Hotrod Build Thread

[Milkmansound]

thats a really good idea, I will see what I can find at the hardware store

maybe the caps on gregs boards will fit in there too with that little extra room

 

[Milkmansound]

nice call on the spacers - they work like a dream. I think I gained about 2.5mm with them and that was enough to make the case clear gregs boards and also the JLM trannies.

I just drilled out my panel - now I need to wire everything up and put the 2 caps in that I am waiting for from mouser which should arrive tomorrow

just out of curiosity - whats better to have close to the toroid if anything is going to be - the input XLR or the output transformer? Its tough to squeeze this project into a 1U case for some reason - either that or I am having a spacial relations brain fart. Maybe I can find a piece of metal to put in between to act as a shield, but something needs to be kinda close to the power transformer either way.

 

[Greg]

The Sowter won't fit in a 1U. And as you stated the big caps won't either. I'm in the process of getting mine in a 2U. I have it completely drilled and engraved, but I've been swamped at work so I haven't started wiring it up yet.

Not sure about the toroid question... I just try to keep everything as far away as possible, then deal with issues at a later date if they come up. I built my prototype with an open frame PSU in a 2U and didn't have any hum issues.

Once I get it completed I'll post back here. I have all my parts just need to make time to get it done.

 

[sintech]

Glad to hear the spacers work...as I'm building 1U it's my kinda backup plan also. :thumb:

I'm going to have a listen with the Psu sitting in the rack first, then decide if I build it external or not. As I'm using Marinair 31267's backwards with one winding to emulate the 10468 input iron, but sacrificing the humbucking action.

 

[Milkmansound]

grounding:

so, do all of the audio grounds from the XLR tie into the 0V line, and then I ground the "earth" on the hotrod board to the chassis and and 3rd pin on my IEC power inlet?

or does everything get grounded together?

on the hookup guide for the JLM go between it looks like the XLR input ground goes to 0V - and in gregs picture it looks like the ground on the XLR output goes to the chassis ground. Should these be grounded together - cause it looks like there are seperate grounds on the hotrod baord.

if someone could elaborate on the grounds a little, I would be psyched cause thats the last little hangup I have.

I am really close to having one channel done - got everything hooked up except the transformers and the grounds.

 

[Milkmansound]

ok - my hotrods are FINISHED!!!!

I am excited, because they friggin sound awesome.

Still need to iron out a few details though - like installing the 48V LED's. Also, the 2W 47R resistor in the JLM power supply gets hot as hell - need to figure something out about why. I can't remeber if I used a 2W or 1W in there - that might have something to do with it.

also, man, those output transistors get nice and toasty. Is that normal? I guess since they are always on thats just what happens right?

one of my 283 cards has a sketchy trimmer on it - might replace it since its the original and only works in one position without massive noise and no signal passing through. Probably should replace them both.

you can see my fingernail filings on the front panel especially around the DI because the nut just does not fit with the thickness of my panel. I might just glue them in place when I am done because I do not really know of another solution since its a switching jack and the through plated PCB is nearly impossible to desolder (already tried one and broke a trace)

Thanks to Greg and especially Joe for making such an awesome project - will post some audio when I get the last tiny details ironed out!

without further ado:

 

[dissonantstring]

hey milkmansound,
very nice job! :thumb: can't wait to get mine built.
are you using JLM in and out tx?
what thickness is your front panel?
i'm concerned as I was thinking about ordering the JLM go-between/DI kits but I want to make sure the DI will fit the panel thickness.
thanks.
-grant

edit: thanks milkmansound par-metal series 10 panel thickness = .125" (3.17mm). :thumb:

 

[Milkmansound]

yeah. JLM iron, and I am not sure how thick the panel is but its a par-metal 10 series.

 

[enthalpystudios]

looks nice!

so whats the difference between using 1 jlm input trannie and using 2?

I mean obviously the ratio, so theres less passive gain, but has anyone heard a 283 type circuit with one jlm input and another with 2 jlm inputs in series (I think is how its wired when using 2)

I just saw that on a wiring page for one of joe's other kits, micro 1290 maybe, there are 2 jlm input tx's used.

Well, let us know how you like it in use!

Hopefully I'll have this one done soon..... and then I'll send it to my buddy for whom i'm building it ;[

Billy

 

[JLM Audio]

Hi Tim Saw your email. Thought I would put this up here as it might help a few others in there build.

1. You have three 10ohm resistor linking mains ground to audio ground. One on each hotrod PCB and one on the AC/DC PCB. Leave the AC/DC one and remove the other two or just remove the 2 orange wires going to the ones on the hotrod PCB. Remember only one is needed if several modules are mounted in one case. All our power supplies have one 10R with a 0.1uF bypass cap on the PCB.

2. LM series regulators can usually only do about 150mA of current without a heatsink attached. So 2 Neve modules = 220mA. So fit 2 small heatsinks that don't touch each other or use the insulator kits in the AC/DC kit and bolt the regs to the side of the case or a aluminium angle to the bottom of the case.

3. To make a 1:2 ratio transformer to match the 10468 you need 2 x JLM14 per module wired as shown on our 1290 page overlay PDF because the JLM14 is 1:4 ratio. Wiring one straight to the hotrod mod without changing some resistor values will be like setting a 1073 to 300ohm input impedance which is great if you have 50ohm output mics.
http://www.jlmaudio.com/JLM 1290 wiring overlay.pdf

So you could either buy two more JLM14 transformers

or

Change 7 resistors on the hotrod PCB and get 6dB extra gain. The resistors in series that form the input pad setting also are the load resistor to the secondary of the transformer. So with 1:4 ratio will reflect roughly 300 input impedance. So if you wanted to reflect 600ohm you would make each value twice its value or if you wanted to reflect 1200ohm like the original neve make each value four times bigger.

300R - 600R - 1200R input impedance

2k7 - 5k6 - 10k
1k5 - 3k - 6k2
820R - 1k6 - 3k3
470R - 1k - 2k
150R - 300R - 620R
82R - 150R - 300R
110R - 220R - 430R

Yes you do have to be careful with the DI socket. It can only do 3mm panels max and even then you need to make sure the socket is fully forward in the slots on the PCB when soldered in. Also the hole needs to be 12mm so the thread is not deformed when pushed through the panel. Also the hole should be well deburred on both sides and on the front deburring deep so it looks like a countersink helps. A drop of hot melt glue or super glue on the flat front of the socket can help when putting it in and then doing the nut up finger tight + about 5 to 10 degrees is all that is needed. I have looked everywhere is find a PCB insulated TRS with DPDT switch that is better but there is not much out there with that spec.

Depending on the 48v load the 47ohm resistors will run hot. You can always make the resistor smaller to say 10ohms if you want to draw more current as it is just over current protection.

 

[Milkmansound]

wow - thanks Joe!

I will make the necessary adjustments and post sometime later this week.

I was planning on heatsinking these to the case - just want to make sure it all worked before doing something more permenant. Although I have some clip on sinks somewhere... The regs definitely got too hot to touch.

I will probably change out the resistor values for now - but I will be ordering from you again!

as for the DI, I was thinking about looking for a different type of nut and maybe drilling the hole bigger. Maybe I can find one at the hardware store that goes around the input jack kind of like the nut you'd see on a dunlop cry baby. I did deburr, but I will go in and make sure I was thorough. The threads were not damaged because I always drill the hole out just a tad more than I need for wiggle room since I am the crooked panel master.

once again, thanks so much for making that post you are the man!

 

[Milkmansound]

ok - I did some of the mods... and guess what? I took out one of my 283 cards like a dumbass cause I hooked it to 48V by accident.

thats why the 47R was getting hot (and I did put in a 1W for some reason, I switched it out with a 33R 2W that I had lying around) and also, one of the caps on the hotrod PCB was getting hot which tipped me off to the whole issue. Just when I was about to call it done I have to go ahead and mess something up.

I am still debating whether or not to swap out the resistors or just bite the bullet and add the second input transformer to each channel. Its the classic debate between money vs. time and work desoldering all those resistors (at least one side cause I could just put another of the same value in series right in there).

In the meantime I need to mount my torroid, put in the LED's and figure out the DI mounting.

I am my own worst enemy :razz:

 

[enthalpystudios]

wow thanks joe.

I did actually order 2 jlm1:4's per channel, but being the spendthrift diy cheapass I am, I was wondering how using a 1:4 would sound.

If the said resistors are changed, and a 1:4 is used in this circuit with a 1200ohm input impedance, would there be any potential problems, such as saturating the input tx or something else unforseeable to someone like me?

Thanks a lot for the input.

And don't worry milkman, I'll be posting my troubles very soon, just need to start wiring and drilling the bottom out.

Billy

 

[Milkmansound]

oh I am not worried - I purpopsely posted every single tiny issue I had here even if I figured it out myself just to have it in the thread for others.

meanwhile - 1:4 with the original resistors is KILLING. Sounds f-ing amazing just how it is. I decided to order the other 2 transformers when I get back from my vacation. But for now, I have this thing just about done! Just need to label the panel somehow.

This thing has enough gain for me at the moment, I am not sure how much difference either changing the resistors or adding more transformers makes, but I have to say this this is one amazing preamp!!!!

with the heatsinks added, and everything running off the right voltage rail the hotrods are nice and cool. You can safely touch anything and not burn a fingertip.

and man was I lucky - my 283 card that I thought I nuked just had a bad solder joint. I am in business, and about to wire this thing up into my patchbay!

 

[Greg]

Sorry I haven't been around here lately (busy with work)... but I'm glad you got a pair up and running and I'm glad you like them. :thumb: :green:

Thanks for reply Joe.

 

[mattmoogus]

As long as you dont mind loading all your mics with 300ohms, you dont NEED to change the resistors/transformer. It might make some sound not so good though, its hard to say. Certainly it wont be the best for ribbons. Also its getting further and further away from Neve, if thats of any concern.

Re the other question about saturating the input tranformer, well yes you can but thats always possible, and in my experience sometimes desirable. Thats what the PAD is there for anyway, then you can try both ways and see what you prefer on any source.

Also, the mic pre wont really be like anything Neve made, but weather you care and weather it sounds less good, well thats up to you!


M@

 

[enthalpystudios]

hmm.... thanks matt.

I'm definitely more about having a nice sounding preamp first, and 'neve similar' second.

Regardless, I'm going to just use all 4 for 2 channels like the jlm wiring diagram shows.

I don't honestly even know where I'd use them otherwise, just got my cinemag api tx's and all, and have some ouncers to use in a nyd one bottle, etc etc.

I've been trying to 'do it right' lately, since my first couple experiences were lessons in pinching pennies and I've realized that the extra money here and there is worth it ten-fold.

nice frontpanels, quality switches and other parts, etc...

An extra 50-100 bucks for one of these projects is nothing in the long run, wherever it gets applied.

i got to remember that if it weren't for this forum and all the helpful/selfless people around here, I'd have very little cool equipment to work with. very little at all.

thanks

billy

 

[mattmoogus]

[quote author="enthalpystudios"]I've been trying to 'do it right' lately, since my first couple experiences were lessons in pinching pennies and I've realized that the extra money here and there is worth it ten-fold.

nice frontpanels, quality switches and other parts, etc...

An extra 50-100 bucks for one of these projects is nothing in the long run, wherever it gets applied.
[/quote]


Thats very true! Its fine to work to a budget when youre building a project but I find its never worth trading a few dollars for a lot of extra hassle or a project that looks much worse than it sounds.

You always thank yourself for going the extra mile during building when you see it sitting in the rack and it looks better than your bought gear.

:thumb:

M@

 

[matta]

Hey Greg (or anyone else),

I powered up my Hot Rods today, sounds great, been a long time coming... though I think I'm missing something...

I've tried to follow the wiring/hookup guide and wired the rotaries as per my understanding of the hook up doc, but it only works with deck 1, after the 6/7th click I get nothing, and it is the same on both Hotrods.

The Gain works well and is incremental as expected but after the 6/7th slick, a slight hum, nothing else...

You mention in the HookUp Doc 'Jump Postion 7A-12A', not sure what you mean and maybe that is what I'm missing?

Any suggestions?

Cheers

Matt

 

[Greg]

If you take a look at the JLM Schematic, you'll notice that starting with the 7th gain position, the input is being de-balanced by the input transformer, then taken directly to Pin U on the BA283AV. Without the jumpers in place, you'll get no input signal into the BA283AV.

The 7A-12A means the 7th through 12th positions on the first deck.

Sorry for the brief explanation. Hope this helps.