Bravo Headhone Amp Modification

[Kornbread]

Posted this continuing adventure on https://diy.midwestaudio.club/discussions. PE sold a metric schitt ton of these tiny hybrid tube/ss headphone amps, not to mention the bay and the bigA place, so I figured there would be some interest here.

This entire episode has been brought to you courtesy of a f*ing virus.

Some of you guys might recognize or own this cheap head amp. Bought two of these many years ago from PE for ~$70. They can now be found all over the net for about the same price. This particular variant uses the 12au7 instead of the more popular 12ax7.
Definitely, IMO, not a highly resolving sound but very easy to listen to, powerful, and fun type of sound. My Aune and both boy's Schitt and cmoy headamps are more resolving. Anyhow, the tube in one of them turned white and it came to a halt. A new tube did not remedy the situation.
I've been on [https://rockgrotto.proboards.com/")] for years, rarely posting, but none the less enjoying the chatter.
Time to revisit an old mod thread specifically aimed at this cheap little headamp. https://rockgrotto.proboards.com/thread/5297
As far as mosfets, voltage regs, etc., I'm really liking ... the big M place ... they have a huge parts selection and orders are always well packed and arrive on time. Other retailers take note!
Time to mod. New irl530 to replace the irf630 that rolls off the highs, better lm317at (later changed to lm317t due to availability) voltage regulators, pair of 5k trim pots to dial in the bias which comes way off (generally 12v vs 16v) from the factory, and real Nichicon caps to replace the oem imitation Nichicon caps. There is also a crosstalk mod involving cutting a trace and solder a jumper. Still have the old original to compare it against.

[Kornbread]

Solder sucker and other stuff came in today but there were more important tings on the agenda.
The parts list is really simple. Maybe I can pull up the order from the bigM place (a few of these parts can be sourced from PE) and post that if this winds up being worthwhile.
I agree with Ken, the Bravo is easy on the ears but the better irl530 mosfet isn't supposed to roll off the top end like the stock irf630 so this may not be the answer for someone wanting to tame hot recordings. As is, or as was, it had a fun and inviting sound, totally opposite of an analytical pick the fly $hit out of pepper sound. Hopefully these mods keep that inviting sound.
And I need to weight the oem capacitors vs the real Nichicon replacements. One post states that the 'imitation Nichicon' caps weighed noticeably less than their real replacements. I've seen pics of caps on some of those cheap Chinese tube amps cut open where there's nothing but a tiny cap glued into a large empty cap body.
Update; no surprise, the larger in value but same physical size 2200uf caps did weigh more that the 1000uf they replaced. The cartridge tracking force scale could not weight more than 5 grams. The large caps weighed considerably more than that so they did not get weighed.

[Kornbread]

Getting old sks.

What are you looking for?
Magnifying glass.
Why do you need a magnifying glass? Is it time for bifocals?
No.
Do you need to borrow my bifocals?
No.
Do you need to borrow my reading glasses?
No. Quit bothering me.
Thirty minutes later after several failed attempts at desoldering ...
What are you looking for?
Reading glasses ... and cue comments from the peanut gallery.

[djg]

I had cataract surgery some years ago. Amazing vision improvement, but I can no longer focus super close, I must maintain a bit of distance.

[Kornbread]

In my case it's karma. The wife has always worn glasses or contacts and of course I'd tease her about being older than I (she's 1 year older). Now I'm the one eating crow. Anyhow, glad surgery helped, it's amazing what they can do today.

[Kornbread]

After double triple checking everything, the amp was still doa. The board is cheap, traces thin, and the unleaded solder takes a lot of heat to melt. Had to set the solder station at 430*c. to get a good melt. If you touch the board anywhere other than a solder joint at that temp, poof. Checked every solder joint and trace multiple times. Nada. After replacing everything on the board, many twice, and getting nowhere, I decided to measure the old resistors. So much for reading schematics101. 7r5 is 7.5∩ no 7.5k. ∩. Same with 47. I had replaced the oem resistors with 47k and 7.5k Dales. AFter several days of struggling, problem solved.

Board with oem resistor values.

[Kornbread]

For the crosstalk reduction mod, cut the traces at the red circles. Then jump from tube pin 5 (heater) to the top (as in picture) post of the LM317T. The short blue jumper top center and longer green jumper were suspect traces. For ease of bias adjustment, drill two small 1/8th" holes directly above the 220∩ resistor so a multimeter probe can touch the left (as pictured) solder joint. Visit the aforementioned rock grotto site for more detailed information. https://rockgrotto.proboards.com/thread/5297

[Kornbread]

5k trim pots are in. One outside leg of the 3 leg pot will need to be severed leaving one outside and one middle leg. Be sure to sever the same outer leg as this will affect the direction of adjustment. Except for the reused resistors (face palm) all others are .5w Dales. The 25v (why 25v when the power supply is 24v? Not much margin for error) Nichicon (?) caps are replaced with real Nichicon 35v/105* caps. As mentioned in another thread, going larger than the 6800uf oem value is not favorable. 4700uf for the power supply cap and a pair of 2200uf replacing the too small 1000uf oem value. Replaced the 1uf input caps with 1uf film Wima. The Wima caps are the pair of red Chicklets sitting between the tube and volume control.

[Kornbread]

Those chips run hot. Carefully drilled some extra ventilation holes above the mosfets to hopefully improve airflow and for ease of access to the trim pots.

[tvrgeek]

Getting old sks.

What are you looking for?
Magnifying glass.
Why do you need a magnifying glass? Is it time for bifocals?
No.
Do you need to borrow my bifocals?
No.
Do you need to borrow my reading glasses?
No. Quit bothering me.
Thirty minutes later after several failed attempts at desoldering ...
What are you looking for?
Reading glasses ... and cue comments from the peanut gallery.

Yes getting old stinks, but I do not like the alternative.
I find the flip up headsets to be invaluable. Get the set with different power lenses. I was OK until after cataract surgery, and then my focus is about 5 feet. As I have stigmatism and prism, I can't wear dime store reading glasses. If you can, then you can get them in several powers and swap around depending on the task.
I also got a little USB microscope which helps when working on some SMD parts.

I still use my old Weller station 700 degree tips, 60W. Pick the tip with the right dimensions. You get on and off fast so as not to lift the pads. Never more than a second on a joint. A little paste flus helps with older joints and keeping the tip wetted helps. Before I go to unsolder, I and a tiny bit of new. Something about how it crystalizes over time. I suffer with the little red R/S bulbs now as I have not been able to find the big blue suckers for years.

[Kornbread]

Yep, using the little red sucker bulb. Actually have an RS desoldering iron with the bulb built on that works pretty good but the tip was too big for this job nor do I think it would have gotten hot enough to melt the lead-free solder. Found that adding a little leaded solder to the iron tip helped melt the oem joints. A learning experience fro sure. Vision issues aside, a good light and a pair of helping hands would come in handy.
Sob getting old story, but not so long ago I had to crawl under the house to repair a water leak. I'm a bit claustrophobic to begin with and of course the leak was about as far away from the entrance as possible. Wiggled waaaay back there. The floor is inches from my chest, can barely move my arms, and when I get there, the water line is literally inches away from my nose. It's all a blur, I can't even clearly see the water line. Talk about MAJOR internal struggles. Trying to work on and fix something I can't see while fighting back the growing urge to panic. Topping it off was the water running in my face and ears. Yep, getting old suks but like you said, beats the alternative.

[Kornbread]

Spent several hours listening to the modded vs stock Bravo head amp. While I was supposed to be comparing differences, I got lost in the music. The verdict ... the modded Bravo is now my favorite head amp.

Notes ...

Modded has a top-end. Maybe not the sky is the limit top, but it is now present and it's not over the top or highlighted. Much more linear freq response than oem. This might be something to keep in mind if using this amp to make unlistenable mixes listenable. Played some 80's hair bands and what can often be described as strident highs on some systems, was not an issue with the modded head amp. It still has that magic midrange but now there is treble and clarity. Voices retain that charm, not as creamy as oem, but they are so much cleaner/clearer now. Like a clean window vs a dirty one. (after an extended listening session last night, I now think vocals are much improved over the oem rendering while still offering that tube goodness!)

At first listen bass seems to have taken a back seat to the rest of the presentation but give it a little time, the bass is there and stronger than oem in the bottom/very bottom end. Modded bass is more controlled everywhere, especially the bass/mid bass? region oem emphasis. Listening to EDM, yep, much better modded, dare I say more enjoyable. Modded is way tighter where oem is loosey goosey. Bjork _Hunter _ excites that wooly part of the oem bass and it can override the rest of the performance. It's still there modded but cleans up nice and tight.
Oem more closed-in, smaller space, where modded opens up the space. More dynamic.

For someone on the fence about hacking up their amp, do the (Mod1 ~$14) buy the better caps, they are a reliability concern, along with a pair of mosfets and trim pots. If you do not like the sound with the new mosfets, put the old ones back in and leave the trim pots thereby retaining the ability to adjust bias. If you want the complete wash n wax (Mods2 +$12) add the Dale resistors, Wima caps, and do the crosstalk mod. Although the crosstalk mod includes cutting two traces, they can be undone with a jumper. The (Replace) mods were replacing some components that may, or may not have been damaged due to a bad tube. The parts were super cheap so it was feasible to simply replace suspect parts than mess with trying to diagnose.

To make it easier, a parts list is included. Some of these parts can be sourced from PE, some cannot. Due to PE's rules, I have removed any link or reference to another vendor who may carry parts similar to those PE carries. I encourage checking PE for parts availability before sourcing elsewhere.

[Whitneyville1]

Kornbread, Thanks for the hard work on these headphone amps that needed it. Several years ago I bailed and got the Bottlehead Labs battery powered headphone amp (the 9 volts last a couple of years surprisingly) which work very well with Sennheiser 'phones. I saw a U-toob vid saying audio gear is going obsolete-being replaced by mono Alexia speakers and Idiot phones and such. 21st Century no-fidelity gear. Just like phones replacing cameras (NOT!).
I coulda/shoulda told you the trick about lead solder on RoHS "solder" to re-work surface mount devices without a re-work station. "Vaping traces" was already a way of life nearly 20 years ago at Fish-Lo-Ka-Tors Inc. on the re-work line. Liquid flux is about required to keep from lifting traces, and I cheat, using used non-insulin diabetic drug syringes (27 ga. needles Dremled square) as solder suckers. I can get them into places only a $4000-6000 constant vacuuming re-work machine needle will get into. Wonder why Heiko knows that???
FWIW, my Bottlehead Labs headphone amp is easily 4 times the area of these little boxes to give room for fingers and real caps and stuff. It's no longer available either, sorry. I honestly don't know of a decent headphone amp for under $400 ready-to-go now with $400+ headphones. I'm not sure I know of any decent $400 headphones for sale today either. Prices have gone crazy.

[Kornbread]

Kornbread, Thanks for the hard work on these headphone amps that needed it.

Just to give credit where credit is due, AFAIK, the initial modifications appeared in https://rockgrotto.proboards.com/ several years back. This is just a rehash of their hard work. I wanted to do the mods back then but other things caught my eye. For the past several weeks, I've had plenty of free time and no paycheck. This was cheap, easy, and IMO, worth way more than the sum of the parts.

Several years ago I bailed and got the Bottlehead Labs battery powered headphone amp (the 9 volts last a couple of years surprisingly) which work very well with Sennheiser 'phones. I saw a U-toob vid saying audio gear is going obsolete-being replaced by mono Alexia speakers and Idiot phones and such. 21st Century no-fidelity gear. Just like phones replacing cameras (NOT!).

I am honestly amazed, or is that ashamed, at what passes for musical reproduction these days, but ... have you actually listened to some of the stuff they are calling music today? Maybe it's better not heard.

I coulda/shoulda told you the trick about lead solder on RoHS "solder" to re-work surface mount devices without a re-work station. "Vaping traces" was already a way of life nearly 20 years ago at Fish-Lo-Ka-Tors Inc. on the re-work line. Liquid flux is about required to keep from lifting traces, and I cheat, using used non-insulin diabetic drug syringes (27 ga. needles Dremled square) as solder suckers. I can get them into places only a $4000-6000 constant vacuuming re-work machine needle will get into. Wonder why Heiko knows that???

Using a syringe sounds like a terrific idea. Wish you'd told me earlier. Boy wants his amp modded after hearing mine. Maybe I'll get to try that on his.

FWIW, my Bottlehead Labs headphone amp is easily 4 times the area of these little boxes to give room for fingers and real caps and stuff. It's no longer available either, sorry. I honestly don't know of a decent headphone amp for under $400 ready-to-go now with $400+ headphones. I'm not sure I know of any decent $400 headphones for sale today either. Prices have gone crazy.

With a lot of help from Tom_s and pwryd, I built a 4s Universal 12xx7 preamp. It's probably 6 times the size of the Bravo amp and crammed full of wirewound resistors and poly caps. Heck. a pair of the caps is almost as large as this head amp. It's fun to play around with different resistors and caps, not to mention tubes, then hearing the results.
Bought a pair of hdxx off of Drop, they're decent and Drop seem to have a lot of planar phones from time to time that have me interested. I think Drop has had a large affect on the headphone market.

xxx

[Whitneyville1]

Korn, the 12a#7 tube series ain't my fav tube; high noise floor, lots of shot (plate) noise in the design, but it's cheap and available and too many toobs aren't. I love 23's or 83's in push-pull in a final amp, but try and find those Coke bottles today, much less a transformer for under 5 bills and a year and a half wait. Anyway, I appreciate the effort.
I'm not sure if "music" ceased to be created after 2001...just slightly cynical OK? I dig thru my 1960's LPs of forgotten solo acts and bands (many "none hit wonders") and play some of the garage label pressings and I'm still amazed at some of the music that was turned out on albums I paid a quarter for in the "cut-out" bin. Blue Turtle Records anyone?

Ricky-Pooh

[Kornbread]

Korn, the 12a#7 tube series ain't my fav tube; high noise floor, lots of shot (plate) noise in the design, but it's cheap and available and too many toobs aren't. I love 23's or 83's in push-pull in a final amp, but try and find those Coke bottles today, much less a transformer for under 5 bills and a year and a half wait. Anyway, I appreciate the effort.
I'm not sure if "music" ceased to be created after 2001...just slightly cynical OK? I dig thru my 1960's LPs of forgotten solo acts and bands (many "none hit wonders") and play some of the garage label pressings and I'm still amazed at some of the music that was turned out on albums I paid a quarter for in the "cut-out" bin. Blue Turtle Records anyone?

Ricky-Pooh

No luv for the 12au7? Out of the 12xx7 the 12au7 or 12at7 seem to be the preferred 'audiophile' tubes. Building a 4sUniversal tube preamp http://diyaudioprojects.com/Tubes/Un...-Preamplifier/ allowed rolling? rowing? a bunch of different tubes and although the pre's universal nature meant virtually none of the tubes were at optimal operating parameters, it did enlighten me as to how different those 12xx7 tubes could sound. By a landslide, my favorite for female vocals was a Raytheon 12at7. Female vocals were magic, but it suked at everything else. No highs, no lows, and come to find out the tube was probably bad, or on its way out.
Warning; My $.02, IMO, YMMV .... So, if the Raytheon was bad, why did it sound so darn good? The distortion, possibly excessive distortion, it was generating was primarily that of a pleasing nature to my ears which complimented the female voice. We've heard the phrase that an amp should be nothing more than a 'straight line with gain' but some people find that a not so enjoyable experience and prefer a more distorted but pleasing sound. Look at how the 'golden ear' reviewers gush over high distortion, single ended, flea watt triodes.
Maybe it all comes down to our listening preferences: do we prefer every last bit of information out of the recording (objective) or do we prefer to sit back, sip a refreshing beverage, and enjoy the performance (subjective). Ultimately, the choice is in the ears of the beholder.

And my favorite place to discover (rediscover) new music is an old milkcrate sitting in the very back corner of the Goodwill store. There is a lot of superb music trapped in those old vinyl grooves waiting to be discovered.

[Whitneyville1]

Korn, we must be getting old or sumthin'...I remember Packards and Nashes and Kaisers and Fraisers (filling them with gas!) and International pick-ups. Straight 8 Buicks anyone? Hudson Wasps with 7 cylinder RADIAL engines! Yours in senility...

Ricky-Pooh