Freitag, 10. Oktober 2014

MPC Ren Vs. MPC3000

Hi Akai friends,

I read so many posts about the MPC Ren, Vintage Mode and the comparison with the MPC3000. Let's find out whats goin on with the MPC Ren and converters.

Akai and SOS was writing: “In addition, the analog output circuitry in MPC Renaissance is identical to the highly regarded MPC3000.”

So what does mean? Akai is very inaccurate in describing which part of the output circuit is identical to the MPC3000. A guy from mpc-forums found out, that they only copied the anti aliasing filter behind the digital analog converter (dac) and the output jacks. Basically a two pole low pass filter without any resonance, and with its -3dB point at 26 KHz.
The MPC3000 sound is a combination of the digital filter, the 18 bit Burr Brown dac and the anti aliasing filter with the opamps. We dont know what kind of dacs were used in the MPC Ren.
Getting started:
So my first test was checking the sound of the MPC Ren DA converter and the sound directly from my external motu audio interface. It’s nearly the same sound, nothing special with the Ren DA converters. So I can’t notice a big difference in the sound, if im using my motu soundcard and bounce a track or using the DA converters of the MPC Ren and record it.

If you are using analog summing, or analog master bus, the sound is quite different for sure, but that’s another story.

MPC 3000 AD DA Converters:
The early s-series samplers used the MPC3000 engine and AD and DA chips and output boards they have a crisp analog sound.

Let's have a look at the electronic components, what makes this crisp MPC3000 Sound.
In the output section there is an 8x oversampling digital filter, followed by the 18Bit serial digital anolog converter. I saw that the MPC2000XL is using almost the same ICs in the output section.
The PCM69A is a dual 18-bit DAC low cost, dual output 18-bit BiCMOS digital-to-analog converter utilizing a novel architecture to achieve excellentlow level Performance.
PCM69A digital offset occurs at bit 4, making it an excellent choice for digital musical instruments and audio DSP.

Most of these DACs utilize a one-bit DAC with “noise shaping” techniques and very high oversampling rate to achieve the digital-to-analog conversion. Basically, the trade-off is from very accurate but slow current sources to one rapidly sampled current source whose average output in the audio frequency range is equal to the current desired. Noise shaping insures that the “undesirable” frequencies associated with one-bit DAC output lie outside the audio range.

These “Bitstream”, “MASH”, or one-bit DACs overcome the low level linearity problems of conventional DACs, since there can be no major carry error. However, this architecture exhibits problems of its own: signal-to-noise performance is usually worse than a similar conventional DAC, “dither noise” may be needed in order to get rid of unwanted tones, a separate high-speed clock may be required, the part may Show sensitivity to clock jitter, and a high-order low-pass filter is necessary to filter the DAC output. The PCM67/69A is a cross between these two architectures. It includes both a conventional laser-trimmed, current-source DAC and an advanced one-bit DAC. The conventional DAC is a 10-bit DAC where each bit weight has been trimmed to 18- bit linearity. The one-bit DAC has a weight equal to bit 10 and employs a first-order noise shaper to generate the “bitstream.”


A key specification for audio DACs is usually total harmonic distortion plus noise (THD + N). For the PCM67/69A, THD + N is tested in production as shown in Figure 12 (Datasheet). Digital data words are read into the PCM67/69A at eight times the Standard compact disk audio sampling frequency of 44.1kHz (352.8kHz) so that a sine wave output of 991Hz is realized. The output of the DAC goes to an I-to-V converter, then to a programmable gain amplifier to provide gain at lower Signal output test levels, and then through a 40kHz low pass filter before being fed into an analog type distortion analyzer.

(Extracted from: Burr Brown PCM67/69A Datasheet U.S.A. August, 1993 )

Akai was also using several converter chips. If someone got some more infos about the Asahi convertes (Datasheet, in which samplers Akai used em?) please send me an email. In the MPC3000 service manual I only see the PCM69.

Asahi Kasei AK5328VP - AD converter Japan

Asahi Kasei AK5326VP - DA converter Japan



PCM69AP-4 – 18 bit serial input DA converter


PCM69BP - BVR - Brown Corporation Advanced 1 Bit BicM05 Dual 18 Bit Digital to Analog
The NJM5532D is a high performance dual low noise operational amplifier.

It shows better noise performance, improved output drive capability, and considerably higher small Signal and power band-widths.
The M522OL is a dual low noise operational amplifier, designed for a preamplifier in audio equipment of stereo and cassette tape decks. High gain and low distorition, suitable for application as an equalizer and tone control amplifier of stereo equipment and tape decks.

Test construction:

Test files: WAV 16 bit 44,1kHz Recording: DA Ren and DA MPC3000, Motu AD 24 bit 44,1kHz

Sample converter: Awave Studio (for the MPC3000)

Test Summary MPC Ren Vs. MPC3000:

The MPC3000 sounds very analog and warm, great transients on the snares and hihats. The stereo image was reduced cause the samples converted to mono.
MPC Ren Normal Mode: Very close to the original sample, neutral sound. Sharp hihats and snare like the original sample.

When I was checking the metering, I noticed that the Ren sounds a bit louder than the MPC3000, but the RMS loudness is 1dB lower. I thought the same like a guy from mpc forum, Akai using a software compressor/ limiter in the master chain.

MPC Ren Vintage Mode MPC3000: Very subtile difference

MPC Ren Vintage Mode MPC60: Bass enhancement, more bottom end, but not even close to MPC60 sound. I got a S950 here in the studio. Maybe I will post the MPC60 and even the MPC2000XL beat.

Most people like the Ren and say it sounds very neutral, equal or even better than any hardware MPC. I really share this opinion, it’s a great neutral sounding MPC. I’m only missing the creamy and crispy sound of the old Akais. But that’s the point why I still work with my old S-Series.
Sounds like magic, pressing one button and you got MPC3000 or MPC60 sound. We only know, its a pure software emulation (dsp algorithm).

Let’s see what the future bring us, maybe someone is opening the Ren and can tell us what kind of converters used in the output section. Akai said: "In addition, the analog output circuitry in MPC Renaissance is identical to the classic MPC3000." I would say: next time ask Universal Audio how that exactly works :) cheers

Donnerstag, 2. Oktober 2014

USB Floppy Emulator with MPC


Troubleshooting Floppy Replacing

With the help of this blog we have been able to repair some old akai sampler. I hope they work another 20 years flawlessly :)
Since every problem a repair is different, I'll post some details.

Daniel de Graaf from NYC wrote me:

lovely tutorial on replacing the floppy drive in the akai s1100. I have followed your instructions and replaced a 235HF-270u with a 235HF-217u like in your tutorial. I have matched the pinout too etc

The issue I have is that the drive will read discs but not format, write, or load to RAM . I get a few errors "DISK NOT READY!" and "NO DRIVE" and "NO DISC" ... Also I only have s950 discs and a few blank discs. It will read the s950 discs and see programs and samples, but the akai freezes when i try to upload those samples with "P+C".

the electronic retailer I bought this from assured they are all tested to write,read, and format on PCs before they are sold. She mentioned there may be a firmware issue happening.

Do you have any idea how and if I can fix this? I also had her ship me out a few other floppy (another 217, a 240?...) drives to test.

I answered him:

sounds like the jumpers not set correct. The problem is, there are different versions of the 235HF-217-U. Seems like later versions don’t have the DC/RY Jumper so you have to solder the pinout.

The jumpers/sliders to change are 2: one selects which drive enable line it will use and one selects what line will be used for floppy detect. The Drive Select jumper is rather easy to find as it is usually labeled "DS": DS0 (for Drive Select 0) and DS1 (for Drive select 1) - you must move it from DS1 to DS0.
Now for the trickier part: you have to change the Floppy Sense or Disk Change to Ready signal. This may be labeled DC/RY. This is a deviator type jumper or slider (usually 3 pins, 1-2 for one setting and 2-3 for another) but can also be a 2pin jumper *or* a "rotatable" jumper if located in a jumper matrix (check 1st pic). This means you need to rotate a jumper left or right 90 degrees from it's default position around one of it's 2 pins. This simply modifies the pin 34 signal (which is usually Disk Change) and reassigns it to send the "Ready" signal.

Well that's it. If you manage to reconfigure these 2 settings, you have a perfectly compatible AKAI (and Amiga) floppy unit which you can use again.

One last note: if you don't have any reference on your floppy for this DC/RY jumper, you may discover it by trial and error - I did this many times as it took me less to try the 3 or 4 settings than to understand where the jumpers went and study the pcb. A good hint on knowing that you hit the right jumper is that when you move it your AKAI shouldn't report a "floppy not ready" or similar error when you have a floppy inserted. Infact line 34, which the AKAI interprets as the Ready Signal is (before the re-configuration) the Disk Change signal. As they behave with inverted logical values (one is active low the other active high) if you leave no disk in the drive, the AKAI will think that the drive is ready and try to read from it! So this will give you some feedback on the jumper you are toggling or moving if it stops doing that (you may have hit the jackpot). 

The sources of the Infos are these other great sites. I really want say thx to all people who sharing so usefull Information.