Behringer VM1 Vintage Time Machine

[Scruffie]

Help?
The MN3102 provides a supply voltage and to antiphase clocksignals to the BBD chip. What exactly would make it quieter??

Weaker clock pulse?

[JiM]

Help?
The MN3102 provides a supply voltage and to antiphase clocksignals to the BBD chip. What exactly would make it quieter??

Depending on the semiconductor technology, the clock signal shape can impact the way the BBD transfers the charges along its stages.
I've got this info from an old book (as old as myself ) about CCD, which are improvements over BBD. However, the principle looks the same.

So, with a two phase BBD, you're alternating the "height" (aka potential) of two interleaved groups of "buckets" (MOSFET capacitors) by applying an out-of-phase clock signal to each bucket group, and "pour" the charges from the higher buckets to the lower buckets next to them. But how do you ensure that the charges don't "spill" in the wrong bucket, towards the input ? There are several ways :

• use more than two phases. Obviously not the case for MN3xxx.
• use ion-implatation or variable oxyde thickness under the gate to give the bucket a slanted, or staircase-like shape, in order to direct the charges in the right way
• give the clock signals a trapezoïdal shape, often asymetric with a sloped falling edge, again to "pour" or "push" the charges in the right direction.

I suppose that the MN3xxx use either of the latter two techniques (or something different, not being a CCD. Maybe that's the reason for Vgg ?), but you may notice that the datasheet specifies a crossing point of the antiphase clocks that is not in the middle of their voltage swing, despite having the same frequency and a 50% duty cycle. There is a "wave forming" thing in the MN3102 block diagram, that may be intended to provide this specific shape for improved charge transfer in a two-phase device. This is something that a 4047 might not provide, with proper steep-sloped antiphase square waves.

There is also quite a big capacitive load to drive, especially for bigger brigades like MN3005 : a fanout of 2048 CMOS gates is something you would absolutely avoid in a digital circuit ! The MN3102 output buffer is intended to drive that, again the 4047 is more general-purpose therefore not optimized.

From what i've read i'm led to beleive the 3201s are limited to the amount they can drive, so a 4047 may deliver a stronger output yes... Also the 4047 is cheaper.

Actually, with a 5V power supply the MN3102 can source 5mA whereas the 4047 sources or sinks just 1mA. Maybe it's the opposite at higher voltages, but it's not fully specified in the datasheets.

So this might explain some differences in sound or efficiency. But i won't risk stating that one sounds better than the other ...


By the way, i eventually purchased a VM1, so i'll be able to double check my schematic. I can already report the values of the LFO capacitors : 330nF for vibrato, and 2.2µF for chorus.
Now, let's talk about mods !

[ssmc]

Help?
The MN3102 provides a supply voltage and to antiphase clocksignals to the BBD chip. What exactly would make it quieter??

Well,I just thought like that because MN3102 was built for MN3xxx,and 4047 was general-purpose IC
Anyway I got some MN3005's and MN3101 so I will try that combo,and MN3005 with 4047,and see what I get.

Sorry for offtopic

[rep_techy]

I changed the mix/blend pot from 10k audio taper to 10k linear like the DMM and got better more equal pot travel, 12 o'clock is now actually 50% wet/dry, much more usable, also used 12V 1 amp DC power supply which makes pedal warmer/more usable overall

[rep_techy]

Anyone have mods for chorus/vibrato to match DMM, I read somewhere that changing the 4558 ics to TL072 ics produce better tone.

[Dirk_Hendrik]

Anyone have mods for chorus/vibrato to match DMM, I read somewhere that changing the 4558 ics to TL072 ics produce better tone.

Source???

[uncleboko]

Anyone have mods for chorus/vibrato to match DMM, I read somewhere that changing the 4558 ics to TL072 ics produce better tone.

Nonsence

[sinner]

I bet reptechy refers to FAQ section of out friend Mikey http://www.analogman.com/faq.htm#analogdelays

Memory Man op-amp IC chip upgrades

There are a few web sites and posts about improving the sound of an EH deluxe memory man, by replacing the normal 4558 op amps with some high tech chips. The noise and tone in a memory man comes from the BBD chips, not the op amps. The BBD chips have about 10,000 times more noise, and very low fidelity. That is normal in an analog delay and nothing can be done about that, it's why people love their sounds. So replacing the op amps will have little benefit, or so I thought.

After writing the above I got some new DMM pedals, they are now using ST electronics MC4558CN dual op amp chips. I replaced all five of these chips while I was in there (those knobs are a pain to remove) with new Texas Instruments TL072 chips.

Dry sound when playing clean - it is improved. Put the mix to pure DRY (no echo) and the tone when playing clean is a little purer. I was surprised.

ECHO SOUND: also clearer when you listen to 100% delayed sound, much clearer and closer to a digital delay sort of tone. Seems to be more difference at lower delay times.

When I turn up the MIX for about 50% delay I tested for noise by playing a low string gently. The modified pedal is a bit noisier, may be a unit to unit discrepancy or could be the TL072 chips allow more high end through which contains the noise.

OVERDRIVEN sound : running a good OD pedal into the DMMs, with the gain knob set for unity gain (LED just glowing) the sound of the stock one seems a little warmer to me, both dry and echo sounds. But the modified one is clearer again.

DISTORTION : Running a good distortion pedal into the units, the modified one is clearer, the repeats are almost too clear. The stock one has repeats which are darker and more in the background. At this point in the test I brought out a '59 reissue Les Paul with burstbuckers 1 and 2 and played through the Maxon SD9/808/silver, into the DMM into a '66 blackface Deluxe Reverb plugged into a '73 Marshall 4x12 cabinet and just played for 45 minutes as it was a MAGIC combination! Gilmour, Hackett, Page sounds were flowing... best tones I ever got for leads.

Anyway, the difference with changing the op amps is noticeable. But not sure whether I like it enough to go through the hassle of pulling the board out... depends on what you want, clarity or a warm background echo. Also the new 2006 classic style DMM pedals do not use sockets so the chips need to be desoldered, a lot more work. These are the EC2002_REV_E boards which can use four MN3008 chips or two MN3005 chips, and use a relay to switch the pedal on and off. The new XO memory man uses tiny surface mount op-amp chips, so they are VERY hard to replace.

BTW, anybody have a service manual of DMM? I have one here totally missbiased

[rep_techy]

Here are some mods I've done that bring the vm1 closer to dmm spec.
Replace the vibe cap c3(330nF) on jack board with dmm value(500nF), c6(.047uF) with dmm(.1uF), c7(47uF) with dmm(22uF), c9(47uF) with dmm(10uF), and VR2 10k audio taper pot with 10k linear like dmm. You may have to tweak the two trim pots @ the middle of the main pcb to get rid of bad distortion on the delay trails, can do it by ear with guitar, pedal, and amp. All of these changes make the vibe setting come alive. Just grab a herdim pick and start chiming away. Will post audio files of the modded pedal for those interested.

[benqbasic]

Hey Would be really interested in those sound clips.
Btw have you modded it to true bypass?

[ace]

Hey Would be really interested in those sound clips.
Btw have you modded it to true bypass?

+1

it would be great if the VM1 can be true bypass
because it makes the sound harsh, when it is off, it's as radical as a crybaby would be

another thing it doesn't sound like a DMM at all, not even close, this effect looks like one DMM only

[rep_techy]

Will post the sound clips asap. Yes, I did mod it for true bypass also with a 3pdt switch and changed the brightness of the blue led in the process(increased the series resistor for less current draw which lowered the blue glare), the led actually turns completely off now. Results: Great tone, no pop, and really enhances the use of the preamp as a boost. Sounds great for ambient delays when stacked behind another delay pedal. I use a 12VDC power supply currently and am curious about using a 15VDC power supply. The caps on the main board are rated for 16VDC so the 15VDC supply should be okay. Am thinking about installing an overdrive in the same pedal b/c of the extra empty space in the chassis. Have a BBE Green Screamer that would go perfect with it. I would also install an effects loop for modulation or volume pedal use. Would cut down on pedalboard space considerably. Gear snobs really snub their noses at these for some stupid reason, they care too much about gear popularity and coolness than about tone and technique.

[rep_techy]

I studied the DMM schematic and the VM1 schematic, then replaced key components in the exact same locations so that the VM1 is basically a DMM with a different clock circuit and small surface mount components(note:the newer DMMs are supposed to have small surface mount components also). Tonally, it sounds pretty close to the DMM now only with a little distortion decay on the trails, which may be due to the lower power supply voltage than that of the DMM. I am also debating about installing a tap tempo circuit.

[benqbasic]

I studied the DMM schematic and the VM1 schematic, then replaced key components in the exact same locations so that the VM1 is basically a DMM with a different clock circuit and small surface mount components(note:the newer DMMs are supposed to have small surface mount components also). Tonally, it sounds pretty close to the DMM now only with a little distortion decay on the trails, which may be due to the lower power supply voltage than that of the DMM. I am also debating about installing a tap tempo circuit.

+1 for a tap tempo design.
Been wondering about the distortion on the trails. Tried to qweek it out but so far no luck.
I may try a higher voltage too. Looking forward to doing these mod's and true bypass. Just so fiddly with smd.

Cheers

[JiM]

I studied the DMM schematic and the VM1 schematic, then replaced key components in the exact same locations so that the VM1 is basically a DMM with a different clock circuit and small surface mount components

Great ! Could you please post this comparison schematic (unless it contains copyrighted material from EHX) ?
BTW, isn't the preamp always on in the DMM ?

Tonally, it sounds pretty close to the DMM now only with a little distortion decay on the trails, which may be due to the lower power supply voltage than that of the DMM.

Are all your mods you described above ? I like the sound of my VM-1, but sometimes i'd like the repeats to be less dark.
Do you have any idea to make the chorus mode usable ? At higher settings it's more of a "sea-sick" effect !

I use a 12VDC power supply currently and am curious about using a 15VDC power supply.

Did you modify the zener-based regulator for higher voltage ? If not, boosting power supply voltage won't affect the BBDs ...

I am also debating about installing a tap tempo circuit.

This looks like a task for a small microcontroller (PIC or AVR) and a digital pot.
Then it might as well take care of the LFO for chorus/vibrato, allowing full control over frequency and waveform.

Am thinking about installing an overdrive in the same pedal b/c of the extra empty space in the chassis.

Me too ! Right now my old Rocktek is just sitting on top of the VM-1, but maybe a Big Muff copy (VD-1) would be better suited for integration. This would need some switching jacks, so they are chained internally when nothing is plugged in, but still can be wired as independant pedals. Where do you plan to put the footswitch, besides or above the existing one ?

[rep_techy]

Great ! Could you please post this comparison schematic (unless it contains copyrighted material from EHX) ?
BTW, isn't the preamp always on in the DMM ?
The schematic can be found on Schematic Heaven website. The VM1 schematic is in prior posts. Don't know if the DMM preamp is always on or not, I wouldn't like that personally. Some pedals react differently to others and I always try to go the true bypass route if at all possible. Doing the VM1 true bypass mod allows the preamp to be used as a boost when you turn on the pedal. Good for lead work. I usually put a clean boost pedal after overdrive anyway to raise the volume up a couple of dbs to cut through the mix for solos. With the true bypass mod on the VM1, I can somewhat do the same thing. I don't know about the zener diode regulator. I suppose you could raise the zener voltage value to allow higher VDC for the delay circuit, but you would have to check with the chip manufacturer datasheet to see what is safe, also the surrounding SMD may or may not be affected also. Until someone comes up with a quick n dirty fix for the slight distortion on the trails, I am quite satisfied with the sound of the modded pedal. If you don't like the chorus sound you could try changing the chorus cap to twice larger or smaller the original value and see how it sounds. Very cool circuit to experiment with.

[rep_techy]

Will email audio clip of the mod. Just PM

[JiM]

Great ! Could you please post this comparison schematic (unless it contains copyrighted material from EHX) ?
BTW, isn't the preamp always on in the DMM ?

The schematic can be found on Schematic Heaven website. The VM1 schematic is in prior posts.

Yes, i know. (i did the VM-1 schematic, after all).
The question was if the combined schematic could be made public, in order to ease comparison and mods.

I don't know about the zener diode regulator. I suppose you could raise the zener voltage value to allow higher VDC for the delay circuit, but you would have to check with the chip manufacturer datasheet to see what is safe, also the surrounding SMD may or may not be affected also.

As you can see in the schematic, the power supply for the preamp and compander (Vcc) is unregulated, whereas the power supply for the BBD (Vdd) is treated by T5 and D4. Raising the power supply would increase the headroom of the preamp, which could then enlarge the compressed signal, which in turn would come closer to the regulated supply rail of the BBDs. This ends up in less overall headroom !

Until someone comes up with a quick n dirty fix for the slight distortion on the trails, I am quite satisfied with the sound of the modded pedal.

Some distortion is normal with BBD, that's why people love analog delays.
If it's more distorted than normal, it could be caused by the power supply voltage increase, or some mis-bias.

If you don't like the chorus sound you could try changing the chorus cap to twice larger or smaller the original value and see how it sounds. Very cool circuit to experiment with.

I'll look at a way to add a proper speed control to the LFO. For example, messing with R43.

[Zokk]

Hello

I've just bought a VM1, it is so cheap so I couldn't resist...
First I must say the sound is awful, really dirty, not what I expected from this pedal. I use a lot the Ibanez AD190 which sounds a lot clearer and cleaner than the VM1... and I expected a bit more definition and a lot less distortion in the bass area...so I won't use this pedal with guitar but with synths, my amp is too clear.

I have done a simple mod to have a really slow LFO for the chorus, I like the step delay effects. So I have put a SPDT switch with 2x 22uF back to back on one side and 2x47uF back to back on the oher side. It gives me the "good" rates for my ears: slow and slower...
But I would like to have more depth for the modulation, the stock possibility is really weak. I don't know what is the best to do to achieve this:
1/ adding a jack input to feed with an external +-5V LFO?
2/ putting a resistor in // with R51 and R52?

Could someone help me with that?
Thanks in advance.

edit: JiM the DMM schematic at schematic heaven seems to have many errors. PM me if you need a valid schemo.

[Zokk]

Hi,

so I've ended with a 1N914 instead of the 4148 as D3.
This gives me more depth with the modulation.

I still strike to get rid of the extreme distortion...
Any advice?