Bravo V2 :Summary mods necessary ;-)

[floriangerard51]

Hello!

I'm new on this forum and that's a huge source of informations! Thanks all for helping others and sharing stuffs that can be very useful....I just bought the Bravo V2 amp and would like to mod it. I search a lot about the subjet and as the genric amp (indeed, bravo...) have several models i would like to be sure of the mod that i have to do:

1. Soft start : replace 1K with a 10K resitor between the LEDs and place parallal to the red LED a 100uF/10V cap

2. Ohmms mod for crosstalk 2 cuts on the board and 1 blue cable

3. Bias voltage setting: replace the 3k with a 5K pot and 1k in serie

4. Time Damaging cap: replace the 6800uF/25V with a 3300uF/35V Nichicon

5. Better extension: replace 1000uF output cap with 2200uF/35V 105°c Nichicon muse

6. Better extension: replace IRF630's with IRL510

7. Put 2 bias cathode caps 470uF/10V electrolyte. But anaybody has a picture of the mod please? to see the exact pins connections...

8. Change input cap 1uF-> Wima 4.7uF/63V cap not really necessary?

9. Change the LM317's with LM317AT

10. Place big aluminium/copper heat spread and reroot LM317's on it. Best thing is to place the resistor closed to the LM for better result? and just get 2 cables connection of soldering directly the resistor. But the value is 7.5 right or not??? No need to desolder the old ones as there will not be connected with the LM's...

11. Change the output resistor from 47 to 63 true? Have you any favorite trademark for music purpose? Vishay's?

12. Best is to buy or DIY a linear PSU for the amp. I'm looking for a 338 based one kit or DIY LM1083 based PSU. Rating are above limit with respectivily 3A and 7A that's enough. But what is the best option?

13. Loads of people say that directly feeding heaters with a small PSU will increase the amp perfs. So i saw a small TRACO mod but better is to get directly a LM317 setup with 6.3V and plugged it directly on the big heat spread on the board of the amp no???
Anyboday has then the good plug pin for the + and - of this mod? Is it compatible with the cut of the 1. for crosstalk?

14. What are the mod that don't really change the sound please?
And if anybody has good pictures of the mods he realized then share it please ;-)


Thanks a lot guys for helping me. This is so great to mod a small amp. I'm sure it will give me the DIY envy and do another try with a bigger amp ;-)

[Deleted]

The most sound changing in order of magnitude:
1: IRL510 (highs extension)
2: crosstalk cut
3: bias voltage setting (depends on tube)
4: heater mod (distortion reduction)
5: output resistance change.
6: output caps
7: input caps

V2 (12AU7) has no cathode resistors so cannot place cathode caps.
the other mods don't have sonic implications, although some may surely feel otherwise.

[floriangerard51]

Thanks for your response!

I'll get the parts for the mods. But can you tell me about the heater mod if it"s better for a TRACO SMPS supply or better to use a LM317 setted to 6.3V ? For this mod have you any picture of the pin + and - connections to the heater?

For the output resistance what's the better value? 68ohms? i'll use high impedance headphones like HD650s

For the bias voltage setting have you any pictures of the mod? Cauz i need to get a 1K reistor + 5K pot insteed of a resitor so that's not quite obvious to get it on the small pcb...

And sorry for my english by the way ;-)

PS: I'm asking questions about the DIY PSU to use with the bravo, there options between the LM317/337, the LM338, the LT1083 and a simple transfo+diodes+caps.....What's the range of the supply voltage? If i get 23V is that bad?

[Deleted]

Traco is simplest.
With an LM the LM will get VERY hot even on a large heatsink when fed from 24V.

For HD650 I would install 27 Ohm (wouldn't place anything lower in it)

no pics as I don't have one of those amps.

22V to 28V is no problem (in case 35V caps at the input is used)
Bias voltage should be adjusted accordingly.

[floriangerard51]

ok you're right! LM will see a 24-6.3V = 17.7V so depending on the heating current it should be dissipating a lot.
I'll get the traco mod ;-)

For the PSU for the Bravo if i only use a transfo+diodes+caps to get a 24V it should be great and enough or the use of a regulated chip like LT1083 or LM338 is a plus for heating and protection purpose???

[Deleted]

The power supply must be regulated.
Just a trafo, rectifier and caps will result in a low level hum as this design has a very poor PSSR.
The regulator should have at least 3V across it, so unregulated at least a 27V voltage.

[floriangerard51]

what do you think of this type of power supply:
cgi.ebay.fr/Low-noise-High-Current-dual-power-supply-LT1083CP-kit-/160664659893?pt=LH_DefaultDomain_0&hash=item25685c27b5#ht_5892wt_1031

or this:
www.ebay.com/itm/5-Amps-Voltage-Regulator-Module-Out-1-5-32V-Based-LM338-/130646831374?pt=LH_DefaultDomain_0&hash=item1e6b28710e#ht_8880wt_982

thanks

[floriangerard51]

Hi,

I just received my amp and all the parts from MOUSER....

list of mods:
1: IRL510 (highs extension)
--> DONE easy

2: crosstalk cut
to do

3: bias voltage setting (depends on tube)
I have only 5K pots do i need to put a 1k resistor plus the pot instead of the original resistor?

4: heater mod (distortion reduction)
I can't find anything about this mod on the 17AU7!!! only on the indeed pdf by solderdude and this is a different PCB ! Can anyone help me?

5: output resistance change.
to be done as soon as possible...

6: output caps
--> DONE easy (my fine gold NICHICON are too big to replace the originals so be careful of the diameters before buying!)

7: input caps
--> DONE easy

i'm also building a supply power 24V 3A with a JLH POWER SUPPLY PCB bought via ebay and i'm still waiting for a LT1083CP which is not easy to source for personnal buy (like impossible via radiospare, not available on FARNELL, mouser...) any suggestion?

[Deleted]

3: bias voltage setting (depends on tube)I have only 5K pots do i need to put a 1k resistor plus the pot instead of the original resistor?

Not obligated but recommended.
mounting only the 5k pot (wiper and one of the other pins) can be done.

4: heater mod (distortion reduction)I can't find anything about this mod on the 17AU7!!! only on the indeed pdf by solderdude and this is a different PCB ! Can anyone help me?

I will need good pics of the PCB topside and bottom side.
Where do you intend to mount the LM317's (as in the Miridiy mods ?)

[floriangerard51]

Hi,

Ok then i'll get the 5K pot and the 1K resistor soldered and then try to place that combo instead of the original resistor. I'll make good pictures of that mod for people interested of...

For the heater mod, pictures would be welcome ;-)
I have bought some big black aluminium spreaders and i'll place them on each side of the amp. I have solder the originals IRF630 heat spreaders on the bottom side of the PCB and use them only to place a screw between them and the new big spreaders...

I also solder cables on the LM's and IRL's PCB pins....And as soon as i'll have the big spreaders fixed to the PCB i'll try do cut the smallest lenght of cables as LM's should be cabled with minimum length for it's resistor and cap in the adjust pin true?!

I already have the heater mod TRACO soldered (i'll make picture tomorrow) and i only need now to have picture of this mod with the bravo V2 amp....

Also is the crosstalk mod compatible with the heater mod??? coz i saw that ohmms has cut the connection between the two pin of the tube but what's the blue cable coming from one LM317 role?

[Deleted]

The heater mod solves crosstalk and heater issues at the same time.

If you post good pics of top and bottom side of the PCB I can draw in instructions.

Make sure the LM317 and IRL's have insulation sets and that these are fitted as supposed to.

[floriangerard51]

Here is the starting point, desoldering the spreaders and the LM's and IRF's... ;-)


IMG_0245 (Small) par florian.gerard51, sur Flickr

[floriangerard51]

and the bottom PCB view with the spreaders bceoming fixed mounted for my new big spreaders and the soldering of the cables....

Do you also recommend to get the smallest length for cables???


IMG_0248 (S) par florian.gerard51, sur Flickr

[floriangerard51]

i'll get better pics tomorrow....and better i'll make a tutorial to mods entirely the BRAVO V2 as it could be very good for others to get directly the good stuffs to do...I spend loads of time over the web to compile all the datas and it could be a good thing to also have a tuto like the one you did about the INDEED G2 amp ! with pictures ;-)

But for the moment i had to much time....This weekend i'll get my EOS7D for best pictures! And also has i'm building the linear power supply i'll put it inside the tuto ! that's a great amp ! Not as good as my little dot MKIII but also much more smaller! I'll sell my LD MKIII next week and buy a LA FIGARO 339 for my home setup. The BRAVO V2 would be for office working hours....

[floriangerard51]

ok i have checked the crosstalk mod and before the mod (correct me if i'm wrong)

the two LM317 outputs are connected together and goes to the PIN4 which is also connected to PIN5....So the two heater's PINS are connected to the two LMs together (in parallal)

Then i do understand than cutting the 2 pcb wires and addind the blue wire will connect each heater seperatly and then solve the crosstalk....But why the manufacturer have connected these LM together???that's curious??? to balanced the charge???

So if i'm right for the TRACO mod, i'll have to supply the PIN4 and PIN5 together??? with the output of the traco power (the SB140 ending to the PIN4). And connect the 100uH to the + of the input cap and the middle traco pin to the ground....
I'll have to cut the pcb wire going from the left LM to the pin 4 and then cutting also the right side from the LM (like the ohmms crosstalk mod)

But if i still have the tube PIN4 and PÏN5 connected together we would have crosstalk no??? or that's because we don't goes from the 2 mosfet to the LM to the heaters that we don"t have crosstalk???

Also if we use the TRACO instead of the LM's what should we do with the LMs? just leaving them

[Deleted]

keep the wires running to the LM's and IRL's as short as possible,
They can be thin wires, there are no substantial currents present.

Why they decided to connect the heaters and create crosstalk is probably because, both heaters would still have the same voltage on it when one channel was not 'preset' above it's minimal value.
In this amp the crosstalk mod (cutting the connection wire) alleviates the crosstalk problem but doesn't solve the distortion issue.
Traco mod does by ensuring the minimal voltage drop that is needed for an LM to work linear is never reached anymore.
Without the Traco mod the LM317 'switches off' each time the output voltage swing reaches this minimal voltage.
This happens when playing a bit louder or driving inefficient headphones.
The point where this happens depends on the bias voltage setting which, in this amp (standard) cannot be set and you are thus dependent on tube quality.
This mod also makes sure the heaters always get the correct VOLTAGE so they are more stable and easier to adjust.

Traco mod:
connect pin 4 and 5 together again (so the cut track is undone essentially)
disconnect the LM circuit completely from the heaters (ADJ and GND pin via resistor)
Connect the anode of the SB140 to pin 4/5
middle pin of the Traco to the - of the big power cap (as close as possible with shortest possible wires)
+ of the Traco through 100uH (may be any value between 10uH and 470uH as long as it can handle the DC current) to the + of the big power cap.

You can leave the blue LED connected to the heaters.
If you want to measure heater voltage you can (because of this) only measure it with the tube in it.

The LM's are an essential part of the class-A (single ended) output circuit as well as providers for a constant CURRENT for the heaters.
The heaters, however, would prefer a constant VOLTAGE.
They have a double function so the parts count will be smaller.

Now for the LM's they have to be connected to ground now instead of to the heater in exactly the same way as they were connected to the heaters.
Meaning ADJ pin to ground and GND pin via resistor to ground.
Do this for both channels.

Because there is a LOT more voltage across those LM's and the same current flows the power (IxU) is considerably higher and thus they get MUCH hotter as well.
Therefor the heatsink for the LM317 must now be even bigger than those of the IRL's.

[floriangerard51]

Hello guys,

HEre is the new state of the amp
list of mods:
1: IRL510 (highs extension)
--> DONE easy

2: crosstalk cut
--> DONE easy

3: bias voltage setting (depends on tube)
--> DONE easy made of 1KOhms resistor + 5KOhms pot

4: heater mod (distortion reduction)
I can't find anything about this mod on the 17AU7!!! only on the indeed pdf by solderdude and this is a different PCB ! Can anyone help me?

5: output resistance change.
not yet,

6: output caps
--> DONE easy (my fine gold NICHICON are too big to replace the originals so be careful of the diameters before buying!)

7: input caps
--> DONE easy

8. Power supply:
--> almost done i'm waiting the LT1083CP....;-)

This amp is awesome for the price!!!! ;-)

Here some picts of the mods. I'll make a tuto as soon as everything is finished! Like the one solderdude did for the indeed G2 ;-)

Comments: Solderdude you will find one good pic of the backside of the PCB could you described me the TRACO mod??? please???

The heat spreaders on the sides are running very very hot with bias setup to 13.5V....i can't leave my finger more than 5secs...normal?

Also the heater pin 4 have like 5.5V and the heater pin 5 have 6.2V that's normal???

here the link for the pics:
dl.free.fr/h2TSu6sg0

[Deleted]

I have the distinct feeling you didn't read reply #15 where I describe what needs to be done.

The LM's they have to be connected to ground now instead of to the heater in exactly the same way as they were connected to the heaters.
Meaning ADJ pin to ground and GND pin via resistor to ground.
Do this for both channels.

Both heaters need to be connected again so can't possibly have different voltages anymore when the heater mod is done.
the voltage will be around 6.25V

The pictures don't show the heater mods are done yet.

Even with big heatsinks the temperature will still feel hot.
The heatsinks are big enough though so temperatures should remain below 45^OC.
Much bigger than the ones I used on the G2.

Note:
When using the isolator kits with mica insulators heatsink-compound must be used.
When working with the silicone it isn't needed and heatsink-compound won't aid in better cooling.

edit:

Heater mod in your case:


heater mod with standard 12AU7 board:


You can use this pic in your tutorial with the permission of Oohms (his pic, my directions)

This should work.
Let's hope I didn't overlook something.

[floriangerard51]

I'll get the mod done tonight....i'll do some pics and let you know if it sounds better ;-) That's quite interesting to understand the meaning of the amp circuit ;-)

One question, for the resistors, if i use the HD650 (which are 300 or 600ohms i don't remember) what type of resistor should i use? As you mention before lower resistor than originals??? from 47 -> 33

As you said i didn't read your reply post number 15 ;-( i'm sorry....so young so fast....;-(

Can i use the pics and also some of your comment on the PDF INDEED G2 mod to build the new tuto PDF for the 12AU7 i'll use my pics for most of the work but also some of the pics from ohms as i didn't make pictures of the before mods...

Thanks

[Deleted]

If you mention the source of the pics / info you can use them in your pdf.
Can't speak for Oohms but when you give him the deserved credit he probably won't mind as it is not for commercial enterprises.

Output resistance:

HD650 sounds best on low Ohmic outputs. (HD650 is 300 Ohms b.t.w.)
If these are the only HP's you have, simply solder in a 1 Ohm output resistor.
If you have low Ohmic headphones as well or intend to buy some in the future go for 33 Ohm minimum.
For AKG K701 (and also some other HP's) place 100 or even 120 Ohm.

If you think the heatsinks are allowed to become even hotter than they are now, you can consider increasing the class-A current.
This allows the use of lower output resistances even when low impedance headphones are used.
The output resistance can be made lower than 33 Ohm in this case.
In this case the resistors connected to the LM's need another value.
That's all that needs to be done.
This can ONLY be done when the heater mod is performed.

Important NOTE:
Keep the wires to the TSR (input and ground) as SHORT as possible and directly connected to the pins of the big cap.

[floriangerard51]

Traco mod done ! that's just awsome !!!! ;-)))))) I now will solder the 33 ohms resistors....For the heatsinks i'm going to look for biggers one next week and increase the current ;-) Just to get the best of this amp ! What type of resistor should i use for the LMs???

I made a comparison with my LD MKIII and that's not bad ;-) there is more soundstage on the LD MKIII and highs are very much details on the MKIII but for the price of the BRAVO + mods that's not a bad Price/perf ratio !

And thanks to guys of this forum this amp is awsomeeeeeeeee

I'll see in the new few months with my friend to make a different PCB with the LMs on the sides and the IRL also.... Better space for caps....I'll make you know about this next project.

This week will be the week of the tuto making ;-) and i'll post you the link to check out if there is nothing wrong then male it visible for everyone...

I hope other would choose to make this mods as it's amazing. Tube world is amazing!

[Deleted]

What type of resistor should i use for the LMs???

The value will depend on:

a: size of the heatsinks (^oC/W)
b: maximum temperature of the air around it (room temperature in the summer).
c: maximum temperature you want the heatsinks to become.
d: minimum headphone impedance to be used.

[floriangerard51]

well i'll go for heatsinks like to 2-3°C/W like the ones i have but in the double height
the room temperature will be set to 28°C as in summer that's quite hot in Grenoble(France) so summer = 32°C inside house and winter = 17°C inside house....28°C should be considered to be good
The heatskinks can run 45°C max
The min impedance headphones would be 40ohms but most of the time i'll use the HD650. Just to be sure if i plug a K701 one day ;-)

i'll check on farnell and give you the dimensions and the spec °C/W....

[floriangerard51]

what do you think of something like that ? but with fans running at 600rpms it should be very quite no?! one on each side.

www.akasa.co.uk/update.php?tpl=product/cpu.product.tpl&no=181&type=CPU%20coolers&type_sub=Low%20Profile&model=AK-CC1101EP02

[floriangerard51]

Here are the pics of today mod:
dl.free.fr/k5IDyKOoN