie question but I'd rather be safe than do something stupid.
Thanks again,
Dave.

Feb 14, 2010 23:18:56 GMT PinkFloyd said:

Feb 14, 2010 22:13:11 GMT @davek said:

Hi Mike,
Thanks for that. I believe the Va is 225 and, IIRC, this is the actual TX:

uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4225332

Hope this helps you (to help me).
Thanks for your help.

Jesus.... 225VA is "Overkill" but there has never been anything wrong with overkill..... a 225VA will have better regulation than a 30VA (8% as opposed to 18%).... ALL GOOD STUFF..... go for it

[PinkFloyd]

The original



The indeed (almost identical)



Some good info here guys: www.head-fi.org/forums/f6/sijosaes-hybrid-amp-better-433156/

[Deleted]

Well... you're never to old to learn !

made a simple emitter follower (in this case the equiv. of a source follower)
Biased it at 1A !!! and 15 Volt output (24 Volts supply voltage)

freq. range DC to 170 kHz (-3dB)
signals on scope look very much alike with no strange artifacts. (no dist measurements done) ;D
GS dropout voltage always constant at 1.24 Volts (no surprise there)
the input resistance is kinda low to replace an RF630/RF610/RF510 or whatever MOSFET as this LM317 circuit will load the tube too much (the tube needs to 'see' a high imdedance) namely an impedance of 350 kOhm in this case (always a 45uA bias).

You could make a nice end stage with the IC's and opamp output I reckon..

I would not recommend using this as a substitute for the MOSFET in the Bravo/Indeed/Sijosae amp because of the rather low input impedance of the follower though, the MOSFET should be far superior in this aspect.

Some RG members might have different opinions/views on this and the vented opinion is only mine.
I will make no comments on 'audible aspects' for founded reasons .

Frans

[oohms]

Ok so i took out that 10nF cap that i stupidly added to my bravo.. so its now just LM317's instead of IRF630's, with everything else as stock..

WOW

The highs suddenly opened up, and to me this sounds better than the IRF630

Will the low input impedance of the LM317 cause damage to the tube over time?

[Deleted]

No... it'll just makes the 'distortion *' go up a bit and the gain might be slightly less..
The tube doesn't mind.
Check the anode voltage to see if the LM317 loads it too much.
If the voltage is lower with a LM317 this is the case and you might need to re-adjust the anode voltage.
If the anode voltage with a MOSFET and LM317 are almost the same ignore my 'load' reservations as I can't check it because don't own this amp for certain reasons.

People who like tube amps love 'distortion *' anyway ... that's what separates these things from well designed SS amps LOL
* This type of 'distortion' sure can make 'm sound sweet though.

If you like it... use it .. and adore it

Frans

[oohms]

I prefer accurate sound, but i bought one of these to at least have a go at tubes, even if they probably aren't my thing. Plus its a fun little thing to tinker with

I'm thinking, the 220R 'gate' resistor can be removed, and i can wire up an opamp buffer, to see if it sounds better

[Deleted]

you can leave the 220 Ohms in place, I tested the follower with a 1kOhm series resistor.
the 220 Ohm will help in isolating the input capacitance (did not measure) of the LM317 and reduce the chance of this influencing the tubes performance..

Tinkering is fun.

You can use an opamp to buffer between the LM317 and the tube..

But check the anode voltage first.
If it doesn't go down by much when attaching the adj. pin of the LM317 then you don't need to bother putting in an opamp and can use it as it is (leaves it's appearance in tact too)

I designed/built my own HP tube amp for exactly the same reasons ...

[robertkd]

If you want to decouple the anode form the gate capacitance you could wrap an emitter follower between the 220R and the gate

[oohms]

upload.wikimedia.org/wikipedia/commons/thumb/b/b8/NPN_emitter_follower.svg/180px-NPN_emitter_follower.svg.png

would I have to add bias resistors and coupling caps?

[PinkFloyd]

I'm still waiting for these IRF510's to arrive, I wish they would hurry up ;D

[Deleted]

Just check if the anode voltage doesn't change too much when you connect/disconnect the adj pin.
If the voltage does not vary much leave it as it is now (with the 2 LM317's if you like it)
The input capacitance of the LM317 will be lower than that of the MOSFET.
The LM317 is already a darlington emitter follower in essence.
Adding an extra transistor won't do much good with the LM317.
It can do something when a MOSFET end stage is used.
No need to decouple an emitter follower when you keep the leads short and close to the connected parts.

[oohms]

With the IRF630 connected before, the anode voltage was 12v, with the LM317 its 11.2v, so it looks like it is loading the tube a little.

[Deleted]

I thought as much.
try to turn up the anode voltage to about 16 Volts.

[oohms]

Might be hard.. the cathode is connected straight to ground, and there's a CCS between positive and anode

[robertkd]

if your referring to this amp

rockgrotto.proboards.com/index.cgi?action=display&board=b&thread=4948&page=18#62792

The cathode goes to ground via the 2K2 variable resister, the tube is a typical self bias arrangement. Varying the 2K2 resistor will effect the bias Vgk thus the the anode current.

So you should be able to adjust the Va by adjusting the 2K2 cathode (k) resistor.

[JohnnyBlue]

I only recently discovered this forum, after asking a question elsewhere about a CMOY kit I'd just bought, and repeating the question here gave me many useful responses.

Now, I've looked at other threads, and waded through the 19 pages on this thread, and of course have become very interested in these Indeed/Bravo amps, even though I've always set my face very much against valve amps.

From what I've gleaned here, the Indeed seems to have a slight manufacturing and (more importantly) sonic edge, but there's a second version due out later. Is the new one an update/upgrade, a replacement or an additional (and thus presumably more expensive) version?

And where are you guys getting the HD-681 (another thing I've only discovered from this forum!) for £15: the cheapest I can find it for is about £20?

[Deleted]

Feb 16, 2010 16:09:19 GMT JohnnyBlue said:

And where are you guys getting the HD-681 (another thing I've only discovered from this forum!) for £15: the cheapest I can find it for is about £20?

Hi Johnny,
Google 'Music King, Halesowen' for the HD 681 at £15 + £3 P&P.

[PinkFloyd]

www.themusicking.co.uk/superlux-hd681-headphones

They appear to be out of stock "call for availability"

[JohnnyBlue]

Thanks for the Music King links: I'd forgotten I'd already stumbled across their website, but also took "call for availability" to mean "out of stock" (plus the P&P charge brings it up almost to other sellers' prices)!

I still can't really believe that something for less than £20 can be so good, and of course for that money they're worth a punt, but the flood of recent (relatively minor) expenditure on head amps is beginning to draw unwanted attention from the Wifely Gestapo, and I'm not sure I can explain yet another pair of headphones away easily!