Bravo / Indeed Headphone amplifiers

[PinkFloyd]

Jun 5, 2010 9:16:36 GMT @davek said:

Hi Mike,
Sorry to read of your over exposure - hope your appetite returns soon. At least the timing is a good as such a thing can be - plenty of other things to do on these long warm days. Let's hope normality returns in time for those long dark winter evenings .
Dave.

Hi Dave,

Yes, couldn't have chosen a better time to put things on the back burner.... I've spent the entire winter sitting inside, it's nice to be able to "air off" in the sun for a change

[Deleted]

Differences between Bravo and Miridiy..

Same schematic, same layout, different output/input connectors, different quality PCB, Bravo has lin vol pot, Miridiy has log volpot, and some other small differences.

BIG difference in the way the LM317 operates as it driven out of proper operation above 0.6Veff (300 Ohms)
Bravo does it by just stopping to function as a current source and becomes more like a resistor.
Miridiy does it by oscilating on that point on 12MHz.
It's in both channels so no fluke or faulty measurements.
Of course you can't hear 12MHz so it is not directly audible but the 12MHz can interfere with other HF signals and it's products might be very audible.
Driven from a clean source and a PS with little or no harmonics pollution you will probably never notice it.

Very likely caused by the manufacture of the LM317.
Will have to check this to be sure...

[Deleted]

Jun 7, 2010 17:39:35 GMT @solderdude said:

Differences between Bravo and Miridiy..

Same schematic, same layout, different output/input connectors, different quality PCB, Bravo has lin vol pot, Miridiy has log volpot, and some other small differences.

BIG difference in the way the LM317 operates as it driven out of proper operation above 0.6Veff (300 Ohms)
Bravo does it by just stopping to function as a current source and becomes more like a resistor.
Miridiy does it by oscilating on that point on 12MHz.

I find the Miridiy a little more subtle than the Bravo was on the volume increase Frans. Maybe the Log pot? Both as prone as each other to noise pickup.

Which one is being driven out of proper operation?

[Deleted]

Log vol pots have better travel.
It's not a different material that is used, not even another value.
The only way they differ is how the resistance is spread over the entire range.
In lin pot it is linear (so pot halfway and the resistance on either side of the middle is exactly the same) i.e. 6dB less as when it is at 'full' setting.
When a pot is log type it has it's resistance devided differently over the travel range.
when the pot is halfway the resistance is not 50/50 but more like 20/80. i.e. 14dB lower then 'full' setting
More close to the way our hearing reacts to increase in sound pressure.

All these amps drive their LM317's out of proper operation (including G2) as soon as the output level goes beyond 0.5 to 1V.
Depending on IRF/IRL MOSFET and anode voltage (bias) setting.
IRL shifts this point more towards 1.5 - 3V and every increase (above 13V) anode voltage also increases this point (with a factor 0.7).
It's because of the way the filaments (heaters) are inside in the audio path and have (too) little voltage across them.
This is why their cooling fins can stay small (little voltage, little power).
For high efficience HP's this is already a very respectable volume b.t.w.
Miridiy (HH's in any case) does this by oscilating and I expect other Miri's too.

< edit> Exchanged both LM317's for LM317A and the oscilations are gone !

In your modded Bravo the LM317A's cannot be driven outside it's proper operation point anymore.

As said it is very likely not audible in most cases.
Only in special cases where the 12MHz can interfere with harmonics and produce sideband products.
The Bravo before modding did this in another way (at least not oscilating)

I'll explain sideband products for those that like to know.

You can hear 1kHz... that's obvious.
You cannot hear 100kHz..
BUT if you have a freq. of 100kHz and another one at 101kHz AND there are nonlinearities there CAN be a product of these frequencies audible (1kHz).
Intermodulation distortion is another word for it.
In the audioband usually very low but the problem with most amps is they are NOT operating linear anymore at very/extremely high frequencies (way above the audible bands) so the chances of sideband products becoming audible increase in certain freq bands.

[PinkFloyd]

Frans, your G2 ships tomorrow. I have included the stock EH 6922 as well as a brand new E88CC (out of a V8) for you to play about with.

Have fun

[Deleted]

Thanks Mike,

It's adventures will be posted on the forum.
Now only have to make time to play/fool around with it ....

[Deleted]

For those who want to 'see' what replacing a IRF630 to IRL510, LM317 to LM317A and output cap to 2200uF/25V and fitting cathode caps does see the graph below.

Blue line = original Miridiy with IRF630+LM317T+1000uF/25V
Green line = IRL510+LM317A+2200uF/25V
Red line = IRL510+LM317A+2200uF/25V+470uF/10V cathode caps.



replacing the LM317 cured the oscilations.
Going from IRF to IRL cured the crosstalk (@ 13.5V bias voltage)
Going from MOSFET 630 to 510 increased the freq respons.
(When using IRL530 the graph is between the blue and green line. (-0.5dB @ 20kHz)
Going from 1000uF to 2200uF extended the low end (far beyond the reproducable but with 32 Ohms load it might be noticeable)
Adding the cathode caps increased the frequency respons even further.

[zephyr]

so, after realizing that I'm too stupid to understand even half of the talk from this thread, what is the best option for a noob to get? Noob as in, I can't solder.
Far as I can see the Miridiy has trim pots which is good I suppose.
The Bravo V2 does, on most photos. The Indeed G2 doesn't, am I correct?

[Deleted]

It's not about being too stupid to undertstand .
I think most members don't have knowledge of electronics.
You don't have to know about it to enjoy audio.
It comes in handy with these amps as they need some modding to get the most out of them though.

The newest G2 (acc to Judge Buff) will come/comes with IRF510.
IRL510 would be better but at least the freq range is decent.

Only the Bravo 12AU7 version doesn't have the ability to set the biasvoltage (has no trimpots).

To set the bias properly you would have to own a voltmeter/multimeter at least.

[zephyr]

Jun 9, 2010 16:40:01 GMT @solderdude said:

The newest G2 (acc to Judge Buff) will come/comes with IRF510.
IRL510 would be better but at least the freq range is decent.

Only the Bravo 12AU7 version doesn't have the ability to set the biasvoltage (has no trimpots).

So, basically the G2, V2 and Miridiy are good enough as they all have trimpots? With the G2 being the best of the three due to the IRF510?

I've been looking at the Miri because it's smaller and cheaper but I wonder what exactly the disadvantages are. I'm willing to swap the tubes if the ones supplied aren't good enough.

Just from the looks of it, the miri PCB looks rather crappy, so does the power switch but meh. Only RCA in/mini out. That would do for me, though.

The 6922 Bravo has the same crappy power switch but looks better on the pictures, and has an additional mini input. Nice, but at 90$ shipped it's rather expensive.

The G2 seems most well-made, has many input/output options, though not useful for me right now it might be good in the future. Green PCB looks crappy but the power switch seems better than the bravo/miri ones. I kinda miss the red LED. This one is rather expensive as well.

Jun 9, 2010 16:40:01 GMT @solderdude said:

To set the bias properly you would have to own a voltmeter/multimeter at least.

I do, I have used it to measure voltage outputs of my PC power supply...I do know some basics about electronics since I'm a PC geek but I don't know much about resistors, distortion etc...

[Deleted]

The Miridiy I am modding did oscilate at 12Mhz at only one side of a sine wave (the positive half) from 0.5 V output voltage and above in stock form on both channels which turned out to be bad quality LM317 (current sources).
The Bravo I modded before that didn't have this affliction but did have other ones. (rustling noises)

Al these amps except for G2 have crappy switches.
All these amps have 25V power caps with 24 Volts on it and should be replaced by 35V caps.
All these amps have a freq response as in the blue line 4 post above (i.e. rolled of highs)
They all 'need' the MOSFET changed to IRL510 unless you prefer the rolled of highs (makes them sound warmer, lusher)
G2 is the most expensive one but does seem to be the best standard type (especially with IRF510 already fitted)

Standard they all sound quite alike except for the G2 which is better in general.

The Miri PCB is of better quality then the black Bravo PCB b.t.w.

the 12AU7 version is just as good as the other types.
You just can't set the bias voltage (it can be modded so you can set the bias)
If you just plan to listen to it/use it in stock form it's just as good.

[zephyr]

Jun 9, 2010 18:31:29 GMT @solderdude said:

If you just plan to listen to it/use it in stock form it's just as good.

I do, but the thought of having one channel louder than the other haunts me so I'd rather have the option to set the bias. Especially since my ears have over the last few months been giving me a feeling like one side is in fact louder than the other so having an improperly biased amp would make that worse.
Also, if I do get my hands on a soldering iron within the next months, how difficult and how expensive would the mods be for someone who never soldered before? (the essential ones, at least)

[Deleted]

the bias setting pots have nothing to do with left being louder then the right channel (or vice versa)
It has to do with optimal tube (anode voltage) settings.
The trimpots (bias) do not affect the volume.

If you haven't solderded before I strongly recommend NOT to try and mod it.
The PCB materials aren't that good and the copper traces break or get loose fairly soon.
Even I have to be very carefull AND use the right tools for desoldering pads without destroying the PCB.
And I've been soldering for over 30 years (both for hobby and professional)

All amps have the same amplification (same tube) of about 20-21 times.

Spend some more by buying the newest G2 (IRF510) and you don't have to do much to get the best sound.
It'll last longer too.

If you don't mind rolled of highs you can buy any of these amps.

[zephyr]

Jun 9, 2010 19:51:20 GMT @solderdude said:

If you don't mind rolled of highs you can buy any of these amps.

I don't, usually, as I'm just a youngin and therefore sensitive to highs.
Also, thanks for the soldering advice. It always looks easy but I really can't say that I have a steady hand, nor do I have any equipment to desolder. I'm going to learn it someday, I'm sure it's really rewarding, thinking of all the cables and phones I would usually throw away... And thinking of all the recables and DIYs I could do...

[Deleted]

Lots of people are very pleased with unmodded amps like these.
Enjoy...
For unmodded amps I recommend to set the bias around 15 Volts (they are usually set at 12V ).
When an IRL is fitted 13 to 14 Volts.

[Seamus]

Zephyr, the way I did it was to get the V2 12AU7 version (you can get them for around £25 shipped in an auction) to see how I liked the basic sound of this design, although the stock Chinese tube isn't up to much and should be changed for something like this:

cgi.ebay.co.uk/5963-PHILIPS-ECG-12AU7-ECC82-TUBE-VALVE-1-PC-/370378915328?cmd=ViewItem&pt=UK_Consumer_VintageAudio_RL&hash=item563c4dbe00

I loved it and now have a G2 on the way, they can be had for around £60 shipped in an auction if your lucky. I don't think it's worth modding the V2, as Frans said the pcb is pretty crappy and what it does it does well (the sound that Frans described of warm mids and rolled off highs) perhaps the G2 is better quality and more worthy of modding. You probably wouldn't want these as the only style of amp that you have but they really are fun, musical little amps.

[zephyr]

You got a G2 on the way? Great, how much for your v2?

[Seamus]

You got a G2 on the way? Great, how much for your v2?

I couldn't sell it, my girlfriend likes the look of it too much

[PinkFloyd]

Jun 10, 2010 15:28:06 GMT Seamus said:

You got a G2 on the way? Great, how much for your v2?

I couldn't sell it, my girlfriend likes the look of it too much

Swap it out with a vibrating "dildo"...... she won't notice it's gone

[Seamus]

Swap it out with a vibrating "dildo"...... she won't notice it's gone

Given what Frans said about them oscillating, maybe that's why she likes it

[Deleted]

Here is a write-up I did about modding Mick's Miridiy amp.
A technical article for those that are interested in the workings of this amp. (1.6MB pdf file)
expanded with tutorial for the mods.
You can download the file from this location:

www.mediafire.com/file/vzdwnrlnjjz/modding of a Miridiy amplifier.pdf

Here are the schematics of the mods described in the pdf file above.

[Deleted]

A 10 times greater bandwith expanding far.. far.. beyond the edge of audible awareness.

Frans
I respectfully disagree. That is not quite recent thinking in many areas.
Otherwise, an excellent,well documented , and thoughtful paper.
Kind Regards
Alex

[Deleted]

@ Alex,

hmm 250 kHz is far beyond audible awareness for most people certainly for me I can't hear beyond 100kHz . ;D

Thanks for checking my beta version b.t.w.

[PinkFloyd]

Jun 11, 2010 21:51:13 GMT @solderdude said:

@ Alex,

hmm 250 kHz is far beyond audible awareness for most people certainly for me I can't hear beyond 100kHz . ;D

Thanks for checking my beta version b.t.w.

I cant hear beyond 14kHz

Am I a "SUPER FREAK" (yeh) ??

[Deleted]

Jun 11, 2010 21:51:13 GMT @solderdude said:

@ Alex,

hmm 250 kHz is far beyond audible awareness for most people certainly for me I can't hear beyond 100kHz . ;D

Thanks for checking my beta version b.t.w.

Frans
As you well know, I don't claim to hear those kind of frequencies either. However I am well aware, (with digital sources at least) of the improvement that much wider bandwidth makes. It may even come down to digital artifacts not fazing much wider bandwidth amplifiers ?
Many recent design SS amplifiers even have input filters with a -3dB point as high as 1.9MHZ !
Alex