Indeed G2 tweaks and bias adjustment

[geetarman49]

lynxo323: i noticed considerable differences when testing tubes in my unmodified bravo, but most of my tube stock is now out for cryo'ing. Of my 2 remaining tubes, both seem slightly better than the stock eh6922 (in the g2). i am not sure i could readily identify which is which in a dbt. i have some 12au7's on the way and i will comment further.

wrt stand-offs: after much searching, i stumbled upon brass stand-offs from 'electronics-salon' on the 'bay. a pack of 12 assorted quads with 50 screws M3 ranging from 5 to 50mm length for $US 9.99 + 3.80 shipping (should be enough to cover a couple of mods)... many other parts available ... probably suitable for non-signal path usage.

cgi.ebay.com/Brass-Hex-Stand-Off-Pillars-and-Screw-Assorted-Kit-/260615903541?pt=LH_DefaultDomain_0

[Deleted]

I measured the frequency graph of the G2 with 4 different tubes.
The frequency graphs of all 4 tubes are exactly identical.
At this point I stopped measuring as I have some more (all old and used) tubes.
There is not even a difference of 0.1 dB at both ends of the spectrum (0.9 Hz is determined by the output capacitor, and the upper limit, about 100kHz, by the capacity of the MOSFET loading the anode current source).
Didn't measure the differences in harmonic distortion these could account for perceievd differences.
There is a slight difference in gain though between tubes and tube halves too as there is no overall feedback and the gain is (almost) completely dependant on the tubes amplification factor.
Also the noise level is tube dependant.
I use the standard tube supplied with it.

Just because I can't measure nor hear any differences between too doesn't mean there aren't any or it could be I am just not able to hear it ?
The mods bring very measurable and noticeable changes though.
The IRL/IRF 530/510 and output resistors bringing the most differences in EQ an IRL/proper anode voltage adjustment and most of all the separate filament power/crosstalk mod bring down distortion quite noticeably and measurable.

[Deleted]

Didn't measure the differences in harmonic distortion these could account for perceievd differences.

Frans
Do you have the necessary gear to do that ? It could help provide some answers. (or NOT ! )

Alex

[Deleted]

I have a DSS that can do FFT but my tone generator doesn't supply a very 'clean' sinewave.
I might be able to substract a reference trace from a measured trace though but this will take up much time to analyse ...
At this moment I am swamped with work and also have something planned for the 'variation on a single ended' thread Robert started and bled dry...
Have to work that out first as I plan on doing uncharted territory for this amp.
then I plan to attempt to make electrostatic HP drivers based on my un-tensioned electrostats.

time ....

[geetarman49]

Frans ... i have received my tsr's today... thankU.

i have also tested one of a quad set of 12au7's --- 'organ pull' rebranded rca cleartop. these are very nice tubes and still available at low $. without any bias tweaking, just popped into 12v mode, it sounds much better than the stock eh6922. i will have to check these against the telefunken pcc88, but offhand, these may be preferable.

measuring and trimming the bias is a bit of a nuisance & while Mike's wire attachment idea helps, i keep thinking about a jig that allows u to drop the g2 (once the bottom perspex is removed or holes drilled) into position onto 3 'probes' which make contact with the requisite solder points which are wired to a switch which is then connected to one of those cheap encapsulated digital volt meter displays. measure, adjust...switch, measure, adjust --- done....remove from jig. alas, i have neither the tools, skills, nor resources to make this a reality.

don

[Deleted]

taking off the bottomplate and laying it on it's side is easiest when doing adjsutments.
adjustments are lots easier/faster and stable with the TSR filament power b.t.w.

[geetarman49]

Aug 25, 2010 7:48:13 GMT @solderdude said:

taking off the bottomplate and laying it on it's side is easiest when doing adjsutments.
adjustments are lots easier/faster and stable with the TSR filament power b.t.w.

i'm a bit clumsy ... i think i would need 4 hands & two pairs of eyes to do this w/o causing a short .. javascript:add("%20;D")

Frans ... i keep running across a few comments about your filters for the 681. are they still available?

don

[Deleted]

I have parts left (inductors, caps and resistors) and 2 boxes if an external filter is needed.

Take off the bottom plate.
Lay it on it's side.
Put something heavy on the amp so it won't shift.
Connect the - lead of the voltmeter to the shield of an RCA. (using a peg if you don't have a clamp)
With one hand I press the + lead of the meter against the PCB on the tube foot.
Then I use the screwdriver in my other hand to adjust.

[Deleted]

I have just fired up my G2 for the first time since installing the Frans upgrade parts, along with my Aluminium baseplate, and receiving it back from Frans after inspection. Sounds fantastic, the bass is tight and loooow, the mids and top end are crisp and full of detail, most of which was not apparent before the upgrade.

It still retains its previous character, but this just brings out so much more detail, with a wonderfully accurate bass line, superb i think.










I am a happy bunny, the Frans mods transforms this Amp from good to brilliant

[Deleted]

Glad to see it all worked out so well, Mick!

I have yet to get started with Frans's mods on mine i.e., the Traco Power supply, etc., as well as installing the beautiful aluminum baseplate you sent me! I intend to do this soon after I take care of too many necessary daily chores.

The photos show very well what an excellent job you have done in this somewhat complex mod. It inspires me to do the same soon.

By the way, I noticed on another thread that you have the Neco Dual-Mono 9V rechargeable portable HD Amp. How does the Indeed G2 compare sound-wise to your ears?

I do not want to get too far off-topic, but I also just received the above amp (the upgraded AD8610 version with the 300mAh battery), and am tremendously impressed by it -- so much so, that I just ordered Neco's High Spec Mosfet Amp as well. The Neco portable is decisively more transparent, to my ears, than my Indeed G2 in its present state of only a few mods, such as the IRL530 Mosfets, upgraded LT317s, bigger output and bigger PS caps and output bypass caps. The Neco is also much tighter in the bass region, although I still very much like the bass on my Indeed G2 with its bigger caps, etc. I will see how it fares after I do the baseplate and the Traco Power mods.

Congratulations on a very professional looking soldering job, as well as the beautiful aluminum baseplate!

[Deleted]

I do not want to get too far off-topic, but I also just received the above amp (the upgraded AD8610 version with the 300mAh battery), and am tremendously impressed by it -- so much so, that I just ordered Neco's High Spec Mosfet Amp as well. The Neco portable is decisively more transparent, to my ears, than my Indeed G2 in its present state of only a few mods, such as the IRL530 Mosfets, upgraded LT317s, bigger output and bigger PS caps and output bypass caps. The Neco is also much tighter in the bass region, although I still very much like the bass on my Indeed G2 with its bigger caps, etc. I will see how it fares after I do the baseplate and the Traco Power mods.

Hi Israel,

Thank you for your generous remarks.

Yes the G2 mods went quiet well,(took me approx 8hrs) the only problem i encountered after having completed the mods, was achieving the 6.3volts as specified by Frans on the valve socket pins before inserting the valve, mine were 24v, so i thought that i had done something wrong, but it appears that because i had kept my blue LED as before, it needed to be checked with the valve inserted.

I have the same spec Neco portable as you, and yes i think its a great sounding little Amp, and lasts forever on a charge. I actually prefer it to the V2 MOSFET which i also have, i am not saying that it is better in all or any departments, just prefer it with my number one HP`s the Senn 250 linears, however i think the V2 MOSFET sounds great with the 701`s, to my ears anyway!!.

I find it difficult to compare Amps that i have, all sound different, but all sound good to my ear, in slightly different ways. This is effected by the mood i am in, and also the type of music that i feel like listening to at any given time. If someone walked away with all but one of them, the one remaining which ever one it was, i could happily live with.

If it was possible to combine the best parts of the SQ on all my Amps, and then make a single unit which contained all of there best qualities that would be great, if its out there!! i haven`t heard it yet.

Regards Mick.

[Deleted]

Hi, Mick

Still somewhat off-topic, but I wanted to tell you that at Neco's suggestion on the portable Dual Amp I decided to roll the AD8610s with the OPA627s, which I just got today, and though still not burnt-in, I like them very much and will leave them in to let them cook for a week or two to see what happens. Right now they sound somewhat less toppy (though not less transparent), and somewhat fuller than the AD8610s, but time will tell.

I have yet to get started on the G2, but will soon. Just ordered an AKG K701 pair. Should have them in a couple of days. I understand they will take a long time to play-in. I am thinking of re-cabling them right off the start, even before breaking them in. I like the way Cardas cable makes my headphones sound, and have re-cabled with Cardas a bunch of my favorites, including the HD600, HD650, HD25-1-II Sennheisers, and three pairs of the Superlux HD681. I also have a couple of all-silver Moon-Audio cables, which I liked at first, but now prefer the Cardas, which sounds much more transparent, and has a wider frequency response. I know that there are people here that do not believe that the cable makes much difference ("De Gustibus Non Est Disputandum!!!" ), and I was one of them until I let my ears do the judging, and now I am sold!

Darn! I got off-topic again! This is supposed to be the G2 tweaks thread!

All the Best!
imagemaker18

[Deleted]

My G2 is simply amazing with the Frans mod, the base extension is remarkable through my Senn 250`s, the mids are clear and well defined, and the treble is sweet and giving superb detail. Well worth the time and effort on my part, its a really nice non tiring Amp to listen to, and presents music with a realistic sound stage, lovely!!.


PS. The Arcam irDock , 6th gen ipod classic, through solid silver cryo phono interconnects, to the G2 makes a GREAT SOUNDING combo.

Mick.

[wadiaman]

I am having problems setting the bias on my G2 and would welcome any suggestions as to what might be amiss.
The amp in question has most of the mods suggested on this thread (including IRF 510s).It is almost impossible to get both left and right readings the same and changing the left pot alters the right bias and vice versa.Even after a lot of juggling if I do get equal settings and switch off,the next time I switch on they are all over the place again,usually about 2/3v difference ! I get the same scenario with the stock 6922 valve and an ECC88.....all very strange,anybody else had this problem ?

[Deleted]

You probably have not done the separate filament powersupply mod (TSR-2465).
This mod ensures proper workings of the bias adjustment amongst other improvements.

Also adjust without any input signals on it.
This influences the bias signal so only adjust without any input signals.
(The TSR-2465 mod also makes sure the bias is NOT musical content dependant)

With IRF-510 you will have to adjust bias to around 15.5 Volts (+/- 0.5V) on the first channel and then the second channel right after that.
With IRL to 13.5V (+/- 0.5V)

Then wait 1 minute (minimal) and fine tune both channels, everything within 0.5V apart will be good.
They don't have to match exactly and the bias will be different again 10 mins or an hour later also.

When using IRF and adjusting bias to 12V the bias won't be stable and be all over the place and dependant on the bias setting of the other channel, the sound will be far from optimal too.

[wadiaman]

Thanks for that Frans,sounds as if I'll need to do the power supply mod' for sake of sanity !
I have no inputs connected when checking but maybe your final comment is key to current problem,I've been aiming for approx 13v,I'll try for 15.5v and see if that gives more stability.
Cheers !

[Deleted]

It should,

12V and 13V anode voltage with IRF is too low.
The LM317 current regulators are not operating in their proper range and thus the filaments do not get enough power.
Enough to glow and work but the voltage increases when the anode voltage increases.

Each time you adjust the anode voltage (when set too low) you also alter the glowing voltage and thus emission which results in a different anode voltage because of the CCS anode circuit is keeping the current the same.
a vicious circle.

[cadorne]

Hi everyone, this is my first post here after being a regular lurker for a few months.

I need your help.

I got a G2 on which I tried the mod where I added cathode capacitors. Right after the mod, I connected everything back and now I don't get sound. I havn't tried adjusting the bias yet as I still do not have a voltmeter but I thought that I would get some sound to come out. (If sound did come out I was planning to adjust bias by ear. )

Could I possibly have done something wrong?
Do I need to adjust the bias to get sound to come out?
If there is a need to adjust bias just to get sound, I saw on the pdf file "modifying the indeed G2 amplifier" download that I need to increase the voltage by 1 to 2 volts. Should that be a clockwise or counter-clockwise direction?
Do you remember how many turns (clockwise or counter-clockwise) did you need to do for let's say an additional volt?

I apologize for asking too many questions. Your answers and suggestions are much appreciated.

Regards,
Ed

[Deleted]

Hi Ed,

Welcome to the G2 owners club.

The cathode caps (if placed correctly across the pins of the small trim potmeters) do NOT influence the bias nor will it need re-adjusting after they were installed.

Even when accidentally installed the wrong way around (+ on the ground, - on cathode) it should still work but you should connect them the right way around.

It is possible you did not connect them in the right position.
IF by accident you did not connect them on the cathode but on the grid or anode you will be getting NO sound.

TIP: Just unsolder them and see if it works normal again.

You only need the extra 2 volts IF you have replaced the IRFxxx for an IRLxxx.
The small bias potmeters are 0.75 turn so they only need a small adjustment in many cases.
A voltmeter is obligated IMO but you could try to adjust by ear.
You would have to be playing pretty loud in this case IF you looking for optimal dynamic range (clipping on the positive and negative half of a sine wave simultaniously)

HOW much the bias pot needs to be adjusted and in what direction is depenedent on the used tube and how long it has been switched on and what the intial setting was (to high or too low).

There is no rule except that factory adjustments are usually WAY off !

[cadorne]

Thank you Solderdude.

I removed the cathode capacitors and I got the sound back on only one channel (left) . when I tried to turn the bias pot on the right channel (and I just learned that it is a single turn pot), smoke came out from the pot . Do you think that I need to replace the bias pot or did I burn something else? I feel so bad that I don't even have a multi-tester with me right now.

Any tips on how to test/troubleshoot this? Do I need to remove the bias pot? I also tried to re-solder the points where I removed the caps but to no avail. Help please .

Regards,
Ed

Edited as I missed the post by Solderdude.

[Deleted]

IF the G2 works correctly (the CCS in the anode circuit, the tube (foot) and the MOSFET being O.K.) there cannot possibly run a current in the cathode circuit that could ever destoy or let magic smoke out of the little pot.
The tube must be totally shorted (or the soldering on the tube foot ) for this to happen.
a shorted tube is EXTREMELY unlikely.

There is (very likely) something more NOT O.K.
a short by a 'solder blob' is most likely the cause.

Trouble shooting without a multimeter is not possible as one needs to know some voltages.

Buying a cheap (digital) one will be MORE then adequate.
They don't need to cost more then GBP10.- (D.I.Y store or internet)

[cadorne]

Thank you for those very fast responses, solderdude. They are really much appreciated.

I did try to connect another tube and I got the same issue. At least I'm sure it's not the tube itself. I think you're right that the issue more likely is not the pot itself. It could be the mosfet though I still feel the heatsinks heat up. Oh well, this will need an expert now.

Thanks again! I will report back when this gets fixed. (And hopefully it gets fixed soon.) BTW, I already bought another unit and I should be getting that within a week or two (delayed because of the christmas rush.)

I also have a DMM on the way, it was shipped around a week ago. I actually bought that since I was thinking of doing the G2 mods but I couldn't wait for it to arrive .

Now look what I've done . Now I am listening to the G2 with my AVR (onkyo 604) set to mono just so I can get the two channels working.

Regards,
Ed

[cadorne]

Hi all,

I just got the time to fix my Indeed G2 and yes it did get fixed.

Here's what happened:
I replaced the LM317 and the IRF 510 (they were cheap...all parts cost only less than US$4), still the same issue (only left channel works)

I then replaced the trim pot.... and the miracle just happened... everything works now.
BTW, the trim pot I installed is a 203 (20k instead of a 2K). The channels then were unbalanced so I replaced the other one too.
Result: the gain somewhat became less but the sound was improved (IMHO). But now I feel can adjust the pot more precisely as the pots were easier to turn.

So now that everything was fixed, I then replaced the 1000uF capacitors with a 1500uF 16V 105 degrees Celsius capacitor (JackCon brand) because the shop didn't have a 2200uF in stock.
Result: WOW! This gave a night and day difference IMHO. To all you out there who have not tried this mod, I highly recommend you try it. It should not be a problem to try as you can just put the original caps back if you don't like the resulting sound.

Another thing, I found the mistake I did about the Cathode Capacitors, I had connected the negative foot of the capacitor to one of the feet of the heatsink for the IRF510. This was due to my lack of attention to details. I only looked at the picture in the pdf file (Modifying the Indeed G2 Amplifier page 3/11) without realizing that the heatsinks there were moved to the side. I then looked at other pictures posted here and in other forums and saw where I really should be placing them (across two feet of the trim pots). Anyways, I learned my lesson.

Thanks to y'all (especially solderdude) for helping me and so many others like me who are benefiting from your knowledge and expertise.

Now back to enjoying the music...

Regards,
Ed

[Deleted]

The caps makes sense as there is 24V on the heatsinks of the IRF.
As soon as you turned the 2k pot to lower values it burned out (the puff of smoke) because there was 24V over the pot (and the capacitor).

a note of caution.
At start up of the amp (when it is not heated up yet) the output caps have 18-19V on them when an IRF is fitted, when an IRL is fitted even 20-21V.
the 16V rating is a bit low during startup (lasts a min or so then drops down).
Most caps can handle this short over voltage but lifespan is probably shorter because of this.
I recommend 25 V types for this (you vcan use the same value and brand)

when the G2 is in it's operating point the value of Rcath is between 500 Ohm and 1500 in general.
This would be easier to set with a 2k pot as thisone would be more in the middle.
a 20k pot would have about 10% travel in this rage and the other 90% will never be used.

It is possible ofcoarse to use a 20k pot for adjustment.
during normal operation there is about 11V on it (when biassed correctly that is)

Enjoy the music.
Them is not bad amps at all.

[cadorne]

I replaced the 1500uF/16V caps with ELNA 2200uF/25V 105C caps. The bass became too much for me, muddy and was overall just terrible, right off the bat. I knew I had to burn these in so I did for around 300 hours+. My Rating : 3/10

After around 30 hours, the bass became more tamed, much better than before and is now tolerable but still with too much bass for me. The bass was overwhelming the Mids and HF. Rating 5/10

After around 100 hours, I feel that the mids have now emerged but the Bass was still too much for me. My Rating: 7/10

After the 300 hours burn in time, not much had changed and I still thought that the bass was too much. My Rating: 7.5/10

I could not wait anymore so I soldered the 1500uF caps back and immediately I got back the tamed, controlled, and tight bass I was enjoying before. Rating 9.5/10

Did anybody else get the same results as I did with the 2200uF? Should I be getting another brand of cap? Or should I burn in the 2200uF further, though in my opinion, they no longer provide perceivable improvement for the last 100 hours they were installed.

BTW, I have this connected to my AVR and speakers 80% of the time and only listen through headphones 20% of the time (HD202).