Spectral DMA 150 Upgrade

Jon Q

VIP/Donor
Jun 16, 2019
90
43
150
Lisbon
Hi ack

Good question.

The reason for not choosing a recent version is the components of SMD topology. It is not easy to upgrade, this has several reasons. De-soldering SMD components and soldering again a new component, there is always a risk of damaging the printed circuit, even if it is of high quality.
After choosing certain components, they always have larger dimensions, for example capacitors. This was one of the reasons for my choice for this model.

I recently had a spectral preamplifier for a possible purchase, the classic DMC20 series II. I saw a potential in it in case of an identical upgrade DMA150, but did not advance. First, there is no remote control, then I didn't want to have two boxes, pre / power.

Possibly the choice would be the DMC30SL, it has the DMC20 II board and has remote control, this only in a box. The main update would be the volume potentiometer, the same to the latest series, then it would be the same as the one made in the DMA150.

I currently have a Wadia 6 that I bought in excellent condition, incredible that does not have a risk. I am doing the same upgrade, but this one is more complex and many upgrades come from my professional sector (recording studio maintenance). The clock, reclock and power supply is designed for this unit only. I have many CDs and about 90% are from Japan and the USA. This unit is only used as a transport, the internal DAC is removed.

Possibly I can open a topic here, I think many people might like.
 

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ack

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May 6, 2010
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I had both a DMC-12 and then the DMC-20 Series 2 - this was my foray into Spectral, in the early 90s. Beautiful sounding preamps. People still use the 20 for its phono board (optional back then)
 

Adimon

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Jan 4, 2011
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Adimon

Overall all the modified steps improve. Mechanically , the replacing 10.9 steel screws made a big difference (attention to lengths).
But the best, was replacing the four "ridiculous" rectifier bridges of power supply to voltage amplifier, and customizing a small pcb for ultra fast diodes, that was the biggest difference it made (see pic. 16 and 17).

About the noise of transformers, this is strange on your DMA260.
On my DMA150 this problem was the first one I noticed. Solution was to replace the damping rubbers because they were already very .... very hard (see fig.11).
This is normal because of their lifetime. But your DMA260 seems to be a not too old model.
I replaced with another type with more elasticity. The rubber damping has also been added to the aluminum panels (see photo12). Thus the noise of the transformers is reduced to the minimum possible.
Note: if you are thinking of doing this task, be careful to first discharge the capacitors 10000uF / 80V, this in the DMA150 spectral, the DMA260 I don't know.

Jon

I asked the local Spectral's distributor.
And they said that the noisy transformer is a spectral habit.
The DMA 100S and now the DMA 260.
But the noise varies from time to time.
I notice that in my listening position.
And I want to reduce that.

I tried everything, from netfilter to DC blocker, but without result, except that the SQ became less.
Now my question is how easy is it to get to the transformer.
 

Jon Q

VIP/Donor
Jun 16, 2019
90
43
150
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TooCool4

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Feb 7, 2013
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I asked the local Spectral's distributor.
And they said that the noisy transformer is a spectral habit.
The DMA 100S and now the DMA 260.

I can’t say I have noticed any noise coming from my DMA-100S, but then I am using them on the end of a Emerson Liebert GXT4 3000VA regenerative UPS.
 

Adimon

Well-Known Member
Jan 4, 2011
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925
I think this problem only applies to the 240Vac 50Hz version.
 

TooCool4

Well-Known Member
Feb 7, 2013
960
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Mine is a UK 240V version and i have no problem with noise.
 
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Adimon

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Jan 4, 2011
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Mine is a UK 240V version and i have no problem with noise.
Yes that's strange.
I measure mains voltage of 230V ac and that would be perfect.
If the mains voltage were contaminated, a mains filter or DC blocker would still have to improve slightly.
But not at all!?
The strength of the noise of the transformer that can be heard depends on the location of the amplifier.
In my case the amplifier is in the middle between the speakers.
But as I said here, the problem has already been recognized and confirmed by the dealer.
 

Jon Q

VIP/Donor
Jun 16, 2019
90
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I had both a DMC-12 and then the DMC-20 Series 2 - this was my foray into Spectral, in the early 90s. Beautiful sounding preamps. People still use the 20 for its phono board (optional back then)

Yes I am aware, and you are right, there are many people using the board phono DMC 20.
 

Jon Q

VIP/Donor
Jun 16, 2019
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I can’t say I have noticed any noise coming from my DMA-100S, but then I am using them on the end of a Emerson Liebert GXT4 3000VA regenerative UPS.

I think the DMA 100 series II, uses toroidal transformers, has less noise than the [E / I] series and don't usually have problems with the 50/60 HZ
 

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Jon Q

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Jun 16, 2019
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I think this problem only applies to the 240Vac 50Hz version.

yes, probably the transformers in the iron core factory should be "cut" to 60Hz and not to 50Hz. I have some friends who use Manley amplifiers, and they all have vibration problems (50Hz noise), some of them returned to the supplier because the noise was insurputable.
 

Jon Q

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Jun 16, 2019
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Yes that's strange.
I measure mains voltage of 230V ac and that would be perfect.
If the mains voltage were contaminated, a mains filter or DC blocker would still have to improve slightly.
But not at all!?
The strength of the noise of the transformer that can be heard depends on the location of the amplifier.
In my case the amplifier is in the middle between the speakers.
But as I said here, the problem has already been recognized and confirmed by the dealer.

I mentioned how I did to reduce the noise of transformers as little as possible.
Another situation that was made and not mentioned here was the insulation, transformer cables whith rubber (neoprene), they have no physical contact with the isolation chassis, (See pic. 2 and3 marked in red).
It may also be a possibility that the transformers have little physical contact with the isolation chassis, just remove the three nuts on each side (marked in yellow). The chassis alone, it rises about 0.5mm. Access is easy if you have the proper tool.
 

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Jon Q

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Jun 16, 2019
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Finally, the adjustments and some simulation tests on the protection circuit. The temperature (with the help of a laser thermometer on the transistor outside the heatsink), fig.5.1, activates the red led. Test protection [DC off-set] with the introduction of a small positive and negative DC voltage (without the speakers), triggers the yellow led, + 2.75V, and -2.9V.
To reduce the noise of the green LED (power ON) was added the same concept that I mentioned here about the relay (XRL-ON), but the mosfet is now a 2N7000. For personal reasons, the lamps "Spectral logo" were removed.

I think Spectral should be the only manufacturer that uses an individual bias system for each power transistor (mosfet). Calibration requires four digital multimeters for each channel and a little patience (Figs. 9 and 10).
When "finished perfectly" the adjust, this is amazing in its sound, especially the focus and silence of the musical instruments, a simply fantastic idea from Mr. Keith O. Johnson & Richard Fryer.
Note; (The choice of bias value was based on many hours of listening, slightly higher than the original value).

The off-set adjustment (fig.11) after three hours was below 2mV (fig.12). This is excellent for an amplifier that has no servo circuit. I think the newer models don't have them either. Personally I am not adept, even well calculated is bad for final performance.
 

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Jon Q

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Finally the placement of the feet, and "... music ...."

jon
 

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dan31

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Jul 22, 2010
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It will be interesting to see how the amplifier settles with the new parts. You must be very happy with your project. Enjoy!!

I can see reworked Spectral preamp in the works.
 

Jon Q

VIP/Donor
Jun 16, 2019
90
43
150
Lisbon
It will be interesting to see how the amplifier settles with the new parts. You must be very happy with your project. Enjoy!!

I can see reworked Spectral preamp in the works.

Hi dan

Yes, I am quite surprised by the end result , marries very well with the Vandersteen. About the pre spectral is still too early to disclose.
 

ack

VIP/Donor & WBF Founding Member
May 6, 2010
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Fantastic work again! I hope you took videos too - "Spectral Mods, the Movie" :) What is so impressive to me is that you took it all apart, rebuilt it, and was *confident* it will make sound in the end (and great sound at that). You had a plan from the very start and went at it with a mission. I have not seen such an impressive thread anywhere else. Congrats!

Each output mosfet does not only have its own bias, but entire power supply and regulation as well, as you see. Not sure who else does this. And, yes, there are sliding bias servos now in the 400RS and newer designs.

And here's a new challenge for you: see that NPD5566 chip in the preamp board pictures (c3.jpg)? If I recall, it's in the amp's driver board as well. Can you design a better circuit?
 
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Jon Q

VIP/Donor
Jun 16, 2019
90
43
150
Lisbon
Hi ack

When I first heard the DMA 150, it was very far from my expectations, but I saw a potential in case upgrade.
At first, I just wanted to upgrade to version II, but I didn't get any response from the spectral dealer. I decided to upgrade this amplifier different from others. The reason is very simple ... it's a piece for my personal system.

I had not in mind putting here the development the upgrade, but then I thought .... and why not!!!
The update was not difficult, it is the experience over 25 years of work in this area. The problem is the lack of time. I already mentioned that I have two works, one is in studio (maintenance and development video / audio broadcast - production), and another is development of linear sources for audio / video. One thing is what you hear in an audio system, another thing is what you hear in a recording studio.What I want is to hear as real as possible. That's what I saw with an update on this amplifier in synergy with my system.
At the moment I am doing something identical with a Wadia 6, it will only be used as transport, the DAC is external. The mechanism and servo system is from teac, the Spectral SDR3000 also uses the mechanism and servo from teac possibly the model P2 !!!
Is a crazy update and funny. The reason ... I have a lot of CDs, and great recordings. It's not my fault that I like music.

Yes I can make some videos and put here. Cameras is not lacking in studio. There is everything, from 4K UHD.... up until Phantom 12,500 fps. When I have time available I will do this.

I know NPD5566, and the challenge you poses is interesting. If choose an alternative to a DMC 30, the manufacturer would be InterFET ....
https://www.interfet.com/



jon
 

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