Sm Pro Audio PR8E?

[Pentium]

HI Peterc / SOT......

I have been told under good faith that the PR8/ PR8E is prone to this and
so this small addition of 2 caps would greatly improve the crosstalk in this device, I will check this by running a snare through one channel and record the 7 other channels and listen back, If I do not hear anything I will not be bothering.

Will report findings.

I am going to put a few channels into use next weekend on a session.

Thanks peterC, much obliged.

 

[Pentium]

I am also going to try out an National Semi LM4562 today and a
LM6172 when I can source them.

This has turned into a longer term project to get all 24 channels how I want them but I think they will be pretty rockin' once I am done.

I think I will be running a variety of 5532, OP275, LM4562 and LM6172's
based on what I here being suitable for various sources,I suspect the 5532's
will work a treat on kick and Toms as there is plentiful low end. If the LM4562
is as natural and transparent as others say these will be Overheads and other
acoustic instruments, this is serious fun and there is nothing quite like a piece of unique and personalized kit!

I have noted that 5532 and LM4562 run hotter than OP275, this I suspect is cause they both draw around 10ma per chip, you can still keep your finger on them but they are hotter than say a 4558, TL072 or OP275.

It would be possibly unwise to run the PR8E filled to the brim with either of the 10ma drain chips, it might end up lowering headroom though the
external PSU is quite beefy looking and 1000ma 17V AC rated,

Cheers

 

[12Bass]

Did you install a small ceramic bypass capacitor from both the positive and negative pins to ground? It's good practice to ensure stability on new, fast op amps. Oscillation resulting from this omission is one possible explanation for the high temperatures.

Another op amp you might consider is the AD8599. Unfortunately, it is only available in SOIC, so you would need to use an adapter (BrownDog or similar). Compared to the LM4562, I find the AD8599 is warmer, and less revealing overall, but still quite detailed in the highs.

A pair of AD825s on a BrownDog adapter also make a nice sounding dual FET replacement.

My experience with the LM6172 is that it is similar to the LM4562, but not as good to my ears. Some have claimed it is more transparent, but I don't hear it. The design is a few years older.

Initially I liked the sound of the OP275, but over time I came to dislike the coloration it imparted. I'm not sure how to describe it, but I hear what sounds sort of like "spongy" distortion or compression of low-level details with the OP275. It also seems to lose a bit of high-end detail compared to an LM4562.

 

[Pentium]

Thanks for the reply, well the LM4562 has just literally been put in.

The OP275's run cool as a cucumber and it has 22V uS slew and the
LM4562 20V uS so I can currently only account for the 5ma Vs 10ma
current drains (unless of course it is oscillating)

The price of LM4562 in the UK is VERY high indeed £6.45 each is the cheapest
I have found them so they better sound good ! (Sun was out today so went out and did not test them!)

Black Lion Audio are using the LM6172 in the front stage of their mod and
they seem to be getting much praise, people even comparing them to Audient ASP008. I can get the LM6172 for £2.82 each.

The LM6172 has a rather bizarre slew rate of 3000V uS what is that all about?
It seems bonkers.

I am planning to add the caps above as mentioned but currntly none
of the opamps have a cap from -/+ to ground as yet.

 

[SonsOfThunder]

I doubt seriously that 5532 will oscillate in this circuit. I have a whole PR8 full of them for nearly two years with no problems.

HTH!

 

[Pentium]

SOT, I think you are correct, I have also heard nothing, they sound clean as a bell without undue artifacts.

I will audition the LM4562 tonight hopefully and compare with the OP275
which is already a large improvement over the stock 4558 chips.

Then I will put in an order for some LM6172 and also do some crosstalk tests to see if I need to add -/+ caps or not to the opamps power.

One thing I am not quite getting at the moment from my supplimentary reading is that I thought capacitors "block DC", in this case DC passes to
the opamps so they work, how is this so?

In additional Capacitors impede Low frequencies and allow HF to pass

How does this eliminate crosstalk? if that is the case I am guessing the
caps act like a LPF.

 

[peterc]

When you put a cap from power rail to gnd, it acts as a resevoir. So when there is a large draw on the opamp, the rail will not dip & affect all the other opamps. That is why they should be close to the opamp.

Peter

 

[hugoderwolf]

[quote author="Pentium"]One thing I am not quite getting at the moment from my supplimentary reading is that I thought capacitors "block DC", in this case DC passes to
the opamps so they work, how is this so?[/quote]

It depends on how the cap is placed. If you put it in series in a signal line it becomes a highpass together with the input resistance of the next stage (CR-network).
If you put it in parallel with the input it becomes a lowpass filter together with the source resistance (RC-Network). This is because the cap passes AC and so the resistance "pulls AC to ground".

Hope I could make it clear for you. You may want to check here for better understanding:
http://en.wikipedia.org/wiki/Low-pass_filter
http://en.wikipedia.org/wiki/High-pass_filter

 

[Pentium]

Eureka ! well kind of..... it took you guys to explain it to me.

Thanks for that.

In electronics there is much to get confused about.

You see this PR8E modding is not just making pre's better, but I am learning a lot through your patience.

Cheers

 

[quadwould]

Pentium

So what are the results.??


would it be possible to list each opamp combination (on input and output) and what the the results are?

any chance we could here these too?

I am thinking of getting 16ch worth myself.

cheers
david

 

[Pentium]

I don't see why not, my plan is as follows:

In due course I will have the following:

1 channel OP275 in/out
1 channel LM4562 in/out
1 channel LM6172 in 5532 out
1 channel 5532 in 5532 out

OP275 is less agressive in mids but does not have quite the airyness the LM4562 has, the LM6172 has yet to be installed so I don't know (I am keeping this in turn with the 5532 on the output like BLA have done their mod) how this sounds.

The 5532 channel has a very full bass sound.

I plan a controlled shoot out which is a little way off yet
this will involve speech and acoustic guitar.

It will happen but it may take a while.

It is worth doing for the low cost, subtle tonal options it provides.

 

[Pentium]

Here is a set of room mics on a drum kits on the OP275 channels
recorded yesterday.....

http://www.7161.com/track.cfm?track__dt_track_id=15289&user=9575&start=1&end=1&select_flava_id=&music_type=1&name_search=SafeandSound&music_group=1

Considering the 2 mics used cost £12.50 each and each channel of preamp
cost about the same, that is a good recording.

 

[Pentium]

I did some crude crosstalk tests today with my PR8E.

I vocal clicked into a mic and took the mic within a few dB of clipping
on a number of channels and recorded a few channels outputs either
side of the channel with realistic gains setup which had the click going into it.

The result was absolutely zero audibility of the click, just for good measure I took the clicking into total clipping red light full on all the time and no clicks were bleeding through at all, even with a 20dB boost on the audio file + maximum volume closed back headphone monitoring.

Not a sausage.

So they seem crosstalk free to me.

I also recorded an acoustic guitar in stereo using the LM4562 channels
and they sound warm and detailed, I am astonished how these preamps
sound now and every bit of effort put in has paid of 100Pct. The 5532 channel recorded a kick drum with bags of LF depth.

I would love to do an A/B against something like a DAV BG-1, I reckon it would give it a run for it's money and I have 24 channels worth.

It's been a lot of fun and rewarding to, that's called a win, win situation.

: )

 

[bitman]

Thru-Hole!!!

Concider yourself lucky. Those 4458s would have been 5532s already!

:shock:

 

[Pentium]

Bitman I cannot comprehend your post?

 

[SonsOfThunder]

>>>So they seem crosstalk free to me.
Exactly what i expected. But testing trumps "expectations" and "what I read on the internet" every time. Good job, Mr. Pentium!!

Thanks for sharing. Glad you are enjoying and using those pres.

Peace!

 

[aortizjr]

Wow there is some great info in here.

Anyway I have the PR8, the mods have really opened it up. Its biggest weakness though is that the "Gain" control is not a gain control at all.. but an Output level.

Does the PR8E still have this issue? Or is the "Gain" control really a gain control.

Thanks!

 

[Pentium]

Hi there it'e been a while since I visited here but I think the PR8E has a gain control now, I cannot be 100pct sure about this though.

They are still going strong and actually work for me in money earning situations. Well worth the time IMO.

I have purchased 4 x 20dB inline pads in case levels on condensers on drums get too silly.

 

[the19thbear]

hi.. i just bought the sm pro ep84.
it has 4580D IC's.
Anybody know of any good IC's i could use to upgrade this thing??
thanks alot!!

 

[the19thbear]

anyone?