Bravo 12AU7 Mods and Appreciation thread

[Deleted]

I recommend IRL530 or IRL510 as these have the lowest Qgs and best HF performance.
another advantage of the IRL types is the LM317's remain longer in their linear operating area decreasing distortion because of their low Vgs.

High value caps are more likely to damage the on-off switch then the PS itself IMO.
These things are short circuit protected and start-up surge is only for a very short time.

The coils won't help much as the inductance you would need to soften (smear) the puls would be very high and so will the impedance be.
The big cap on the PCB is where the low impedance comes from and is not dependant on the PS so the coils will not affect HF.

I once experimented with special capacitors in the power supply.
These are specialised caps and are dedicated to be shorted and to deliver VERY fast transients.
You can find these caps in flashers for camera's.
their sole purpose is to deliver very much power in the shortest possible time (a flash can be 1/10,000th of a second).
VERY low ESR and MUCH lower inductance compared to normal caps.
These are around 47 to 100uF and 400V types.
Just use a 35V type cap (4700uF for instance) in the Bravo and put one like THESE in parallel.
Now THAT's transients and HF response for ya !!

Try making a flashgun with normal capacitors, even the best caps cannot supply the fast transients that these things can.
I am really amazed that I never read about this in any forum/mag/article.
I sure as hell can't be the only one experimenting in Audio, Photography and Electronics.

short a normal cap (with a screwdriver) and you here a 'poff' and maybe a 'paff' if you know what I mean.
Short one of these guys and you hear a sharp 'TAC' and a intense spark.
How's that for an idea ?
Give it a go ..

All my power amplifiers have these caps parallel to the PS for over 20 years now..
never tried it on a HP amp. I used only speakers in that period.
HP's is only a thing for me in the last 15 years or so.

replacing the output caps to 2200 is likely to give the most increase in bass response though.

[Deleted]

May 8, 2010 21:57:38 GMT @solderdude said:

I recommend IRL530 or IRL510 as these have the lowest Qgs and best HF performance.
another advantage of the IRL types is the LM317's remain longer in their linear operating area decreasing distortion because of their low Vgs.

Thanks for the suggestion, Frans! I finally took delivery on several IRL530's, and replaced the IRF530's on my Indeed G2 with the former. The difference in HF response is dramatic! I did an A-B listening test with my other Indeed, which still has the IRF530's installed, and, while on first listen, the latter sounds pretty good with seemingly flat response, ::)upon switching to the Indeed G2 with the IRL530's the whole spectrum extended, especially in the HF, creating the impression of a window opening up, letting the live performance of a 100-piece symphony orchestra in! This spurs me on to replace the IRF630's on my 2 other 12AU7 Bravo amps, as well as the IRF530's on my other Indeed.
Great stuff!

[Deleted]

The LM317 A has tighter specs.
I doubt they sound different..

You should try to find IRL510 instead of IRF510
the IRF530N doesn't do a better job the IRF630
When using IRL the LM317's get a lot hotter, but the crosstalk and distortion will be much better.

6800uF/35 will be much bigger and won't fit.
For a mechanical fitting 35V cap you will have to use 3300/35V (perhaps 4700/35V)
If you want bigger caps in there you will have to modify the topplate or fit them elsewhere.
KEEP the wires VERY short !

leave the gate resistor at 220 Ohm not much to gain there.

[meins321]

oh i just forgot, my blue led was dead from start and as i read on the other thread it could be shorted or desolderd..... can i leave it in place as the amp is working without it from start? (never noticed that as the blue led was a no-no feature for me)

and i will add 2 Nichicon 3300uF 35V 105°C in Parallel to the back and reposition the powerplug (removing the stupid switch and replacing it too as it is getting rusty lol ).
+
my 1000uF 35V 105°C Panasonic FM capacitors should be fine then :-P
(they are dxH= 17mmx25mm)

EDIT: the Mosfet i could source
www.conrad.de/ce/de/product/162789/TRANSISTOR-HEXFET-IRL510-TO-220-IR
www.conrad.de/ce/de/product/162795/TRANSISTOR-HEXFET-IRL530N-TO-220-IR
www.conrad.de/ce/de/product/162798/TRANSISTOR-HEXFET-IRL540N-TO-220-IR
look and compare the last two, i thing the last one might be useful ( wrong description?) as the RDSon is very low ^^

i think i got a trimmed down version
as it is rusty on the phoneplug and switch after a short time. ( And no i didn't water it myself, it is green patina thus ni that was used instead of metal and silver on it )
+
no ceramic caps at all on my pcb ( wima here we gooo!)

[EDIT2]
Whats the difference between IRL510 and IRF510?
I have some good/new IRF510 here but could buy IRL510 if its a ultra big difference ^^

[Deleted]

You can leave the Blue LED as it is or short it (preferrred) as it is probably shorted itself already.

RDs on is of no importance in these amps as it is only important in switching applications with high currents.
It's the Qgs that needs to be as low as possible.
Qgs is the charge that is needed for the gs(Gate Source) capacitance to charge so that the S can 'follow' the G.
This GS capacitance is charged by the current flowing through the tube (anode current).
This is a very low current (because of the low voltage it operates on) of 400uA.
At higher frequencies (10kHz and above) this current is not able to fully charge the GS capacitance (of the original IRF630) and thus the S (=output of the amp) cannot follow the gate anymore resulting in high frequency roll off.
You cannot change the tube current so the Qgs needs to be as low as possible.
the resistance of the gate resistor (220 Ohm) is so low compared to the equivalent resistance of the Anode circuit (about 30kOhm) that it does NOT influence the HF roll off even if you half or double it's value.
IRL has lower Qgs AND lower Vgs (half that of IRF).
because of the smaller voltage drop of the IRL (with the same anode voltage, which ideally should be between 13 and 13.5 volts)
the LM317 remains longer in it's operating point (acting as a true current source) and thus the distortion won't pop up until you play really loud.

You can use the IRF510 too but the IRL has more benefits.
IRL keeps the bad distortion (non linear) further away and extends the freq. range slightly further then IRF

because there is a higher voltage (IRL) across the LM317 it will get MUCH hotter.
I suggest to change the cooling fin to something bigger that will still fit (preferably black, this cools slightly better)

the www.conrad.de/ce/de/product/162789/TRANSISTOR-HEXFET-IRL510-TO-220-IR is good.
Caps are good too.

The power switch needs to be replaced as it breaks anyway within a few months.
Very crappy mechanical and electrical properties not suited to accomodate the high switch on currents because of the huge capacitors used.

[Deleted]

IRL510 GS charge = 2.6nC
IRL510 total Gate Charge = 6.1nC
IRL510 Vgs = 2V

IRF510 GS charge = 2.8nC
IRF510 total Gate Charge = 8.3nC
IRF510 Vgs = 4V

IRL530 GS charge = 3.8nC
IRL530 total Gate charge = 28 nC
IRL530 Vgs = 2V

IRF530 GS charge = 4.8nC
IRF530 total Gate charge = 34 nC
IRF530 Vgs = 4V

IRF630 GS charge = 7.5nC
IRF630 total Gate Charge = 45nC
IRF630 Vgs = 4V

IRL510 is the fastest one (this one gives a very nice -0.5dB @60khz) very well extended
IRF510 is next in line but has double the Vgs. (this one gives a nice -0.5dB @55khz) well extended
IRL530 has half the Vgs as IRF. (this one gives a very pleasant and full sounding -0.5dB @30khz)
IRF630 is the worst ! (this one gives -0.5dB @10khz) warm but rolled off signature

There are plenty more possible replacements.
There is differences in manufacturers with the same typenumber !
These specs are from IR (International Rectifer)

IRL keeps the nasty distortion further away then IRF

[jeffc]

I bought one of these Bravo 12AU7 hybrid headphone amps for $50AUS delivered from eBay a while ago and have modded it as per the instructions here to remove cross talk, dim the blue LED, modify resistor values for optimum 12AU7 supply current/life, replace the 1 uf input coupling electrolytics for Wima MKS film types, replace the IRF630 mosfets with IRL types, me being different I decided to use IRL520s instead of IRL510s or IRL530s, why, because specs were inbetween and I could get them from Futurlec for nicks amongst other parts I was ordering. I also added a low-mass 1/8” socked under the board under the 1/4” socket as all my phones have 1/8” plugs fitting and I don’t like using adapters. Also added a 100-120uf photoflash cap under the big reservoir cap, replaced the on/off switch with links and made a couple of other minor changes. Mosfet heatsinks were also changed to higher mass types that provided a large top surface area for adding extra heat sinking on top cut from an old CPU heatsink. The mosfet heatsinks now run only warm rather than too-hot-to-touch. Tube in use at the moment is a clear-top RCA 12AU7 and with this tube the LM317 heatsinks are just warm, maybe 30C. Another story with other tubes but thats another story.

Sound.. absolutely terrific fed from the 32 ohm out of my LiHM battery-powered Trends UD10 USB DAC.

i337.photobucket.com/albums/n390/jeffc_pics/P8011321.jpg[/IMG]
Bravo all lit up with my Trends UD10, short solid 0.5 mm dia silver wire interconnect cable.

Bravo wings and red Wima coupling caps

1/8” socket mounted under the PCB

Mosfet heatsinks

Rear showing switch links and photoflash cap soldered to power socket pins


For the ridiculously cheap price, this little amp is dynamite, delivering very musical sound, and it looks cute too.

cheers .. jeffc

[PinkFloyd]

Aug 1, 2010 5:41:08 GMT jeffc said:

I bought one of these Bravo 12AU7 hybrid headphone amps for $50AUS delivered from eBay a while ago and have modded it as per the instructions here to remove cross talk, dim the blue LED, modify resistor values for optimum 12AU7 supply current/life, replace the 1 uf input coupling electrolytics for Wima MKS film types, replace the IRF630 mosfets with IRL types, me being different I decided to use IRL520s instead of IRL510s or IRL530s, why, because specs were inbetween and I could get them from Futurlec for nicks amongst other parts I was ordering. I also added a low-mass 1/8” socked under the board under the 1/4” socket as all my phones have 1/8” plugs fitting and I don’t like using adapters. Also added a 100-120uf photoflash cap under the big reservoir cap, replaced the on/off switch with links and made a couple of other minor changes. Mosfet heatsinks were also changed to higher mass types that provided a large top surface area for adding extra heat sinking on top cut from an old CPU heatsink. The mosfet heatsinks now run only warm rather than too-hot-to-touch. Tube in use at the moment is a clear-top RCA 12AU7 and with this tube the LM317 heatsinks are just warm, maybe 30C. Another story with other tubes but thats another story.

Sound.. absolutely terrific fed from the 32 ohm out of my LiHM battery-powered Trends UD10 USB DAC.

i337.photobucket.com/albums/n390/jeffc_pics/P8011321.jpg

[/IMG]
Bravo all lit up with my Trends UD10, short solid 0.5 mm dia silver wire interconnect cable.

Bravo wings and red Wima coupling caps

1/8” socket mounted under the PCB

Mosfet heatsinks

Rear showing switch links and photoflash cap soldered to power socket pins


For the ridiculously cheap price, this little amp is dynamite, delivering very musical sound, and it looks cute too.

cheers .. jeffc[/quote]

Very nice job Jeff

[Deleted]

5k pot:

that one will do.
It will always need a bit of ingenuity to fit them.
one of the outer contacts and the middle one needs to be connected.
Which one of the outer ones you connect determines if the bias voltage goes up or down when turning clockwise.

The big one needs to be replaced because of it's voltage.
If you can fit a 4700/35V or 3300/35V depends on the diameter and height.

I also replace the 1000 by 2200/25V to lower the cutoff frequency and because a 105oC will las longer near those hot LM317's

I loose the 2 small caps near the volpot and mount a strap instead


You can also use this MOSFET (Mouser nr):
844-IRL510PBF

I would only replace the volpot if the adjustment of the volume isn't going as you would like it to.

[Garage1217]

Thanks for the feedback Solderdude! I was actually logging on to message you for your input as I value it after reading your posts. I would be happy to share the double sided board layout I am working on with you to see what you have to say and get your input on the design. Also, I already spec'ed the bias pots at 10K 25 turn 1/2 watt bourns units, simply because of the way my fav tube runs, I needed more resistance as the 5K did not cut it. A 6V switch is a great idea as well.

Here are the mods I am implementing so far...
- Double sided board
- 25V 4700uF fake rubycon power supply cap changed to a 3qty of 2200uF 35V Nichicon KT series caps for a total of 6600uF..
- RCA jacks removed / only 1/8 jack input?? just a thought at this stage or maybe just have rca's instead? No need for both IMO as it clutters the board. Also re-route the input to the back of the board for a cleaner look
- Crosstalk mod built in / circuitry re-routed
- Input signal capacitors eliminated rather than removed and jumpered. Or maybe leave a provision for them and a jumper to eliminate?
- Blue LED turned WAY down brightness wise with a 10K resistor + 100uF 10V cap added for soft start
- 25 turn 10K 1/2w bourns bias pots for precision bias adjustment. Along with easy to access points to check and change bias with a standard multi-meter
- Output signal capacitors changed to Nichicon 2200uF KT series caps
- Larger heatsinks for both 530's and 317's / larger more open board design at 4x6"
- IRF630's changed to IRL530's or IRL510's for massive extension of the top end / rather than cutting falling off at 10K
- LT317's changed to Linear technologies LT317A's which are of better quality
- All resistors will be 1% Vishay / dale mil spec units
- Power switch maybe located on the top lid portion of a custom laser cut acrylic chassis (similar to the current design)but with a quality switch
- Improved symmetrical board layout / I would like to add an artistic touch to the look and layout without sacrificing functionality
- Debating on just having solder points for the volume potentiometer as I am not a fan of the stock alps unit... so one could choose what style they want. Same with the 1/4" output jack... The 1/4"stock unit is not bad and common so could leave it on the board. Still debating with myself on it.

Keep the feedback rolling, Want to make this the best unit I can.

[Deleted]

I suspect the outer ones will be 1k (brown, black, black, brown, brown) and the output resistors 100 Ohm (brown, black, black, black, brown)
difficult to tell with certainty from the pics.

crosstalk mod, but still using the heaters, as in the the first page of this 12AU7 thread, cannot be done as this amp only takes 6V tubes and not the 12V types.
It is more like the original bravo/indeed/miridiy thingies in that aspect.
It can only be done by adding the extra power suplly (as described in the G2 article) and cutting some traces.

The IRF630 I would replace with IRL510 (or IRL530 if you want to retain a bit of it's current character)
adjust the bias voltage to 13.5V with IRL fitted, with IRF 15.5V
The input cap I would replace with a 35V type (around similar value but higher voltage rating) mind the diameter and pin distance (footprint).
The output caps I would replace for 2200/25V type, in this case you can lower the output resistors a bit too (do not go lower than 47 Ohm)

The 2200/25 caps will be bigger and/or have a bigger diameter.
You can mount them away a bit from the tube on longer legs.. would secure them somewhere (tie-wraps or hotmeld glue?) in that case.

[tomco]

Thanks for the info, I'll see if I can place an order for the components during the week.

Just a bit of clarification needed here:

The IRF630 I would replace with IRL510 (or IRL530 if you want to retain a bit of it's current character)
adjust the bias voltage to 13.5V with IRL fitted, with IRF 15.5V

So with the current IRF630 I should adjust the bias to 15.5V? I thought it was 16.5V?

Also, is there anything I can do about "noise"? I'm not really sure where the noise is coming from but I'm getting a rythmic clicking noise and buzzing. The amp seems to be quieter in some places and noisier in others.

Am I right in thinking this is interference to the tube from a wireless device?

[Deleted]

Pictures of the bottom please !

DON'T use IRL540 even more highs cut-off then IRF630
use IRL510, IRL520, IRL530

hint:
UNDO the mods and see if it works O.K.

[Deleted]

Note: quotes form various people:

The output caps I would replace for 2200/25V type, in this case you can lower the output resistors a bit too (do not go lower than 47 Ohm)

As I've mentioned the output resistors are 100 Ohm. Why would a lower value (68 Ohm?) be any better here? AFAIK my headphones have 73 Ohm.

The IRF630 I would replace with IRL510 (or IRL530 if you want to retain a bit of it's current character)
adjust the bias voltage to 13.5V with IRL fitted, with IRF 15.5V

I've changed the MOSFETs to IRL510 and tried to adjust the bias to 13.5V. Sadly on one side I can't go below 18V. Is there something else wrong or should I just replace the control pots from 3k to higher ones (5k or 10k). Adjusting the voltage with the included ones sucks anyway.

Also, is there anything I can do about "noise"? I'm not really sure where the noise is coming from but I'm getting a rythmic clicking noise and buzzing. The amp seems to be quieter in some places and noisier in others.

Am I right in thinking this is interference to the tube from a wireless device?

This amp is very sensitive to electromagnetic distortion. My mobile phone caused it to do loud noise in a distance of 0.8m. I had to increase the distance to at least 1.5m to use the amp.

I have Bourns 3295 and according to the data sheet W103 on the top means 10k ohm.

This means 10 * 10³ = 10k.

[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.

[zasboy]

Wanted to get my feet wet with tube amps and decided to pick up a Bravo Audio V2. Using a SuperLux HD 668B headphone, everything sounded much better. I'm not a very detailed audiophile but I noticed a good change and I liked it. I was curious if I can improve the sound qualities that with the modifications that people have done in this thread. So here are the list mods that I have done:

- Replaced both IRF630 with IRL510
- Replaced both LM317 with LM317AT
- Replaced both 2N3906 with BS170
- Replaced the big rear cap with Nichicon 4700uF/35V
- Replaced the two front caps with Nichicon 2200uF/35V
- Replaced 3K resistor with Bourns 5K trim pots(bias voltage adjustment)
- Shorted the two small caps under the volume pot(should have taken out the capacitors and jump it)
- Crosstalk mod
- Replaced 7.5 resistor with 8.8
- Soft start mod
- Replaced China tube with RCA 12au7 clear top(side getter)

Then I ran into a slight problem. I don't know where to measure the bias voltage. Looking at the tube socket from the bottom, I measure Pin 9 to Pin 4 and 5 and both are getting 7 volts. Adjusting the trim pot doesn't change the values.

Weird thing though, initially, the vocal was more on the right channel. Adjusting the pot, I got the vocal to be center.

Note: The tube was warm up for at least 30 minutes.

For now, the difference with the modification is amazing. Everything sounds more alive and I like it. But I do wish I can measure the bias voltage and set it correctly. I did search and couldn't find the answer. Any help would be great.

[PinkFloyd]

Apr 1, 2014 22:09:17 GMT zasboy said:

Wanted to get my feet wet with tube amps and decided to pick up a Bravo Audio V2. Using a SuperLux HD 668B headphone, everything sounded much better. I'm not a very detailed audiophile but I noticed a good change and I liked it. I was curious if I can improve the sound qualities that with the modifications that people have done in this thread. So here are the list mods that I have done:

- Replaced both IRF630 with IRL510
- Replaced both LM317 with LM317AT
- Replaced both 2N3906 with BS170
- Replaced the big rear cap with Nichicon 4700uF/35V
- Replaced the two front caps with Nichicon 2200uF/35V
- Replaced 3K resistor with Bourns 5K trim pots(bias voltage adjustment)
- Shorted the two small caps under the volume pot(should have taken out the capacitors and jump it)
- Crosstalk mod
- Replaced 7.5 resistor with 8.8
- Soft start mod
- Replaced China tube with RCA 12au7 clear top(side getter)

Then I ran into a slight problem. I don't know where to measure the bias voltage. Looking at the tube socket from the bottom, I measure Pin 9 to Pin 4 and 5 and both are getting 7 volts. Adjusting the trim pot doesn't change the values.

Weird thing though, initially, the vocal was more on the right channel. Adjusting the pot, I got the vocal to be center.

Note: The tube was warm up for at least 30 minutes.

For now, the difference with the modification is amazing. Everything sounds more alive and I like it. But I do wish I can measure the bias voltage and set it correctly. I did search and couldn't find the answer. Any help would be great.

Hi Zasboy,

Please check your private messages... I have given you the link to the world's expert on these amps. I am sure he will be more than happy to answer your questions.

All the best,

Mike.

[maximalz]

hi sandyk,

thx for this information an the link.

please understand, i know that the bravo/indeed/muse is a cheap chinese poor design. but by the way i search for this mods to save my muse lifetime, that save my money for it - too

so is there any member in this forum they made the mod and his amp works today???  (please tell me)

or is my muse the only one that is not killed by overheating ??

if the mod work - i will do my very best for a giant new greater cooler to save the IRL510's and the LM317A's 

best regards - maximalz

[mrqs]

Gents

I've got recently an amp, which seems to be a newer version of the Bravo 6922 amp (also the seller describe it as an improved design).
It's built with chinese 6n11J tube. The rest is standard: 2x LM317 and 2x IRF630.
My intention is to (at least) replace the stock IRF630 to IRL510.
After switching the amp on, I can hear constand buzz (or self-oscillating like) noise plus tome "tap, tap" sound every 3-5 seconds.

I've decided to try another tube and got Zaerix E88CC.
No more self oscillation, but still (however, much more silent this time) "tap" sound.
The biggest problem, however, is that the E88CC might be broken - one channel is silent and one LM317 seems to be hotter than the other one.
Need to try different tube (as soon as I get something).
Until that - any chance that this buzz can be eliminated still using the chinese tube?

The headphones I'm using are Sennheiser HD598

Thanks in advance for help!

[cpcustoms66]

Ive been reading some other forums on this little beauty, my amp comes in a couple of days. I an new to tube amps but not to electronics. I ordered the IRL510 mosfets to swap and im going to do the supply cap change to the 35v 2200uf as well as doing the crosstalk mod. But some of the other forums have stated that they also had success with 12AX& tubes. I know that the 12 series tubes would be interchangeable, but would rolling to a tube like the 12ax7 with such a higher gain cause problems? does anyone have any experience with what kind of sound difference this would make? Going to be runnig it with a pair of Senn HD598's

THANKS!!

[infernet]

Hi everyone,
I'm new here!
After reading your posts I decided to try and improve my bravo audio...
I made this mods :

• cap input swap with nichicon 3300uf 35v
  
• cap output swap with nichicon 2200uf 35v
  
• swap IRF630 with IRL510
  
• swap LM317 with LM317AT
  

So... I switched it on and the sound was terrible! dirty, with no bass ... I wonder what's happened!!  solders seems to be ok... would you please help me? 
some photos here:






THANKS A LOT!!!!

[nighthawk]

Hey guys,

I am planning to mod my V2 and I would like to ask which mods are essential?

1. Changing mosfets from IRF630 to IRL510 (btw is IRL530 better??)
2. Tube swap (I already did that)
3. Crosstalk mod
4. Cap change mod
6. Changing 3k resistors with 5k trims

Anything else ?

[PinkFloyd]

Oct 29, 2017 4:55:27 GMT mvneufeld said:

Hi,
I do have one more question. Can I replace the IRF630 MOSFETs with IRL530s and not worry about overheating? Is it necessary or just optional to do other mods to deal with the increased heat? Thanks in advance!

I've forgotten quite a lot about this amp but Frans (Solderdude) said:

"You should try to find IRL510 instead of IRF510
the IRF530N doesn't do a better job the IRF630
When using IRL the LM317's get a lot hotter, but the crosstalk and distortion will be much better."

Read more: rockgrotto.proboards.com/thread/5297?page=2#ixzz4wu6iWxCM

I would definitely go with what Frans said, he's a genius with electronics and has designed many good amps.

Mike.