|
|
Post by ruinevil on Jun 24, 2012 0:41:32 GMT
So... I see a green brown blue gold brown resistor (5R1 confirmed by multimeter), directly above the LM317 heatsinks, to the right and left, but behind the tube, and between the IRF630 MOSFETs.
I should switch them with a 2ohm, or run a 10ohm parallel?
Tried running in parallel the 39ohm resistors I had lying around, bring the resistance down to about 4.5, but no change in the bias.
Since I'll be getting a IRL530 next week, I'll just put the amp away until then, and deal with the bias with the new mosfet.
I might even get a new tube by then.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jun 24, 2012 9:30:06 GMT
These are not the ones that need changing.
Between the heatsinks there are 2 rows of 3 resistors.
It probably is the one nearest to the back.
Very hard to tell from the pictures but the PCB looks very similar to the Miridiy.
It should be 3k0 (orange, black, black, brown, brown(or red)) or 3k3 (orange, orange, black, brown, brown(or red)) or a value close to that.
On the bottom side of the PCB simply solder a resistor in parallel to the existing one.
Values between 3k9 and 5k6 will probably do the trick.
L and R channel the same value of course.
|
|
|
|
Post by ruinevil on Jun 24, 2012 18:32:35 GMT
Wow, the filaments are burning brighter at 15.6V, and the sounds a lot better.
|
|
|
|
Post by ruinevil on Jun 25, 2012 17:40:28 GMT
Thank you for all your help Frans. I think this amp is sounding better and better, and I still haven't replaced the MOSFETs or the tube.
Could the buzz that I hear in the right channel at superhigh (pot turned to 9 o'clock) volumes be caused by oscillations from the LM317? I can't easily get LM317As, would a generic LM317 be better than whats inside right now?
Also, with the heater mod, is a 6.5V variant required. I can easily get regulators at 5V, 6V, and 12V from NTE, but not 6.5V.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jun 25, 2012 18:53:43 GMT
The Miridiy had problems with oscillations so it's possible.
You can change the LM317 for a better brand (or A type).
I figure the oscillations were there because of poor quality (cheap ?) regs are used in the cheaper models.
Another thing that can be done is replace the 220 Ohm Gate stopper resistor (red, red, black, black) next to the resistor you lowered (the ones in the middle of the row of 3) by 470 Ohm resistors.
The heater mod requires a switch-mode regulator.
TSR1-2465 or Recom R-78B65-1.0 are suitable.
Can't use other voltages as you need 6.3V (the diode in series lowers 6.5V to 6.25V)
|
|
|
|
Post by ruinevil on Jun 25, 2012 23:26:35 GMT
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jun 26, 2012 6:43:36 GMT
The heat issue is certainly there.
With the heater mod the LM317 heatsink must be even bigger tan the current MOSFET heatsink.
The one you linked to won't cool much better.
It might mean relocating the hot parts and constructing a way to fit bigger heatsinks.
|
|
|
|
Post by ruinevil on Jun 27, 2012 23:36:51 GMT
Are the v1 and v2 amps significantly different electrically? Because 12au7 tubes are a lot easier to get.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jun 28, 2012 4:59:56 GMT
yes they are.
different heater arrangement and the 12AU7 versions cannot be adjusted.
Not interchangeable either as the heater arrangement differs.
There are lots of ECC88 types (and equivalents) available.
see post #816 on page 33.
|
|
|
|
Post by ruinevil on Jun 30, 2012 1:56:26 GMT
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 2, 2012 18:59:28 GMT
Indeed as you already stated it differs little from the IRF630 (7.5nC)
It does have a lower voltage drop and is almost equivalent to the IRL630 (5.5nC).
The smaller voltage drop only has as a benefit the max output power is a few dB bigger.
NTE2987 Qgs = 6 nC where the IRL510 = 2.7nC so the 510 is twice as 'fast' in this particular circuit.
Somewhere between the IRL630 and IRF630 therefore there is little audible difference.
The NTE2987 is also much slower than the IRL530 (3.8nC) which already has a -0.5dB point of 20kHz.
|
|
|
|
Post by ruinevil on Jul 6, 2012 21:31:53 GMT
I switched the NTEs with some IRF510 that I got from Radioshack.... and now I get no sound. The red and blue diodes light up, but not the tube, and the mosfets do not heat up. Neither does the LM317s. From the positive pole of the power cap, to the legs of the mosfets closest to it, there is 22V, and 22V on the farthest leg.
The anode resistor that I added extra resistors to in parallel runs 1.1V across, 22V to ground, the resistor that is normally set to 14-16V is running at 1.1V to ground.
I tried both the 6N11 and the 6DJ8 I had.
Do you think it might be defective MOSFETs?
------------- 1 hour later
Yep... it was the new mosfets.
The buzz is gone in the right channel gone, the frequency curve now mimics my DAC.
I also added some 4.7k resistors across the middle and rightmost jumpers of the potentiometer, so I have a sane volume knob.
|
|
|
|
Post by kcvip on Aug 18, 2012 10:46:26 GMT
I recently picked up a Bravo V3, and was happy with it until it died on me. I am not sure if it is the tube or something else that went out on me.
I had about 40hrs of burn in on it and was absolutely pleased with the results. I then noticed two little knobs on the board and did a little research. I found an article on how to set the bias on the amp and I think that's where it all went wrong. The tutorial showed where to check the voltages, and said to set them to 16.5v. I raised the left one from 10.2v to 16.24v and the right one from 8.9v to 16.25v. I then rechecked them about 10minutes later and they seemed stable.
About 10mins after double checking the voltages I heard a nasty crunching noise then the volume cut out. I turned the unit off and let it cool down before I re-assessed it. The bias settings were still at 16.25v on both sides, but all I got was this odd buzzing and hissing sound. The volume knob didn't seem to do much in terms of turning up the volume of the music, and adjusting the knob during the waves of static had no change in the noise.
I shot off an e-mail to Bravo asking if they have any sort of warranty or replacement for the poor little guy. I had it just over a week before it died. I explained the symptoms and am hopeful for a response.
I wish I had more experience with circuit boards and how to test things and knew what symptoms might mean what but I really have no clue. I can get audio samples when I get home and post audio/pictures if that would help anyone help me figure out what is going wrong with my poor little amp.
Other than the thing dying on me, I was absolutely blown away by this little amp. At first it was not very impressive, but after 20hrs of burn in it was really starting to warm up the sound, and all the crunchy guitar goodness. After I adjusted the bias I was enjoying my big grin listening to my music until horror struck my face when it died.
|
|
|
|
Post by mscosta on Sept 4, 2012 22:32:57 GMT
hello guys i purchased an amplifier muse g2 has the same design as the g2 indeed, the input sensivity works at 50mvolt I wanted to connect a CD player but the player's output sensivity is 1volts how can I modify my amp to work with?
i can add some capacitadors or changing the potentiometer?
I have some knowledge of electronics but am no expert,
can give me a hand...
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Sept 5, 2012 5:16:49 GMT
Forget the specs they are a bunch of lies anyway.
You can safely use it with a CDP.
It's just that you will only be able to use the first part of the volume control.
If you want to use the complete volume control and lower the overall gain you can change a resistor value in the input circuit.
Changing the potentiometer value will not change anything.
|
|
|
|
Post by PinkFloyd on Sept 19, 2012 13:31:22 GMT
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Sept 19, 2012 14:44:09 GMT
 Whenever I see pictures of mucho valves together (mostly Mikes) I think of some mad scientific experiment or Sci-Fi movie like "Clone Wars". Is Mike ( aka Blofeld ) planning a world take over scheme  |
|
|
|
Post by ruinevil on Oct 12, 2012 6:33:38 GMT
So... my 6922 was pretty awesome until today. I'm getting an annoying intermittent hum in the right channel. It doesn't appear to be amplified, even when the potentiometer is at its lowest or highest level the buzz still appears in the right channel at the same volume. The buzz also appears when the DAC cables are pulled out.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Oct 12, 2012 8:01:00 GMT
So... my 6922 was pretty awesome until today. I'm getting an annoying intermittent hum in the right channel. It doesn't appear to be amplified, even when the potentiometer is at its lowest or highest level the buzz still appears in the right channel at the same volume. The buzz also appears when the DAC cables are pulled out. I gave up with those types of amps. I really liked the sound a lot but unfortunately, noise issues were a problem and after a while, the amp was crackling and fizzing so I left it. I've had the same issue with the Horizon now as well. My feeling is perhaps heat gets the better of them. I've move to the T1 which is a lot coller. I had problems with the Bravo, Indeed, the Muse - all went the same way...... Worst was the Muse, best was the Indeed but they all seem to start making noises after a while and need repair unfortunately. |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Oct 12, 2012 11:31:35 GMT
I gave up with those types of amps. I really liked the sound a lot but unfortunately, noise issues were a problem and after a while, the amp was crackling and fizzing so I left it. I've had the same issue with the Horizon now as well. I never could get on with the Indeed G2. I eventually did all the mods but the overall character remained the same. I just found it a boring listen, uninvolving and bland. It's been laying in a box somewhere forgotton for over a year. As the Sunrise/Horizon was based on it I didn't go there. 99 times out of 100 it's solid state all the way for me. I do have a soft spot for the MF V2 though, it's not perfect but it is musical, in a calming, comfy, old friend kind of way. |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Oct 12, 2012 19:13:44 GMT
Oh yes ..... I still love my old V2 although that's starting to get noisy as well.  I'll have to have a look and see if the valves are ok. The T1 seems more robust and cooler and I really like its sound as well. In fact, I use it a great deal now. I'm starting to wonder whether a hybrid design is better for me in that it gives the valve flavour but seems more reliable in the long run. |
|
|
|
Post by ruinevil on Oct 12, 2012 22:28:12 GMT
Switched the tube... and the buzz is gone. Chinese tubes are no good...
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Oct 12, 2012 23:49:07 GMT
Switched the tube... and the buzz is gone. Chinese tubes are no good... Far too many ebay type offerings appear to be giving problems after several months use due to iffy tubes or overheating. I would suggest that anybody wishing to use anything like this long term, contacts Mike and gets some quality tested spares. Also , if it's running quite hot, to find a way to reduce excessive heat by some method, possibly including the use of heatsinks, and using in a well ventilated area. The one in the photo from Mike may look pretty, but surely it lacks adequate ventilation for long term reliability ? Alex Attachments:
|
|
|
|
Post by ruinevil on Oct 12, 2012 23:57:53 GMT
imgur.com/a/m3RmxI jammed one of the output capacitors under the PCB because it was sitting next to the MOSFET and Voltage Regulator. Also, I replaced it with a GE NOS tube, probably produced in their factory's last year. The sound is too accurate now.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Oct 13, 2012 7:41:39 GMT
How can sound be 'too accurate'?
|
|
I'll have to have a look and see if the valves are ok.