Trasformerless (class A) DOA mic preamp - design discussion

[dogears]

I didn't read it as sour grapes at all. I enjoy your anecdotes JR, thanks for sharing them.

 

[Winston OBoogie]

That was known to me as the 400 000 rule (20Hz-20kHz, 40Hz-10kHz...). I've seen variants.

You'll find examples written in old textbooks (R.D.H. for one) which were based on studies done regarding an optimum (most natural sounding) balance of frequency response for radio sets.

 

[JohnRoberts]

OMG JR. Yes, Mackie kicked you in the balls. Get over it.

You asked and I answered...

If it makes you feel better, I sincerely doubt it had anything to do with the circuitry.

why would that make me feel better... ?

The problem is that the Peavey brand never got a ton of respect from the pro-audio community.

The problem was not the pro community, ironically Peavey actually got more respect from objective professional users. It was the wannabe/posers who were too cool to be seen using Peavey

People are fickle. They buy stuff because of how it looks. How it works is important. It has to work. But as long as it does, it's actually secondary to how it looks.

Uh... I literally invested decades into this so I have some observations. Inexperienced consumers do not want to be embarrassed by their purchase, they don't want to think they made a bad choice. 

If they just changed the logo alone that would have boosted sales literally 100%.

wow... don't get me started on that...  The old logo known inside Peavey as the "lightning bolt" logo, was designed by Hartley on his notebook cover when he was in HS, and it looks like it. Everybody hated it except Hartley.  Many of us inside preferred the new "block logo" much more modern looking and promising to not be your daddy's Peavey. Near the end of my time working in product management I was about the last PM using the new logo while every other PM had switched back to the lightning bolt logo because of threats from Melia Peavey (RIP) to not even show the new logo to Hartley for approval. 

The Peavey logo looked out-dated by ~1986 (and IMO it was never cool). I grew up in the 80's when Peavey stuff was high profile in the stores.

it depends in which stores... Back then Peavey had limited distribution, and winning a Peavey dealership was like a license to print money, so Peavey enjoyed enthusiastic dealer support from Peavey dealers, disdain from those who were not authorized dealers.

However the market changed by the late 80's. One of Greg's gigs between Tapco and Mackie Designs, was consumer (AudioControl).  It was there he learned about the power of advertising.

I recall Mackie's first mixer the 1604 IIRC, not much of a mixer, but a brilliant marketing campaign, supported by numerous full color, full page ads in almost every magazine you could imagine. I estimate his ad budget back then spent promoting that one SKU was approaching Peavey's total ad budget for over a thousand different SKUs. Peavey's advertising was more about promoting a brand image and more about keeping the limited distribution network of dealers happy, then selling direct to end users.  Greg upset the apple cart by hard selling his one mixer as a does everything for everybody. He included an obscure function (PFL) then with advertising made it a must have feature, even though the majority of  customers didn't even know what it was or what it did, but had to have it.

The dealers had a fairly easy decision to make when customers walked in with money in hand demanding to buy that magical pre-sold Mackie SKU. It was a very successful program and I still have the scars. 

I still have a Renown 400 buried in my mom's attic somewhere. My impression was that Peavey stuff was popular for PA applications and cheap guitar amps. If you needed some watts, you get some Peavey stuff and put it in the background. People also get bored easily. So some new thing comes out and all of the sudden it's all-the-rage. You never had a chance.

Peaveys problem was not image but being stuck in a dealer centric business model. That (bricks and mortar) is even more obsolete today, but the wheels were falling off it even back then.
=====

If I haven't put you all to sleep yet with my whining, let me talk some more about advertising.

No amount of my arm waving and pointing at Mackie ads was going to get me relief, so I undertook a new strategy. Peavey operates under a very sharp pencil pricing discipline. When products are designed and released for production, there is a very precise profit calculation, approved by Hartley.  I had the opportunity of a next generation re-release of a series of small mixers. To secure an advertising budget for just those mixers I included it in the price/profit calculation. I negotiated and Hartley signed off on an  X dollars ad budget for every mixer shipped. Thinking my problems were over, I enjoyed a self funding ad budget that was actually working (duh).  8) Then I ran into the Peavey bureaucracy brick wall. First problem I had advised the factory scheduling guy to increase my mixer build numbers because of expected demand generated by my increased and regular advertising... But months later I had dealers calling me up direct and complaining that they can't get mixers.  I went back to the scheduling puke and asked him why he didn't schedule more units like I told him to, and he said, all the product managers tell him they will sell more but never do. : I was ready to strangle him, but instead I took out my anger on some innocents at the gym.  After I finally got him convinced to load in more schedule, the factory still dragged its feet and left me with a chronic backorder still, months later.

I finally had a face to face meeting of the minds with the factory manager. It turns out that I had shared with him at some earlier point that I would be releasing another new generation of small mixers to replace this current series a couple years in the future (something Peavey routinely does). His primitive mind could not grasp the benefit of filling all the backorder of sales between now and some vague future version come into production.  He considered it a waste of his precious time to invest in a product that will get obsoleted at some future date. Guess what, every single product in his factory gets obsoleted and refreshed.

OK, this ugly journey is not over... the final insult came when a new ("empty suit", a technical term) Director of marketing took my mixer ad budget and used it for some pet project of his... I wanted to smack him but his nose was so far up Hartley's ass I might have hit Hartley by accident.

I eventually gave up when I found myself arguing with the man who has his name on all the buildings and signed my paycheck. I know that I not a marketing/advertising genius, but I knew when I was right. And even with proof my sales-funded ad campaign was working it got shut down.

You can lead a dumb horse to water, and even get it to drink some, but a really dumb horse stops drinking, even after being shown how easy it is.  8)

I really do not enjoy reliving this, Peavey had great potential and pissed it away (IMO). I have slept great ever since quitting.

JR   

 

[Bo Deadly]

Well I hope you got a cathartic experience from that JR but it might be TMI for the Internet.

 

[radardoug]

Well I enjoyed it. History of our industry can be fascinating.

 

[user 37518]

Well the schems are all on the Mackie site (which is fantabulous BTW and one of the reasons why I just recently stolebought a basically mint 1402VLZ4) and indeed I can see that early on the caps were a little small. In particular, the Micro Series 1402 VLZ used 4.7R / 470u for a cutoff of 72Hz. But later models it seems they abandoned the idea and went whole-hog for 3.32R / 3300u. Personally I think they should have kept the 470u. LC would only kick in at the very end of the pot travel.

Thanks for the tip on Mackie schematics, I just checked the VLZ1402 schematic, the mic pre doesn't have global negative feedback, its just a CFP with an opamp.

 

[Gold]

In the 80’s Peavy made stuff others didn’t.  Who else made a PA head with a couple of aux sends, EQ and reverb?

I remember liking a bass.  The T40 was a nice bass. I just saw they go for a lot on reverb so I guess I’m not alone.

Some really nice tube guitar amps as well.

 

[Bo Deadly]

Thanks for the tip on Mackie schematics, I just checked the VLZ1402 schematic, the mic pre doesn't have global negative feedback, its just a CFP with an opamp.

Yeah it looks like they didn't start doing CFIA until around 1998 with the "VLZ PRO" series.

 

[JohnRoberts]

In the 80’s Peavy made stuff others didn’t.  Who else made a PA head with a couple of aux sends, EQ and reverb?

Yup, the topbox powered mixers were under my Mixer engineering group. That was a thousands per month SKU back in the day. There were multiple generations of the iconic XR600, I think I was over the xr600"E" generation redesign.

The spring reverbs were a huge design PIA to keep hum low while sharing a relatively small package with a couple hundred watt power amp. Later the digital EFX spring replacement greatly simplified that engineering task.

I remember liking a bass.  The T40 was a nice bass. I just saw they go for a lot on reverb so I guess I’m not alone.

Some really nice tube guitar amps as well.

The 5150 guitar amp designed for/with Eddie Van Halen was well respected, but the cheaper "classic" series tube amps did not suck, but I am not a tube guy. The former Peavey engineer (James Brown) who worked on the 5150 design is now at Fender over the EVH series there.

I rather liked the tube mic pre (VMP), and tube compressor  (VCL) designed for Peavey's AMR studio line. Jack Sondermeyer (RIP) knew his way and around the plates. A junior engineer did the grunt work cranking out the designs, but Jack as analog engineering director,  kept him straight. My only contribution to those SKUs was feature set and general design approach (I also suggested making the gain control on the VMP go up to 11).  8)

JR

 

[Aleguitarpro]

A little update about this project.
I started testing old designs (that corp1512) with SMPS .
I can share the module I used (by meanwell) but is well dimensioned and I have a loud noise at max gain setting I can't remove.
I used a standard lm317/337 with about 4700uF caps after rectifiers (before lm317/337) and the circuit works as it should.
What I missed?

Noise of SMPS is in high frequency but it's impossible to remove.
Someone tested a preamp like this with an SMPS with good results?

Thanks

 

[Bo Deadly]

A little update about this project.
I started testing old designs (that corp1512) with SMPS .
I can share the module I used (by meanwell) but is well dimensioned and I have a loud noise at max gain setting I can't remove.
I used a standard lm317/337 with about 4700uF caps after rectifiers (before lm317/337) and the circuit works as it should.
What I missed?

Rectifiers and 4700uF? That doesn't make sense. Post a schematic with part numbers. If you don't have schematic capture software, just draw it on a piece of paper and take a picture with your phone. If the schematic is detailed and includes part numbers and grounding layout, I can almost certainly identify the issue.

 

[abbey road d enfer]

I started testing old designs (that corp1512) with SMPS .
I can share the module I used (by meanwell) but is well dimensioned

What do you mean "well dimensioned"?. SMPS are supposed to be used at no less than 20% load. If you use the tiniest Meanwell SMPS, it's a 15W type. Powering a THAT 1512 would load less than 1%. The SMPS would be in permanent hiccup mode.

Someone tested a preamp like this with an SMPS with good results?

I do that more and more. I always complement them with CLC filters and linear regulators.

 

[Rusan]

Powering a THAT 1512 would load less than 1%. The SMPS would be in permanent hiccup mode.

Indeed.  If the supply you're using doesn't have a built-in active load on its output to maintain loading when no external load is connected, I'd betcha the underloading is likely the cause of your PSU noise source.  Expounding on what Abbey called "hiccup mode," when you under-load a SMPS its PWM turn-on happens in narrow, sharp pulses.  The inductor can only operate intermittently when fed the narrow pulses, which causes its output voltage to rise sharply as well as possibly generating new harmonic frequencies (as inductors sometimes do when not happy).  The supply becomes unstable, and the high peak voltage from the inductor can possibly fry the catch diodes and switching transistor.  Underloaded SMPS = not good. 

Rusan

 

[Aleguitarpro]

Rectifiers and 4700uF? That doesn't make sense. Post a schematic with part numbers. If you don't have schematic capture software, just draw it on a piece of paper and take a picture with your phone. If the schematic is detailed and includes part numbers and grounding layout, I can almost certainly identify the issue.

This is psu I used and works as expected with the circuit I tested
No noise at full gain

 

[Aleguitarpro]

What do you mean "well dimensioned"?. SMPS are supposed to be used at no less than 20% load. If you use the tiniest Meanwell SMPS, it's a 15W type. Powering a THAT 1512 would load less than 1%. The SMPS would be in permanent hiccup mode.
I do that more and more. I always complement them with CLC filters and linear regulators.

I used a RPT-60C because I need 5V for digital microcontroller.
+15V rated at .1-.65A
-15V rated at .1-.5A

Total load in circuit is about 195mA on +15V rail so over 20% of load of SMPS (I have other parts not only that 1512).
That 1512 preamp circuit is separated from the rest of the circuit in which I have relays and leds.
The -15V rail is underpowered because it supply only That1512+THAT1646 and 3x TL074+3x Ne5532.

Probably it causes the noise.

Thanks

 

[abbey road d enfer]

I used a RPT-60C because I need 5V for digital microcontroller.
+15V rated at .1-.65A
-15V rated at .1-.5A

Total load in circuit is about 195mA on +15V rail so over 20% of load of SMPS (I have other parts not only that 1512).
That 1512 preamp circuit is separated from the rest of the circuit in which I have relays and leds.
The -15V rail is underpowered because it supply only That1512+THAT1646 and 3x TL074+3x Ne5532.

Probably it causes the noise.

Thanks

Add some load on one of the rails and see what happens. It's the total load that counts.