Hotrod Build Thread

[indigom]

Ok guys, here's what i have maybe it could clear some things up with my 1272 problems.   Images of transformer wiring, boards, and scope pics here:

(2010; link removed, pics no longer online)

cheers~
Jay

 

[Greg]

Something doesn't seem right with the input transformer output. Can you link me to a datasheet for it? It's tough to tell anything solely from the wiring pics.

 

[safe as milk]

hi re the input trafo-

6 ground
tie 3+4,2 hot in,5 cold in

tie 8+9,7 hot out,10 cold out

hope this helps
cheers

 

[Greg]

Is the loading the same as the Sowter?

A datasheet would be nice for my files as well.

 

[Greg]

I'd recommend not jumping pin 6 to pin 10. Just take pin 10 (cold) to the Hotrod PCB. Then take pin 6 to star ground.

 

[safe as milk]

hi greg,
i used the neve trafo page on dan alexanders site,
and a 1073/1084 schematic for the outputs i think

 

[indigom]

[quote author="safe as milk"]hi re the input trafo-

6 ground
tie 3+4,2 hot in,5 cold in

tie 8+9,7 hot out,10 cold out

hope this helps
cheers[/quote]

guys, thanks for you patience and input!

Your description about the input transformer is the way that I had it wired, except i had pin 6 jumpered to 10, which were then wired to star ground. Now 6 goes to star ground, and pin 10 is the cold output.


Still no big difference in the output of this thing, I has about 6 gain settings that are different. ranging from very low gain to all the same higher gain but not overloading my Metric Halo Audio interface input (which is set to instrument level, and -10line works but is lower signal).

Here's the breakdown of what the switch does:
12-7= highest level output, all the same. Using the jumpered deck A and Deck B. All the same level out.
6=lower than 7 above
5=lower than 6 above
4=lower than 5 above
1-3 = barely signal have to turn the audio interface's input to +6db to hear anything, which is below -42db out.

Basically I'm not getting the obvious gain out of it that I'm used to with the N72.

Interesting though, when I put basses and kickdrums, any sound with energy below 300 Hz, and I get more obvious gains then a high-passed snare, loops, etc.. which don't seem to gain at all.

Example, I put a snare highpassed at 390Hz set to 0db output from my sound interface, and at the BA283's highest gain setting then got -0.3db to 0db back in. No gain.

I try this with a sub-bass or a kickdrum and woooah.. i have to turn the output way down, and these definately become gained and sound great. The swiches still do not offer many choices still though, as described above.

Am I missing something here with switch wiring, and/or has something gone bad that isn't obvious? It's really strange how it gains only sounds below 300Hz.

thanks in advance,
Jay

 

[AnalogPackrat]

Are you sure the second stage gain setting resistor is 1k5? It's the one on the side next to the 12R on Greg's board. In your photo it's hard to tell if its brown-green-black-brown (brown) or brown-green-black-gold (brown).

Did you do any bench testing of the BA283 without the hotrod board to prove it is working?

<edit> Potentially silly question, but did you trim the output stage bias with RV1? What bias current did you end up with?

A P

 

[Greg]

I think the input trafo is fine, but disconnect pin 7 and pin 10 and verify that the input trafo is working. It shouldn't be offset like it is in your picture anymore.

So let's move to the gain switch. I don't remember having to jump around the mounting post on the gain switch. Also it likes it might be touching the mounting post. If it is, it'll short 7A-12A.

 

[indigom]

and for the ba283nv side:
r9=120k
r10=68k
r11=33k
r12=47k
r13=5.1k
r14=470ohm
r15=1.5k
r16=10k
r17=2.2k
r18=390ohm
r19=1.8k
r20=51k

oppps found an error- r10 was a 68ohm, not 68k on both boards. i just replaced them.
going to try some audio on it in a few minutes..

Jay

 

[safe as milk]

here's the info for the trimmer.
http://www.groupdiy.com/index.php?topic=19648&postdays=0&postorder=asc&highlight=zobel&start=45

 

[indigom]

all small transistors are bc184c
and for caps I have:

starting from the left side of the board this time:
c1=10uf tant
c2=220pf 50v
c3=4700pf 50v
c4,c7=100uf 25v elec
c5=330pf
c6=100uf 25v

c8=10uf 63v
c9=100pf 50v
c10=1500pf 50v
c11=680pf 50v
c12=22uf 50v elec
c13=100uf 25v elec
c14=22uf tant
c15=22uf tant
c16=1000pf 50v
c17=400uf 25v (330 specified)

all caps verified on my test board. simple enough.

 

[indigom]

oppps found an error- r10 was a 68ohm, not 68k on both boards. i just replaced them.
going to try some audio on it in a few minutes..

Jay

OK, this 68Ohm resister @ R10 caused the BA283 boards not to gain. Now they gain. Big time. I have to use the pad switch on my in's now. Sweet!
:grin:
It's always the stupid little errors, isn't it? I found my bag of 68K resistors contaminated by a few 68ohms. So the error was only on 3 of 8 boards that I made. Normally I check each resistor before soldering, but this one got past Q/A. :green:


The only problem left is trying to figure out what I have done wrong with the 2-deck gain switch. It still only has a few positions that work, with most of them being the same.

-Jay

 

[matta]

[quote author="indigom"]

oppps found an error- r10 was a 68ohm, not 68k on both boards. i just replaced them.
going to try some audio on it in a few minutes..

Jay

OK, this 68Ohm resister @ R10 caused the BA283 boards not to gain. Now they gain. Big time. I have to use the pad switch on my in's now. Sweet!
:grin:
It's always the stupid little errors, isn't it? I found my bag of 68K resistors contaminated by a few 68ohms. So the error was only on 3 of 8 boards that I made. Normally I check each resistor before soldering, but this one got past Q/A. :green:


The only problem left is trying to figure out what I have done wrong with the 2-deck gain switch. It still only has a few positions that work, with most of them being the same.

-Jay[/quote]

Sounds like you haven't jumpered the 2nd deck. Do the few few postions work and then it cuts out? If so there is your problem.

I don't have the hook-up in front of me but if I'm not mistaken you need to jumper 7-12 on the 1st deck.

If you look at Greg's hookup it explains this.

Cheers

Matt

 

[indigom]

Sounds like you haven't jumpered the 2nd deck. Do the few few postions work and then it cuts out? If so there is your problem.

I don't have the hook-up in front of me but if I'm not mistaken you need to jumper 7-12 on the 1st deck.

If you look at Greg's hookup it explains this.

Hi, Thanks for the tip, I saw the problem that you had initially with the 7-12A jumpering and then caught the note on Greg's hookup and did it.

I have sound on all switch positions now, and it is incremental..
until I hit position 7 which is the highest gain... basically 7-12 are all the same gain now and they are wired together on deck A. This is where deck B should kick in and engage the second amp on the BA283 from what I understand.

Deck B 7-12 even though they are connected to the proper places on the hotrod (i checked them and the resistor values), doesn't change or give any more gain.
This problem I suspect goes back to the BA283. Are the open connections on deck B supposed to be wired into anything? The JLM hotrod schematic doesn't seem to indicate so.

hmmm what to do.. what to do. At least the unit is useful to me now.




thanks,
Jay

 

[Purusha]

Can someone just confirm if I need the 2x24 or 3x24 Elma switch for the gain switch?

:roll:

 

[Greg]

You only need 2x12.

 

[Purusha]

Thanks :thumb:

 

[guavatone]

What are the actual gain values witha 10468?

the JLM Hotrod has a "-" next to the values. I am guessing that the 65 to 10 numbers are the gain. right?

 

[safe as milk]

hi
yeah they are the gain amounts.
i believe they're labelled, how much gain to get up to 0.
from -10dB (min gain)
to -65dB (max gain)

seems strange at first,
but then sensible once your used to it