SlewMaster Builds

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#2,021
tonza75 said:
ignore last post.

You have it pretty good if music for a few hours is main problem.
You did not have this problem before putting this in enclosure?
With test tones and load was it stable before enclosure & "music" ?

Discribe your testing sequence would, and data for from before enclosure solve the issue as before driver changes it plays music for hour or two before hot indicates as stated problem but it plays. I would keep it.

Have any of you tested 2SC4883 or 2SC2837 as driver in a slewmaster or other amplifier?
To your question about drivers, [ELMAG] 2SC4883 2SA1859 tranzystory SANKEN 6 z? (6539032154) - Allegro.pl - Wi?cej ni? aukcje.
From iamp100 bom.
Click to expand...
Yes everything fine and stable. The amplifier gets more warm now as it´s placed in a shelf system on the wall (driver heatsinks to hot to touch)
I will drill more holes in the shelf system and in the bottom of the amplifier then it will Work okay.
I have have also mounted a bimetal contact in each side of the amplifier that cut the output if the alumium brackets - holding the the top grill reaching 60 egrees. I have also ordered a relay so Whole amplifier can cut of if it´s gets to hot🙂
 
#2,022
tonza75 said:
Have any of you tested 2SC4883 or 2SC2837 as driver in a slewmaster or other amplifier?
To your question about drivers, [ELMAG] 2SC4883 2SA1859 tranzystory SANKEN 6 z? (6539032154) - Allegro.pl - Wi?cej ni? aukcje.
From iamp100 bom.
Click to expand...

If I can add my 3 cents there, I have use this drivers a lot and they work OK. They have wider SOA than popular tosiba drivers too, suitible for multi pair output stages. [ELMAG] from allegro --> highly recommended seller, I am buying stuff for a good few past yeares of him and all is OK. The sankens are oryginal and are comming with mica isolating pads. The only thing about sanken's 2sc4883/2sa1859 is that the surface of the transistor is not glossy/shiny, I have the same transistors from differend source and the plastic case is perfectly glossy -> no idea if it is important in this case.

Regards
Peter
 
#2,023
borys said:
If I can add my 3 cents there, I have use this drivers a lot and they work OK. They have wider SOA than popular tosiba drivers too, suitible for multi pair output stages. [ELMAG] from allegro --> highly recommended seller, I am buying stuff for a good few past yeares of him and all is OK. The sankens are oryginal and are comming with mica isolating pads. The only thing about sanken's 2sc4883/2sa1859 is that the surface of the transistor is not glossy/shiny, I have the same transistors from differend source and the plastic case is perfectly glossy -> no idea if it is important in this case.

Regards
Peter
Click to expand...
Hi Boris,are you sure that aren't some <<renamed>> parts?
 
#2,025
borys said:
If I can add my 3 cents there, I have use this drivers a lot and they work OK. They have wider SOA than popular tosiba drivers too, suitible for multi pair output stages. [ELMAG] from allegro --> highly recommended seller, I am buying stuff for a good few past yeares of him and all is OK. The sankens are oryginal and are comming with mica isolating pads. The only thing about sanken's 2sc4883/2sa1859 is that the surface of the transistor is not glossy/shiny, I have the same transistors from differend source and the plastic case is perfectly glossy -> no idea if it is important in this case.

Regards
Peter
Click to expand...
Thanks I am just thinking if i could get even better sound quality if i change from 2SC4159/2SA1606 to 2SC4883A /2SA1859A ( the type in plastig house )?
☺They seems quite linear and newer type than 2SC4159/2SA1606.

Best regards
 
#2,026
tonza75 said:
ignore last post.

You have it pretty good if music for a few hours is main problem.
You did not have this problem before putting this in enclosure?
With test tones and load was it stable before enclosure & "music" ?

Discribe your testing sequence would, and data for from before enclosure solve the issue as before driver changes it plays music for hour or two before hot indicates as stated problem but it plays. I would keep
Click to expand...

I always test a New /repaired amplifier module with a variable built in current limiter PSU to set bias and check everything is okay.
No. 2 then i test with full output power and with around Half power output to get maximum power dissipation in the main heatsink☺in around one to two hours each (best if heatsinks temperature stay under 60 degrees)☺

How long do you test with test tones and load?

Kim
 
#2,029
Checking for load sharing

Hallo All.
I just wonder how many people check the load sharing among the multiple output transistors or Fets after a build. My fets are deviating with 10mV between some of them.They were supposed to be matched !! So If you adjust bias across a source resistor of 13mV then the rest sits around 3mV and are never going to work. The higher biased fets are going to do all the work. They stand a chance to blow while others are idling. Am I wrong ??
 
#2,030
Hi Jan, I've got the OPS with 5 pairs of IRFP240/9240 in each channel (CF-FET V2.0 project). They are roughly matched before soldering. Each of them has got a 0.22R resistor at the source.
I have set 17mV across the source resistors in average with no signal. Voltages vary between 15.5mV and 18.5mV, which is fine in my opinion. Bias tracking works very well, heatsink temperature is stable when idling.

Cheers,
Valery
 
#2,031
Thanks Val,
I have only 10 of each so I will vgs match them tomorrow and see what I get. I would be very happy to just have a 3mV difference between them. The OP stage still has the loopback resistors in for testing at 44V. The bias is very solid, no deviation at all.🙂
 
#2,032
Finished one slewmaster channel. Used a clamping bar to clamp the mosfets. Luckily no blitzen and sparken !! 😀
 

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#2,034
sum the output device Pmax and divide by 5
eg 5pr of 200W devices = 2000W
divide by 5 gives 400W.
That's roughly the maximum power using sensible heatsinking for domestic duty into severe reactance speakers.

One then chooses the transformer to allow that power to be delivered into your speaker impedance.

Using the same output stage you will get some builders claiming upto double that output power.
 
#2,035
I am now working on my second Slewmaster. This time the IPS is a Spooky and the OPS have five pair 5200/1943 as output transistors.
I tested OPS yesterday with my buble lamp. Light faded down after a short time. I measured 10 mV on one emitter. So far so good.

Today I fired up the IPS with 10 ohm connected to NFB and ND-/PD+. I measured 0.61 over 10 ohm. Over R12/R13 I could easily set 3.8 mA. Offset a dissapointing 50 mV with a TL 072 connected.
I also measure the voltage between PD+ and ND- and came up with 1.2 V !!!???

In my first Slewmaster I changed TL 072 to another TL 072 with a dramatic fall in offset. So far I have not tried another IC here. By the way, can I use a OPA 134 instead of TL072?

Eivind S
 
#2,037
Liliya said:
I am now working on my second Slewmaster. This time the IPS is a Spooky and the OPS have five pair 5200/1943 as output transistors.
I tested OPS yesterday with my buble lamp. Light faded down after a short time. I measured 10 mV on one emitter. So far so good.

Today I fired up the IPS with 10 ohm connected to NFB and ND-/PD+. I measured 0.61 over 10 ohm. Over R12/R13 I could easily set 3.8 mA. Offset a dissapointing 50 mV with a TL 072 connected.
I also measure the voltage between PD+ and ND- and came up with 1.2 V !!!???

In my first Slewmaster I changed TL 072 to another TL 072 with a dramatic fall in offset. So far I have not tried another IC here. By the way, can I use a OPA 134 instead of TL072?

Eivind S
Click to expand...
An opamp used as a DC servo requires low offset and low drift in offset as temperature changes.
Both these are stated in the respective datasheets.
TL07x are poor as DC servos.
LF412 is better. but it is very old and there are many newer opamps that can do a lot better. Any that do significantly better are usually much more expensive.
When you find a cheap alternative that is significantly better than an LF412, please shout it out so that we all can go buy them.
 
#2,039
Yes, LF411 / LF412 (single / dual) are the perfect choice for the purpose.
They are internally trimmed for low offset and demonstrate very low temperature drift.
I think, at around $2 per piece they are rather inexpensive.

There's also an enhanced version from Analog Devices - AD711 / AD712 - I used them as well as a servo with great success, but they are 3x...4x more expensive.

I never noticed any difference between particular instances of the same type - all of them performed equally well.
 
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