The Multi Amp aka Dynalo Mk2

[GrindingThud]

Can you peek at R54 also...

[Kerry]

The value is right at 10k but the part number is wrong.

[Pars]

10 hours ago, Kerry said:

Also R1 and R3 should go to to 424 ohms.  I also want to double check the LEDs in the bom as well.  I can look at that when I get home later.

424 isn't a std. value. 422 is. Close enough? PN is TNPW0805422RBEEN

PN for R54 should be TNPW080510K0BEEN for 10K.

Edited December 18, 2016 by Pars

[Kerry]

I was out and trying to remember the value.  So yes to 422 ohms and the part number for the 10k resistor.

I'll try to go through the BOM today to give a full review.

[nopants]

damn I already placed an order, nbd though

on a related note, have you listened to the amplifier with and without the sig78/79 regulators? curious if there was a marked difference, it adds a fair amount of cost to the build. 

[RudeWolf]

On 12/17/2016 at 3:51 AM, GrindingThud said:

What would be the best hand technique to solder that regulator?

For 95% of the folks the answer is - hand it over to someone with an oven. It's doable by hand, especially with a hot air station for the power pad and then dragging along the side pins.

Most likely I'll be buying a pair of AMB regs.

[luvdunhill]

It's tough even with an air station to get the heat pad optimally soldered

[GrindingThud]

4 hours ago, RudeWolf said:

For 95% of the folks the answer is - hand it over to someone with an oven. It's doable by hand, especially with a hot air station for the power pad and then dragging along the side pins.

Most likely I'll be buying a pair of AMB regs.

I went and got a pair of sig78/79 regulators from AMB's site. Would love to try and get the little guys attached to the main board though. 

Edited December 18, 2016 by GrindingThud

[Pars]

On 5/19/2016 at 7:10 PM, mwl168 said:

Another SS Dynalo lives. 20 VDC rails 255 235 ohm bias resistors. (see EDIT)

Running single ended input and balanced output which, using the same Buffalo II/Ivy DAC, does give up something to running fully balanced.

 

EDIT: With 255 ohm bias resistor on 20 VDC rails, the temperature on the output devices reached 95C after 90 minutes running with the chassis cover on. At that temperature the MPSWx6 max dissipation is derated to about 440mW. Even though they may be still running at the edge of their operating range, the amp sounded lean and harsh. Had to lower the bias resistor to 235 ohm which, upon fully warmed up, yields about 14mA current and the BJT case temperature is at a more reasonable 75C.  

 

Just fired one board of mine up tonight with the GRLV, almost perfect +/-20Vdc. I had been running 301R bias resistors with the previous +/-18V sigma22, with a bias current of 17-18mA. With the same bias resistors, it was now at 18-19mA, and had I run it longer probably would exceed 20mA which is too much.

With 249R, the bias current was only around 10mA (didn't let it run long). With 261R, it was at 11-12mA. I currently built up 277R with a pair of resistors, and the current was around 16mA when last checked.

I'm wondering why Michael's seems to bias higher with lower resistor values? The only difference that I know of is I am running FET inputs (sk170/sj74) and not the THAT bipolar. Mine is out in the open, and I don't have an IR thermometer, so I can't check temps. I've run it and used it for several months now at 18V with the 301R in place.

[nopants]

i still have a pair of boards i haven't been able to trouble shoot, my offset was way off, something around 2v. need to fish them out sometime

[Pars]

Anyone have a spice model of the dynalo mk2 built? If not I'll (try to) do one myself.


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[sbelyo]

Have we decided on a case for the mini?  I'm thinking we could just use FPE for the whole thing.  There was over 100 boards ordered so the price should be somewhat affordable at that quantity and we could make all the sides of the case work to our benefit with vents and such plus it would look awesome too.

[muskyhuntr]

I would be in on that group buy.

Me

[GrindingThud]

1 hour ago, muskyhuntr said:

I would be in on that group buy.

Me

same here

[GrindingThud]

On 7/28/2016 at 11:51 PM, Kerry said:

I ordered a couple of sig78/79 regulators from AMB's site.

What voltage did you set the boards at and what R values did you select to achieve it? The AMB website has some standard values and a formula for others. I'm assuming 20V is the target for this build?

[JoaMat]

I run my mini Dynalo at +/-20 volts. AMB voltage regulators, positive 10K and 133K, negative 10k and 160K resistors.

[GrindingThud]

12 minutes ago, JoaMat said:

I run my mini Dynalo at +/-20 volts. AMB voltage regulators, positive 10K and 133K, negative 10k and 160K resistors.

Thanks!

[Pars]

Still playing around with my dynalo, now with the GRLV at +/- 20V and finding some interesting things (at least to me).

Mine is using 2SJ74/2SK170BL input JFETs. I had noticed that the balance between the + and - sides of each of the boards was off about 1mA. I determined that the JFET combos were mismatched, and got that corrected. One board has Idss of around 8.4-8.5mA while the other is 6.7-6.8. The higher Idss board has bias ~ 0.5mA higher than the one with the lower Idss JFETs, which makes sense. Using some JFETs that are matched (octal), they are both even, which also makes sense. Using bias resistors of 261R, after about 1/2 hour, bias is at 13.5 mA. I don't currently have an IR thermometer (Santa?), but nothing feels hot, just barely warm, including the GRLV pass transistors.

just for fun, since I don't have any THAT340s, I put some 2SA970/2SC2240 BLs in (accounting for the pinout diff of E-C-B vs. the THAT E-B-C), I was seeing the same bias currents on the one channel that I tried these in as I had with the FET input. The BJTs had hFE of ~530, vs the 100 or so for the THAT chips, so the hFE doesn't seem to make a lot of difference.

In my previous post, I had noted that bias resistors of 277 gave ~16mA; it was actually up to 17 mA once I let it run in for quite awhile.

Kerry sent me his ltspice file for this (thanks Kerry!), but so far I haven't been able to get it to even come close to real world currents; it is running 4.7mA or lower. I'm pretty new to spice models though. It appears that his BJT models came from Fairchild, and have a strange hFE (BF?) of 12.16K. Real world on these is more in the 300 range for mine. If I modify that parameter, the output stage Ie current drops to 3mA or less. I was hoping to use this to narrow down the bias resistors, as the 301R I had in there would have hit 20mA.

Sorry for the tl;dr, but just thought I would post this. I would guess with the mini that it will be toss it together with no matching. The BJTs in mine are matched pretty well, as I had 100 of each.

[nopants]

Kerry's BOM lists SMD LEDs with a 1.9V forward drop, compared to the 2.1V we've historically used. Just wanted to double check these are ok since Kerry was planning to scrub things anyway. 

 

This thing is a pain in the ass to solder by hand

[Pars]

35 minutes ago, nopants said:

Kerry's BOM lists SMD LEDs with a 1.9V forward drop, compared to the 2.1V we've historically used. Just wanted to double check these are ok since Kerry was planning to scrub things anyway. 

 

This thing is a pain in the ass to solder by hand

The LTST-C170CKT that he switched to a few posts ago is 1.8V Vf. The ones normally used are 1.7V, not 2.1V.

[nopants]

oh I was comparing to the Lite-ON 859-LTL-4213 that I use for the larger boards.. so does it matter then? will I just have a harder time adjusting the offset/balance if I use the 1.9Vf I grabbed?

also has anyone tried to use bog-standard 7x15 parts for this?

[GrindingThud]

16 hours ago, Pars said:

The LTST-C170CKT that he switched to a few posts ago is 1.8V Vf. The ones normally used are 1.7V, not 2.1V.

Looks like the one in the BOM is backordered at Mouser...plenty of these if it is a suitable substitute. I did not see where this one was mentioned previously.

I start building after the holidays.

[Kerry]

I bought a bunch of LEDs to test the voltages.  I liked the LTST-C170CKT since it had a high Vf.  Changing the LED will have a big effect on the output current if it's not matched to the resistor. 

[Pars]

On 10/6/2016 at 10:31 AM, Kerry said:

Here's the original BOM for the mini

SS Dynalo Mini BOM

There some mods.  The LEDs were changed out and the current resistors should be modified as well.  Also, there were a couple of changes for the resistors if you are using external regulators (AMB has the sig78/79 that can be used).  I think Joamat had some good values here.

The new LED is: LTST-C170CKT 

Also, the 402 resistors on the current sources should go to about 424 ohms.  This should bring the current sources back to 2.5mA.

Those are the differences I'm remembering.

Sorry, it was in the group buy thread. Also he mentioned that R1 and R3 should be 422 ohms, not 402.

I got my Dynalo all back up and running, offset dialed in, GRLV. Listening, it sounds very good. I can't tell if it sounds better than it did with the sigma22; I think so but going from memory. I also had found that I had miswired the switch I use for SE->BAL input; it had left the - input floating when in SE mode, so I corrected that. Flipping back and forth, I couldn't tell any difference. Might have to actually listen to this with balanced in one of these days, if I can get my XLRs back from my son

Edited December 23, 2016 by Pars

[nopants]

Let me aggregate some of the details so I'm on the same page:

1) R1, R3 = 422r (CCS resistors)

2) R13, R15, R28, R30 = 402r

3) Targeting -/+20: 

AMB regulators: sig78 10K and 133K, sig79 10k and 160K

4) LED =  LTST-C170CKT 

Using the AMB stuff we can just leave the underside of the PSU section unpopulated