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?
