Serious preamp (line amp) question:

[J!m]

Okay. I got an idea. Far from original but I’m thinking I want to do a nice preamp now.

I have some ideas based on the MBL 6010D. Loosely based- as in it will also use op amps. And that’s about where it stops.

You can get “clones” of the circuit but I don’t know how reliable it is. But some have been built and they perform well/sound like nothing.

I got to thinking someone who designed op amps would be a good person to ask about taking the MBL and making a fully balanced version of it. Perhaps some of the noise lowering techniques and flat frequency response of the phone pre could be brought to bear- with a much lower gain.

So I asked. And got a reply. Not a “no” but the yes is conditional on the specification. I started writing one, having never done one before. It’s probably crap.

So, I’m asking here (finally), what details are important to you in your line amp? What features do you find most useful? What sort of “really neat” implementations or HMIs have you run across that made you say: that was an treat idea? And what made you say: “ WTF were they thinking?!?

In writing this spec I’m not fully sure where I should be “specifying”; the electrical specifications are beyond me- stuff like THD within X frequency range NTX bla bla. (Engineering specifications) So im focusing on the features and HMI aspect, while I will be asking the question directly, I thought input from others who appreciate a quality product and have used more than a few over the years.

What is known:
Line stage only (phono pre external)
Fully balanced internally
True dual mono out to the power supplies
Provisions for single ended (any sonic compromise will affect SE to preserve balanced operation)
Stepped attenuators only- no pots
Possible balance control(s)
Probably a high and low gain mode
Tape loop!!!

 

[J!m]

No comments? I have fleshed out a spec sheet for the designer. No idea at all if that is what he's looking for, but hopefully the conversation will continue...

I'm looking for "feature" ideas from you guys- what do you like and dislike in preamps you have, or have used.

One "different" feature I may incorporate is a pair of VU meters, which will prevent you from using an overdriven input. This may expand to individual attenuators for each input, so you can "trim" them to be equal. So, switching from phono to CD won't have a massive volume difference, for example. But, keeping the levels within reason will keep the distortion as low as possible. Sound quality is the primary concern here, so it will be dropped entirely if performance suffers for it.

These days, most people don't even need a line amp. They might have an integrated with direct digital in (onboard DAC) and that's the deal.

For us dinosaurs that prefer to build a system, I think this VU feature has value.

 

[George S.]

I like the PL2000 Series 2 preamp with it's foot print, form factor, looks, integrated phono section, and tape loop. Think it sounds excellent after upgrades. I wish it had a additional phono input, and didn't have the built in reverb.
This is a opamp based preamp, not a line preamp. I have never had a line preamp to play with.

 

[George S.]

Oh, and only preamps I've ever had is a Marantz something in the garage system and a Dynaco PAT4?? long ago. The upgraded PL2000 is superior. So never had anything high end, and most probably never will.

 

[Lazarus Short]

I'm looking for "feature" ideas from you guys- what do you like and dislike in preamps you have, or have used.

Many years ago I was lucky enough to score a TM-1001 tuner from a fellow who also owned an Ampzilla and two huge Saba speakers - he raved about it and after I used it I raved about it too. It was one of the best tuners I ever owned. Then I goofed, went to my local Radio Shack and bought the matching SA-2001 amp. It had gobs of features, BUT in time I learned that it just did not sound good. I also learned that most of the problems were in the preamp section. So I learned that if all else is equal, more features, worse sound. Some may disagree with that but that is my stance, and I'm sure there are exceptions.

Roll forward to the present, where I use a recapped Cyrus 2 as a preamp. The features are simple: gain and source. Sound is excellent. I know, bad, sketchy examples, but again: if all else is equal, fewer features, better sound. I'm done with "features."

 

[J!m]

To address you, Laz, up front: no "feature" will be added, if it degrades performance. All single-ended connections will take any compromise required for operation. If switches or additional circuitry is required to convert up to balanced line from SE to proceed through the preamp, that is where it will take the hit. But, even so, I am hopeful this will be 100dB down in the noise, a nd not creeping up into audibility.

I will not have the phono preamplifier integrated in (this) design. That's not to say a later version won't have it. It would require some significant re-engineering and I don't think it could be an "upgrade" option on this go-around.

The idea of being able to add a second phono input (outboard phono preamp) could be accomplished via another port on the back. Maybe I change the naming convention to "AUX" or, maybe a user-changeable label system (since they're never "right")... I asked, because it may be necessary to utilize a buffer on the tape loop, so if you are listening to a record while also recording it, there are no loop/feedback issues possible. Might not be necessary, but I'm asking the questions.

I may also incorporate VU meters. I was reading about how today's "hot" digital sources can often overdrive the input on a preamp, and cause totally avoidable distortion. I think the headroom will be massive in this design, but just in case... It may further expand into 10-turn trimmers on each input so all sources can be "dialed in" such that switching from CD to record does not show a massive drop in volume, or, conversely, massive gain switching from phono to CD. I know I had to be mindful of this with my 47k v. CD on my rig...

Currently a 2-chassis design. Power supplies will be in a (hoping for) 1u box, connected to a 2-3u main box. Similar/complimentary aesthetics as my WP-1 phono preamp (silver face with copper accents), which would be on top of the pile. So, it would be a 5-6u (plus foot room) size preamp all-in, with MM and MC phono capability (both can be connected at once since there are two independent boards in the phono pre).

 

[Lazarus Short]

So far, I think you have it well thought out.

 

[WOPL Sniffer]

I'd skip the 2 chassis idea. Can't you just make a shielded portion for the traffo? I've seen some "Dead Quiet" pre's with the transformer in the same box. Maybe use a toroid which can be a bit quieter? Myself, I'd avoid buying the 2 chassis design. There are $10K preamps with 1 chassis. Just my 2 cents

 

[krellmk]

Okay. I got an idea. Far from original but I’m thinking I want to do a nice preamp now.

I have some ideas based on the MBL 6010D. Loosely based- as in it will also use op amps. And that’s about where it stops.

You can get “clones” of the circuit but I don’t know how reliable it is. But some have been built and they perform well/sound like nothing.

I got to thinking someone who designed op amps would be a good person to ask about taking the MBL and making a fully balanced version of it. Perhaps some of the noise lowering techniques and flat frequency response of the phone pre could be brought to bear- with a much lower gain.

So I asked. And got a reply. Not a “no” but the yes is conditional on the specification. I started writing one, having never done one before. It’s probably crap.

So, I’m asking here (finally), what details are important to you in your line amp? What features do you find most useful? What sort of “really neat” implementations or HMIs have you run across that made you say: that was an treat idea? And what made you say: “ WTF were they thinking?!?

In writing this spec I’m not fully sure where I should be “specifying”; the electrical specifications are beyond me- stuff like THD within X frequency range NTX bla bla. (Engineering specifications) So im focusing on the features and HMI aspect, while I will be asking the question directly, I thought input from others who appreciate a quality product and have used more than a few over the years.

What is known:
Line stage only (phono pre external)
Fully balanced internally
True dual mono out to the power supplies
Provisions for single ended (any sonic compromise will affect SE to preserve balanced operation)
Stepped attenuators only- no pots
Possible balance control(s)
Probably a high and low gain mode
Tape loop!!!

Just get this and upgrade the op amp
https://www.ebay.com/itm/1854871903...MI0rS-lI-u-QIVionICh1lcAAgEAQYBCABEgKDnfD_BwE

https://www.aliexpress.com/item/225...29975876__pc__pcBridgePPC__xxxxxx__1659648270

 

[J!m]

Funny- that’s where this started… despite XLR connections, it is not a balanced design. But the original one is very highly regarded. And also not balanced. And the China versions are probably not a true clone circuit and may well contain counterfeit parts. Building up from a bare board is the way to go but then why not build up something unique?

in the MC phono preamp, the op amps are run in parallel (2 per channel for one gain stage, then a single for the next gain stage) and this significantly lowers both noise and distortion at high gain levels. The MM side uses single op amps in each gain stage (different ones).

I’ve asked the designer to bring that parallel op amp technology to bear on a preamp, based loosely on the MBL, but a dual op amp (quad op amp really) fully balanced design.

If I go to a linear power supply, it will be both larger and much more expensive. I was dead set against using a switch mode power supply but with the optimized filter board, it has been built (by others) with the power supply in the same box as you suggest with good results. I will have two power supply’s as well as an incoming power filter in the power supply box (dual mono) so it would get big with all that hardware. I could probably put the switching supplies in the same case but if it does cause any noise (I’m hoping for lower than -100dB) I’d have to re-engineer the whole thing. Mu Metal is expensive for making shields- about the same as an external box.

Keep the ideas coming!

 

[Bob Boyer]

Three tape loops; R2R, Cassette, and DAC/ADC. Better yet, the inputs that would take signal from an external phono pre could go straight to some really good ADC circuitry. USB out or other for computer link. Good internal DAC circuitry on the way back in from the computer or DAP.

 

[WOPL Sniffer]

Too much junk.

 

[WOPL Sniffer]

How about a built in Cigar lighter, a 100 foot extension cord which reels inside like a vacuum cleaner. Maybe some stadium lighting and a hotdog cooker.

 

[Lazarus Short]

How about battery power with automatic recharging when turned off?

 

[George S.]

Why not use a Thinkpad power supply. Used to use them on old Linksys wireless routers. They're very abundant and cheap.

 

[J!m]

How about battery power with automatic recharging when turned off?

This is an idea I always liked. I figured it would be required for the phono preamp, but it isn’t. With proper filtering, the NeanWell power supplies are really amazing.

 

[J!m]

Three tape loops; R2R, Cassette, and DAC/ADC. Better yet, the inputs that would take signal from an external phono pre could go straight to some really good ADC circuitry. USB out or other for computer link. Good internal DAC circuitry on the way back in from the computer or DAP.

There will be one tape loop. Which is 100% more than any other new preamp as far as I’m aware. One input will be slated for a digital source but it will be an analogue line. No DAC in here, and most DACs double as preamps.

I suggest an Apogee Rosetta or Benchmark DAC.

 

[J!m]

Today I did some more designing. I can do a minimalist design with outboard power supplies that perfectly compliments the phono preamp.

But, in order to include all the features I want, I did a new 3u single chassis design.

I then did some market research to see what is out there that is dual mono fully balanced. And I was able to find a few current production preamps. Wven more if you include tubes but I didn’t. Only solid state.

They’re pretty expensive too. Not that mine won’t be, but it seems I inadvertently nailed a few points in my design that are being addressed by others- and some thing not addressed by others

For both designs, it is designed to compliment the phono preamp, using similar “design language”. If you guys have seen the Naim seperates, that’s a good example.

 

[J!m]

For those who like visuals... Here is a (already obsolete) mockup of my phono pre on top of one possible embodiment of the line amp.