Bravo 12AU7 Mods and Appreciation thread

[Deleted]

Feb 10, 2013 0:37:43 GMT twinster said:

Hello, I'm expecting a new Bravo Ocean and was wondering if it would be possible to lower the gain of 30 db on it. I'm planning of using it with low impedance can so lower gain would e better.


Thanks

Do youi have a schematic for this version ?
IF it has cathode resistors, you could try removing any cathode bypass capacitors.

[daveman]

Great thread! I have ordered most of the items from mouser to do these mods. This evening I did the crosstalk mod, but did not eliminate crosstalk The left channel does not bleed into the right channel, but the right does still bleed into the left..

i have verified that it isn't my phones, with only R signal detected I can measure small signals on the headphone socket left channel, but vice-versa with only left connected i get basically 0v on the right channel

Any thoughts thanks

[luis]

Apr 5, 2010 15:10:41 GMT oohms said:

Power supply filtering
If you want to stick with a switchmode power supply, adding an inductor in series with the supply voltage (before the big filtering capacitor) the switching noise should be reduced.
One step further would be to upgrade it to a linear regulated power supply.

What effect would have using a ferrite choke at the PSU cable like this one www.dataq.com/images/products/accessories/choke.jpg instead of having it past the power switch?

[boomer47]

Some nice tips for mods.  However, a couple of comments:

1.  Gushing about the "tube sound is fine but realize that you are probably feeding this circuit from a solid state source, either transistors or ICs.  No one gets a direct feed from an optical head or magnetic head. 

2. Anode current, according to my calculation should be 283 micro Amps.  The constant current source puts one end of R13/R14 at 24 volts and the other at 23.15 volts, assuming a 1.5 volt forward voltage drop across the LED and a .65 volt drop across the emitter/base junction of the 2N3906 PNP transistor.  This leaves .85 volts dropped across the 3K resistor, .85/3000=.000283A.  If you wish to double it to 566 micro-amps, change R13 & R14 to 1500 ohms.

3.  If I were to make a mod, it would probably be replacing the output resistors R8 & R10 with a 33 ohm resistor in series with a 82 ohm resistor with a SPST switch across the 82 ohm resistor to change from 33 to 115 ohms output impedance.  This should allow most headphones to sound good.

I invite comment.

[luis]

Hi there, I just got my Bravo V2 and I'm planning on making the suggested mods by solderdude but I have a question regarding thermal management. I'm replacing the IRF630 for IRL530 and the LM317 for LM317AT. Should I use larger heatsinks for both the IRL513/LM317AT or only one or the other? Thanks in advance.

[twinster]

Feb 10, 2013 6:31:10 GMT @sandyk said:

Feb 10, 2013 0:37:43 GMT twinster said:

Hello, I'm expecting a new Bravo Ocean and was wondering if it would be possible to lower the gain of 30 db on it. I'm planning of using it with low impedance can so lower gain would e better.


Thanks

Do youi have a schematic for this version ?
IF it has cathode resistors, you could try removing any cathode bypass capacitors.

Sorry for the long delay.

No I do not have the schematic. I received this amplifier and my concern were valid. Using my Shure SRH-940 I can not go over 8:00 on the pot. I'm feeding it with a UD100 DAC.

Also based on the picture and video that wee posted by Leon on this thread do you think the current MOD's recommended for the V2 can work on the Ocean?

Many thanks

Simon

[luis]

I have a question that hopefully you guys will be able to answer. I did the followings mods:
- replaced power supply cap for a 4700uF 35V nichicon
- replaced IRF630s for IRL530s
- replaced LM317s for LM317As
- replaced output caps for 2200uF 25V nichicon fine gold caps
- cut traces and added jumper for crosstalk

Now when I turn on my amp I immediately get audio on right channel but left channel takes a few seconds to star working. What could be causing this?

[Deleted]

Now when I turn on my amp I immediately get audio on right channel but left channel takes a few seconds to star working. What could be causing this?

Luis
Are you saying here that you are getting the same volume level immediately on switch on , as you get from the other channel seconds later ?
If so, that should not be happening due to valve warm up time. In that case, I would recommending carefully checking all of your work,
and if you can't see any error to reverse the modifications.
Alex

[luis]

Alex,
I just tried it again and noticed that the right channel starts about 10s after turning ON the amp and the left channel starts about 3~4s later. Is this expected behavior?

Also, can I just replace the stock 12AU7 tube with let's say a Genalex Gold Lion or do I need to do the bias/pot fix first?

Thanks,
Luis

[Deleted]

Apr 19, 2013 17:29:34 GMT luis said:

Alex,
I just tried it again and noticed that the right channel starts about 10s after turning ON the amp and the left channel starts about 3~4s later. Is this expected behavior?

Also, can I just replace the stock 12AU7 tube with let's say a Genalex Gold Lion or do I need to do the bias/pot fix first?

Thanks,
Luis

Luis
I will have to leave those questions to someone here who has done the mods. I haven't played around with valve amplifiers for many years, let alone these hybrid versions.
Alex

[luis]

Apr 19, 2013 20:29:29 GMT @sandyk said:

Apr 19, 2013 17:29:34 GMT luis said:

Alex,
I just tried it again and noticed that the right channel starts about 10s after turning ON the amp and the left channel starts about 3~4s later. Is this expected behavior?

Also, can I just replace the stock 12AU7 tube with let's say a Genalex Gold Lion or do I need to do the bias/pot fix first?

Thanks,
Luis

Luis
I will have to leave those questions to someone here who has done the mods. I haven't played around with valve amplifiers for many years, let alone these hybrid versions.
Alex

Alright, thanks for the help anyways. Once both channels warm up this little amp sounds great, better than my FiiO E10.

Hopefully somebody can answer my questions above.

Thanks,
Luis

[broben05]

So I have yet to modify my amp, but today suddenly the amp stopped working. Both Led's stopped working, in addition the tube seemed to have dropped out of the amplification. The heaters are not warming the tube and the ifr630 are heating up much more than they had previously. The overall output is lower than direct from the computer I am listening to. When I went through to test the voltages across the leds the red one was registering 24v and the blue was blown as a result the red led came back on when I took the reading of the blue led. I have yet to short the blue led pins I suppose I will try this when I get the chance to see if it resolves the other problems.

[maxbara]

Hi I'm new to this forum, I have a Bravo V2, I done the mods in this order:
Crosstalk: Ok
then I switched to the IF510 and 3300 35V cap on feed and 2 2200 25v
Now when I fire the amp for a 10 seconds I hear crackles from the left channel then the IF510 burns..
I'm sure I done everything right have you an idea from where to start?
Max

[siles1991]

Hi guys im new to the forum and got the parts required for most of the mods.

LM317AT
Nichicon 6800uf 35v
IRL510
Nichicon 25V 2200uF

Already did the crosstalk mod and was wondering if anyone can tell me what else can I do?

I'm new to tube amps so I was wondering how does the 5k pot works for bias because I have no idea what bias actually does.

Im using a JJ Gold Pin ECC82 tube. If i do all these mods is it a must to get a bigger heatsink?

UPDATE: After soldering on both sides for IRL510 only left side is heating up and right side stays cold and no sound comes out. When soldered 6800uf 35v was still working fine. And the tube is not heating up i'm guessing.

[siles1991]

This is my bottom view

[micross50]

Hi all,

I have a quick question for you all. I did the heater mod on indeed G2 amp. And I can set the vbias voltage without problem. The problem is when I increase the volume one side is ok the bias voltage increase with the volume but on the other side voltage decrease with higher volume causing distortion and sound lost.

What is my mistake?

Thank you a lot

[Deleted]

May 10, 2013 2:10:49 GMT micross50 said:

Hi all,

I have a quick question for you all. I did the heater mod on indeed G2 amp. And I can set the vbias voltage without problem. The problem is when I increase the volume one side is ok the bias voltage increase with the volume but on the other side voltage decrease with higher volume causing distortion and sound lost.

What is my mistake?

Thank you a lot

Hi
You will need to contact the designer of these modifications for assistance.

[PinkFloyd]

Apr 30, 2013 22:03:56 GMT siles1991 said:

This is my bottom view

Are you sure you have actually cut the tracks? Looks to me like you've just scraped the coating off.... you need to actually BREAK the copper track underneath with a sharp knife or drill bit.

[PinkFloyd]

May 10, 2013 2:10:49 GMT micross50 said:

Hi all,

I have a quick question for you all. I did the heater mod on indeed G2 amp. And I can set the vbias voltage without problem. The problem is when I increase the volume one side is ok the bias voltage increase with the volume but on the other side voltage decrease with higher volume causing distortion and sound lost.

What is my mistake?

Thank you a lot

Can you upload a photo of the bottom of the board please?

[luis]

Do you guys know if the Bravo V2 has enough juice to power some DT880 600ohm cans?

[draconothese]

hello im new to the forums. I am having issues with my bravo v2 hopefully one of you can help me out.

the issue is if I plug a cord into the input without anything plugged into it there's a awful hiss sound from my headset it goes away partway when its plugged into a source but its still there. also if I touch the metal plug they gave me and touch the heat sinks for the irl 630's I get a little shock. is it a grounding issue?, how can I fix this its driving me crazy.

if there's nothing plugged into the amp there's a hum that gets louder if I turn up the volume knob. the hum starts to go away if I grab onto the adapter that came with the amp the 1/4 to 1/8 adapter

also most of the hum goes away if I lift it just off my desk or tilt it on its side

is there a grounding issue or something how can I fix this

[Deleted]

May 21, 2013 5:38:23 GMT draconothese said:

hello im new to the forums. I am having issues with my bravo v2 hopefully one of you can help me out.

the issue is if I plug a cord into the input without anything plugged into it there's a awful hiss sound from my headset it goes away partway when its plugged into a source but its still there. also if I touch the metal plug they gave me and touch the heat sinks for the irl 630's I get a little shock. is it a grounding issue?, how can I fix this its driving me crazy.

if there's nothing plugged into the amp there's a hum that gets louder if I turn up the volume knob. the hum starts to go away if I grab onto the adapter that came with the amp the 1/4 to 1/8 adapter

also most of the hum goes away if I lift it just off my desk or tilt it on its side

is there a grounding issue or something how can I fix this

You could try fitting heatsink washers to the IRL630s.
Do you have a desktop fluorescent lamp ?

[draconothese]

yes I have a cpf bulb in my lamp but even with it off and unplugged it still does all that is there a way to ground one of these amps I am wondering if its not grounded and that's why it shocked me

[Deleted]

May 24, 2013 23:10:47 GMT draconothese said:

yes I have a cpf bulb in my lamp but even with it off and unplugged it still does all that is there a way to ground one of these amps I am wondering if its not grounded and that's why it shocked me

The drain of the IRL630 MAY be connected to it's metal tab, which means that if it is not mounted using an isolating washer to the heatsink, the heatsink will be "live "
Some data sheets are not too clear on this. You can verify this with a DMM by checking for a s/c between the centre leg of the device and it's mounting tab when switched off.
Alex

[darkarn]

Hi, thank you for the mods (which also helped to deal with a strange buzzing noise I am having since a few weeks ago!). I have swapped out the input and output capacitors to Nichicon gold caps, did the crosstalk mod, changed the power switch and shorted the blue LED, which led to some audible and operational improvement. However, I need help in the following:

1. I have already shorted the blue LED underneath the tube. The blue LED does not light up anymore, which is what I wanted. However, why am I not seeing that signature orange glow that most vacuum tubes make?
2. I have done the crosstalk mod already (and triple-checked to ensure that the copper tracks are cut), but I am still hearing stuff from the left channel when I am testing for crosstalk by plugging out only the left input RCA cable. Did I miss out something?
3. Is it possible to just stick with the default heatsinks should I change the MOSFETs? My table is too small for those big heatsinks lol...
4. I am seeing two small capacitors right below the tube. Should I swap them out too?
5. Is it recommended to remove/short the red LED too?

Thanks!