Compact desktop line mixer?

[JohnRoberts]

Indeed. Soundcraft desks. Typically 5534 in the micpre (and typically 2SB737 transistors) .

I discovered 2sb737s (pnp) and 2sd786 (npn) developed by a small company in Japan for phono head amps (from reading an IEEE journal article). That small company was purchased by ROHM to market them internationally. When I published a 1980 MC phono preamp kit design using them in Popular Electronics (500k circulation) a marketing guy from ROHM thanked me for the publicity.

I recall writing a letter to Studio Sound back then, and mailing a few pieces of 2sb737 in response to an article in SS from a UK "expert" claiming that discrete bipolar devices that quiet did not exist.

I was pleased to find out that Peavey already had the 2sd786 (NPN) in their system when I started working there in the mid 80s. The 737 pnp was slightly lower EIN noise voltage but the 786 was more than good enough for mic preamps, so I started using them. They went EOL obsolete around the turn of the century. Probably because mic preamp ICs became too good to not use them in production designs.

Maybe 5532/4 some other critical points. TL072 everywhere else.
Similarly with DDA desks that also have a Soundcraft link. A&H similar. Probably lots of others but those are the ones I'm most familiar with through work or ownership. E&OE.
afaik his use of parallel circuits as discussed is more a thing in his own hifi / diy oriented designs.
I believe that Gareth Connor ex of Soundcraft may be a member here (at least has been) and would have much more accurate detail than myself

At this point it is kind of old news, but worth observing that back in 70s/80s when those parts (553x/07x) were brand new they were faster than needed for audio reproduction. Now decades later they are still faster than needed for audio.

JR

 

[Newmarket]

I discovered 2sb737s (pnp) and 2sd786 (npn) developed by a small company in Japan for phono head amps (from reading an IEEE journal article). That small company was purchased by ROHM to market them internationally. When I published a 1980 MC phono preamp kit design using them in Popular Electronics (500k circulation) a marketing guy from ROHM thanked me for the publicity.

I recall writing a letter to Studio Sound back then, and mailing a few pieces of 2sb737 in response to an article in SS from a UK "expert" claiming that discrete bipolar devices that quiet did not exist.

SS = Studio Sound ? The expert in question ? (or DM if prefer not to say here)

I was pleased to find out that Peavey already had the 2sd786 (NPN) in their system when I started working there in the mid 80s. The 737 pnp was slightly lower EIN noise voltage but the 786 was more than good enough for mic preamps, so I started using them. They went EOL obsolete around the turn of the century. Probably because mic preamp ICs became too good to not use them in production designs.

Yes. There is also the idea that the demand for them was in large part due to the decrease in vinyl - and hence phono stages.
Given the relatively recent increase in vinyl sales - I don't know what current phono stages are using for gain. Maybe the newer generations of "uber" opamps ? And the most touted replacements for them - SA1085 etc IIRC - are now long obsolete ?
Sort of amusingly , you can pickup budget products on Ebay etc - eg a Soundcraft Spirit Folio Notepad (I have a couple fwiw) that have 4 mic channels with 737s, so that 8 off. Usually inexpensive because untested/no psu - largely a function of Soundcraft using probably the world's worst and unobtainable power connector
But yes - the micamp ics became very attractive depending on the manufacturing model.
IIRC AMEK used SSM2015 in one or more desks. More expensive but less components, inventory, assembly, pcb estate etc. Swings / Roundabouts.

At this point it is kind of old news, but worth observing that back in 70s/80s when those parts (553x/07x) were brand new they were faster than needed for audio reproduction. Now decades later they are still faster than needed for audio.

JR

Come on...you must know by now that you need opamps with a bandwidth extending into at least high MHz to be useable for audio.
Do you not read Gearspace ?
How else could you use them in a transistor radio
( Boring Caveat: Actually some extended bandwidth is useful wrt linearity wrt hf interference but it's not the place to deal with real rfi )
Seriously though, I remember when first getting into electronics - my nearest city (Cardiff) had a Tandy store (Radioshack) that sold 5534s. IIRC they were around £5 each in a blister pack. This was super expensive in around 1980 !!! I think I went to the proper hobbyist shop (another story) and picked up some TL07x. Actually probably more appropriate as I was building stuff for HiZ (passive bass) use.

 

[JohnRoberts]

SS = Studio Sound ? The expert in question ? (or DM if prefer not to say here)

I literally don't remember (and don't care) who but there was a small handful of experts who would pontificate in print about how much more they knew than everybody else. I took great pleasure in mailing them some low noise transistors that they said did not exist.

Yes. There is also the idea that the demand for them was in large part due to the decrease in vinyl - and hence phono stages.

Um I don't think so... MC preamps were a small fraction of the vinyl food chain.

Given the relatively recent increase in vinyl sales - I don't know what current phono stages are using for gain. Maybe the newer generations of "uber" opamps ? And the most touted replacements for them - SA1085 etc IIRC - are now long obsolete ?

Phono preamps are and were easy lifting compared to mic preamps.

Sort of amusingly , you can pickup budget products on Ebay etc - eg a Soundcraft Spirit Folio Notepad (I have a couple fwiw) that have 4 mic channels with 737s, so that 8 off. Usually inexpensive because untested/no psu - largely a function of Soundcraft using probably the world's worst and unobtainable power connector
But yes - the micamp ics became very attractive depending on the manufacturing model.
IIRC AMEK used SSM2015 in one or more desks. More expensive but less components, inventory, assembly, pcb estate etc. Swings / Roundabouts.

Come on...you must know by now that you need opamps with a bandwidth extending into at least high MHz to be useable for audio.
Do you not read Gearspace ?

I recall when high slew rates were briefly in fashion. Thankfully like most fashion trends that too came and left. Several people tried to invent novel names for slew rate overload distortion (TIM, SID, etc) but the mechanisms were already known to experienced design engineers.

How else could you use them in a transistor radio
( Boring Caveat: Actually some extended bandwidth is useful wrt linearity wrt hf interference but it's not the place to deal with real rfi )
Seriously though, I remember when first getting into electronics - my nearest city (Cardiff) had a Tandy store (Radioshack) that sold 5534s. IIRC they were around £5 each in a blister pack. This was super expensive in around 1980 !!! I think I went to the proper hobbyist shop (another story) and picked up some TL07x. Actually probably more appropriate as I was building stuff for HiZ (passive bass) use.

Even back in the 70s 553x and tl07x were good value for the price.

Back in the 70s I was buying TL074s in 1,000 piece lots for my kit business. In the early days I had to test them 100% but after several years they got their quality up.... In the kit business I needed to be able to tell my customers that I knew the ICs I sold them were good.

JR

 

[Newmarket]

Um I don't think so... MC preamps were a small fraction of the vinyl food chain.

I see that. I guess the relevant figure would be the number of mixing desk mic channels vs the number of phono preamps.

Phono preamps are and were easy lifting compared to mic preamps.

Yes. Moving Coil presents challenges to get the most out of it. Although some "just" use a transformer to sort it.

 

[JohnRoberts]

I see that. I guess the relevant figure would be the number of mixing desk mic channels vs the number of phono preamps.


Yes. Moving Coil presents challenges to get the most out of it. Although some "just" use a transformer to sort it.

To put this in perspective the source impedance of a typical moving magnet cartridge is around 1.5k ohm, a low Z mic nominally 150-200 ohm, and a moving coil phono cart closer to 10 ohms.

Transformers have been used to scale impedance for all while MM preamps were cost effectively handled directly with ICs since the 70s. As I already shared the uber low Rbb 737/786 devices were developed by a small Japanese company specifically for MC head amps (instead of using transformer impedance matching). The 737/786 was arguably lower noise than needed for low Z mic preamps but widely used. Now competent mic preamps IC have taken their place.

I will have to take your word for the state of the MC phono preamp market. I haven't sold my kit since the early 1980s, and my later preamp design was MM only.

JR

 

[Newmarket]

just for clarity - I was commenting on the technical challenge to get the best out of a very low Z MC cartridge.
I don't have any current info' on the commercial market for them now.
But your post did make me wonder how many are being bought in the current "Vinyl Revival" and how that stacks up against MM types.
fwiw my own TT is out of commission atm due to stylus / cat interaction

 

[JohnRoberts]

just for clarity - I was commenting on the technical challenge to get the best out of a very low Z MC cartridge.
I don't have any current info' on the commercial market for them now.
But your post did make me wonder how many are being bought in the current "Vinyl Revival" and how that stacks up against MM types.
fwiw my own TT is out of commission atm due to stylus / cat interaction

Back when I was selling my MC preamp kit, I got favorable comments (privately) compared to using a step up transformer from an audiophile rag publisher (we had a friend in common who gave him the preamp to listen to).. Of course there were far more variables involved than just the transformer.

JR

 

[OneRoomStudio]

Back to the topic of a compact desktop line mixer

I started drawing up the master section (minus monitoring since that will be a different board). This is just mix bus, mix insert, solo bus, and output amp. I still need to add the VU meter circuit, but I wanted to get the basics down first.

 

[MidnightArrakis]

Back to the topic of a compact desktop line mixer

I started drawing up the master section (minus monitoring since that will be a different board). This is just mix bus, mix insert, solo bus, and output amp. I still need to add the VU meter circuit, but I wanted to get the basics down first.

Do the -- Ferrite-Beads -- have a value to them?

Is your -- TQ2-12V -- a "reed-relay"?

Is there a reason on why you're using a -- +/- 16V -- rail instead of the common -- +/- 15V -- rail as produced by common devices?

/

 

[OneRoomStudio]

Do the -- Ferrite-Beads -- have a value to them?

Is your -- TQ2-12V -- a "reed-relay"?

Is there a reason on why you're using a -- +/- 16V -- rail instead of the common -- +/- 15V -- rail as produced by common devices?

/

I've never seen ferrite beads for audio list a value on a schematic before. I don't think the specific value matters much, other than the ability to withstand the amount of (miniscule) current going through them. Something like this would do just fine.

TQ2-12V is a very common signal relay.

I think +/- 16V is actually more common in audio. All 500-series equipment is +/- 16V, and I believe most equipment from API, Amek, Mackie, and many many others is the same. It's no problem to build a +/- 16V supply using LM317/337's.