Bravo / Indeed Headphone amplifiers

[Deleted]

There is only 1 100nF film cap (I should have drawn it in the 'shared' section, will correct it when I do not forget)
The quality of it is more then sufficient and doesn't need changing.
(small blue cap: 104 means 100nF)
Changing it to another make/brand won't mean less spurious HF components.

[Judge Buff]

Since I've only read about a third of this thread, I won't comment other than to say my little modded Indeed is incredible...

[Deleted]

May 22, 2010 17:52:37 GMT Judge Buff said:

Since I've only read about a third of this thread, I won't comment other than to say my little modded Indeed is incredible...

I prefer the staight Indeed to the straight Bravo and in spite of the faults of design, I still find them unbelieveable addictive.

Makes me feel as though I can't possibly be a hi fi buff!!

[Deleted]

in spite of the faults of design, I still find them unbelieveable addictive.

Yes me to Ian, my G2 should have gone out of the window a couple of weeks ago, but because it sounds so nice, it got reprieved, with a suspended sentence.

[Deleted]

May 23, 2010 7:52:04 GMT @heliharris said:

in spite of the faults of design, I still find them unbelieveable addictive.

Yes me to Ian, my G2 should have gone out of the window a couple of weeks ago, but because it sounds so nice, it got reprieved, with a suspended sentence.

Sorry Mick,

I've just realised how you in particular would have read my post. I meant the sonic failings, not the fault that yours had.

There was no excuse for that particular fault. Pure bad design and something that we all need to look out for.

Reading your post about that made me feel bad if I'm honest. You know, we all go on about how good an amp sounds and then someone gets that happen to them. Really poor.

The worst thing is it happened twice. I had a good long look at mine after your post and now look at it with much more mistrust.

My apologies if you thought I was referring to your mishap.

Ian

[Deleted]

My apologies if you thought I was referring to your mishap.

No, didn`t even cross my mind Ian, I totally agree, they are a very addictive,warm listen. To be honest Ian, it could be argued that the centre pins on my "Chord" RCA plugs are longer than need be, as all my other RCA connectors don`t even come close to the heat sink when FULLY inserted.

These little Amps, even with there rubbish on-off switches, and other inferior cheap parts, can, with a little bit of time and effort, and not too much expense, be made a great sounding and reliable Amp, and still remain very good value for money IMO.

Mick.

[Seamus]

These really are fun little amps aren't they. I got the Bravo V2 12AU7 version first to try them out ( They're available for well under £30 shipped eBay ) and I've enjoyed it so much I'll have to get the Indeed G2 now.

Despite the design flaws ( some serious as you found out Mick ) and inherent technical limitations they're a musical little thing. Just wondering what's the longest anyone on here has owned one and kept it running? I suspect it will be an enjoy it while it lasts sort of thing, but then it is so enjoyable!

Seamus

[Seamus]

They've also spawned imitators like this one:



It's a cute little thing.

www.littledot.net/forum/viewtopic.php?f=9&t=927&sid=3170ed1dd7d9872c2d1cf3ace20b99b6

[leo]

May 23, 2010 22:42:08 GMT Seamus said:

They've also spawned imitators like this one:



It's a cute little thing.

www.littledot.net/forum/viewtopic.php?f=9&t=927&sid=3170ed1dd7d9872c2d1cf3ace20b99b6

Bloody cheesy

[mrarroyo]

Some might confuse it w/ an ashtray!

[Deleted]

Hello, Frans

I have done a few modds on both my Indeed G2 and the MK2 6922EH amplifiers: I replaced the PS caps with 10000uF ones, the IRF630 MOSFET's with IRL530's, the LM317 with LT317A's and the output caps with 2200uF caps.

It all worked out fine with my G2 - it plays well with no problems. But, my Mk2 6922EH Indeed, after playing for about 1/2 hour suddenly shuts down with a loud click , and won't power up again until it cools off. I, for the life of me, can not figure it out! The LT317A's are of good quality - they are Linear Technology brand, but I am wondering whether they are the culprit. They seem to heat up pretty well, but they don't shut off the other amp (the G2) The amp plays great until it suddenly quits as I said above. I suspected the tube and replaced it with others, but it did the same thing with them. So, I am confused!

Your expert help to sort this out will be greatly appreciated!

[Deleted]

Do both channels cut out at the same time ?
Then it is likely to be the power supply.
Do the LED's still work when it cut's out ?
Replacing the power supply with a more Amp type helps in this case.

If they go one at a time it is likely to be the LM317

The LM317's have internal temperature protection and will shut down until they have cooled down again.
That's the only disadvantage of using the IRL types.
The distortion happens only at higher volumes because the LM317's remain longer in their operating conditions.
The voltage across the LM317's is higher and thus will get warmer.
Therefore I have mounted them on a bottom cooling plate (when taking the filaments out of the audiochain they would heat up even more)

You can:
Mount them on a larger heatsink.
Lower the anode voltage by 1 volt (you will still have the IRL advantages)
Change the LM317 for another brand (each brand may have their temp cut-off point at different temp's.

The G2 is more open and the LM317's are in a slightly better position to cool themselves.
That might very well be the reason why the G2 still works.

If you can't keep your finger on the cooling plate the temp is over 60 degrees !

[Deleted]

May 24, 2010 8:30:52 GMT @solderdude said:

Do both channels cut out at the same time ?
Then it is likely to be the power supply.
Do the LED's still work when it cut's out ?
Replacing the power supply with a more Amp type helps in this case.

If they go one at a time it is likely to be the LM317

The LM317's have internal temperature protection and will shut down until they have cooled down again.
That's the only disadvantage of using the IRL types.
The distortion happens only at higher volumes because the LM317's remain longer in their operating conditions.
The voltage across the LM317's is higher and thus will get warmer.
Therefore I have mounted them on a bottom cooling plate (when taking the filaments out of the audiochain they would heat up even more)

You can:
Mount them on a larger heatsink.
Lower the anode voltage by 1 volt (you will still have the IRL advantages)
Change the LM317 for another brand (each brand may have their temp cut-off point at different temp's.

The G2 is more open and the LM317's are in a slightly better position to cool themselves.
That might very well be the reason why the G2 still works.

If you can't keep your finger on the cooling plate the temp is over 60 degrees !

Hi again, Frans

Thank you so much for your response! It gives me ammunition to hunt the problem down.

Both channels cut out at the same time with a rather loud snap; >:(the LED's stay on for a short time and then go out as well. After it is unplugged for a little while, and the amp is cool again, it re-powers.

I have the anode voltage at 13V with a very strong Telefunken ECC88 tube. I will try lowering it to 12V, and see if it functions after that. I also have a couple of external regulated power supplies on order, and they should be coming in sometime soon, I hope.

Thanks again , and I will keep you posted about my progress (if any ) sometime later today or tomorrow.

All the Best!

[Deleted]

'Smells' like the power supply is the problem.
Does it get very warm ? (warmer then one would expect ?)
See if the (when the amp works) and you flip the on/off switch or pull the power plug out if the behavior of the amp is the same (maybe except for the loud click) and if the LED's go out in a similar way.

Lowering the anode voltage won't help in this case.
Only replacing the power supply will.

[Deleted]

May 24, 2010 14:29:58 GMT @solderdude said:

'Smells' like the power supply is the problem.
Does it get very warm ? (warmer then one would expect ?)
See if the (when the amp works) and you flip the on/off switch or pull the power plug out if the behavior of the amp is the same (maybe except for the loud click) and if the LED's go out in a similar way.

Lowering the anode voltage won't help in this case.
Only replacing the power supply will.

Frans,
Thanks for all the suggestions! I have tried to replicate the problem by doing what you suggested, and was not able to conclude anything , so I again let the amp heat up and cut out , let it cool off, and then decided just for the hell of it to lower the bias voltage to 12 volts -- that did nothing, and the amp again heated up , cut out while I had the leads connected to both my multimeters; the amp was still hot, still connected with the power switch on, but had gone dead; I then turned the bias trim pots further down, and the thing came alive! I checked the bias and it was about 11 Volts, give or take some. I let it run a little longer, adjusted the voltage to exactly 11.00V, disconnected the multimeters, and let the thing burn for about an hour without a load. Then I connected my Sennheiser HD600's, and played some music -- it sounded great! The amp continued to function fine for another 2 1/2 hours with no problem, so I believe that the LT317A's don't allow me to have the bias higher than 11V, and obviously, they both did cut out at the same time. I don't think I will do anything to the anode voltage, unless I change to another set of LM317's that can tolerate higher voltages.

What puzzles me however , is that on my G2 amp I had set the anode voltage to 13.75V, and it doesn't cut out after burning for hours, even though it has the same LT317A's installed. A giveaway may be the fact that with the G2 I have to turn the volume control to about 12 o'clock to get the same volume that I get with the amp that had the problem (the one that now has the 11.00V anode voltage) with volume control set at 8:30 o'clock, using the same 300 Ohm Senns HD600!

I forgot to mention that on the amp that had the problem, I had also installed a 80uF 330V photoflash capacitor in parallel with the 10000uF one, as you had suggested in one of your posts. I must say, that now, even with the lower 11.00V bias, I notice a very clear transient response with the flash capacitor installed, as opposed to my G2 amp, which doesn't have it.

Thank you so much for all your help! You steered me in the right direction!

All the Best!

[Deleted]

hmm

The LM317's need better cooling in this case.
Try this:

turn the bias up again to 13 Volts and put a fan next to it that blows air through the amp.
If it's the LM317's that heat up too much they should work now with the fan blowing.

The LM317's in the G2 are in spaced further from the tube allowing more airfolw (cooling)
That might be just enough not to cut out.

Re-install the old LM317's and see if they can take the heat.

load/no load, music, no music shouldn't make a difference.
Because it is class A it will always heat up the same regardless of load or signal.

If one of the LM317's cuts out the glowing current will be halved too and thus the other channel will cut out too but not EXACTLY at the same time.
(there should be small time differences)

When it has cut off by itself measure the voltage of the power supply.
Is it still present ? (24 Volts ?)
It should and the LED's should stay on.

the difference in vol pot setting is very likely to be caused by one amp using a log vol pot (has an A on it and should be the 11 o'clock pot) and a lin vol pot (has a B on it, likely to be the 8:30 pot)

please check this.

The power supply MIGHT have a problem with 10,000 uF + photoflash.

It is still strange that the LED's go out (the power supply is switched off in some kind of overload protection when this happens.)

[Deleted]

May 25, 2010 7:19:05 GMT @solderdude said:

hmm

The LM317's need better cooling in this case.
Try this:

turn the bias up again to 13 Volts and put a fan next to it that blows air through the amp.
If it's the LM317's that heat up too much they should work now with the fan blowing.

The LM317's in the G2 are in spaced further from the tube allowing more airfolw (cooling)
That might be just enough not to cut out.

Re-install the old LM317's and see if they can take the heat.

load/no load, music, no music shouldn't make a difference.
Because it is class A it will always heat up the same regardless of load or signal.

If one of the LM317's cuts out the glowing current will be halved too and thus the other channel will cut out too but not EXACTLY at the same time.
(there should be small time differences)

When it has cut off by itself measure the voltage of the power supply.
Is it still present ? (24 Volts ?)
It should and the LED's should stay on.

the difference in vol pot setting is very likely to be caused by one amp using a log vol pot (has an A on it and should be the 11 o'clock pot) and a lin vol pot (has a B on it, likely to be the 8:30 pot)

please check this.

The power supply MIGHT have a problem with 10,000 uF + photoflash.

It is still strange that the LED's go out (the power supply is switched off in some kind of overload protection when this happens.)

Thanks for all the help, Frans! I will try and do the above experiments sometime later today or tomorrow. I no longer have the old LM317's for I cut the leads off of them for easier desoldering in order to protect the PC Board, which we all know is fragile, and easily damaged. I ordered another bunch of LM317's from a seller at eBay, and should have them in soon. I may experiment with them, and see what happens. The power adapter (power supply), which is 24V/2A, has a green pilot light on the casing, and after the amp had cut out, the power supply light still stayed on, perhaps indicating that the PS had not turned off , but I will also use my multimeter and measure the voltage at the power entrance point of the amp.

Thanks again, and All the Best!

[Deleted]

May 25, 2010 7:19:05 GMT @solderdude said:

hmm

If one of the LM317's cuts out the glowing current will be halved too and thus the other channel will cut out too but not EXACTLY at the same time.
(there should be small time differences)

When it has cut off by itself measure the voltage of the power supply.
Is it still present ? (24 Volts ?)
It should and the LED's should stay on.

the difference in vol pot setting is very likely to be caused by one amp using a log vol pot (has an A on it and should be the 11 o'clock pot) and a lin vol pot (has a B on it, likely to be the 8:30 pot)

please check this.

The power supply MIGHT have a problem with 10,000 uF + photoflash.

It is still strange that the LED's go out (the power supply is switched off in some kind of overload protection when this happens.)

I do recall that after the amp would cut out, and I put my finger on the right hot heatsink with the LT317A, with the headphones still in my ears, I could hear that the right channel would momentarily come on, and at the same time I heard a low hum (rumble) in the left channel, and when I let go the amp went dead, so it leads me to believe that the problem must be the LT317's , and there indeed was a slight short interval between the cut off in left and right, but it was minimal - perhaps about 1/4 second or less. I haven't gotten around to do the rest of the experiments, and I plan to do this to come up with some conclusions, with your help, of course, for which I am grateful!

In the meantime, the amp works at the lower bias setting of 11.00V. The sound is great as it is , especially with the photoflash cap installed. Is there any harm in leaving the anode voltage at 11V?

Thanks, and all the Best!

P.S. I did check the vol pots, and you are absolutely right! The G2 has the logarithmic vol pot, marked with an 'A', and the other has the linear one with the 'B' marking.

[remolon]

I am not sure but I think it could be of help the knowledge of the voltage at G and S of the IRL530 and at both sides of the LM317 resistor (7R5)

[Deleted]

May 25, 2010 7:19:05 GMT @solderdude said:

hmm


Try this:

turn the bias up again to 13 Volts and put a fan next to it that blows air through the amp.
If it's the LM317's that heat up too much they should work now with the fan blowing.

The LM317's in the G2 are in spaced further from the tube allowing more airfolw (cooling)
That might be just enough not to cut out.
<snip>
when it has cut off by itself measure the voltage of the power supply.
Is it still present ? (24 Volts ?)
It should and the LED's should stay on.

the difference in vol pot setting is very likely to be caused by one amp using a log vol pot (has an A on it and should be the 11 o'clock pot) and a lin vol pot (has a B on it, likely to be the 8:30 pot)

please check this.

The power supply MIGHT have a problem with 10,000 uF + photoflash.

It is still strange that the LED's go out (the power supply is switched off in some kind of overload protection when this happens.)

Frans,
This morning I turned up the bias to 13V, and let the unit burn with a little fan blowing. It functioned for two hours, and then I tried to make it cut out by turning the fan off, but the unit burned, albeit hot, for another hour and a half without cutting out . I then turned up the bias to 14 V , let the unit burn and heat up for another hour, hoping it would cut out, but it did not. So, I turned up the bias to 15V , and let it burn for two more hours without any fan cooling - the unit refused to cut out. I tested it out for a few minutes with my HD600 Senns, and it sounded great. The unit is still burning - it has been about five hours already, and it wll not turn off!

While leaving the unit on, I connected the G2, and turned up its bias to 15V, and let it burn for about an hour without any fan cooling. :(It suddenly cut out , and by the time I got my multimeter ready to measure the voltage of the PS, it came back on again , (about less than a minute). I waited for it to cut out again, but it burned for another hour until it cut out for a moment, but this time I noticed that the pilot light of the power adapter (PS) went out momentarily , and then it came back on again along with the amp , which is still working without cooling, and this time it refuses to cut out. ::)I am confused , but I wonder whether some of the components needed to burn-in for awhile, and now the unit may be more stable as a result. Both units are now on with the anode voltages at 15V, and they will not cut out! To reach the 15V the trim pots had to be turned almost to the end of their travel for almost the lowest resistance. I wonder if I am harming the tubes by doing this. I decided to turn up the voltage to 15V, because I remember reading someone comment that even 17V is OK for this type of amp, but I am not sure.

As always, your input will be greatly appreciated!

All the Best!

[Judge Buff]

Apr 26, 2010 14:05:30 GMT mrB said:

I just read about using cathode bypass capacitors over at the Bravo thread on Head-Fi. What do you think about this issue?

www.head-fi.org/forums/f5/bravo-audio-funny-looking-little-tube-amps-444400/index48.html#post6570489

Hi Everybody,

I have read this entire thread now and except for a little good-natured squabbling, I really like the flow and exchange of ideas here. One of my head-fi buddies in the UK was here already, so I kinda felt "at home" as we say in the US.

No one has taken up the question that mrb has posed above and it is to the detriment of the entire community of Indeed/Bravo amp owners that hasn't made this mod. I was talked into it by Avro_Arrow in the head-fi thread referenced and it is not to be overlooked if you want these little amps to sound their best. These aren't by-pass caps, they are basically reservoirs.

If it is covered in another thread, excuse me. It has been more dramatic than even the 10K PS cap mod and we all know how sweet that was for cleaning up the floor and increasing the overall bass response. While my current photo upload doesn't show the mod, it can be seen in the head-fi link. It's too easy to make and has too much positive effect to pass up.

[Deleted]

if you want these little amps to sound their best. These aren't by-pass caps, they are basically reservoirs.

Judge Buff
The cathode bypass capacitoirs are not basically "reservoirs". They will further increase the amplification of the amplifier, where most people have found that it already has so much gain that volume control action is fairly abrupt, and in most cases the setting from 12 oçlock omwards is basically unuseable. The volume control is also likely to have channel mismatching at low volume control settings.The absence of the cathode bypass capacitor also gives a degree of local negative feedback which enhances the SQ , not detracts from it.
Many RG members are finding that the typical gain (amplification) of many commercial headphone amplifiers is excessive already, without further increasing the gain.

SandyK

[Judge Buff]

The exorbitant gain is definitely true for the 30dB Bravo, but not for my 20dB Indeed G1, in the manner I use it. I am using the headphone jack off of a Zune with an excellent interconnect and depending upon which of the 40 some odd tubes I roll, I can even crank it to 3 o'clock with the Zune at 50%.

I have made the mod. It definitely has not "detracted" from the SQ. I also got rid of the crappy pots, too.

It also isn't a true 'by-pass" role for the cap and each increase in capacitance that I have experienced also increased the breadth and depth of each tube's sound stage. Increased imaging also. I went from a 470 to a 680 to an organic polymer 1000 and the SQ was cleaner and broader with each increase. I have no channel mismatch at low volumes...

The amp has no crosstalk and no hiss. A quiet hum that ends when the tube warms-up is the only aberrant sound. Makes my Zune sound like a stereo system with Shure 440s. I've had it since last November and I listen daily.

But I do appreciate your opinion, SandyK... while not agreeing with it in the least. I'd still recommend the mod to anyone with a G1 Indeed.

[Deleted]

Hi Judge Buff,
Welcome aboard..

I respectfully disagree with some of your views.
All these amps have about 27dB amplification.
The specs that come with these amps have NO truth in them at all.
They are 'invented out of thin air' so to speak.
Do NOT trust the specs from all these different branded vendors.
Don't believe me ? ... measure for your pleasure... tone generator and oscilloscope needed
Especially the frequency range and amplification are complete nonsense.
They are all basically the same design.
Differences come from amplification factors of the tubes but most of all from the volume potmeters.
The ones that are thought to have such high gain simply have linear vol pots.
The ones with 'lesser' gain have log vol pots.
So the reason for different settings of the vol pot does NOT originate mostly from amplification factors but vol pot characteristics.

pots with an A on it are log type and have better travel, pots with a B on it are lin type and already start playing loud when you barely touch the vol pot making you think they have higher gain.

The only way to really check total gain is by comparing them with the vol pots at maximum setting and use the volume control of the source

SandyK is right on my account regarding the cathode caps IMO.
I'm a gonna do experiments and measurements on this subject on HH's amp.
As I like to validate all my mods (I know a stupid non-audiophile reason)

All these amps have crosstalk when unmodded. (it's because of the design.. it has the filament as a shared component, the audiosignals of BOTH channels pass through it and crosstalks to the other channel via the LM317 current source... that causes it.)
Simply pull one of the input plugs and listen to the channel that is supposed to have no sound on it.
Now cranck up the volume !!
Then tell me there is no nasty sounding crosstalk above a certain level.
The nasty sounding crosstalk above a certain (high level) point is caused by the LM317 not being in it's minimal required operating point.
IRL MOSFETS put this point further then IRF types, so higher levels are needed to reach the point of horrible crosstalk.
In normal operation the output signals are in phase so it isn't that bad in practice but there are certain passages (with very stereo signals) that won't sound anything near optimal

@ Imagemaker:

I still suspect your powersupply !
Them is cheap crappy chinese PS.

Set the bias level around 13 ... 13.5 Volt.
It's the optimal setting for the tube if you want symmetrical clipping.
This will give an output voltage of around 12Vpp (so around 4.2Veff)
Ofcoarse this is when loaded with 300Ohms.
With 32 Ohms the output voltage will have dropped to around 2Veff.

Use lineair regulated power supplies with these amps.
Highly recommended as these amps are very sensitive to the noises on the powersupply rails.

[PinkFloyd]

Hi Judge,

I notice you have used Nichicon MUSE 1000uF (NON POLAR) coupling caps.... have you checked the voltage across these caps?