Travis1000

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #200 on: April 13, 2014, 10:27:56 PM »
another pic, this time of the inside...


Re: [BUILD] 1108 DIY project and PCB layout
« Reply #201 on: May 01, 2014, 03:26:39 PM »
I'm sorry to intrude, and also sorry for not having read all topic pages yet.

But I made a search on the site using the word Vactrol, as I am exploring implementing a limiter with a Vactrol or Silonex optocoupler, and I wonder if use any of them as such.

Did you?

dustbro

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #202 on: August 05, 2014, 02:47:11 PM »
Any recommendations to add a quick DI to this circuit?
thanks in advance!
Dan

hildy

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #203 on: March 25, 2015, 02:46:56 PM »
Hiya. Been loving and watching this thread for a while. I'm about to jump into this project.

I couldn't find any info on the current draw for the 1108. Anybody have any specs? I'd love to get four of these amps in a single rack, with an external PS, and I'm wondering if the Mnats PSU design will meet the current requirements.

Also, I really appreciate all of the contributions to this thread. You all have done a lot of heavy lifting.

hildy

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #204 on: March 30, 2015, 04:21:02 PM »
Answering my own question (again), according to mnats' site, each preamp uses 45mA. boom.

hildy

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #205 on: May 17, 2015, 08:03:33 PM »
Sounds beautiful.  Couldn't have done it without your help,  Thank you,  guys and gals!
« Last Edit: May 19, 2015, 12:31:35 PM by hildy »

Whoops

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #206 on: February 14, 2016, 07:40:50 PM »
Hello,
I will do this project soon.

Did anyone tried an UTC A10 for the input?

I checked this post of Bil Wilson:

For the input transformer a UTC A-10 would do very nicely. It has a winding ratio of 1 to 10 & has the necessary taps on the primary. The secondary impedance is 50k ohms & will take +15dbm before the core saturates. The freq response is down only 1 db @ 30cps & .5db @ 20kcps,
(oop's hertz), forgive me but I cut my teeth on tubes back in 52.

The A-10 will work for the 1008 & 1108 as they are to single grid & single FET; it will not work for 1016 as it is a balanced circuit configuration & requires a split primary. A UTC HA-114 will work well as the output xfmr. for the 1016, it is 30k ohms split primary w multiple secondaries covering all the pro output impedances & will handle +23dbm. It is perfect for a 12AY7/6072 in push pull. Freq. response -1db 30hz to 40khz. Input trafo. for 1016 would be a UTC A-12, it has split windings on the secondary for push pull.
Have not take the time to look @ 1108 in detail so cannot give you anything but a guess on the output trafo's impedance but could be around 600 ohms.

I can guarantee the frequency response of the A-10 as I used them in a 6 input 3 channel mike muxer in 64; when I was doing on location mastering for a couple of small rcord co's.

Hope this helps.
Bill W.

P.S.: the dbm figures on the transformers are for the 600 ohm impedance.

The post is in this thread:

http://groupdiy.com/index.php?topic=32729.20#


cdeboda

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #207 on: July 09, 2017, 11:12:20 PM »
Old thread, I know, but I was wondering where I could go about obtaining either the pcb or self etch file for the CM-2511 input transformer. Been through these threads front to back more times than I can count.

I've finished a working mnats power supply and stuffed the 1108 board, just struggling on wiring the input tranny. Any help would be so very much appreciated!

isophase

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #208 on: March 11, 2018, 12:29:21 PM »
Hi all,
I need some help with my 1108 preamp.
I build a pair of 1108 mic preamp some time ago and very happy with the sound! The gain range of the potentiometer however is not correct > all the gain arriving "too soon" when turning the pot. i've been living with the "problem" ever since i build the unit and even if its not a so big issue now i would like to correct it for good. I have read this thread a few times and can't find the solution to this problem. i'm using a 1Meg Log pot for the gain control as suggested here, but when the pot reaches 12 o clock position, it seems the unit has already reached maximum gain and between 12 o clock and fully CW  nothing happens, no gain increase.
i'm thinking of mabe using a x12 position "lorlin" type rotary switch as the gain control instead of the potentiometer, so i did some measurements and experiment.
i disconnected the potentiometer of one of the two channels and took a measurement at 12 o clock position (were the gain is at apparent maximum) and read about 180Kohms on the multimeter. So i thought lets try to wire a 180Kohm log pot in there and see what happens? i'm thinking the range should be better "spread" over the whole track??
Closest value i found in my stock is an 200Kohm log pot, i wired it. For comparision, i connected both channels of the preamp to my sound card in a loop and using a sound generator feeding the preamp low level program material to mimic the output level of a microphone. All set. I dial in some gain, when i compare one channel against the other there is only a slight difference in the gain range, and it still doesn't "feel" right. Its slightly better with the 200Kohm log pot, but only 2dB increase between 12 o clock position and maximum level (other channel with the 1Mohm log pot increases less than a dB between 12 o clock and maximum!)
So i'm sure you guess my question :-) whats the best way to do it?

I did some search and reading on the subjet and also about stepped attenuators, i am aware of the limitations when implementing a gain control this way (attenuation before the preamp) that it can generate a bit of noise and mabe load the microphone and change the tonal balance. I also know the original circuit uses a vactrol + 300 ohm linear pot to control the gain, i 'm curious to know if this should work better because in this case the gain is also implemented in the same manner > attenuation before the fixed gain preamp, so i guess same disadvantages apply? mabe the range is better? i don't have a vactrol to test right now.

The original circuit shows a Hi/Low gain setting in the feedback loop, i did wire a toggle switch for that in my unit and i seldom use it (its on Hi gain setting most of the time) I'm thinking if it would be a good idea if i put a gain control there in the feedback loop? i guess it would work but what are the drawbacks? this switch is very noisy in my unit when i toggle between the Hi and Low settings, i guess its comming from the 130mVDC i can measure on the switch. I'm afraid if i wire a rotary switch there for gain control i will get nasty cracks and pops when setting the gain so mabe not the best way? mabe solve the problem with adding a capacitor but i have no idea if its possible? and mabe changes the sound a bit?

Ok thats it for the questions, too much! :-)
My preamp works well and sounds VERY good, i just would like to have a better control of the gain range and do it the proper way. All suggestions welcome, thank you for your help!
   
« Last Edit: March 11, 2018, 01:09:52 PM by isophase »
"we'll fix it in the shrinkwrap" fz

Whoops

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #209 on: March 11, 2018, 01:57:46 PM »
Hi all,
i'm using a 1Meg Log pot for the gain control as suggested here, but when the pot reaches 12 o clock position, it seems the unit has already reached maximum gain and between 12 o clock and fully CW  nothing happens, no gain increase.

whats the best way to do it?
 

I would love to help you but I still didnt build my units (have 2 pcb's), Im planning to build it in the future.
It seems no one is building this project any longer, the last finished project that was posted was in 2015.

It would be great to know the opinion and experience of other members on the issue that you have in the Gain control,
at least to know if other builders have the same problem or not




isophase

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #210 on: March 12, 2018, 03:39:31 PM »
Indeed, i was thinking of creating a new thread to ask some help about the gain control issue but since it concerns the 1108 i thought it was more appropriate to post inside the dedicated subject..
Will post back when i find correct solution
"we'll fix it in the shrinkwrap" fz

ln76d

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #211 on: March 12, 2018, 05:52:15 PM »
1M is ok = look at the schematic of original, there was a version with handwritng. There you have showned what should be resistors for fixed gain setup. Mnats schematic shows full gain resistor value. If you will go lower then you will be able to set proper levels with 1M pot.

Whoops

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #212 on: March 12, 2018, 08:48:25 PM »
1M is ok = look at the schematic of original, there was a version with handwritng. There you have showned what should be resistors for fixed gain setup. Mnats schematic shows full gain resistor value. If you will go lower then you will be able to set proper levels with 1M pot.

I searched in my archives and I have those notes, it's a 2.9meg pdf file.
pm me your email if you want me to send you the doc

isophase

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #213 on: March 13, 2018, 06:17:12 AM »
Whoops, thank you for the 1108 document!
« Last Edit: March 14, 2018, 05:37:21 AM by isophase »
"we'll fix it in the shrinkwrap" fz

isophase

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #214 on: March 14, 2018, 05:37:39 AM »
Can someone confirm that the feedback resistor is indeed R17 (8.2k) please ? or is it between the pads E and 5 (8.2K) ?
thank you
« Last Edit: March 14, 2018, 07:17:18 AM by isophase »
"we'll fix it in the shrinkwrap" fz

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #215 on: June 15, 2018, 03:18:34 AM »
I'm still a very long ways off from being ready for a project like this but want to do it one day....anyone who's seen this through to completion, what are you doing for the front panel? is there anywhere to find a front panel for this build?

dustbro

Re: [BUILD] 1108 DIY project and PCB layout
« Reply #216 on: June 03, 2019, 02:54:24 PM »
Does anyone have a chart of transistor voltages I could reference? I have a unit with low output.
TIA!!


 

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