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~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~
Old 28th March 2013
  #1
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Evil Genius's Avatar
 

~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~

Hey Guys recently got finished on a mod/upgrade for my PRE73 Mark I which i think was from the 2nd or so shipment of these pre's, So i've had this a few years, the stock unit is pretty good and 'useable' but i felt lacked abit in the top end and was generally crunchy don't know if others felt this way about the unit. But I recently got a few Marinair & Sowter transformers so decided to have a go at modding. Here's whats changed
  1. Marinair T1442 On MIC input (is a line input tranny but still works well, hopefully i can get a MIC input Marinair in the near future)
  2. Sowter on output (no markings on this so i don't know part number)
  3. RCA 2N3055H transistor
  4. NE5532 Op-amp (much hated I know but I've seen them in so many pieces of gear that sound great they can't be all that bad!)
  5. Tantalum caps
  6. All LED's changed to 'modern' water clear ones (my own color choices)
  7. Classic Neve style Marconi knobs

Very pleased with the result, had just the sowter on at first, made the unit darker and thicker, top end got even more unclear though the addition of the marinair and tantalums changed this very clear top end and still great low end response, I feel the pre is past usable now and has got more of the flavour i want. Does it sound like a 1073... No! lol i did not intend for the unit to sound like a 1073 just to sound more in the ball park of a 'boutique,' 'High end' pre sound which i think it does now.
Not the cleanest job I know but everything works properly and is quite secure moving it around.
Attached Thumbnails
~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~-img_0746.jpg   ~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~-img_0756.jpg   ~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~-img_0761.jpg   ~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~-img_0763.jpg   ~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~-img_0766.jpg  

~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~-img_0772.jpg   ~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~-img_0777.jpg  
Old 29th March 2013
  #2
Lives for gear
 

adding all the tantalum caps is about the dumbest thing you could have done and based on all the mods out there the output transformer matters the least.

glad your happy with it though.
Old 29th March 2013
  #3
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Evil Genius's Avatar
 

Lol thanks for the kind words, why all the tantalum disdain there seems to be conflicting information one school of thought says they're great to use especially in an application such as this, while the other says they're absolutely terrible and stay away from them? would love to get upto speed on this; I also assume you're not a 1073 fan then or not familiar with it? the caps used here are caps that were tantalum's in the original 1073 build (remember this unit is supposed to be a clone) the output transformer may have the least effect of the two however it does change the sound definitely, the input transformer does have the largest impact however, not sure what you're getting at here?

Zen Pro Mods use tantalums too: http://www.zenproaudio.com/1073test.aspx

http://mixguides.com/consoles/vintag.../caps-op-amps/

"Yes, you can argue that different capacitor materials have a sound. Dave Hill of Crane Song once told me a story about replacing the tantalum caps in an old Neve module. Apparently, the non-tantalum replacements changed the sound of the module. Dave's research determined that tantalum caps contributed more even-order harmonic distortion, not as clean—but pleasing."
Old 31st March 2013
  #4
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well for one they fail more often then any other cap I encounter and 2 they suck for audio. I don't care if the 1073 used it or or not. It sucks the high end out of your signal . I as a engineer want control over my high end. I can suck it out if i want to that's my choice not the preamps.
Old 31st March 2013
  #5
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Evil Genius's Avatar
 

Well i agree with your first point they are more troublesome and even a bit more dangerous than 'lytics, but i completely disagree about the top end i think you're opinion also is a direct opposite to most others, They tend to add bite or even sibilance to signals rather than suck out implying an almost low pass or shelving of high end frequencies which is just simply not the case, if you've tried them in a circuit or mod before i'd look at other parts of the circuit before blaming that on the tantalums that's just not their character. Given the individual characteristics of both the sowter and marinair in this mod the tantalums give a great top end response. I doubt anybody would describe the Neve 1073 as having bad top end!

https://www.gearslutz.com/board/8106226-post3.html
Old 31st March 2013
  #6
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um that is not what I'm implying. I'm saying that tantalum caps do not handle high frequency well they lose detail.



this is the frequency response of my gap 73 with 60 db gain switched

probably more like 50 db actual gain.

you can see the rise in the high frequency its a slope that pushes about 1 db at its peak but it acts like a high shelf from 4k up that's alot of detail to be lost.

.
Old 4th January 2016
  #7
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Quote:
Originally Posted by Evil Genius View Post
Here's whats changed
  1. Marinair T1442 On MIC input (is a line input tranny but still works well, hopefully i can get a MIC input Marinair in the near future)
  2. Sowter on output (no markings on this so i don't know part number)
  3. RCA 2N3055H transistor
  4. NE5532 Op-amp (much hated I know but I've seen them in so many pieces of gear that sound great they can't be all that bad!)
  5. Tantalum caps
  6. All LED's changed to 'modern' water clear ones (my own color choices)
  7. Classic Neve style Marconi knobs
Hi Genius! Thanks a lot for your post.
I'm thinking to mod my Pre73 mk2, but I'm a guy that can just hold a solder...
I wanted to ask you if you can tell what are the capacitor values you used and if they have to be all the same or different.
I also wanted to ask if there are other components to change to let the circuit work properly.
Thanks a lot and sorry for my bad English,
Giorgio
Old 6th January 2016
  #8
I was given one so I changed a few things. All the BC transistors are now 2SC3329BL Toshiba, much less noise, less transistor spit. Coupling caps are Panasonic FR series with WIMA MKP-2 .01 uf bypass caps added underneath. Transformer tuning and small caps are WIMA FKP-2. The output transistor, 2N3055 is On Semi. The 072 meter drive opamp was decoupled from the 24 volt supply with an R/C network. THD drops from that.

All the larger psu related el caps are swapped to larger valued FR series. .1 uf mono ceramics are used as bypass caps. The output knob was shorted out, don't need that.

The input transformer is stock and sounds ok. The output transformer is a POS and should be dumped. It robs the low end badly. I used a Jensen 1/2 ratio, 80% nickle. Now I can use it for bass guitar or kick drum.

Tantalum signal caps are always removed here, they are not ideal for audio. Small size and the lack of drying out is their selling point, impedance is no longer their advantage as the FR series are 2/3 less impedance than tantalum caps.

As much work and material I put into this thing, I still don't like it. Maybe someday I'll find a use for it, but my current feedback fast stuff and my super clean tube stuff eats Neve's for breakfast here.

Last edited by Jim Williams; 29th February 2016 at 05:59 PM.. Reason: last word...
Old 28th February 2016
  #9
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JakePaul's Avatar
 

kind of hurts to read this...tantalum caps are horrible. there was an audio test by a famous audio engineer and scientist, speaking about the quality jump between the different kinds of caps. tantalum are some of the worst stuff you could put in there. get yourself styro and mkp/fkp, the distortion will still be beautiful, but the transients will be there...and it WILL be boutique!
Old 23rd November 2016
  #10
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It's been a long time I unfortunately lost my original login details I am the one who started this controversial post many years ago

To JakePaul et al I kind of find it funny...

Has nobody stopped to question the function of the Tantalum caps both in this circuit and the original 1073, or even glanced at the 1073 schematics?

I can't pretend to be an expert and still learning as much as I can... but to me these look like bypass capacitors, not at all in the signal path! I'd even bet changing them back to Electrolytic would have negligible effect on the audio.

The cap values changed were 22uF people... Let me say that again 22uF
So JakePaul good luck finding a 22uF Polystyrene Capacitor, and yes there are probably other film caps available at 22uF but is there really a point in ending up with more cap than preamp, for bypassing?

This was 3 years ago I am still learning but can't believe people are glossing over the details of where the capacitors are used in the circuit!

I did a swap back to the original output transformer to take some measurements for doulos30 back in 2013, that was a long time ago now and have since lost that data. So if doulos30 is still around he'll have to take my word for it that there was more than a negligible difference in measured frequency response between the two output transformers.

Since the original Mod I luckily acquired a dedicated MIC Level Marinair transformer so have a complete set on the input now.

My advice to anyone modding their GAP PRE73 is to concentrate on the Transformers mainly you can experiment with other components, but I think you're unlikely to gain much from it. Familiarize yourself with the schematics of the 1073 (Which this is based on) to help you make decisions.

I still stand by my reasoning for chaning to Tantalum caps; the original 1073 use them instead of electrolytic capacitors. But
I doubt this change made much of a difference, and now would probably not bother with the change.

Jim Williams made some good points about the FR Series Caps

I still use my GAP PRE73 with all the mods from the original post with NO problems, no death by tantalum yet! It gives me the bite and frequency response I was looking for.
My main pre is a GTQ2 (thanks for the great pre Geoff ) and an API 512c (in The Channel Strip package) in among those this modded PRE 73 still finds a place now and then, and is a lot more portable!

With that said I think it's time to drop the mic and
Old 16th January 2017
  #11
Lives for gear
 

To the op. You did the right thing. Ignore the "techs" who replied here. They obviously have not the slightest idea of how to treat a neve. The tantalums belong in there replacing them with modern lytics is plain wrong and will not sound like a neve. If people dont like neves maybe they should work on cleaner gear insted of giving this unqualified advice. I had a similar topic about tamtalums recently and received similar bad replies like you did at first. At some point more knowledgable posters came in.....
Old 9th February 2017
  #12
Company Rep
Quote:
Originally Posted by EvilGeniusNew View Post
It's been a long time I unfortunately lost my original login details I am the one who started this controversial post many years ago

To JakePaul et al I kind of find it funny...

Has nobody stopped to question the function of the Tantalum caps both in this circuit and the original 1073, or even glanced at the 1073 schematics?

I can't pretend to be an expert and still learning as much as I can... but to me these look like bypass capacitors, not at all in the signal path! I'd even bet changing them back to Electrolytic would have negligible effect on the audio.

The cap values changed were 22uF people... Let me say that again 22uF
So JakePaul good luck finding a 22uF Polystyrene Capacitor, and yes there are probably other film caps available at 22uF but is there really a point in ending up with more cap than preamp, for bypassing?

This was 3 years ago I am still learning but can't believe people are glossing over the details of where the capacitors are used in the circuit!

I did a swap back to the original output transformer to take some measurements for doulos30 back in 2013, that was a long time ago now and have since lost that data. So if doulos30 is still around he'll have to take my word for it that there was more than a negligible difference in measured frequency response between the two output transformers.

Since the original Mod I luckily acquired a dedicated MIC Level Marinair transformer so have a complete set on the input now.

My advice to anyone modding their GAP PRE73 is to concentrate on the Transformers mainly you can experiment with other components, but I think you're unlikely to gain much from it. Familiarize yourself with the schematics of the 1073 (Which this is based on) to help you make decisions.

I still stand by my reasoning for chaning to Tantalum caps; the original 1073 use them instead of electrolytic capacitors. But
I doubt this change made much of a difference, and now would probably not bother with the change.

Jim Williams made some good points about the FR Series Caps

I still use my GAP PRE73 with all the mods from the original post with NO problems, no death by tantalum yet! It gives me the bite and frequency response I was looking for.
My main pre is a GTQ2 (thanks for the great pre Geoff ) and an API 512c (in The Channel Strip package) in among those this modded PRE 73 still finds a place now and then, and is a lot more portable!

With that said I think it's time to drop the mic and

You did a fine job buddy. I use them too on my 1073 and I have pretty much tested every single variation on iron and components for this schematic.
Original 1073's had tantalum (for whatever reason), most engineers love a vintage 1073, it is the best selling preamp ever, so good or bad for audio they belong there, it is part of the chain.

Enjoy your preamp!
Old 30th May 2019
  #13
Here for the gear
Well, well, well

Quote:
Originally Posted by JakePaul View Post
kind of hurts to read this...tantalum caps are horrible. there was an audio test by a famous audio engineer and scientist, speaking about the quality jump between the different kinds of caps. tantalum are some of the worst stuff you could put in there. get yourself styro and mkp/fkp, the distortion will still be beautiful, but the transients will be there...and it WILL be boutique!
6 years on guess what caps GAP used in the "premier" version of the PRE 73 hmmmmmmmmmmmmmmmm I wonder

I rest my case.

Again take a look at the 1073 schematics and components used on board, can you see why the choice was made for tants on the 22uF caps? Also they have used polystyrene caps in place of the previous lower valued film caps used in the earlier 'red' PRE73.
Attached Thumbnails
~{GAP PRE 73 Marinair, Sowter, RCA Mod!!!}~-golden-age-premier-73-inside-carnhill.jpg  
Old 30th May 2019
  #14
Here for the gear
Quote:
Originally Posted by joshuanaconda View Post
You did a fine job buddy. I use them too on my 1073 and I have pretty much tested every single variation on iron and components for this schematic.
Original 1073's had tantalum (for whatever reason), most engineers love a vintage 1073, it is the best selling preamp ever, so good or bad for audio they belong there, it is part of the chain.

Enjoy your preamp!
Thank you! It's still going strong, was reminded of this post as the On/Off switch needs replacing now. Has done some mileage
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