Spectral DMA 150 Upgrade

kennyb123

Well-Known Member
Nov 30, 2012
856
796
1,155
Kirkland, WA
This fuse is the protection of transformer located next to it. That transformer is the power supply for protection circuit.
Change the fuse? yes, I had a positive result, see also the guidance that the manufacturer recommends
Thanks!
 

Adimon

Well-Known Member
Jan 4, 2011
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925
Finally i got the right bolds for the poweramp.
1607698794649.png

Another question Jon.
Did you replace the rectifier bridge (power part of the DMA150)?
I read a topic about Rectifier diodes cause ringing of the transformer.
 
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Jon Q

VIP/Donor
Jun 16, 2019
90
43
150
Lisbon
Another question Jon.
Did you replace the rectifier bridge (power part of the DMA150)?
I read a topic about Rectifier diodes cause ringing of the transformer.
hi

see the link.... #16
 

Adimon

Well-Known Member
Jan 4, 2011
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10
925
Thanks Jon,
Yes, I saw that you used the RHRP860 as far as I can see.
But I actually meant the GBU806 rectifier
 

Jon Q

VIP/Donor
Jun 16, 2019
90
43
150
Lisbon
Thanks Jon,
Yes, I saw that you used the RHRP860 as far as I can see.
But I actually meant the GBU806 rectifier

Yes, I used this model on the basis of the data sheet by the manufacturer. I had 4 references all from the same package and superior features, by original model used by Spectral. But the GBU806 reference was the one with the best sound performance, for my personal taste.

I didn't use ultra fast rectifying bridges, because I didn't find in market this type of package and more than 6 amps
 

Adimon

Well-Known Member
Jan 4, 2011
136
10
925
Hi John,

Sorry but i do have another question and maybe you can give me an answer.
Does the transformer have more primary windings for input voltage?
220Vac - 230Vac - 240Vac
 

Jon Q

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

Sorry but i do have another question and maybe you can give me an answer.
Does the transformer have more primary windings for input voltage?
220Vac - 230Vac - 240Vac
Hi
Good question, when I upgraded DMA150 the transformers had more option above 230V. (possibly 240V). "except the protection circuit transformer, it is limited by resistor" .
In my house I am lucky to have a transformation station about 400 meters away. But at night, sometimes I have 238V. For this reason I selected the highest winding (240V!)
 

roger70

Member
Jul 12, 2021
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4
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53
Hi,
my DMA150 S2 had two swollen capacitors. I decided to change them all. It was hard work unsoldering the snap-in caps ... a few pads went and I had to rebuild. I put photos of the work. Thanks to Jon Q for the very helpful photos your job.
 

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roger70

Member
Jul 12, 2021
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Question for Jon,
how should you check the bias (4 blue trimmers)?
The offset?
 

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Jon Q

VIP/Donor
Jun 16, 2019
90
43
150
Lisbon
adjust offset (select input for RCA, shunt center pin to ground "rca".
place the multimeter on the speaker output connectors and adjust offset trimmer to 0V.
Confirm and if necessary repeat this adjustment after 3 ... 4 hours. repeat the same on the other channel

Bias... on 0.22R resistors of the "drain" of output mosfets, set the same value for all of them. (I don't know what the value is for DMA 150 Series 2). Each potentiometer corresponds to a transistor. I recommend 4 digital multimeters simultaneously to make this adjustment. Consider carefully whether you want to adjust the bias. A simple blunder/error and everything is spoiled.
Confirm and if necessary repeat this adjustment after 3 ... 4 hours. repeat the same on the other channel

...!
 

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kennyb123

Well-Known Member
Nov 30, 2012
856
796
1,155
Kirkland, WA
my DMA150 S2 had two swollen capacitors.
What lead you to discovering that? I have the same amp. Was it something you heard?
 

roger70

Member
Jul 12, 2021
6
4
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53
thanks Jon Q, next week it will be done! report obviously.
Did you get all the schematics of the 150?
 

roger70

Member
Jul 12, 2021
6
4
8
53
hi, it was not necessary to adjust the bias, because it was the same (+/- 5%) on all row. Offset: first 70-80 mV, after 5 mV.
With the new capacitors we have better control and dynamics, I would say we have managed to improve.
 
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Oct 2, 2021
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Thanks Jon Q. Unfortunately I do not own a Spectral component, but every time I have the chance to listen to it, I am blown away by that special crisp clean and defined sound. That and due to the fact, that they measure almost perfectly I wonder if Spectral uses some sort of error correction, like Halcro did way back then, or Bob Cordell wrote about it quite some time ago. What is the secret of Spectral to achieve that special sound?
 
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Adimon

Well-Known Member
Jan 4, 2011
136
10
925
Thank´s ack



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
Hi Jon,


I did make a stupid Fuse change in my DMC30-SS.

Replaced the stock fuse by a SR blue fuse a few years ago.

I was iritated by the sibilance in a lot of my records.

Forgotten about the fuse change till yesterday.

Replaced the SR fuse by the stock fuse and that helps a lot.

Don't ask me why!?
 

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