KG Balanced Dynahi build discussion thread

[spritzer]

They are a direct match but check the pinout.  I would match them personally but the amp will function without matching them. 

[Aive]

They are a direct match but check the pinout.  I would match them personally but the amp will function without matching them.

Thanks for the confirmation Spritzer I'll buy a few and see if I can get a good match going heh

[Aive]

Hey Kevin,

 

Would it be possible to get a copy of the silkscreen (or gerber) for the balanced dyanhi PCB design from Lil Knight's first GB (lol it's rather specific) - alternatively, your latest balanced dynahi design based on Toshiba sand? I've ordered a set of boards from LK, and I've been told that they use Toshiba components, which makes me think it's from his first GB batch and not later batches which were for your revised design using THAT340 chips... Gerber's would be great as I can then look at getting replacement PCBs made if I make a mistake on LK's boards ><

 

A schematic for the original design was linked here: http://gilmore.chem.northwestern.edu/dynahiver2a.pdf - but I don't think it captures everything. E.g. it seems to be missing 2 x trim pots for example.

And an alleged layout was linked here http://gilmore.chem.northwestern.edu/dynahibal.jpg but I think that's a preliminary version and the GB boards were different based on posts: 

- 

-  (which has photos of a dynahi board that look different to the layout picture - again, layout only details 2 x trim pots and photos show 4 per board)

 

I'm basically trying to put together a BOM for the passive components so I can get an order underway (I live in Australia and want to try and get the order as complete as possible so I don't have to pay additional shipping fees - yes I'm cheap!). I started with Vortex's BOM linked in the first post but I don't think it's 100% accurate based on info above. 

 

I've been trying to follow the dynahi journey of others as best I can, rolling in changes/fixes into my BOM as I continue my research, but I just can't find an exact schematic/board layout.

 

Sorry for the verbose post. Thanks for your help Kevin, appreciate it

[kevin gilmore]

i need to know what the version numbers are for the boards you have.

way to many, and no idea which boards were the first GB.

I switched to the motorola parts because in general the toshiba parts

are not available, and they are not pin compatible.

[Aive]

i need to know what the version numbers are for the boards you have.

way to many, and no idea which boards were the first GB.

I switched to the motorola parts because in general the toshiba parts

are not available, and they are not pin compatible.

I think as a rough estimate, it'd be the same version board as what Steve and Vortex initially received. But I can wait till I receive the PCBs and respond. Yeh I complete understand why you switched away from the toshiba parts, deep down inside I was hoping LKs boards were your newer design so I could save some cash buy buying the newer, cheaper bits

Will post a response when I know more.... Thanks KG!

[Aive]

Ok, I've been doing a little bit of research while I wait for all my bits to arrive Just wanted to run my understanding/theory re setup of this amp past the guru's here just to check if I'm on the right track (I am trying my best to figure things out as much possible without asking dumb/annoying questions ).... I know I'll be repeating a lot of what is already on the interwebs but am just including it for completeness:

 

Reference circuit: http://gilmore.chem.northwestern.edu/dynahibal1.pdf

 

RV3: Compensate mis-match between 2SK170 pair (2SK389)

RV4: Compensate mis-match between 2SJ74 pair (2SJ109)

RV3 Procedure: Start wiper at mid-point -> measure voltage across R7 and R8 -> adjust RV3 till voltage equal = equal collector current flowing through pair

RV4 Procedure: As above, but match voltage across R13 and R14

 

And this is where my theory understanding falls apart a little...

Increase R1 & R4 to 680 ohms. Original 500 ohm values may be too low resulting in too high bias in drive transistors.

RV1/RV2: Compensate imbalance between components in (not sure of the term)'positive' and 'negative' sections of balanced circuit (LEDs, CCS transistors Q1, Q2, drive transistors) => Minimise DC offset and set bias of drive transistors. Iterative process of adjustment -> check bias (resistor voltages) -> check DC offset -> adjustment.

RV1 Bias Procedure: Start wiper at max, 10 k point -> reduce RV1 till close as possible to >= 0.75 V (minimise heat dissipation) across R24-R27 and R37-R40 resistors = correct bias through drive transistors Q15-Q18, Q27-Q30. 

RV2 Bias Procedure: As above but measure voltages across R28-R31 and R41-R44 resistors = correct bias through drive transistors Q19-Q22, Q31-Q34.

DC Offset: Ideally, drive transistors are matched to provide equal current through each leg (at least matched set in positive section, matched set in negative section of circuit) however, if individual drive transistors are not matched, will end up with varying voltages across resistors = sum to a DC offset in output. To compensate for DC offset, reduce RV1 (continue reducing resistance since we just reduced resistance to reach min. bias level above) and see if offset approaches 0 V. If not reset RV1 position and reduce RV2 resistance.

 

Whole reason for wanting to understand the process is I don't think I'll get much success from matching of components so I'll probably need to balance amp manually - I just don't have the quantities which seem to be required to make decent sets....

 

Hopefully the above is sensical, and thanks for all the help, appreciate all the input and advice I've received from you folk since I joined

 

Oh and Kevin, is dynahibal4.zip the latest and greatest design based on Toshiba sand?

[kevin gilmore]

dynahibal4 was the last version with all Toshiba parts

dynahibal5 has Motorola transistors and tosjiba jfets and Toshiba duals

[Aive]

dynahibal4 was the last version with all Toshiba parts

dynahibal5 has Motorola transistors and tosjiba jfets and Toshiba duals

 

Thanks Kevin 

[kevin gilmore]

http://gilmore.chem.northwestern.edu/dynahibal4.zip

 

in case you have not already found it

[Aive]

Awesome thanks Kevin. Will need to get boards made of those if I seriously stuff up LKs boards ><

Also is my bias/offset setup understanding above correct?

[Aive]

Well, I've done as much as I can until my tap arrives and I buy my drill press Gotta clean the boards too at some point.

 

Exciting

 

 

Oh thanks to everyone so far for all the solid information!

[Aive]

I need help  

 

I have one bal. dynahi channel setup and am now in the process of dialing in the bias and dropping the offset.

 

So dialing in the bias is easy enough, I tweak RV1 and RV2 evenly till I get minimum of 0.75 mV on the resistors on the output transistor circuits. Oddly though, I get varying voltages in the output branch resistors of ~100 mV. I suspect this is fine so long as they're all biased > 0.75 mV for Class A? 

 

Now with the bias dialed in, I measure 300 mV of DC between O+ and O-. How do I get rid of this? I can reduce the offset via RV3 and RV4 - but it means dialing one of these in very far in one direction, is this ok? I was dialling these in a rather ad-hoc fashion but am thinking of desoldering these trimpots, resetting to mid-point and starting again in a more systematic fashion....

 

Thanks in advance!

[DefQon]

Are those Sigma 22 power supplies in your previous picture?

[johnwmclean]

Yes they are Sigma 22s.

Why do you need to desolder to reset the trimpots?

Try walking each pot in, by smaller turns, incrementally, wait a little between each turn for some stabalisation, take your time.

Edited September 18, 2014 by johnwmclean

[Aive]

Yeh they're sigma22's. 

 

I think I got there - I was trying to do this at around midnight last night, bad idea. Thanks for listening to my whinging lol.

 

I sat down with schematic this afternoon, thought about it and went through the process properly (I'm supposed to be an EE ffs ><).. 

 

I set main bias resistors to max and then decreased them evenly till I got around the 0.75 V point for the output transistor resistor branches. I then tweaked the other two trimpots in turn to reduce offset and while measuring across the 5 k resistors in the FET circuit to keep them relatively even - I sacrificed this for better offset though.

 

Got there in the end, little bit of imbalance here and there around the circuit but overall offset close to 0. Had to retweak again with OPA445 installed, but all good - hope it holds...

 

Question though - I did a multimeter measurement for offset upon initial power on and it spikes to 30 mV (could be more but that's what the meter picks up) - will this damage headphones if they are plugged in on power on? 

[johnwmclean]

Take a 32ohm headphone, the current would be 0.030/32 = 0.9375mA, so definitely no damage.

 

[Aive]

hehe thanks for the assurance

 

Oddly enough, I can zero the offset without the servo, but it gets worst when I install the servo..... offset hovers around 10 mV, think I'll just leave it ><

[Aive]

 

Finally, it makes music! Like my current board supports - PCB brush and highlighter plus some random box...

 

I must've spent at least 8 hours biasing/offsetting one channel due to serious mismatch issues I guess, the other channel took half an hour to do lol >< I am very fortunate to have big ass heatsinks so I had plenty of bias headroom to play with.

 

It sounds pretty sweet through my LCD3s. My audio memory is terrible so I can't make any legit comments comparing it to my GS-X mk2, but the music sounds great, the bass is powerful, I don't hear any noise and don't detect any obvious flaws.

 

Thanks KG for the design, LK for the boards, Spritzer for the advice and pot board and peeps here for posting their knowledge

 

Now to spend the next year of my life on the case...

Edited September 20, 2014 by Aive

[fishski13]

biasing the SuSy boards:

 

-before first power up, the pots that flank the THAT340 should be at their mid point.  the outer biasing pots should be as follows, when looking at the board with the heat sinks at the rear: L - fully CCW and R - fully CW.  leave the DC servo opamp out.

 

-bring up the bias by turning the L outer biasing pot CW and the R CCW, keeping tabs on the DC offset.  both pots will increase the quiescent current bias, but also affect the amount of DC offset.  i just turn them in equal amounts until i hit my target quiescent current and then tweak for lowest DC offset.  the offset will fluctuate quite a bit, like 100mV.  small fractions of turns on the pots will cause the off set to jump.  be patient.  i think the best i could do was roughly +70mV to -30mV. 

 

-insert the DC servo.  measure the offset between the O(+) and O(-) - i measured 20 and 25mV.  turn one of the THAT340 pots CW and the other CCW, 1/2 turn each.  note if the DC offset went up or down.  if it went down, then continue turning the pots in the same manner, in 1/2 turn increments, until you reach 0mV.  if the offset went up, then reverse the turns in the opposite directions.

 

-i was able to get less than 0.5mV offset and very stable.  on cold start up, still a very low 2mV.  zero pops or hiccups through my HPs either on power up or power down.  

[G600]

Aive,

 

What kind of pot are you using ?

Have you built the amp with defaut gain (balanced gain of 42) ?

 

Thanks.

[Aive]

Hey fish, I built the toshiba version of the boards - I got there in the end. I spent a lot of time trying to figure out the circuit and make logical progress instead of trial and error. Stared at that schematic a looooong time lol. What you explained sounds very similar to what I did - but one of my channels took a lot of pot adjustment and one side of the mirror circuit had to be ~100 mv more biased than the other to drop the offset. Unsure why - any ideas? Might have more analysis of the circuit and see which component(s) I could swap out to change that... Any ideas?

 

G600 - I'm using an Alps 4-gang 10 kohm resistor I got from "familygate" on ebay. I built boards as per the silkscreen details, so the default gain (but again, I built v4 toshiba sand version of the dynahi balanced).

 

I've mounted all boards onto MDF now - much less worried about something shorting or falling over and blowing my ears out

 

It is a seriously sweet amp, going to be my primary amp going forward.

 

One thing though, music at low volumes seems "mushy", lack of power, clarity, separation, could that be to do with the low input impedance?

[fishski13]

i realized that but went ahead and posted it anyway since other builders may have the same biasing questions.

 

as to your biasing issues, i have no answers other than you possibly have poorly matched devices or fakes.  i would try to re-bias.

[Aive]

Hmm I bought my sand from bdent and Spencer of fetaudio - do you know which devices may be mismatched? I'm guessing its the 2sk389 or 2sa1349...

Edit: after looking at the schematic I am not sure what it could be... I can easily even up the mirror (so that all output transistors are bias equally) so it's not as though there is imbalance in the circuit. It's just that when I do, my DC offset is at 270mV between O+ and -.

Edit edit: it sounds really good as is I might just leave it for the time being and re look at it when I get a CRO

Edited September 22, 2014 by Aive

[G600]

Thank you AIve.

May I ask where you found a PCB for a quad pot ?

[kevin gilmore]

birgir should have some quad pot boards left.

also the layout is in the usual place.