Indeed G2 tweaks and bias adjustment

[statix]

I've noticed a couple of my tubes have started to crackle very loudly now, ever since I increased the heater current. My 6dj8 Amperex Bugle Boy (measuring 6.10V across the heater pins) and the stock Chinese 6n11 (measuring 6.8V) are both distractingly loud with the same crackling noise.

I'm afraid to try any of my other tubes. Could the extra heater current actually be damaging the tubes?


Update: I've noticed that the blue LED in the tube socket flickers a lot. It seems to flicker whenever I hear this crackling noise. Could a faulty blue LED somehow cause this crackling noise I've been hearing? Maybe I should bypass it/remove it.


Update 2: I just removed the flickering blue LED (by shorting out its pins), and now the terrible crackling/popping noise is all gone. All this time I've been complaining about the tube or amp's crackling/popping noise, it turns out it was just the LED. It seems like the LED was weak or faulty, and couldn't handle the voltage going through it (?), I guess. *Shrug*

If I wanted to replace that broken blue LED in the future, what should I look for? Type, specs, etc? I don't want to replace the LED just to have it die on me again.

[csdam]

Hi,
You just replace the blue LED instead to 2.2K Ohm 1/2W resistor, it will works stable for bias and reduce the noise.

Attachments:

[Deleted]

Do you want to replace the LED for the same color, another color or just want to delete it ?

Also I recommend you solder a 100uF/10V (or 16V) capacitor in parallel to the red LED (on the bottom side of the PCB).

Faulty LED's have passed in many threads before on these type of amps, a matter of bad luck in most cases.
Look for 3mm (T1) 'high intensity' LED's if you want lots of light.
current in the range of 5mA to 50mA will do fine.
The color is irrelevant for the working of the amp.
You can always increase the series resistance value to 'dim' it when you find it too bright, even with values upto 10kOhm it works fine.
The red LED (if defective) should be replaced by a red one, unless you want to change the anode bias current slightly.

[funkstar2]

Hi guys,

I just got one of these lovely little amps, but I have a problem. It seems the right channel is 2-3db more than the left channel. I have biased the amp 15v per side to cure the cross talk, but no improvement in balance.

How can I balance the channels? I need a reduction of around 3dB on left side.

//EDIT

I done some tests, and it seems the volume pot is driving the stereo field crazy. My inputs are +4dbu, so at low levels the volume pot is useless.

Would anyone be willing to help me repair it (I'll pay), or be willing to sell me a ready modified example? I have terrible arthritis now, so soldering isn't really possible for me any more.

I'm in the UK, so postage wouldn't be an issue

Thanks for your time,

Tony

[petar]

Hi all,

Just a question about the Indeed G2 headphone amplifier...

I have it connected to my USB DAC (Edirol UA-1EX), which is connected to my laptop. The G2 is connected to the USB DAC via RCA cables. Recently, I noticed a lot of distortion and crosstalk between the left and right channels, even at low levels. It's very obvious and makes listening to music impossible because of the distortion is so heavy.

I tried swapping out the RCA cables but that didn't change anything. I tried using a different power supply, connected to a different power point, and even running the laptop off battery power, but none of that changed anything. I also swapped out the tube (which is a 6922EH), but the problem persisted.

A random thought popped into my mind to try connecting the USB DAC to the G2's 3.5mm input jack (using an RCA to 3.5mm adapter), and low and behold, no more of that heavy crosstalk and distortion.

Being a bit of a newbie with audio/electronics, I'm wondering what the cause may be. Possibly faulty RCA connectors? Faulty switch for choosing between RCA and 3.5mm? Any tips on what I can do to try and fix the problem? I'd much rather use the RCA connections, as I prefer the cables to be connected at the back of the G2, and also, I'd rather have only a single cable going from the DAC to the G2 (that is, no use of multiple cables and a converter).

I'm also keen on doing some mods to the G2, after reading so much of the great information on here. But first, I want to resolve this issue before proceeding to the mods...

Thanks!
Pete

[Deleted]

According to the redrawn schematic that I have seen, it is a simple double pole slider switch selecting the chosen input.
If you have a DMM you should try checking for continuity or a fault in either the switch or the way it is wired.
Alex

[petar]

Hi there,

Thanks for your reply. I ended up soldering together the pins beneath the switch, so that now, the RCA and 3.5mm stereo inputs are always connected. In other words, the switch has no function any longer. I believe solderdude did the same thing (I recall reading it somewhere).

End result = all good now. Using the RCA inputs, I ran some test tones at various frequencies to check the lows through to the highs. Sound produced is as clean as a whistle now.

Must have all been due to a faulty selector switch... now it's time to try some other mods...

Cheers,
Pete

[philfine]

Hello everyone,

Thanks a lot for this great improvements to this awesome amp and more precisely the solderless ones.
I am trying to improve my own but I am unable to get all of the required components in my local area stores.
More precisely the TSR 1-2465.

My question is, does the 7806 is a valid and reasonable replacement to the TSR 1-2465?
Can it be just replaced ?

I am no expert in electronics and although have nice soldering skills, cannot tell if the 7806 is comparable and if I can replace it.

Thanks a lot

[mscosta]

I get the same question... i want to build a regulated heater supply whit a lm317 for my muse g2 whit 12au7 tube, i need 6.3v / 300ma positive in to pin 4 and 5, and the pin9 conect to the groung, correct?
I use a power supply 24v/1.2A
Someone help me...

[pingu]

Hi All, Solderdude,
I have got a G2 type clone from flea-bay for peanuts (p&p cost more than the amp ).
I have been going thro the mods on the web (all twelve pages) and here. Solderdude's tutorial I think, it was really easy and informative...thanks, much appreciated.
Just waitng for the heater psu bits from RS to complete the transformation.
My question is; I have a really small psu, not quite a wall wart but almost, that came with the amp 24v / 2amp (maybe?). Can I use a 24v / 5amp psu that I have spare, from a laptop (I think) or will this be overkill? Plug polarity observed of course.
BTW I have a copy of that G2 tutorial (called "Modifying the Indeed G2 hybrid headphone amplifier.") if anyone needs it. I can not seem to find the link now, I think it has gone down.
Any help comments appreciated .... thanks.
Chiarra is on the bench ATM.
Martin
Happy Christmas all, or for the B'ham Council "Happy Wintervol", will they ever live that down?
Not confused just a Welsh Sheeps

[pingu]

I get the same question... i want to build a regulated heater supply whit a lm317 for my muse g2 whit 12au7 tube, i need 6.3v / 300ma positive in to pin 4 and 5, and the pin9 conect to the groung, correct?I use a power supply 24v/1.2ASomeone help me...

Don't bother use the use the TSR switched mode mod it is easy to do and should really improve things from the reviews.
If you are in UK RS do a free postage on line sales now, no min order like Farnell. Bits cost less than £10.00 too
Martin

[theskybeblue]

Hi to all you folks, just joined up

A quick question, just upgraded from IRF630 mosfet to IRF510. Attempting to adjust the bias and my multimeter reads 22.5v regardless of how i set the trimpots and all it does now is make farting sounds if anything is played through it, the amp I have is a clone by Muse, the only difference is I have the 6N11 version (it has a switch for 6 or 12 series) I have not tampered with anything else (cursing myself for not measuring the bias before changing the mosfets though..)

My first instincts are I've bought nasty mosfets that a are a load of pants and dont work (ebay... nuff said) but thought I'd ask and see if anyone here has any ideas before I desolder them and start again

Is the bias voltage deferent for 6 series tubes? though surely i should be able to change the bias regardless, no problem with my soldering/desoldering(I'm very skilled with soldering, its just everywhere else i fall behind a bit..)

I'm planning on upgrading the capacitors and anything necessary to get the best sound possible, my brother in law is making me an aluminum enclosure to put it in when its finished because I dont like the total lack of shielding and its not going to fit as well in the original enclosure with the upgrades, not sure if that will make much difference to the sound but its worth a shot and will look good so why not

I'm highly impressed with this little amp especially for the low price, I use it as a pre-amp for the front channels of my surround setup through some Kef cresta bookshelf speakers, I have problems hearing vocals in music and I find It really enhances vocals so I can actually hear them without straining my ears and it makes good speakers even better.

Any advice is appreciated, I have plenty of time and patience and will rebuild it from scratch if necessary but I doubt I've messed it up that bad, hopefully just crappy cheap mosfets, I hope.....

the only difference I can see is the tube, I examined the pics at the top of the thread in detail and it is literally a direct ripoff of the indeed G2

[micross50]

Hi all,

I have a quick question for you all. I did the heater
mod on indeed G2 amp. And I can set the vbias voltage without problem.
The problem is when I increase the volume one side is ok the bias
voltage increase with the volume but on the other side voltage decrease
with higher volume causing distortion and sound lost.

What is my mistake?

Thank you a lot

[Deleted]

May 10, 2013 2:47:59 GMT micross50 said:

Hi all,

I have a quick question for you all. I did the heater
mod on indeed G2 amp. And I can set the vbias voltage without problem.
The problem is when I increase the volume one side is ok the bias
voltage increase with the volume but on the other side voltage decrease
with higher volume causing distortion and sound lost.

What is my mistake?

Thank you a lot

Hi
I have already replied to your post and sent you a Private Message.
Regards
Alex

[martestonia]

Hello, my first post in Rock Grotto.
I have read with big interest all these hundreds of postings about Bravo V2, indeed G2 and similar schematics.

My 4nd version of this amp was made as "original looking" as possible.
The hight of radiators is now 40mm and i dont use the acrylic cover.
Tubes I roll are all 300 mA - it was easier to bias them.
I do biasing with wave generator, o-scope and multimeter and afterwards with my ears.
Biggest differences in schematic was MOSFETs - IRL510 was changed to Toshiba 2SK2013.

PS. My writing in english is bad, but i can read/understand everything about this kind of headphone amp.

Here are the pictures:

[mcandmar]

Bump for an old thread..

I recently picked up a Little-Bear P-1 on ebay and discovered its identical to this Indeed G2 but with a 12au7 tube.  I've had a read through all 20 pages and changed a few caps/resistors/blue led for a red etc and its already sounding much better so thanks for the info!

I have two issues i cannot resolve, hoping you guys can help.

1) Mains hum, its there all the time independent of volume level, really annoying with Grados.  Any ideas?

2) Adjusting Gain, is there any way to do it as the minimum volume before i get channel imbalance is roughly my comfort level with Grados, what is the best way to reduce the gain?

I opened the mains adapter (serious piece of crap) and discovered all the inductor positions had jumper wires over them so i fitted a few i salvaged from old laptop power supplies which helped a bit with noise, but i'm still getting that 50hz hum.

Cheers,

Mark

[Deleted]

If the potentiometer has a metal case, you could try running a wire from the case to an earth on the PCB.
Alex

[mcandmar]

Thanks Alex, i just had another look at it and there is a wire running from the pot body to ground already.

I also discovered something the other day, i was listening to the amp and when the music stopped all i could hear was the hum. Thing is i was working on another amp project at the time and every time i touched the pcb with the soldering iron the hum in my headphones went away. I can only assume the iron was earthing the amp i was working on, and in turn its metal case i was resting on was earthing me, and somehow that was earthing the amp i was listening to through the headphones on my head. Very odd..

[Deleted]

There are many reports of these being prone to hum, most likely due to their open construction.
If you have a spare screw terminal type mains plug laying around, you could try just connecting a lead to the earth pin of the plug, then connect the other end to the earth/frame of the G2. Make 100% sure it IS the earth pin !

Alex

[mcandmar]

I had another look at the wire looped around the volume pot and soldered it on = 90% of the hum is gone so thanks Alex!

Replaced the 3.5mm/RCA switch as it was faulty and caused a crackling sound if you even looked at it.  Got an alps one off ebay that works perfectly.

Replaced the two IRF630's with IRF510's and oh my god what a difference, night and day, it went from being a novelty toy to something i can actually use on a daily basis.  If your going to do anything to these amps, ditch the 630's.

I also picked up a russian tube from ebay out of interest (6N1P-VI (6DJ8 ECC88 6922) Russian tubes), set the switch to 6series and the heaters looked fine however it was very very faint at full volume.  Checked the Bias adjustment and both sides were at 24v      Turned both adjustment pots down fully and it made no difference so i powered it down and put the stock chinese 12au7 back in and it worked fine.  Any ideas what the issue is, bad tube, or just incompatible?

TIA,

Mark

[6b4g]

Hi guys,
New to this thread, got my g2 more than 2 years ago, stay idle till now... A lot of interesting mod in this thread which I will seriously consider to mod... some thought also cross my mind, like... can use 24vdc linear unregulated supply with seperate 6v regulated for the tube heater? Or everything must be regulated? Any advise?

[6b4g]

Apr 16, 2010 17:38:49 GMT @solderdude said:

When you fit a International Rectifier IRL530 the LM317 wil run 10oC hotter.
The MOSFET will run a few degrees cooler.
This one will push the border where the awfull crosstalk occurs to a point where you under normal listening won't come anymore.

When you fit a Signetics IRL530 the LM317 wil run 5oC hotter.
The MOSFEt will run 1 or 2 degrees cooler.
This one will push the border where the awfull crosstalk occurs to a point between the IRF510/630 and the IR version of the IRL530.
It will also have a slightly bigger frequency range in return.

When you use the IRL530 I would advice a slightly larger or black cooling fin for the LM317.
The Lm317 has an internal temperature sensor so it doesn't mind too much it is running hotter.
lifespan will be slightly shorter and the 1000uF caps close to the LM's will become hotter too.

Like 'Johan Cruyff' once said:
Every advantage has its downside.

you trade SQ (less distortion and good highs) for heat/shorter lifespan, unless you cool the LM somewhat better.

Me personally doesn't like it hot (well except for women ;D) so cooled the LM317's in another place (under the PCB and did some more to it which will be disclosed at a later date)

If you change to IRL510, will the temperature drop by 10Cdeg also? And LM317 will double the wattage??

[Deleted]

6b4g
Sorry, but Solderdude is no longer a member of this forum.

[6b4g]

For tube rolling, 12au7, 12ay7, 12at7 and 12ax7? Do we need to re-bias the cathode resistor? or change value?

[fasterdamnit]

Big thanks to the OP and everyone else that contributed to this thread. Modded a Bravo V1 for my daughter with all mods but the seperate filament supply and it sounds very, very good with Grado SR225i's. She will get it later this evening for Christmas. I rolled in a PCC88 ('60's vintage) and the clarity took a big step forward. My audio buddies got a chance to listen and were impressed with the quality vs. cost- SO much so that one of them bought one and I modified it for him to give to his son as a Christmas gift.

Well done and Merry Christmas!

Jim.