Bravo 12AU7 Mods and Appreciation thread

[arindra]

I got into trouble after performing the crosstalk mod:

The right channel is GONE. It just has brief bursts of distortion from left channel sometimes otherwise it is silent. left channel is working fine. Here's what i did, i cut the copper traces between pin 4 and 5 and interconnect between the two LM317's. Then i soldered a wire between pin 5 and the left channel's LM317 as shown in the picture.I also notice that the right mosfet is not heating up.

Now i don't know whether i need to join the pin5 or pin4 to the right channel's LM317 for it to work ?

Also if i change the stock irf630 with irl540(which has arrived today), is it necessary to change the bias for them?

[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.

[arindra]

Thanks so much solderdude for helping me and everyone out here

It's strange but both channels works now , just by rebooting it !!

The sound is fabulous now never knew what my Sennheiser hd555 were capable of !!!

[suloveu]

hi guys,

After a year of usage, eventually my Bravo amp adaptor broke down.
I've planned to build a simple sigma25 PSU to replace it, but i wonder how much current this amp draws?
Well it is written 24V/2A on the broken adaptor, but I'm not sure this amp draws that much of current...

[arindra]

You are lucky suloveu that your charger lasted a year, mine broke-down in 5 mins on 1st day itself. I opened it up and found a blown capacitor. Never got a chance to replace it as i bought a printer adapter of 24V,2A rating, which works fine.

[suloveu]

arindra, well sorry to hear that mate... I'm sure lucky enough to have it working more than a day.
Anyway, thanks for adding another choice for me to replace the broken adapter

[arindra]

suloveu,

That was just my temporary solution and when i opened it up, i was astonished to find very low quality circuit, with just a frame-type transformer, 4 diodes and a 2200uf cap - thats it.....

I am now building a double regulated 24v power supply using IC7824 and 7924 (and large caps), which should be even better the original SMPS. I shall post the circuit once i finish the testing of the same.

[Deleted]

I am now building a double regulated 24v power supply using IC7824 and 7924 (and large caps), which should be even better the original SMPS.

What voltage and VA rating transformer do you intend using ?
If you change the circuit to use + and -24V it will no longer bear any resemblance to the original, and will need a major circuit redesign, as well as most likely a great deal more heatsinking, compared to the original which is designed for only +24V operation.
Alex.

[biochoker]

Hi there!
First post on these forums! =p
My Bravo V2 amp will be arriving shortly and will preform the mods shown by oohms and solderdude (Very very nice tutorials!)
Before modding i have to find the parts ;D Does someone know where i could get the IRL530 with shipping to Spain?
Ive got a local shop selling IRL530N but dont know if they will work...
The specs are:
Vgs:16v
Qg:34nC
Qgs:4.8nC

Also in the first post Oohms suggested replacing the LM317 MOFETs with LM317A but seems like halfway through the thread it wasNT being suggested anymore so, should i replace it?

Thanks for all input!

[Deleted]

biochoker

You can try:

es.rs-online.com/web/

es.farnell.com/

Saludos

[addam]

Oct 18, 2011 18:43:54 GMT biochoker said:

Also in the first post Oohms suggested replacing the LM317 MOFETs with LM317A but seems like halfway through the thread it wasNT being suggested anymore so, should i replace it?

Following Solderdude's instructions, I believe LM317AT is the way to go. They are National Semiconductor.

www.alldatasheet.com/datasheet-pdf/pdf/8603/NSC/LM317AT.html

[addam]

Oct 5, 2011 8:02:25 GMT arindra said:

The sound is fabulous now never knew what my Sennheiser hd555 were capable of !!!

Agreed! I have the 558s and read on several forums that an amp was not required and would not produce better sound quality. I went ahead and got an amp anyway and am very glad I did. It makes a huge difference!

[Deleted]

Jul 2, 2011 17:20:50 GMT tomco said:

It uses a pair of IRF630N's and LM317T's.
The input cap is an Elna 25v 1800uf
The output caps are Rubycon 25v 1000uf.

Hi, I've ordered the same red XY Hi-Fi amp. Could you give some size info about the used capacitors? Especially about the lead spacing, so I can buy replacement caps before the amp arrives.
I guess the caps are 12.5 mm diameter and 5 mm lead spacing?

[addam]

Would anyone know if all the mods can be done except for the replacement of the 6,800uF/25V --> 3,300uF/35V or is that replacement critical?

What negative effect would it have if the 6,800uF/25V was left in place?

[Deleted]

Oct 24, 2011 18:01:16 GMT addam said:

What negative effect would it have if the 6,800uF/25V was left in place?

As far as I can see the PSU voltages of these amps are 24V. With a 25V input capacitor there is not much room for an overvoltage left. With some bad luck the capacitor may die.

[addam]

Thanks for the help. I have another question. I am sorry if my questions are very trivial but I am not an electronic engineer and to be quite honest, don't really have a clue as to what I am doing. I try to follow instructions however to the best of my ability.

I have been following Solderdude's pdf guide but got a bit confused when it came to the TSR 1-2465 mod. Could someone please have a look at the pics I've included and let me know if it is correct? I feel I have done something wrong.

The right pin of the TSR is connected to the positive of the big power cap. The middle pin is connected to the negative side of the 100uF cap. The left pin is connected to the Shotsky Diode and the positive side of the 100uF cap. Does this sound right?

Please click the pics to enlarge.







EDIT:

Okay, done all the mods and everything is working like a charm. The sound quality is quite simply stunning! No distortion, no crosstalk, perfect high frequencies.

I would like to thank everyone who contributed to the modding of this little headphone amp especially Solderdude whose patience and knowledge was invaluable.

EDIT:

So bad news

Amp died today after only 1 day of working. I am not sure if it was something I did or not. I replaced the Tube for another one I received. Same make and model.

I then wanted to tune the pots. I did the left one, everything fine and then when I went to go do the right, the amp LEDS (red and blue) both switched off.

The tube filement is still glowing but the amp is dead.

Also when I plug the power cable into the amp there are small sparks... that is obviously not good.

Any ideas?

EDIT:

Looks like it was the blue LED that died. Just in case someone else gets this problem. Short the Blue LED and it will work again. Thanks to Solderdude for the info!

[Deleted]

Oct 24, 2011 11:42:38 GMT @weissglut said:

Jul 2, 2011 17:20:50 GMT tomco said:

It uses a pair of IRF630N's and LM317T's.
The input cap is an Elna 25v 1800uf
The output caps are Rubycon 25v 1000uf.

Hi, I've ordered the same red XY Hi-Fi amp. Could you give some size info about the used capacitors? Especially about the lead spacing, so I can buy replacement caps before the amp arrives.
I guess the caps are 12.5 mm diameter and 5 mm lead spacing?

The amp has arrived:


Power cap: ELNA RJH 1800 uF, 25V, 12.5mm x 35mm, 5mm lead spacing
Output cap: Rubycon ZL 1000uF, 25V, 12.5mm x 20mm, 5 mm lead spacing
Power switch: Salecom T80-T
MOSFET: International Rectifier IRF630N
Linear: STMicroelectronics LM317T

Jacks and volume control seem to be some cheap stuff.

EDIT:

Jul 2, 2011 18:05:27 GMT @solderdude said:

I suspect the outer ones will be 1k (brown, black, black, brown, brown) and the output resistors 100 Ohm (brown, black, black, black, brown)

That's correct, I've measured them.

EDIT2:

Jul 1, 2011 16:48:32 GMT @solderdude said:

e: it appears to have bias test points (like in the sunrise project)

Confirmed. They are labeled TP1 (near the valve) and TP3.

[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.

[Deleted]

The output resistance does not have to match the headphone impedance.
read my tutorial for clarification :
www.mediafire.com/?ms4k8wuqt18x8s3

100 Ohm with this type of amp means the max. output power will be quite low for low Ohmic headphones.
clarification for power and impedance:
www.mediafire.com/?jdpaj1r17x1sos5
Some headphones (AKG and some others) like 100 Ohm (or 120 Ohm) output resistance.
Some like close to 0 Ohm, some sound best somewhere in between.

not being able to adjust on one channel usually means the tube has low emission on that side.
If you have another one please try.
Best to have a tube with 2 channels both having about the same bias current (small pot in about similar position)

you can increase the resistance of the adj. pot or alter the anode current source resistor.
In both cases it means extra compensation to correct a dodgy tube.

radio interference with all open frame tube amps becomes worse with lower anode currents.
The higher this current the lower the influence as the 'internal' resistance of the anode circuit becomes lower.

Shielding the tube (shield should be connected to ground) with a very fine mesh or metal tube may help. The circuit board itself still is open and vulnarable.

103 = 10k (10 with 3 '0's behind it)

[Deleted]

Nov 9, 2011 17:35:21 GMT @solderdude said:

100 Ohm with this type of amp means the max. output power will be quite low for low Ohmic headphones.
clarification for power and impedance:
www.mediafire.com/?jdpaj1r17x1sos5
Some headphones (AKG and some others) like 100 Ohm (or 120 Ohm) output resistance.
Some like close to 0 Ohm, some sound best somewhere in between.

OK, thanks for clarification. I've already thought that the only reason may be to increase power output but I just wanted to get sure if I'm missing something. So I have no need to lower the output resistance because this amp is able to easily blow my ears at 12 o'clock volume knob position

I don't have any other tubes, because this is the first tube amp I own. The tube in the amp is 6N1-J. According to google results I can exchange this tube with 6DJ8/6922/ECC88. Is this correct? I don't want to pay a high price for an exchange tube for this cheap amp, can I get a decent one for ~15 €?

[Deleted]

Mike is an excellent source for tubes.
6n23, ECC88, 6922, 6dj8
You can even try PCC88.

Only if Mike can't help you I have some used, but good (tested) Philips 6jd8-ECC88 left.
Even have RMAA test results of 6922EH and Philips 6jd8-ECC88 in a G2.

[Deleted]

Sorry for my perhaps dumb question (see my post count): Mike is a user here?

Today sucks... I've changed the capacitors now:
I've ordered a Nichicon audio grade 6800uF 35V, which I'm using as power cap now. And I've found some Jamicon 2200uF 35V caps in a box as output caps.
And what's the result? The power supply cannot load the power cap. You can see the LED switching on and off. The power supply probably has a short circuit protection (I can hear a relais noise or something like that).
I've used hot-melt adhesive to fix the caps. Not sure if I can solder them out again.

[Deleted]

No need to take out the 2200uF again.

Only the 6800/35 must be taken out.

It's why I have a 1000uF/35V in my amps.
Having more uF is completely pointless as a switchmode PS already has enough with 100uF.
(the refresh rate of a normal powe cap in unregulated power supply is 100 Hz, in a switchmode the cap is replenished in a 50kHz rate or higher.
Faster than any audio signal.
a bigger cap MAY reduce a small ripple in some cases but can also make it WORSE.
Some say the bass benefits, but it is class A and a regulated power supply.
It's a subjective thing.
measurements I did did not show any difference in frequency range (from a few Hz to 100kHz) even without any power supply caps (0 uF power cap).
Still people seem to hear differences...

solution:
A: get a bigger power supply.
B: Take out the 6800/35 and put in a 1000uF or 2200uF/35V or see how it fares without one.

Sorry my bad.. Mike = the big cheese, the head honcho, the main man, master admin... Pink Floyd.
Drop him a PM...
Might take a while for him to answer... busy guy.
If he doesn't reply within a week send him a kind reminder later.

[Deleted]

Nov 9, 2011 21:29:28 GMT @solderdude said:

No need to take out the 2200uF again.

I know

It's why I have a 1000uF/35V in my amps.
Having more uF is completely pointless as a switchmode PS already has enough with 100uF.

I've ordered the cap before the amp has arrived from China. I've read somewhre taht the Indeed/Bravo/ has such a cap and I've already wondered why such a big cap is in a headphone amp. It should be enough for a power amp. Nevertheless I've ordered it because I've thought there is no real reason to use a smaller than stock one.
Now I know the stock one is 1800uF and I've wondered if should use one of the 2200uF I've already had. Long story short: I put the 6800uF in because I've bought it and had no other use for it

solution:
A: get a bigger power supply.
B: Take out the 6800/35 and put in a 1000uF or 2200uF/35V or see how it fares without one.

I'll see if I can get it out again.
PS: It works fine with a lab power supply.

PPS: thanks for the nice conversation

[Deleted]

Nov 9, 2011 18:57:24 GMT @solderdude said:

Mike is an excellent source for tubes.
6n23, ECC88, 6922, 6dj8
You can even try PCC88.

Only if Mike can't help you I have some used, but good (tested) Philips 6jd8-ECC88 left.
Even have RMAA test results of 6922EH and Philips 6jd8-ECC88 in a G2.

I was bored last night, so I've ordered one from eBay: Philips ECG JAN 6922 (USA). Let's see...