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Post by oohms on Apr 6, 2010 8:49:33 GMT
The switch is easy to replace. Any switch with 2 connectors will do, and if you have a 3 connector one, use the middle connector and one of the other 2 (doesn't matter which one) www.jaycar.com.au/productView.asp?ID=ST0335&CATID=28&form=CAT&SUBCATID=448But DON'T leave your headphones plugged in when you turn on or off this amp. The output coupling capacitor will charge/discharge through your headphones and there will be several volts of DC across them during this time. (Which can kill them, and explains the 'pop' heard when turning it on/off) Best to wait 20 seconds or so between turning it on, and plugging in the headphones. And disconnect them just before you turn it off
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Post by Deleted on Apr 6, 2010 14:23:38 GMT
Thanks for the suggestions, oohms! I usually try to never use the switch with the headphones plugged in! I especially would hate to kill the HD600's which sound so good with this amp. Also, I always turn down the volume to '0' before plugging in, or unplugging the phones to protect my ears as well, for they can't be replaced!
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Post by Garage1217 on Feb 23, 2011 16:28:23 GMT
Received my Bravo V2 12AU7 model yesterday. Took it out, fired it up and gave it a good few hour listen going back and forth between my zunes direct out and then through the amp. It was not packaged that well, and took over a month to arrive but not that big of a deal as it all arrived in one piece. It looks nice / not bad build quality for the price.
How does it sound? As it was out of the package, all I could think is what a flaming pile of crap it was. It was fat sounding in the bottom end, highs and sparkle did not exists really... was a little harsh... just crappy. All I could think about was how much cash I just wasted on the pile.
So I took a break and came back. Yep still sounded like a flaming pile.
After reading about all the mods, I pretty much performed most all of them. - Added in 5K trim pots to adjust bias - Replaced the power supply cap with a 4700iuF / 35V nichicon - Replaced the two 1000uF units with 2200uF 105C nichicon units - Yanked out the two small caps on the input side, right next to the tube and ran jumpers - Replaced the 630's with IRL530PBF mosfets - And cut some traces and so forth per the crosstalk mod
Everyone kept complaining how horrid and fragile the stock circuit board is. The pics looks the same as the unit I have, except I found it to be reasonable. I was expecting a board made with a laser jet and home kit in which someone sprayed black spraypaint on *LOL* The lead free solder was the only part that made it a pain since it is much higher temp. Just used a solder sucker and cranked up the heat on my station and it removed with ease. Mods were cake overall.
On another note, the stock capacitors were very odd. They weighed about 50% less than the nichicons I used even though they were about the same size. Felt like they were made of foam they were so light? Strange.
Sounds like a lot but all of it took me around 30 minutes. Took me a bit to figure out where to test for bias but got it and set it at 13.75ish vdc on both channels. After this, let it sit for around 30 minutes per the guide I read and re-checked it, made some minor tweaks and tossed on my headphones. In all honesty, I still expected rubbish as I was so disappointed previously. So I listened, and listened some more... Wow! Is this even the same amp? Well not really as I made so many changes but whoa! It really sounds good! The murky thick bottom end was tight and smooth, vocals were fantastic and spacious, the top end that simply wasn't prior WAS! I went back and forth between the direct out of the zune and back to the amp. I was able to get the volume almost perfectly balanced between switching back and forth and the little amp simply made the sound much more enjoyable, especially vocals, mid-bass and bottom end. I had read with these mods, the frequency response was almost flat so I thought I may just be dreaming this up so I had some help and did some back to back a/b to see if I could pick out the little bravo amp and every single time I could so it was not a placebo effect.
Overall I wanted to thank solderdude. and oohms for the posts and writeup. These mods are fantastic and make this cheap budget amp SING! This little guy is the steal of the century for sure!
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Post by Deleted on Nov 9, 2011 14:14:05 GMT
Note: quotes form various people:
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.
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.
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.
This means 10 * 10³ = 10k.
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Post by Deleted on Nov 9, 2011 17:35:21 GMT
The output resistance does not have to match the headphone impedance. read my tutorial for clarification : www.mediafire.com/?ms4k8wuqt18x8s3100 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/?jdpaj1r17x1sos5Some 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)
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Post by Deleted on Nov 9, 2011 18:05:04 GMT
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/?jdpaj1r17x1sos5Some 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 €?
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Post by seaton on Nov 13, 2011 0:31:11 GMT
well i figured out why the sound was cutting out ( i think ) my 15 year old senn 580's finally developed an intermittant at the plug where it plugs into the phones. if headphones will last 15 years for me , they will last a lifetime for someone else ;D i guess ill either have to hold my head real still ;D or try to fix them . im 81 on a fixed income so replacement isnt an option they still beat most phones out there. regards , seaton If it isnt baroque, fix it ! PS. the right mosfet heat sink is too hot to touch and the left i can hold my finger on it for 15 seconds so i guess the first mod will be trim pots for bias and change the resistor to reduce v on the tube . my amp is dead quiet ( as long AS IM NOT ON MY CELL PHONE ;D. pecularly the cross talk is minute and just acts like cross feed in the phones. the sound stage sounds a little less "inside the head" compared to what ive been used to for 15 years
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Post by nickseattle on Apr 23, 2012 4:10:20 GMT
Thanks, solderdude. I'll try it tomorrow. The amp is at work, so I don't have access to it. I do have some cheap headphones connected to it - that might explain the issue. I will experiment with my HD650 and see if the cross talk is still there.
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Post by Deleted on Apr 24, 2012 10:26:18 GMT
May be your feeling but technically and measurably things have actually changed. The frequency range has expanded further into the hypersonic range. Your dog or pet bats may appreciate it if your headphones would be able to reproduce it and hyper sonic relevant info would be in the recording (not in CD). All that matters is you enjoy the fruits of your labour, mindset or real... who cares as long as you enjoy music.
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Post by nickseattle on Apr 27, 2012 17:01:41 GMT
Does anybody have problems with very high level of hissing with the amp? Mine is OK with Sennheiser over the ear headphones, but in ear headphones are practically unusable. The hissing doesn't go away even with the volume all the way down and inputs shorted. Tried many different tubes, the same results.
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Post by Deleted on Sept 27, 2012 15:52:25 GMT
If you set the class-A output stage bias to >275mA you can leave out the output resistor if you want. Heatsinks must be big enough in that case ! That way the output resistance of the amp will be just a few Ohms.
Most 32 Ohm headphones prefer low Ohmic amplifiers. Some, however, may sound better on a higher Ohmic amplifier.
I have the HD438 (modded) and a few other HP's.
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Post by szabi on Oct 13, 2012 12:23:39 GMT
It turned out to be a dodgy valve. After the heater overvoltage occured with the 7812, I've replaced the tube. Since than, I was unable to set the bias correctly. (Strarted cutting the top side of the sine even If I grounded the cathode) Interestingly the labels on this tube are barely visible, almost completely washed out. Probably indicating a fair amount of ware and handling. I swapped with a third one, and everything is fine now. How exactly can I calculate the output resistence of this amp? The class-A current is now set to 125mA, and the series output resistor is 47 Ohm. (headphones are 32 Ohms)
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Post by boomer47 on Mar 24, 2013 20:57:54 GMT
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.
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Post by Deleted on Dec 17, 2013 23:14:17 GMT
Ok, here goes, first post here and am early in the stages of learning electronics, but am enthusiastic and teachable. I picked up a couple bravo v2 amps recently and am inspired to mess with them. I have been into audio for some time and have dabbled quite a bit in speaker design, but never beyond that, i.e. never beyond caps, inductors, and resistors. Please be gentle on the noob I'm trying to understand the purpose of each components function to help me understand the changes various mods make. Here are my first questions.. What is the function of the 2N3906 transistors in the V2? what would happen if they were not there? What is the function of the transistor circuit following the tube (the IRF630/LM317) and what would the effect be if it was not there (so just the output cap an resistor coming off the anode to the output. Sorry if this is a little rudimentary, but will help me understand the design better. Thanks! Chris VERY briefly, as I have an appointment shortly. The 2N3906 is a constant current source, and sets the anode current for the valve. The forward voltage drop of the Red LED is typically around 1.8V. The voltage drop across the base and emitter junction of the 2N3906 is a little over 600mV . Subtract that 600mV from 1.8V and that gives you the voltage drop across it's 3Kohm emitter resistor. This is then the anode current drawn by the valve. (I = E/R) The output impedance of the valve is very high, so the FET is used to provide a much lower impedance, and higher current to the headphones via the 1,000uF electrolytic capacitor. Alex
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Post by maximalz on Sept 10, 2014 14:21:41 GMT
70°C after 10min working that is terrible - with this giant cpu heatpipe cooler now i understand, what sandyk says about the overheating problems with the mod. floriangerard51 - 1) you use the amp's every day? 2) and the heat of 70°C is not a problem for you? 3) what is the max heat and was is the low heat - the amp's working? 4) how long you use your amp's in a normal headphone session? 5) the heat is the same problem as over clocking cpu's, is watercooling a possibility? 6) if i want play my headphones with 250ohms and 300ohms - i need a 2,2ohms? thx - maximalz
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Post by mrqs on Mar 31, 2015 22:43:18 GMT
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!
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Post by lemondixon on Mar 30, 2016 16:35:33 GMT
I've searched high and low trying to find an answer online, but so far this mods thread was the closest in terms of relevance and these latest comments were only late January (some others are years and years out of date).
Basically, I've bought a used v2 unit on eBay to play around with but it's faulty and my electronics knowledge is pretty flaky and haven't done any of this since I did my A-Levels before Uni back in the early '90s. I have a multimeter borrowed from a mate of mine and am struggling to know how and where to test it without knackering it up.
The problem is that there's no sound coming out the jack on the left channel, and I was trying to figure out if it is (a) fault at the jack, (b) one of the triodes in the tube has gone, or (c) if it's something to do with a major biasing imbalance. The guy on eBay gave me a full refund but told me to keep it, so I figured it might be worth playing with to try and fix it or modify it in the process; but not if the whole thing is completely shagged!
Here's what I've checked / found so far: 1. Pushing the (male) 1/4" jack 2/3rds of the way in (so the tip is not at the back in it's proper place) gives sound in both headphones, but this is just the right channel duplicated in both cans. Tracks which pan all the way left show this up; 2. The sound seems the same if you swap left/right RCA input around, and if you leave only the left RCA connected you still get some sound but much quieter and still only in the right hand headphone - I'm guessing this is the crosstalk or something? 3. Measuring the voltages for the channel bias (there's no trim pots on this version of course) shows a massive discrepancy - The right channel is 16.1V whereas the left channel is only 10.1V
On this basis, does this rule out the tube being completely knackered (even though the bias is way off) as would there be any voltage on the left if the break in the chain was the triode feeding the left channel (or have I got this wrong)?
Obviously I can't fix the bias without modding the unit anyhow, but wasn't sure if the unit was knackered it was worth getting a new tube for it even if the replacement was properly matched so the output on both channels were more like they should be?
Would be a shame to just throw it in the bin if there is something I can do to test it to see if it's worth repairing. Any ideas?
Thanks for your patience and input.
Cheers,
Steve
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Post by jack on Oct 9, 2017 17:24:30 GMT
Hi, I have a Bravo Audio v2 unmodified. Now it has just turned on and without signal the right channel mosfet immediately becomes very hot, much warmer than the left one. The right channel voltage regulator remains normally warm but after a few minutes it also becomes very hot. In the headphones, in both channels, there is a background noise that grows as the temperature rises. Fearing the fusion I turn off the amplifier. If I apply the signal to the input, the music can be heard on the two channels until it is covered by the noise. If I turn the amplifier off and cool it resumes to work but after a few minutes repeats the problem. Which component can cause this problem? The MOSFET, the voltage regulator or some other? The tube is certainly good, the measured bias voltages are correct. Left channel components always reach a normal temperature in operation. Thank you in advance for your suggestions.
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