Spectral DMA 150 Upgrade

ack

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Hi ack
Thank you.

Dear ack
One question, this model is the XLR input, pin 3 is +, and pin 2 is -.
The recent models of Spectral is same a conection? By rule, pin 2 is the positive and the negative pin 3, pin 1 is always the ground.

If this is a European model, which it appears to be, I am not surprised that pins 2 and 3 are reversed - I don't know how recent models are wired, but the manuals make it clear, and certainly the US versions are the opposite. Could it also be that whoever owned this before went ahead ahead and swapped the pins? Phase orientation is something I always test for, and for example, I discovered years ago that on my VPI's junction box, those pins are also reversed - the astute observer will then notice in my avatar that the red and green wires are swapped on my cartridge!

BTW, I laughed so hard at your washing of the heat sinks. There are obvious signs of corrosion in the fuses, so it looks like this amp was not really cared for. And before I forget, do bypass those silly fuses.
 
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Jon Q

VIP/Donor
Jun 16, 2019
90
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150
Lisbon
If this is a European model, which it appears to be, I am not surprised that pins 2 and 3 are reversed - I don't know how recent models are wired, but the manuals make it clear, and certainly the US versions are the opposite. Could it also be that whoever owned this before went ahead ahead and swapped the pins? Phase orientation is something I always test for, and for example, I discovered years ago that on my VPI's junction box, those pins are also reversed - the astute observer will then notice in my avatar that the red and green wires are swapped on my cartridge!

BTW, I laughed so hard at your washing of the heat sinks. There are obvious signs of corrosion in the fuses, so it looks like this amp was not really cared for. And before I forget, do bypass those silly fuses.


Dear ack
Thanks for your reply.
I already keep in mind, that I would make the connection by default. 2 positive, 3 negative, and 1 gnd.

Yes, the fuses, RCA, XLR connectors, and Binding Posts, in the end I'll make a careful choice.
The connection to the speaker terminals is also updated. At this moment I have the two brands that Spectral uses, the original (Ca ... e) color gray cable, I think it is the same that is used in the Spectral DMA 500 and also have the other black color of the mogami, this is used on the DMA 300.

http://www.spectralaudio.com/DMA300/300_1 Large.gif

The choice is hard, I like both, but I can only apply one of the manufacturers

Now it's the electronics upgrade (voltage amplifier) ... I drew the whole schematic diagram of the DMA150, and there are a few little/very small things that don't go with my concept.

Other things are happening ...

cheers


ps: there may be some errors in writing... my english is no big deal
 

ack

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The choice of wiring will affect the overall circuit capacitance and inductance, and in lieu of the typical stabilizing output inductors, be careful and keep in mind they don't make those wiring decisions lightly, which again, are always in the context of the entire circuit. Same goes for the speaker cable binding posts; but given the chance, do consider the newer Mundorf that so many are using, including their later models.
 
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Jon Q

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Jun 16, 2019
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Lisbon
Yes that's true, the two wiring choices I have under test are the same models the brand uses. About, binding posts, I have two options, Cardas and curiously... Mundorf, in Europe is very easy find Mundorf than Cardas
Both models have no gold, rhodium or silver plating, only copper.

I think from photography, the terminals are the same as the one I have under test from mundorf, TPCU670C but I don't know if it's gold plated or only copper.

http://www.spectralaudio.com/DMA300/300_2 Large.gif
 

ack

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Yes, these are the Mundorf posts, all copper; been using them in my custom speakers as well.
 

Jon Q

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Jun 16, 2019
90
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150
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After several tests on the voltage amplifier, has been reduced gain by the negative feedback and a small increase in the differential amplifier (NPD5566), improving Slew Rate and Settling Time. (as a matter of principle I will not put here the schematic diagram of the spectral DMA 150)

I'm not a fan of RCA connectors, it's just XRL with new Neutrik connectors (NC3FD-L-B-1), but with the possibility of unbalanced connection. (pin 1 ground and pin 2 +), by SW. (same type of connection NAP-300DR or NAP500 of NAIM.
To reduce the noise that is created by the relay when it is activated, (XRL - ON), has been added in series a mosfet 2N7008 with 604 ohm, resistance that limits voltage at 5V (see photo 1) This concept is used in the Nagra.

The MKP capacitors were replaced by Mica capacitors, 1% CDM series of Cornell Dubiler , except for two points, one 220pf of CDE series, and another 68pF from the "suntan" manufacturer. It was a personal choice, could also have another alternative, the polystyrene capacitors. From the link below I think the DMA 500 uses this type of capacitors, two for each channel. (Thank´s ack)

https://www.whatsbestforum.com/attachments/dma-500ar-2-jpg.46377/

The binding posts, initially I gave preference to Mundorf (TPCU670C), but after several tests with the inner wire the final choice was the CARDAS (CCBP-S).
The wire between motherboard and biding posts has been tested by the same manufacturer that Spectral uses, Canare 4S8 and Mogami of various models, 15AWG, 14AWG and 12AWG, the latter being used in the model, DMA300. Interestingly in this choice, I gave preference to the model MOGAMI 2972, 15AWG. This with the Mundorf connectors.

Later the NEOTECH STDCT-14, 99.99998% pure UP-OCC copper hook wire was tested with the CARDAS connectors. This was the final choice ... an excellent wedding. (only in a sense of orientation).

The fixture tubes on the board, my choice was the longest for the terminal - and the shortest were for the positive terminal. In the photo 11.1, it is possible to see that they have a black color mark, as incredible as it sounds, is the sense that sounds the best.
 

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Jon Q

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Another situation in this upgrade is the screws. I am not in fan of the stainless steel type, I prefer black steel 10.9, It´s different result in the resonances that are provoked by several factors in the box.

In fixing the IEC plug whit screws black steel 10.9, the result is surprising. This Spectral had black painted stainless steel, was one of the first things to be replaced.

In the pcb boards the fixation is made with beryllium copper washers, (see pic.8) . The DCS also uses this type of washers, the result for my personal taste is much best, of to the classic, brass or in some cases stainless steel.
Here in Europe it is quite difficult to get inch-size screws, some measurements had to be converted to mm, with screw Tap Drill (pic.5.1)

jon

to be continued....
 

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ack

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Fascinating work!
 

TooCool4

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Wow you have been busy :cool:
 
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Jon Q

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I’m really enjoying the project. I look forward to the next step.


Good question. The next step, will be some parts that will be made in this CNC (photo 27) for Spectral. ...other things are appearing ....
jon
 

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ack

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Dear ack
Let me ask you a question. From your experience, what is your reference / opinion about recommendation of fuse manufacturers in Spectral amplifiers?

jon

To be honest, I really don't know - I bypass mine after discovering that the stock ones in all of my amps to date have run warm, which means there is resistance. And they did constrict the sound. I am taking a risk, but it's a calculated risk. Do keep in mind that in case of a short, the repair will quite likely be expensive. I am on the fence on this issue.
 

Jon Q

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Jun 16, 2019
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To be honest, I really don't know - I bypass mine after discovering that the stock ones in all of my amps to date have run warm, which means there is resistance. And they did constrict the sound. I am taking a risk, but it's a calculated risk. Do keep in mind that in case of a short, the repair will quite likely be expensive. I am on the fence on this issue.

I understand and accept your opinion, we here in Europe (Portugal), the mains voltage is 230V, compared to 115V has the advantage that the same power consumption of the amplifiers, the fuse has a dissipation 4 times lower, so we don't have this problem here, only if it's a very high consumption.

P=R.i2

jon
 

Adimon

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Jan 4, 2011
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Hi Jon,

Did you finally compare the complete heavy modified DMA 150 Amp with the Original DMA150 Amp?
 

Jon Q

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Jun 16, 2019
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Hi Jon,

Did you finally compare the complete heavy modified DMA 150 Amp with the Original DMA150 Amp?

Hi Adimon

Yes, I will give my opinion, of course I am suspicious.

This manufacturer (Spectral) has always fascinated me, not for its sound signature, but for the topology and technology it uses in its equipment. (I admire and respect the concept of Mr. Keith Johnson’s).
In Portugal there are very few Spectral units sold and this amplifier was a business opportunity.
I have two work, both connected to electronics. One is in the areavideo broadcast within, here a recording studio (video and audio). My sector is in the development and maintenance (cameras, video / audio and automation).
The other is linked to development of linear power supplies for audio and video.

But ... back to the DMA 150. When I first heard it, it wasn't what I expected, but it had potential with an up-grade to improve its performance. The low frequencies were confusing, and the high frequencies noisy and shrill, one of the channels had no focus on the instruments.
It was not neutral and often does not correspond to the reality of musical instruments. (I can hear these instruments here in the studio). But the positive was .... fast, very fast and open (stage, side by side) .
Now after this upgrade process and some (minor) modifications, it far surpassed what I expected. It is possible to hear perfectly the disturbance between two cords of a bass, (its undulation), the neutrality, the high frequence is fantastic (this reason is due to the great bandwidth of the amplifier), the silence now is there, among other situations just by listening. (Possibly later, I can make a video and publicize).
The downside is its sensitivity which is now about 1.75V and not 1.5V.,(I explained in a previous topic the reason for this) but this is no problem when you have a good preamplifier.

When possible, I put here the final development of the DMA 150, the new support bases, lamps, bias adjustment, off-set, DC protection circuit test, temp. Among other things.

jon
 
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Adimon

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Jan 4, 2011
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Hi Jon,

Thank you for the comprehensive answer.
Another question is which of the modified steps improved the sound the most?

I adore my DMA 260 but the noisy transformer keep frustrating me.
This noise varies form time to time.
Do you recognize this and maybe do you have any tips to reduce this?
 

Jon Q

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Jun 16, 2019
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150
Lisbon
Hi Jon,

Thank you for the comprehensive answer.
Another question is which of the modified steps improved the sound the most?

I adore my DMA 260 but the noisy transformer keep frustrating me.
This noise varies form time to time.
Do you recognize this and maybe do you have any tips to reduce this?

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
 

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Jon Q

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Jun 16, 2019
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One unpleasant situation I had with the DMA150 was the four damping foot. The former owner possibly removed the originals and placed them in ridiculous plastic (pic 1). I was very upset about this.
I decided to make some identical to the originals, but with some slight differences aluminum (6000 series), in the mechanics / maintenance section in the recording studio to a friend here at work (Thank´s Paulinho, fico-te a dever uma cervejola....) .
After this task, the anodizing in black (see pic.10)

to be continued....
 

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ack

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This is so great; you even made the knurled feet. But now, here's an obvious question: if you are so handy with all this stuff, why not modify one of their newer amplifiers? The 150 probably dates back to the late 90s and was just an entry level piece,of a 1xx series (that included the 160) that was geared towards the then-evolving home theater market (probably a mistake of a decision, and likely pushed through by dealers)
 

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