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Franken amp

Very cool! Keep the camera handy just in case you get some smoke! Sparks are cool too!

What about the face plate? It is going to need something special! :banana:

Ken
 
kenkirk said:
Very cool! Keep the camera handy just in case you get some smoke! Sparks are cool too!

What about the face plate? It is going to need something special! :banana:

Ken
Click to expand...


Some digital meter possibilities for the one of a kind..couldn't find any nice analog meters for the retro look, I think this is the best feature on the Mini-Cooper. Digikey did have some panel mount hour meters, might be fun to watch one spin when the volume is up.;)

Just thinking of the muscle cars of my youth.

I'm guessing a local machine shop would be amused to cut the holes in the existing front bezel for the project, something different.



[url]https://www.youtube.com/watch?v=cCd2DDoz38g[/URL]

2007_mini_cooper_base-pic-14190.jpeg
 
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kenkirk said:
Very cool! Keep the camera handy just in case you get some smoke! Sparks are cool too!

What about the face plate? It is going to need something special! :banana:

Ken
Click to expand...

Had a little smoke tonight- nothing major. TR616 was shorting out in some strange way on the right board (board directly in front of the heat sink) and taking a connected resistor with it. I tested it in circuit with my cricket- was testing fine one way, then acted strange on the test the other way- would beep then fade out. I pulled it, tested it and is passed. Soldered it back in and it passed in circuit. Fired it up to around 110v AC and no more smoke.

I also figured out something interesting about these 3020's. Most larger receivers- say the sx1250 , have a soft start relay. The reasoning behind this soft start relay is due to the size of the power supply caps in the amplifier power supply. Caps of this magnitude act as a dead short in the power supply and can cause major issue within the PS itself- blown fuses, damaged transformers, stressed bridge rectifiers. The goal of the soft start circuit is to limit the inrush current to these main supply caps by the use of a resistor or a pair of resistors- in this case it's a pair of 10ohm 5w resistors across the B+ and B- feed. The difference between the 3020 and others- the 3020's soft start relay IS the protection relay. In the sx1250/1280 and some sansui's the protection relay is separate from the soft start relay. When the 3020 fires up there is a 6 or so second delay before B+- is being fed from the protection relay into the main caps- the resistors are doing the job. Once the soft start relay closes it feeds the speaker relay and the resistors are no longer feeding the large caps- the click between the two is almost instant- in a 1250/1280 for example it's a phased event- the soft start engages instantly (1/2 a second) then the speaker protection relay follows seconds later.
 
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bktheking said:
Had a little smoke tonight- nothing major. TR616 was shorting out in some strange way on the right board (board directly in front of the heat sink) and taking a connected resistor with it. I tested it in circuit with my cricket- was testing fine one way, then acted strange on the test the other way- would beep then fade out. I pulled it, tested it and is passed. Soldered it back in and it passed in circuit. Fired it up to around 110v AC and no more smoke.

I also figured out something interesting about these 3020's. Most larger receivers- say the sx1250 , have a soft start relay. The reasoning behind this soft start relay is due to the size of the power supply caps in the amplifier power supply. Caps of this magnitude act as a dead short in the power supply and can cause major issue within the PS itself- blown fuses, damaged transformers, stressed bridge rectifiers. The goal of the soft start circuit is to limit the inrush current to these main supply caps by the use of a resistor or a pair of resistors- in this case it's a pair of 10ohm 5w resistors across the B+ and B- feed. The difference between the 3020 and others- the 3020's soft start relay IS the protection relay. In the sx1250/1280 and some sansui's the protection relay is separate from the soft start relay. When the 3020 fires up there is a 6 or so second delay before B+- is being fed from the protection relay into the main caps- the resistors are doing the job. Once the soft start relay closes it feeds the speaker relay and the resistors are no longer feeding the large caps- the click between the two is almost instant- in a 1250/1280 for example it's a phased event- the soft start engages instantly (1/2 a second) then the speaker protection relay follows seconds later.
Click to expand...

Interesting about the transistor. Maybe it has come alive now... I would watch it closely. The soft start is a good idea. Its a great project!! :yes:
 
Thanks Ken!

Got the second relay wired in- wired the outputs as well. I wired the left channel to the left board tonight and fired it up on the variac/dbt- biased it up, it plays! There is a buzz but that is probably due to the lack of ground- i'm not on the grounded plug yet.

vp94.jpg


s7iw.jpg
 
Not bad for a boat mechanic... not bad at all!! :D

Its one thing to fix stuff. Its another thing to create something new from junk. It's alive!!!

Needs, skin... :yes:

k
 
Almost ready- waiting on the NOS binding posts to arrive from a seller on the bay- wire up the power switch, clean up the wiring to the amplifiers and it's ready to bolt up. Even with one amp out this sucker pulls half an amp at idle.
 
Is the soft start, simply the addition of the soft start relay, or is there another circuit board?

It appears to be just the addition of the relay, aka it can be added to any system reducing stress.
 
In the cr3020, the soft start relay is on it's own circuit board. In most receivers, the ss relay isn't controlled by the protection circuit, it has it's own resistor/cap and driver transistor to control the relay- it doesn't care if there if there is DC on the speakers. If there's DC on the speakers of the 3020, none of the relays will engage.
 
bktheking said:
In the cr3020, the soft start relay is on it's own circuit board. In most receivers, the ss relay isn't controlled by the protection circuit, it has it's own resistor/cap and driver transistor to control the relay- it doesn't care if there if there is DC on the speakers. If there's DC on the speakers of the 3020, none of the relays will engage.
Click to expand...


Nice added level of safety on the 3020. This seems to be the standard on modern high end receivers.

If I understand correctly, a soft start relay can be "added" to any older amp to ease the shock on start-up, contact will occur regardless of the status of the protection circuit.

I have 10 30 year old pieces of Yamaha gear that I am looking at updating and the addition of a soft start relay to the old systems to lessen stress looks like an easily achievable addition if its just an in-line device.

The prices I am seeing on Digikey at $80 each; does give me pause.
 
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I have not, however I trust Jim's kits as the board quality and components are very good. As for your sister, I have my wife and that's enough for me- i'm sure she's a sweet person however I'd never give up audio for anyone!!!!lol
 
I'm anxious to do some real world testing once it's done. I'm also getting my hands on a Citation 16a, I will now own 4 power amps in which I only need two. M70,Citation,The Dynaha and the Mitsubishi. What I like about the Dynaha is that it's unique, they only made 2000 3020's and never made a pure power amp like this- the rx-a3020 is a modern day surround sound receiver. The scary part will be turning on that power switch for the first time on the mains, it should survive!
 
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