Re: V-241 from scratch
« Reply #120 on: April 16, 2018, 04:30:08 AM »
I received the mic pre and have been recording with the 241-76 mic pre now here for about a week on as many sessions as i can.
And i can say with certainty that its  very classy sounding mic pre indeed !

It has its own character but at the same time sounds to my ears quite flat.

Its been up against some pretty big names, as i have here 6 other mic pre's here that i use regularly.
My favourite for vocals over the last few years has been either of my API's (the 512 or Capi 312) both of which are great. And the V241-76 sounds very bit as good as those and has its own character - which is in short - big and round!

I am especially pleased with how it work well with my vintage C12.

Thank Dave for your great builds, i use them all regularly on my productions here each week .

Ian



Re: V-241 from scratch
« Reply #121 on: April 25, 2018, 05:37:02 PM »
Great to hear! I am currently in the process of building one. Waiting on the cinemag transformers to be built, so it won't be done for a couple more weeks.

Right off the bat I realized that my power transformer didn't have a center tap for the 6.3vac filament. Do any of you guys know if you can use an artificial center tap (2 200r resistors from each side of the transformer to ground) in this situation? I have done some research and it seems like if I only have one ground reference I should be good, but I want to make sure before shorting something out. Thanks!

DaveP

Re: V-241 from scratch
« Reply #122 on: April 25, 2018, 05:52:11 PM »
I have not tried that on a high current circuit, but I guess they would have to be rated for the return current if you are making a DC filament supply.  An ac filament supply will not give you such a low noise spec.

Good luck

DaveP
Soundcloud: Delayed Action.

My3gger

Re: V-241 from scratch
« Reply #123 on: April 27, 2018, 05:25:36 PM »
Using LDO regulator and schottky diodes can get you close to 6,3V on heaters. LDO drop doesn't take much power from PT.
I found EH makes new ECC85/6AQ8. Looks well built like some more expensive EHX, so it is good news for those who didn't know it.
« Last Edit: April 30, 2018, 06:51:46 PM by My3gger »

Re: V-241 from scratch
« Reply #124 on: May 10, 2018, 04:16:37 AM »
Thanks for the help! Very excited to have just finished building this amazing preamp! I tested it with my Apex 460 modded to a C12 and was blown away by the huge low end and clarity on the vocals and acoustic I recorded! I added a switchable Cinemag DBX DI transformer and had a blast playing my  50's Silvertone bass through it. It blows the Altec 1566a I built out of the water.

I am looking forward to running some tests on this version to see how it compares with the others built. I am expecting a higher noise floor/AC hum because i have not shielded the power transformer or cables, but the Cinemag CM-75101A input transformer with a mu-metal casing seems to be doing a great job!

I am planning on making a HPAD output switch so I can get some crunch  while running a good level to my interface.
I was thinking of a 1K impedance on both sides of the pad to bridge the transformer output (output load is around 80 ohms?) But I would love to hear if anyone has other values I should try.

Dave- thanks again for sharing this incredible pre with us! I hope to share the results of my tests this weekend along with some sound clips!
« Last Edit: May 10, 2018, 04:23:25 AM by Alm6mountain »

Murdock

Re: V-241 from scratch
« Reply #125 on: May 10, 2018, 06:39:21 AM »
Looks and sounds nice!
Did you build it according to the original schematic or Dave's modded one?

DaveP

Re: V-241 from scratch
« Reply #126 on: May 10, 2018, 08:37:14 AM »
@Alm6mountain,

It's great that you have made your own V241 and that this project has been helpful.

Another guy's post about the V241 inspired me, and so it goes on, this is why this forum is so good.

Best
DaveP
Soundcloud: Delayed Action.

Re: V-241 from scratch
« Reply #127 on: May 10, 2018, 07:41:28 PM »
Looks and sounds nice!
Did you build it according to the original schematic or Dave's modded one?

This is almost identical to Dave's modified 241-76 schematic found on the previous page. The only changes were to 1 resistor value on the high voltage and 1 resistor on the filament because I am running a a Hammond 115V power transformer at 120V. However, there is no shielded wires at this point.

Re: V-241 from scratch
« Reply #128 on: May 10, 2018, 08:10:33 PM »
Attached is my result from the frequency response test.

I am not sure if my way of measuring is the best that I could have done.  I loaded the output of my interface with a 1.5K pad that fed the preamp. (I added a crude diagram of the signal path attached as well) I used the RightMark Audio Analyzer software with a sine sweep. I have used this a method as a simple way to test builds, and it seems to give me the results I would expect, but I am sure there has to be a better way. I don't currently have a signal generator other than my computer and my oscilloscope is from the stone ages. How do you guys get accurate tests?

DaveP

Re: V-241 from scratch
« Reply #129 on: May 11, 2018, 03:49:57 AM »
A stone age scope is fine!

You just need a basic sig gen with a constant output level.

Take readings at 10, 20, 50, 100, 200, 500, 1k, 2k 5k, 10k,20k, 50k. off the scope.

Convert your readings to 20LOG( *) in Excel then relate them to the reading at 1k

Put them in a table in Excel and choose smooth line graph option, then format the frequency to log scale.

Most amps are totally flat in the mid ranges, but curl up or down at either ends of the spectrum.

DaveP
Soundcloud: Delayed Action.


Pief

Re: V-241 from scratch
« Reply #130 on: May 29, 2018, 12:25:28 PM »
@Davep

Nice work. I was reading up on your project because i.m building a preamp with an Ef86 at the first stage aswell.

I started a thread about this. The Olmsted brdcstr thread.
Wondering if you could shed some light on what to do.

I was wondering. I got my project free of hum. But not free of hiss.

The ef86 is pushing a signal that is really hot and hissy.
Did you experience the same problem?

I have a gain pot between ef86 and second stage.
Thinking about repositioning it before the first stage to control it a bit better. Don.t wanna run a pad just to keep it under control.

Any thoughts?

« Last Edit: May 29, 2018, 12:29:20 PM by Pief »

DaveP

Re: V-241 from scratch
« Reply #131 on: May 29, 2018, 03:05:46 PM »
@Pief

I'll reply on your thread

DaveP
Soundcloud: Delayed Action.