racking up an 1108 pre

[aryl]

-i posted this last night in the black market on accident. i was tired...-
i've done the search.
has anyone has racked up one of these, if so i'd to talk to you. i'm trying to explore my options and approaches to this project. i've email dave(soundguy. he seems to be all about them), but i wanted to see if anyone else had experience with these also.
i am familular with componets and basic theory, but thats about it.
if anyone has any suggestions, let me know.
i have been wondering about the gain control thing. so i'd need to control gain with onother peice of gear or put a buffer at the front end like the 2108, but that requires a transformer that i probably could not get.
also, i found a site on here called www.rollmusic.com , they have built power supplies for $100(doesn't include the transformer) that power both the amp and the phantom power, as well as buffered input jack boards($75, 2 chnls??) that regulate the 48 volts as well as polarity. this seems like a decent option.
how much does racking up an average preamp module cost? parts only vs. professionally.
this seemed like a decent way to get a good pre for a decent price, i just want to be careful.

 

[soundguy]

unless you want to redesign that amp, forget gain control and just run it straight gain. If you were to put an input buffer it would not require an additional transformer beyond the two that are in the amp.

The roll music input cards last time I checked do not regulate the phantom. They are useful, Ive used them in many projects.

you can get a chasis for under $100 and the rest is up to you, what you are willing to spend on parts, could be lots or little. If you dont factor your time, its cheap, if your time is worth anything, its way expensive as it takes a long time to put these things together.

Look for new york daves attenuator if you want a gain control, you could get fancy and put one before and one after the amp.

dave

 

[aryl]

dave, did you get my email?
doesn't the input board that rollmusic has regulate the phantom?
as far as new york daves attentuator, would it just be a knob(buffer?) that brings the gain up to where it would be if ther was not control in in the first place?

 

[al_p]

the attenuator would be like a variable pad. i don't think 'buffer' applies to this or is what you mean...i think.

 

[soundguy]

the gain of the amp is unchanging, a pad before the input transformer will knock the level down that enters the input transformer, a pad after the output transformer will lower the level of the output, but the gain in the circuit itself is fixed.

dave

 

[SonsOfThunder]

I assume we have all seen this schematic? But HERE is a better one. And some notes for it. More notes and More notes 2

So if I get it all correct, the input trim would give you 25dB of adjustment and the High/Low switch changes the amp gain from 40 to 45dB. You should be able to manipulate the gain there at R10/R11 by setting up a resistor ladder and a multipole switch.

This is another of those projects that I would be on if I didn't have to work for a living. I have a pair of output xformers and i built up the ckt on a proto board but haven't touched it in a while.

HTH!
Charlie

 

[soundguy]

hey charlie, thats my site!

You can cram a pot in the LDR socket and that WILL work, but I dont think it sounds nearly as good as leaving it at set gain. Ive dicked around with an attenuator where you mentioned but didnt again, find it very linear sounding. At the end of the day, after lots of experimentation, I think the thing that benefits the circuit best is an attenuator on the input so you can control how much the input fet goes squish and then some form of attenuation on the output. I never got much into modifying the circuit though, I was trying to keep it usable and as close to stock as possible. If I had to have a desert island preamp, this would probably be it...

I wonder, would an LO1166 work as an output transformer on this circuit? It needs a gapped output transformer, right? That could be an interesting marriage...

dave

 

[SonsOfThunder]

[quote author="soundguy"]hey charlie, thats my site![/quote]
Dave,
Don't know whether to feel stoopid or think this is cool.
Guess its a small world! Well I'm certain you know the ckt MUCH better than I. I think this is where we could use some insight from our friend W'oBoogie! I think you must be correct on the trafo being gapped...the problem being that you need that third secondary for the FB. That's supposed to be the "sound" of these pre's and the reason that I bought a pair when I could. Do you know anything of the specs for the input trafo? Where in the world is W'o Boogie! Accck!

I think your plan sounds like a good idea...can you draw it up?

Peace!
Charlie

 

[soundguy]

its the same output transformer thats in an 1176, so if you can find one of those...

I dont have time for jack nimble right now, but there isnt much to draw. I wired mine straight gain and when you need the control just add an external attenuator if you dont feel like putting one in the box with it. It would be wonderful to use a carnhill transformer with this circuit, that woudl be a really unique marriage, neve sound with fet behaviour...


dave

 

[aryl]

ok, a couple questions.
1. the the pre has a high or low gain setting thats 40db or 45db "terminated"/45db or 50db "unloaded." i'm sorry, but what exactly is the difference between terminated and unloaded?
2. will adding a trim pot be tonally different than leaving the LDR, when the pot is set at straight gain?
3. are replacing the LDR and the adding the attentuator at the input that you were talking about, dave, the same thing?

i'm just trying to get things straight here. bare with me.

 

[soundguy]

you have an LDR with yours?

dave

 

[aryl]

i though they all had LDR, based on the posts above. there is one in the schematic. i am a bit confused, as far the "inputrim" being used or not used. thats just attenuator/pot we've been taking about, right?
by the way, my module has a terminal block, not a card connector for the strap.

 

[aryl]

one other thing. there is a number of 24v power one power supplies on ebay for not muich money. are these worth using? also how are sosa supplies?

 

[aryl]

sola, not sosa.

 

[soundguy]

all the ones I have just have the socket. My advice to you is to wire the audio in/out, hook up the power and listen to it. You can answer all the real questions you have yourself by just listening, the info on my site is accurate for my units, so follow those schematics and listen to what you have. You may not mind the pot being there for the control it gives you. Its a unique preamp and worthy of the experimentation time with it. There are several places you can clip a pot for gain control, not that I can remember to tell you where, I just clip leaded a pot and screwed around for an evening. In the end I just left it at straight gain and figured a work around for it.

dave

 

[SonsOfThunder]

[quote author="soundguy"]its the same output transformer thats in an 1176, so if you can find one of those...[/quote] Dave, I have the output trafos...need input! (effect: Johnny Five voice for that last word!) :grin:

Peace!
Charlie

 

[soundguy]

is there something special about the input transformer?

dave

 

[SonsOfThunder]

[quote author="soundguy"]is there something special about the input transformer?[/quote] Dave, I don't know...I don't know anything about it. I had thought about just trying to get an input trafo for an 1176, but I have no clue as to the turns ratio of either piece.

The output trafo is easy...a lot easier than one might think.

Peace!
Charlie

 

[soundguy]

physically the 1108 transformer is fairly large, 1176 just uses an 0-12 wired backwards.

dave

 

[aryl]

thank you all for the help. i think i have a better idea of what i'm going to do. i'm sure you'll be hearing from me when i get the parts i need.
david