The official G9 help thread

tmuikku said:

sam system-d said:

3 - you can avoid this problem with a shield cable from input transfo to jack, jack to Input cap. There's a topic about this, search on the meta Once you've done it, the G9 is really quiet.

Click to expand...

Not until HT supply is done out of the board Check this thread a few pages back, there is plenty of info including pics and FFT charts before and after.

Click to expand...

Thanks for the tip, I'll think abou it for my next G9 

Ok i've found the problem whit channel 1 relay... i've miss 1 solder joint !!  

Now all seem to work fine except the noise from tranformer 2 but is a minor problem.

Thank's to Jakob for make this possible !!


Edit: Added photo

Hi guys !
I finally bought an Oscillo !
I have a probleme with a friend's G9

when feeding it with a sine 1k




I get this at the g2 pin of the input tube



My HT voltage is low !!!! ( approx. 216 V )

tubes are OK ( tested on another G9 )

I have the same problem on both channels !
where should I look ?

maybe here :
http://www.groupdiy.com/index.php?topic=11347

Merci Sam
but I think if the HT voltage is too low, the G9 works
mine doesn't ! I don't think having a low HT can lead to the result I get at g2 !

madreza said:

Merci Sam
but I think if the HT voltage is too low, the G9 works
mine doesn't ! I don't think having a low HT can lead to the result I get at g2 !

Click to expand...

Anyway presuming G2 is pin 2 of the first ecc82 = the grid of the 2nd half of the input = junction C3 and R23.

That waveform looks like is is saturating on one half of the cycle.

Firstly check the grid of the other half of the triode = pin 7 to make sure you have a nice sine wave from your input transformer via C2/ junction of R6.

Next if that is OK (carefully) check the DC voltages on pins 6,7 & 8, plus the heater voltage.

I would initially suspect something structurally incorrect in the wiring on the cathode (wrong value R7? R8? or R9?) (causing a wrong cathode voltage on pin 8 ), because both channels are doing the same thing.

You could also check your G9 with only 2 tubes installed (one channel) and measure your PSU voltage then. Watch out though: the TL783 only really starts regulating once it is supplying about 15mA so do not panic of it is a bit higher than 240V.

BTW you look to be feeding a 3V peak sine wave, which is pretty high for testing. Make sure you're in "line" mode and no 48V phantom power.

You are exactly who I needed
I'm gonna check these right away !
Thanks !

Hi All

Just finished my G9 - seems to be working fine, power supplies are all good, no excessive heat

Extremely quiet using on board psu

-> mains harmonics each less than -92dBu for both channels
-> overall unity gain noise floor of -81dBu (spl) on Motu with -83dBu loop-back noise floor

Lundahl 1530 input traffos (1:7 turns ratio) and Carnhill VTB9057 output traffos (1.73:1 turns ratio)
12AU7 (ECC82) for all stages

- frequency response is very flat with extended low and hi

-> -3dB at 20Hz and -2dB 20KHz  (line input to output), both channels virtually identical

Out of interest, other changes I made were

- seperated the line input from the mic input connections and gave them their own connectors
- used a single psu toroid and changed the onboard rectifier to a 2 diode full wave(traffo hv is centre tapped)
- added led VU meters
- used the DI mod (cut traces and used shielded cable run)
- added relay bypass boards from line inputs to outputs
- changed 48V tripler to a doubler to accomodate the psu toroid available 18VAC winding

Sounds brilliant - very clean, full bass and detailed high, no distortion or oscillations at all!

So - THANX to Jakob (and Swedish Chef for the pcbs circa 2004!).

Very nice performer here, well worth building and worked pretty much first go.

Hey Guys,

I'm having problems to get the "C13,113 // 4U7 250V POLYESTER" capacitor anywhere ..

Can somebody maybe tell me some company name or a certain part number for this?

I've already asked in several electronics stores but they all don't have such big polyester caps with 4,7 uF 250V

I've read that i have to look for "FKP" in the name since this is for audio - but i'm not really sure..

thx for the help

Phil said:

Hey Guys,

I'm having problems to get the "C13,113 // 4U7 250V POLYESTER" capacitor anywhere ..

Can somebody maybe tell me some company name or a certain part number for this?

I've already asked in several electronics stores but they all don't have such big polyester caps with 4,7 uF 250V

I've read that i have to look for "FKP" in the name since this is for audio - but i'm not really sure..

thx for the help

Click to expand...

Not many (physical) electronics stores stock this sort of high voltage high value film capacitor any more.

I'd guess at MKT (metallised polyester) or MKP (metallised polypropylene) rather than FKP. FKP has no metal AFAIK so I guess that'd be some esoteric spend-a-fortune audiophile foil only cap, but I'm not sure they'd ever go up to 4.7uF anyway.

Search for 4.7uF polyester or metallised polyester or metallised polypropylene and then filter on voltage.
Some people say polypropylene is better for audio. I dunno. I'm not one who obsesses about such things.
I think it's one of the less important choices. I'll probably get a flaming for posting such heresy.

Check out the physical dimensions carefully on the following links to make sure they'll fit in your PCB.

Higher voltages would be fine, but they'll tend to be physically bigger too. Do NOT replace with an electrolytic IMHO.

I'm pretty sure I used an Epcos Cap. B32924E3475M in one build and a B32524Q3475K in another.

There are others e.g. Panasonic ECQE2475JF, Vishay BFC237343475 Cornell DME2W4P7K-F
And of course WIMA if you can find them MKM4-4.7/250/5. Some people get excited if you say you've used Wima caps.

Here's a few sites where you can order this sort of cap. I'm sure there are plenty more out there.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=UK&WT.z_homepage_link=hp_go_button&KeyWords=B32924E3475M&x=0&y=0
http://uk.farnell.com/epcos/b32924e3475m/capacitor-class-x2-4-7uf-305vac/dp/1781899
http://uk.farnell.com/vishay-bc-components/bfc237343475/capacitor-4-7uf-250v/dp/1469330
http://gb.mouser.com/ProductDetail/EPCOS/B32924E3475M/?qs=3sWhPqbVdzMIoOKIgh4%2fxw%3d%3d
http://uk.mouser.com/ProductDetail/Cornell-Dubilier/DME2W4P7K-F/?qs=sGAEpiMZZMukHu%252bjC5l7YfjT6scjVP0n3lA19dE5NK8%3d

Be sure to check the specs one more time yourself before ordering....

Thanks, MT2!

sorry for the long wait on the answer - wasn't in the country

thx so much for you help - I just ordered the Epcos as well and hope i can finish this project soon to use it for my next recordings

Another question i have is:

Before i plug in anything, are there some kind of instructions with measurement points etc that i can have a look at?

thx again!!

Today I fired up my G9 for the first time and it works like a charm.  Both channels are clear without any hum, but both transformers make an annoying 50Hz noise which is really loud. Should I be in worry about that?



Uploaded with ImageShack.us

hey there,

i just finished the G9 and .. it's not really working.
I don't get any signal from it - the only thing that happens is that when turning up the gain it gives me a high oszillated tone wich geht's higher the more i turn up.

Is there some way i can check the curcuitry step-by-step?

check for shorts on the pcb?

..and read through this long thread for hints..

Jakob E.

After a year of having the G9 PCB sitting around I've finally ordered 99% of the components  (caps/resistors/switch/tube sockets/I-O trannies etc.). If there is anyone in Australia who needs my cart from X-ON.com.au/Farnell to purchase all the components pretty quickly send me a private message. It took me the best part of 3 hours to sort through everything and make sure all the parts were suitable (and I still won't know until it's finally assembled).

By the way, does anyone know where I can buy the shielded hookup wire locally (Sydney area)? Would there be any benefit in chopping up a Star-Quad Canare lead and using that?
Also, Is there anything I should be really paying attention to with the first revision of the PCB? I've noticed that we're up to #5 or something now?

Other than that I can't wait to get started... what tubes has everyone used (obviously ECC82/12AU7) but is there any point in buying the more expensive models? I'm guessing I should be using a matched pair regardless of the manufacturer anyway.

Thanks guys

Is there any harm in using two of these http://au.element14.com/multicomp/mcfe030-15/transformer-30va-2-x-15v/dp/9531726?
I noticed that it only requires a 12V supply but the voltage should be regulated by the TL783 right?

braeden said:

I'm guessing I should be using a matched pair regardless of the manufacturer anyway.

Thanks guys

Is there any harm in using two of these http://au.element14.com/multicomp/mcfe030-15/transformer-30va-2-x-15v/dp/9531726?
I noticed that it only requires a 12V supply but the voltage should be regulated by the TL783 right?

Click to expand...

I looked at those too. Look like good transformers. Problem is that there isn't an mcfe030-12 AFAIK. Using two mcfe030-15 15V transformers back to back might result in weak HT: the G9 PSU uses a 15V step down from mains and a 12V in reverse as a step up to make sure there's enough voltage there for the HT even after losses. You're right that the TL783 regulates this to 245V, but it needs around a 20V "drop out" voltage between input and output to regulate properly. Also note that transformer model does not come with mounting hardware, so you have to buy 5mm bolts as extras. Might work, might not, depending on core losses, regulation accuracy, your local mains voltage (Aus is historically 240V, whereas we're usually closer to 220v in Europe) etc. So you might want to keep a pair of those for another project (like a GSSL). Try them and see.

I used these ones successfully (also from Farnell....)
http://nl.farnell.com/jsp/search/productdetail.jsp?id=9530312&Ntt=9530312
http://nl.farnell.com/jsp/search/productdetail.jsp?id=9530304&Ntt=9530304

As for matched tubes: what is "matched"? At one operating point? At two points. At three points? Over the lifetime of the tube? The G9 circuit doesn't have any balanced / differential stages anyway. IMHO save your money. Or spend it on something else.

Thanks for that, I guess I'll just have to try them out 8)

Finished this up about a year ago, spent about 2 years on it...Sifam meters with JLM drive board, bigger filter caps, Leeds Radio NOS RCA knobs, Lundahl transformers, mil-spec resistors, separate 48v light with switch, etc! Wiring isn't the neatest but its quiet and it was for my use only. This was the last project my tech/mentor finished before passing away. Obviously sounds incredible, cheers gyraf!

Bench Testing