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lampodigenio said:
anyone help me?

Haima helped you a page back Lamp.

If I'm reading it correctly, Cap 1(offboard) on the spare psu pcb refers to *C14 and Cap 2(offboard) to *C15 on the schematic.

It says 'TO CAP2/245V OUT', i.e its the 245v output connection and the connection for the Cap(offboard) which is rated at 100uF 350V.

Check the circuit diagram and you'll see 'Cap2'/*C15 wired across the 245V output.

Chris
 
microc said:
I've just Morgan Jones books; Valve Amplifiers and Building Valve Amplifiers, great books btw!
I'm also designing a new PSU for the G9. I see a lot of different designs in here. If we follow Mr. Jones we should have all PSU parts on a different board, and screen the board from the rest of the amplifier, even tho the current is very low, and the star-connect every part that needs power. The 12V, 48V and 245V should be place separably from the main board, and no trace on the main board should be used for power. Star-connected heather etc.

no need to go that far in my opinion. the original designs for the 12v & 48v seem to work fine on board as they are. just moving the 245v off the main board fixed the hum problems in both my units, and other people's too.

my guess is that the having the high voltage power supply regulator and rectifier on the main board results in ground current noise circulating, in some builds, perhaps not all - probably related to the circuit board layout and varying AC input voltages worldwide etc.

i actually left the original 245v regulator and caps on the main board, but removed the rectifier and fed "pre-regulated" DC to the main board, a bit higher than 245v so the regulator would still work. the "pre-regulator" board contained a rectifier, some caps and a zener+pass-mosfet "regulator".

i'm pretty sure you'd get a similar result by just not stuffing the 245v part of the main board and just building that part on a separate board. but the above is what worked for me while i was troubleshooting, so i stopped investigating and got on with life....  ::)
 
Hello. This is my first post here. I buld G9 and works great, but if i switch high pass filter in my speakers i have clip. I wont change it give 10M resistors(look at pics). This will be good, anybody know something ?

http://www.aukcjoner.pl/gallery-demo/4160649.html
 

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Hi,

I changed the OEP transformers for these and it sound nice:

Pikatron RUP 817M/1 Mikrofon 1: 3,21 + 3,21
wired 1:6,42

http://myworld.befr.ebay.be/studioemt1
that seller sold mine for 10 euros per transformer!
It's is cheap!  I guess he still has some stock.

While I liked the Oep sound, it made my unit sound too bass shy.
 
Hey guys, trying to get my BOM together for my G9 build.  Was thinking of using polypro pretty much everywhere a film is required as opposed to polyester.  Orange Drops where possible, looks like they'll fit most places - the 10uF & 1u5 will have to be something else.  Anyone see any issues with this or has anyone else does this?  Any reason why polyester would be advantageous over polypro that I'm missing?
 
This is My first post, I have found many answers without asking questions, so hopefully I haven't missed an answer while searching...

I'm in the process of building a g9 still haven't purchased transformers Yet. While I'm good with calculating resistance... impedance is my weak area... i was looking at several Jensen input transformers and was wondering if you could give me some advice.

1st question: Does Jensen transformers give a sort of color to the sound or are they transparent? I'm preferring a sort of color for vocals, which is all I track for r&b and hip hop mainly. Even if not I know this g9 will be better than my ga-pre73, eureka presonus, and digi 003 internal preamp...

2nd question: I'm looking at the specs and I believe Jakob says the g9 input transformer should be a 1:5 - 1:10, I see the

JT-13K7-A      (1:5 150:3.8k) http://www.jensen-transformers.com/datashts/13k7a.pdf
JT-110K-HPC  (1:8 150:10k) http://www.jensen-transformers.com/datashts/110khpc.pdf
JT-115K-EPC  (1:10 150:15k) http://www.jensen-transformers.com/datashts/115kepc.pdf
JT-115K-E      (same as above) http://www.jensen-transformers.com/datashts/115ke.pdf
JT-115K-E60  (dual canned for extra emi block) http://www.jensen-transformers.com/datashts/115ke60.pdf

What impedance does the g9 expect to see on the input? I seen it in one of the threads, and cant seem to find it now. I plan to use different kind of mics sm7/7b, tube mics, condens.,etc I'm assuming for the dynamic mic I would need lots of gain? thats what made me lean towards the 1:10 or 1:8. I also noticed that JT-115K-E60 has 2 shield cans which I thought might be useful when I hear people saying the input transformers pick up hum from toroids depending on placement.

3rd question: If I did use one of these transformers how would I calculate what resistors I would need to match the impedance, if this is the correct way of doing it.

4th question: Would I notice a major difference in using a cheaper input tranny, say like an edcore compared to the jensen?

5th and last: has anyone used the JLM111DC Output transformer http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=25 It can be wired 2:1 I seen one post were someone did use it, and likes it, but didnt go into detail.

p.s. I'm doing the ecc88 on second output stage.


Thanks for taking the time to read this long question.
Marvin
 
marvelouzone said:
1st question: Does Jensen transformers give a sort of color to the sound or are they transparent? I'm preferring a sort of color for vocals, which is all I track for r&b and hip hop mainly. Even if not I know this g9 will be better than my ga-pre73, eureka presonus, and digi 003 internal preamp...

any transformer with a higher ratio will have more coloration - companies like jensen, cinemag and lundahl make efforts to reduce that color to a minimum. so it will be fairly subtle, but still enough color for most vocals IMHO.

the OEP that lots of people use is quite colored IMHO - not always the best choice for R&B vocals...

there's enough color coming from the valves (tubes) and the output transformer. if you want this to be a good universal preamp for vocals i would suggest a jensen, cinemag or lundahl input transformer.

marvelouzone said:
2nd question: I'm looking at the specs and I believe Jakob says the g9 input transformer should be a 1:5 - 1:10, I see the

JT-13K7-A      (1:5 150:3.8k) http://www.jensen-transformers.com/datashts/13k7a.pdf
JT-110K-HPC   (1:8 150:10k) http://www.jensen-transformers.com/datashts/110khpc.pdf
JT-115K-EPC   (1:10 150:15k) http://www.jensen-transformers.com/datashts/115kepc.pdf
JT-115K-E      (same as above) http://www.jensen-transformers.com/datashts/115ke.pdf
JT-115K-E60   (dual canned for extra emi block) http://www.jensen-transformers.com/datashts/115ke60.pdf

What impedance does the g9 expect to see on the input? I seen it in one of the threads, and cant seem to find it now. I plan to use different kind of mics sm7/7b, tube mics, condens.,etc I'm assuming for the dynamic mic I would need lots of gain? thats what made me lean towards the 1:10 or 1:8. I also noticed that JT-115K-E60 has 2 shield cans which I thought might be useful when I hear people saying the input transformers pick up hum from toroids depending on placement.

basically my understanding is valve grid inputs are best matched with a very high ratio transformer - but at some point when winding a the high ratio transformer you hit a point where there is trade offs in frequency response, phase etc. this is why the "115K" is the highest ratio transformer jensen make off the shelf - the believe that's the highest ratio they can go while still retaining fidelity.

so i would go for one of the 115K models - the only reason to use a lower ratio transformer is if you want slightly less color or if your signal source is so loud that a high ratio transformer will overload the input stage - and for that you have the "PAD".

a SM7 can need a fair bit of gain depending on your singer, so again i'd go for the 115K (or maybe the 110K if you only record screamers!).

marvelouzone said:
3rd question: If I did use one of these transformers how would I calculate what resistors I would need to match the impedance, if this is the correct way of doing it.

just follow jensen's application sheet #20 http://www.jensen-transformers.com/as/as020.pdf - they show their recommended zobel/loading etc.

you can use their suggested values for the pad too if you like - or the original gyraf ones will work fine too.

one mod to consider is that you may want to wire the 48v/pad switch separately so that you can access the pad while using hot condenser mics... i think it's shares one rotary switch in the standard design? i can't remember.

marvelouzone said:
4th question: Would I notice a major difference in using a cheaper input tranny, say like an edcore compared to the jensen?

i'd say fairly major - do edcor even make mu-shielded input transformers of high ratio? you might be thinking of OEP?

if you want this to be your BEST preamp for the MOST sources, i'd go with a quality input transformer (jensen, cinemag, lundahl) - at least for one of the channels.

marvelouzone said:
5th and last: has anyone used the JLM111DC Output transformer http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=25 It can be wired 2:1 I seen one post were someone did use it, and likes it, but didnt go into detail.

JLM joe said to me that his output transformer works REALLY well on the G9, and i'd tend to believe him... he said it fixes the bass droop and headroom issues that make the OEP sound "bad" (some people like this sound, but again, unless you are making a "dirty" preamp, i'd go for something bigger sounding)

the output transformer is a lower ratio than the input transformer and doesn't need shielding - so they are much easier to make, therefore there is more "good" options: JLM, jensen, sowter, and for a cheaper option edcor - have a look though this thread for opinions.

if you have limited funds i'd put all the money you can into the input transformer as this will define the sound the most and then try a edcor for output - especially as you are based in the US... the shipping on the JLM might be expensive?
 
ruckus328 said:
Hey guys, trying to get my BOM together for my G9 build.  Was thinking of using polypro pretty much everywhere a film is required as opposed to polyester.  Orange Drops where possible, looks like they'll fit most places - the 10uF & 1u5 will have to be something else.  Anyone see any issues with this or has anyone else does this?  

use whatever caps you like the sound/look of and will fit, within voltage rating i guess. orange drops? i like purple grape fizzy drops :p

i don't know if anyone has done much A/B-ing of different caps on this particular design... (anyone?) but anything anyone says about their preference for tube mic preamp coupling caps will apply here too.

just use the best parts you can afford. if you want to go HIFI and have money to burn then run flying leads to some great big honkin audiophile cap ala manely.

ruckus328 said:
Any reason why polyester would be advantageous over polypro that I'm missing?

price? size?
 
Thanks for the info haima, Just a question on something you said..

JLM joe said to me that his output transformer works REALLY well on the G9, and i'd tend to believe him... he said it fixes the bass droop and headroom issues that make the OEP sound "bad" (some people like this sound, but again, unless you are making a "dirty" preamp, i'd go for something bigger sounding)
You mean something bigger sounding than the OEP correct?


 
In the past, I have used lundahls and oep for input transformers.
I'd say that their sound was quite different. the lundahls were clean indeed & the oep much dirtier.
for pop vocals, I'd prefer the oep sound.  for drum overheads, jazz vocals, acoustic instruments and general recording, I'd prefer the lundahls.
I think your choice should depend on the other preamps you have in your studio. I like to use the preamp as a colour tool and the choice of options is nice..
my 2 cents...
 
marvelouzone said:
Thanks for the info haima, Just a question on something you said..

JLM joe said to me that his output transformer works REALLY well on the G9, and i'd tend to believe him... he said it fixes the bass droop and headroom issues that make the OEP sound "bad" (some people like this sound, but again, unless you are making a "dirty" preamp, i'd go for something bigger sounding)
You mean something bigger sounding than the OEP correct?

yes, i was implying that to some peoples ears the OEP's distortion and bass shy sound can make things "smaller" sounding. of course, in some cases that is a good thing.

if you are unsure about transformer choice, why not make one channel with OEPs and one with jensen/cinemag/lundahl input and jensen/edcor output? then you can decide.

you could use short, twisted, flying leads to the OEPs for testng, in case you don't like the sound - they can be a bitch to de-solder unless you have a desoldering gun.
 
haima said:
you could use short, twisted, flying leads to the OEPs for testng, in case you don't like the sound - they can be a bitch to de-solder unless you have a desoldering gun.
Yes I do have one actually.

So my final decision is going to be 1 jensen JT-115K-E60 , with the dual can to try and keep hum out from power supply, which is fully built off main pcb board. with a jlm 111dc out on 1 channel and a oep in and edcor out on another channel. I don't think I should notice the bass roll off to much on vocals, at least if I do, it shouldn't be that bad on vocals as compared to using it as an instrument preamp..

I was getting  ready to really go overboard and throw a couple of different trans in there and put a selector switch with relays to select which trans I wanted to use for input and output on channels 1&2, but decided to get it built and working first..
 
sounds like you're on track!  ;) those combos should sound great.

if the super shielded jensen is super expensive, i'm sure the standard one should be fine - i've used the standard one a few times and never had problems with hum pickup....
 
I have quite a few Jensen transformers. They tend to be really really good and accurate. And expensive. As in clean and uncolored. I have 6 jensen 115's wich I love. Lundhals I believe are similar. Remember ya can always dirty it up after the fact. But bringing dirt in will always sound like dirt. Which may or may not be a good thing. If ya want a darker warmer sound you can just use a deesser in your DAW. Used properly it will make the most transparent pre sound like it was from the 60's. So you have more options come mix time.

John
 
Hi There!

I just finished my G9 build and want to say this device sounds just like whouuh! A big thanks to you Jakob!!! I am grateful for this project.

In the beginning I had some trouble with oscillation. After I conducted the wiring mod with the trace cut, oscillation is no issue anymore. Everything is fine with one exception: I want to get rid of 100Hz hum. The device is properly grounded. I even changed C14 and C15 with no success. After some tests I discovered, the transformer caps were not grounded. I fixed this. There was no change in hum. Even with no input signal.

I use the G9 for my audio book I am just producing. Between the single words and sentences the hum is audible.
I read the post of Metoo2 and his "minimum hum removing mod" relocating the R37 resistor. Is it just an issue of "moving R37 away from the board" and connect it directly to C15? I used my multimeter to measure ripple voltage across C14 and C15. There was "0V". I can borrow a oscilloscope. I think I have to use series resistors between G9 and scope. But what values? Just a ratio of 1k to 100k to make 3V out of 300V ?

Another question about the phantom power. Do I have to adjust the trim pot to 48V with or without load?


Thanks in advance for any answers!

Chris
 

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Hey Chris - I believe you are describing is a textbook case of the same low level hum I and a few others have experienced with the G9... I fixed it by moving the HV power supply (rectifier, caps, regulator) off the main board - therefore feeding clean DC to the main board. If you read back over the last ten pages or so there should be a few references to this problem.

I think we need a FAQ....  ;D

I really suspect a LOT of G9 builds might have this hum problem - but it's low enough that it doesn't bother some people, or they just think it's what "tube diy" sounds like.... It doesn't have to be that way. I lived with the hum for 3 years (used it on a few released albums!) before i got a chance to try running the pres from an external power supply - now they are dead quiet.

For the phantom power, i'd adjust for 48v at the XLR holes, without load. I believe the 48v will always drop with any kind of load due to those 6k8 series resistors.
 
Today I modded my G9 with an "outsourced" HV-PSU. 100Hz hum completely disappeared. It makes no difference in noise, if the G9 is connected or not; it is dead-quite.  :eek:

I can go on with my audio book...  ;D

Thanks for the help guys.

Chris



 

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