Hotrod Build Thread

[safe as milk]

hi
yeah, i listened to it and it sounds great,apart from the buzz,
did the ba283 trim thing,
it must be a ground loop,
i'm just not sure about how far down the noise floor should be,
should it be ref 1v/1kHz?

i can't post pics till i get home tonight,
but the outputs are bolted to the far left of the rack
and the toroid is far right.

thanks

 

[matta]

[quote author="safe as milk"]hi

i can't post pics till i get home tonight,
but the outputs are bolted to the far left of the rack
and the toroid is far right.

thanks[/quote]

Have you tried taking the torrid out of the rack all together? It was the only way I was able to get a truely quiet rack, this has been affirmed by JLM as well as a couple others.

If you look at most proffessional pres they have external power supplies, having heard the night and day difference I won't put a power trafo back in a pre rack.

Try it an it may help, if the problem lies there.

Cheers

Matt

 

[safe as milk]

hi matta
no i did'nt try that, but i've done a couple more tweeks
and now when the unit is running flat out i read -72dB
on the best channel and -66db on the one nearer the toroid.
that ref to 1v/0dB is -112dB with nothing on the input?

so it's got to be that, no buzz anymore.
just tried it on kick/snare, it clips beautifully.
what noise floor did you end up with on yours?

thanks

 

[enthalpystudios]

[quote author="matta"]having heard the night and day difference I won't put a power trafo back in a pre rack.[/quote]

that really brings me back to my idea to build a power supply to power a rack of mic pres, using 8 pin tuchel/din style screw on connectors.

also, i really feel like a lot of the power supplies i build for projects are way overbuilt... which is fine, don't get me wrong, but if i have over an amp available and i'm using about 80-100ma for a 2 channel mic pre, it really sucks to go and build another supply for another mic pre.

 

[safe as milk]

hi
i think im going to live with my bit of hum.
here some quick pics so you can see the layout greg.
thanks for all your help.
i'll post proper pics when it's finished,
needs a nice front panel etc.

http://www.twin-x.com/groupdiy/displayimage.php?album=106&pos=0

 

[Greg]

That's a killer build !!!

Any comments, in general, on the project?

 

[Underthebigtree]

Hey guys -

I've been working on the hotrod on and off for about a year, and it is nearly done. A couple of questions, if I might. Please forgive if these have already been answered elsewhere - I did a search and couldn't find the answers.

1) I am using the JLM output transformers as a replacement for the LO1166. On Joe's schemo posted on his site, I see a 1.5K resistor and 0.01uf cap in series across the output pins of the output trafo. Are these required for Joe's JLM111DC trafo in this configuration as well?

2) We want to wire the output trafo as 1:1, correct?

3) I'm using Joe's AC/DC power supply, and am a little hazy on the correct hookup for a single rail +24VDC configuration. I have the power trafo wired into the 0V and one of the AC inputs. This is giving me +48V and +24V on the outputs, as well as -24V which I won't use. However, there is another layout on Joe's site that shows running in power trafo into both AC inputs and bridging one of the filter caps into a pair of diodes. Is this arrangement preferable in some way, or am I good just leaving it the way it is?

Many thanks in advance. As soon as I finish this sucker I'll post some photos.

-Nick

 

[safe as milk]

hi
thanks a lot, i loved building it.
although it was a squeeze in a 1u case.
i used to have some 1272's and was missing them,
that's why i started the build.

thankyou's go to your very patient self greg,
joel,cj,nele,fabio,rob higgins & joe for the go-betweens.

:guinness: :guinness: :guinness: :guinness:

 

[JLM Audio]

1) I am using the JLM output transformers as a replacement for the LO1166. On Joe's schemo posted on his site, I see a 1.5K resistor and 0.01uf cap in series across the output pins of the output trafo. Are these required for Joe's JLM111DC trafo in this configuration as well?

Our JLM111DC doesn't need the zobel 0.01uF cap and 1.5k resistor.

2) We want to wire the output trafo as 1:1, correct?

Wire the JLM111DC as 1:2

3) I'm using Joe's AC/DC power supply, and am a little hazy on the correct hookup for a single rail +24VDC configuration. I have the power trafo wired into the 0V and one of the AC inputs. This is giving me +48V and +24V on the outputs, as well as -24V which I won't use. However, there is another layout on Joe's site that shows running in power trafo into both AC inputs and bridging one of the filter caps into a pair of diodes. Is this arrangement preferable in some way, or am I good just leaving it the way it is?

Doing the mod with a single transformer winding will give full use the current of the transformer and also full wave rectification for smoother unreg power to the regulator. Just try the standard way and if you have a problem with the unregulated rail sagging to low then change to the mod.

 

[Underthebigtree]

Straight from the Koala's mouth!

Thanks so much for the info, Joe. As always, you are the man!

Is your little one sleeping well? Ours just turned 25 months, and is keeping us awake every night in a monumental struggle for authority. Just wait till yours gets to the screaming phase :shock: :shock: :shock:

All the best,

Nick

 

[indigom]

Can you describe the behaivor a little more. I don't think I quite understand.

You also mention line signals... what voltage are putting into the unit under test?

sorry, I've been away. back now. so even though I wired the 7a-12a, i still get the same no gain in the 7-12 positions. and the 1-6 positions are lower than my Bowman 1272. Is it because I used sowter input transformers in the N72 and Carnhill in the 1272?
I appogise for not knowing the details of impedance matching and all, but I have not tried plugging a mic into it yet. Only line level from a Metric halo audio interface (+4).

When I hit my JLM pad it takes the signal waaaay down, and when I inject the line into the jack for the instrument, I can barely hear it.

here are some pics of my abomination, if that might help:
http://img.indigom.net/pics_pics/1_carnhill_project/1_carnhill_project.html

I just want to be able to color a line out once in a while. is that wrong?

thanks guys!
-Jay

 

[indigom]

oh and I've verified with the meter like 4 times between the connections and the card connector. and tried to make certain that the input / output trannys were wired ok.

-Jay

 

[safe as milk]

hi
i thought the go-between pad was a -20dB ?
so you should be good for line level stuff with that in,
when your on the min gain setting.
cheers

 

[indigom]

opps yah, the JLM is a 20db pad. That makes my line signal so low that even the highest gain setting doens't make up for it so I can get a full level output.
The level pots, btw, work fine. We get +24 to the board, into the right place, and +48 to the JLM Go-between just fine thanks to a nifty JLM power supply. The Metric Halo analog output is set to line +4.

I'm wondering if my switch wiring is off. I counted the one position as the pole after the deck feed on B and right in front of the deck feed on A, then wired around clockwise. Deck A being the front of the switch nearest the shaft/knob.

Is there supposed to be a connection on all of those open deck B positions?

I did verify with the meter under this wiring method that each pole was going to the right hotrod pad. Both channels exhibit the same behavior.

Bauman's N72/1272 was my first real DiY project and it worked the very first time despite the complexities. Now after four other Gyraf projects and various JLM audio things, there is the hotrod. It is the one that should have been far easier, yet I somehow keep messing it up.



please help!
-Jay

 

[Greg]

First, you should not be putting a line signal (1.23V) into the mic preamp. Do you have any way to put a more typical mic signal?

I'd also recommend double checking your wiring.

If you can't find anything, it's signal tracing time. Do you have a scope?

 

[Greg]

[quote author="indigom"]I just want to be able to color a line out once in a while. is that wrong?[/quote]
The Hotrod is a mic preamp, so trying to use this on a line level will give way too much gain.

 

[indigom]

[quote author="Greg"]First, you should not be putting a line signal (1.23V) into the mic preamp. Do you have any way to put a more typical mic signal?

I'd also recommend double checking your wiring.

If you can't find anything, it's signal tracing time. Do you have a scope?[/quote]

Hi Greg! Yah I have a proper mic, just have to pull it out and plug it in. I've triple checked most of the wiring. We do get signal in and out of the unit just not a hot signal.
I do indeed have a scope. I'll try some things and get back. I have 8 of these ba283 boards, so maybe I'll swap one of them out and see if that makes any difference.

best,
Jay

 

[indigom]

The Hotrod is a mic preamp, so trying to use this on a line level will give way too much gain.

well so far, i get about as much level as i put into it via the line, and less as i turn the gain knob. Never to much so far, and most of the switch positions give exactly the same gain with no change.

I just plugged a Blue mic into it and pressed +48v, and didn't get any signal at all out of the unit, btw. hmmm...

 

[Greg]

When you say "via the line," are you referring to the high impendence DI input from the JLM board.

Well it looks like it's time for some signal tracing. We need to find out where we're loosing the signal.

First up, input transformer. Which one are you using? How did you wire it? Is it passing audio?

 

[indigom]

[quote author="Greg"]When you say "via the line," are you referring to the high impendence DI input from the JLM board.

Well it looks like it's time for some signal tracing. We need to find out where we're loosing the signal.

First up, input transformer. Which one are you using? How did you wire it? Is it passing audio?[/quote]

I'm not using the JLM DI board for my line signals because it seemed to take the input level down even further in my initial tests.

When I get back home, I'll get some detail on the transformers and wiring.
I'm using the Carnhill transformers from the Group Buy.

Yes we are passing audio from the input all the way to the output trannys.

A bit later I'll inject a signal from the sig-gen and trace it out with the scope.

thanks
Jay