Make up gain module build

[Arsun]

id like to make around 10 channels of high quality make up gain modules for my vintage passive eqs using Avedis 1122 op amps.
I see capi has many kits for this. does anyone here have any first hand experience doing something similar and can point me towards the correct kit or direction.
I want to keep it as simple as possible, just one knob that increases gain until it reaches the desired level.

thanks so much!

 

[ruffrecords]

You need to be certain the gain make up amplifier has a sufficiently high input impedance so as not to load the passive EQ and alter its curves. Unfortunately the Avedis web site is very short on specifications so it is hard to see why you would want to use these rather than original API ones.

Edit: Not to mention that the Avedis web site says they do not set the 1122 op amp for DIY projects.

Cheers

 

[Arsun]

You need to be certain the gain make up amplifier has a sufficiently high input impedance so as not to load the passive EQ and alter its curves. Unfortunately the Avedis web site is very short on specifications so it is hard to see why you would want to use these rather than original API ones.

Edit: Not to mention that the Avedis web site says they do not set the 1122 op amp for DIY projects.

Cheers

thanks for your reply.
the Avedis op amp can be bought right here on his website and the specifications are listed on the page https://avedisaudio.com/1122-opamp/#tab-id-2

its buried in the website under the accessories tab so its very easy to miss.
I could definitely use the api op amp, I just own a few of his md7 pres and really like them.

either way, I'm quite the novice with electronics. Do you have a recommendation for a kit or anything like that that I should look at?
im looking to just have around 10 channels of gain with one (maybe lockable) continuous attenuator to increase or decrease gain with precision.

 

[ruffrecords]

thanks for your reply.
the Avedis op amp can be bought right here on his website and the specifications are listed on the page https://avedisaudio.com/1122-opamp/#tab-id-2

Now open the FAQ below where it asks "Do you sell 1122 op amps for DIY projects or personal use?" And the answer given is that they do not.

Does the gain make up need to be discrete? There are plenty of IC op amps that will do the job.

Cheers

Ian

 

[Arsun]

Now open the FAQ below where it asks "Do you sell 1122 op amps for DIY projects or personal use?" And the answer given is that they do not.

Does the gain make up need to be discrete? There are plenty of IC op amps that will do the job.

Cheers

Ian

well I just bought one so that FAQ answer must either be a mistake or some sort of good faith situation.
either way like I said im pretty happy to use an api one if I have to.

I was using a box with IC's in it before (a signal transport synth driver). lately I've been using my Avedis md7 mic pre as the makeup gain and It sounds better. so I want to make a simplified version of the same thing that is lower cost than just buying a mic pre and using that for make up gain. that's the reason im making this thread.

 

[ruffrecords]

OK, you have clearly thought this through. Here is the basic 2520 circuit I recommend for gain make up following my passive EQ designs. The 2k2 is intended to be a preset that you adjust for overall unity gain. If the passive EQ has an insertion loss of less than 14dB you should change the 2K2 preset to 4K7. You need to add the power and decoupling components as well as an output coupling capacitor. I do not know of there is a kit that will allow you to implement this circuit.



Cheers

Ian

 

[Arsun]

OK, you have clearly thought this through. Here is the basic 2520 circuit I recommend for gain make up following my passive EQ designs. The 2k2 is intended to be a preset that you adjust for overall unity gain. If the passive EQ has an insertion loss of less than 14dB you should change the 2K2 preset to 4K7. You need to add the power and decoupling components as well as an output coupling capacitor. I do not know of there is a kit that will allow you to implement this circuit.

View attachment 131412

Cheers

Ian

Thank you!

 

[Arsun]

A mic pre will often have input and output transformer,, in addition to a discrete opamp. So you might not get as much vibe as you are expecting with just the opamp.

This thread might be useful
https://groupdiy.com/threads/2520-based-eqp-1a3-325-utility-line-amp-project-open-source.87393/

Thank you!

 

[Mihobro]

Also consider what the destination device this is driving. If it is a balanced line, you could consider a differential balanced ouput, essentially adding a second output 180 degrees out of phase with the output. It can also be accomplished using output transformers. The advantage being common mode rejection, which is a factor in high RF neighborhoods, and other radiation that is leaking into the lines, especially if you are using long runs 25'+.
Secondly we would also want to make sure the destination input can be fully driven to clipping with some a little room to spare. Finally , it is an art to match transformers with OP amps. Dean Jensen had some really good designs. https://www.jensen-transformers.com/transformers/ . . .Schematics and a lot of information on designing transformer devices.

 

[vintagelove]

Hopefully this doesn't derail, and maybe it's worth its own topic. But...


I always wondered if there was a good subminiature tube, which had a low gain, just enough to make up for a small (6db?) loss for a passive eq, that maybe runs on a low'ish voltage that could be used as a line in, in a tube mixer. Something that would require massive amounts of heat and power for 16 channels.

 

[Mihobro]

Don't know too much about marginal tubes as they are hard to find. Most modern circuits will use common on dual triode 12AX7 or 12AU7, "modern" designs use radically low bias voltages to make them last a lot longer. I don't know off the top of my head. a dual triode theoretically could be used for two channels, but you would still need to deal with the output as classic tube designs as I recall used "power" tubes to drive the transformer outputs. " modern" designs tend to cheat by using an IC or discreet transistor to drive the output stage.
I believe in many cases the "smoothness" of the sound of transformers input and outputs come about by the limiting of the bandwith. Combined with the use of class A circuitry. This eliminates a lot of the crossover harshness in badly designed AB circuits as well as supersonic distortion and RF hash.

 

[ruffrecords]

Hopefully this doesn't derail, and maybe it's worth its own topic. But...


I always wondered if there was a good subminiature tube, which had a low gain, just enough to make up for a small (6db?) loss for a passive eq, that maybe runs on a low'ish voltage that could be used as a line in, in a tube mixer. Something that would require massive amounts of heat and power for 16 channels.

The big issue with tubes is the output stage; that is where most of the power is consumed and the heat produced. A lot depends on what kind of load you want it to drive and to what level. If you want to drive +20dBu into 600 ohms, that is 100 mW of power. If you want to drive +20dBu into 10K that its just 6 mW power.

Tubes get a bad press for heat production, probably because of the huge hot tubes used in the output stages of guitar amps. But preamps consume a lot less power. Your average twin triode operating at normal voltages will consume no more than 5 watts of power. The last mixer I built, which would fit in a 19 inch rack, used 18 tubes and consumed less than 100|W.

Cheers

Ian

 

[vintagelove]

The big issue with tubes is the output stage; that is where most of the power is consumed and the heat produced. A lot depends on what kind of load you want it to drive and to what level. If you want to drive +20dBu into 600 ohms, that is 100 mW of power. If you want to drive +20dBu into 10K that its just 6 mW power.

Tubes get a bad press for heat production, probably because of the huge hot tubes used in the output stages of guitar amps. But preamps consume a lot less power. Your average twin triode operating at normal voltages will consume no more than 5 watts of power. The last mixer I built, which would fit in a 19 inch rack, used 18 tubes and consumed less than 100|W.

Cheers

Ian

For my use, it would be going into your twin line amp configured as the virtual ground summing.

It would just be cool for each mixer channel to have a switch from passive, to "active" with the passive eq followed by the tube makeup stage.

Also, those Russian sub mini tubes are cheap, and many have been praised. Figured if there was one that was a good candidate, it would be a convenient choice.

 

[zzzzz]

I recently laid out a very versatile line amp / make up gain open source project based on the Pultec EQP-1A3 / API 325. Here's the info and gerbers to make your own PCBs: https://groupdiy.com/threads/2520-based-eqp-1a3-325-utility-line-amp-project-open-source.87393/