stay at home type 69 project

[oongbac]

Here's my measurements of voltage of transistors

Q1 1.27 0.71 -2.39
Q2 13.6 -2.4 -2.98
Q3 2.53 -2.98 -3.64

Q5 1.45 0.89 -2.35
Q6 13.9 -2.34 -2.92
Q7 2.71 -2.91 -3.55

Edit: I mistyped values of Q2. I corrected them.

 

[TwentyTrees]

View attachment 118800

It works!!

I moved D2 to position of original regulator(7808) and put 7908 to original D2 position like picture above.

I just tested for a minute so there can be some long-term risk but it works for now anyway.

Thank you very much everybody who pointed this is not just a problem of mine and helped me went through this!

Please point out if there's some problems.

Glad it works! Excellent news, though I'll admit I don't fully understand why it would make a difference!

Before you button the unit up, I'd suggest putting some capacitors across the in and out pins of the regulator as the datasheets suggest - here's how I did mine:

 

[oongbac]

Glad it works! Excellent news, though I'll admit I don't fully understand why it would make a difference!

Before you button the unit up, I'd suggest putting some capacitors across the in and out pins of the regulator as the datasheets suggest - here's how I did mine:

View attachment 118812

Thanks for the tip! I’ll do right now!

 

[oongbac]

Applied! Thanks again!

 

[dogears]

i have no idea why that changes the behavior. but. glad it works?

 

[Janalex]

I measured today on a third card without any wiring to the front panel. One side of the amp measuring perfect on all three transistors and the other is off. I noticed in particular an issue coming of the 8v rail the voltage is fine going into the first resistor off the rail and the voltage drop is already too much on the other side of the resistor. This I think reaffirms maybe that there is not enough current supplied by that regulator. Since my problem seems to be quite similar to oongbac’s original posts I’m hoping to solve it the same way. I am ordering the parts today. Regulator and the caps.

 

[Spacecowboy]

That regulator should provide a few hundred mA without any issue.

 

[Janalex]

Only thinking that since voltage is current times resistance and the resistance is correct then one explanation for lower voltages is lower current. Yeah but can’t fully explain why that is. Something maybe with the diode moving as well..?

 

[Newton In Orbit]

Hi everyone, been loosely following this awesome thread. Any chance of a kit ever being put together ala the CAPI stuff?
I can stuff a board and solder, but not certain I'm following along tight enough to work out some of the issues you guys have sorted over the course of this journey. Some smart people here. If I wanted to build a pair of these, how much pre sorted out stuff, like pcb's, panels etc. are available for purchase?
Also, are the Cyril Jones Lustraphones still being made? Thanks for any help.

 

[Janalex]

I paid approximately $2k for 4 channels. Also yes Cyril has a batch made. I think I bought the first 4 from the batch.

 

[dogears]

well, i still have no idea why the situation is what it is, but i updated to put a 7908 on the -V rail. files are updated in the dropbox to rev 2.

 

[oongbac]

According to datasheet of on semiconductor’s MC7908, they suggest attach 0.33uf instead of 2u2. Leave this for someone who use onsemi’s 7908 like me on rev1.

 

[Janalex]

Hey I got the Texas Instruments one cause that’s what seemed to come up in the mouser search. I can’t seem to find any mention of caps in the data sheet. Am I missing something?

https://www.ti.com/lit/ds/symlink/u...95897&ref_url=https%3A%2F%2Fwww.mouser.com%2F

 

[oongbac]

I mentioned that based on 'STANDARD APPICATION' on their datasheet. A bit shameful to say this, I don't know what is caps role I think you can find some clue to compare their specification.

 

[Janalex]

Yes I see that very clearly in the onsemi datasheet. I think it might be to help with ripple current. However Texas Instruments makes no mention in their data sheet. I don’t think there’s any harm in placing them anyway.

 

[Spacecowboy]

Input side is just supply bypassing, local to the card. Output side improves transient response but is probably not super critical in this case if you have more downstream

 

[Janalex]

Hey tomorrow I will receive the parts. In the meantime was just reviewing the last few pages here and is there any concern that the twentytrees and oongbac voltages although being similar to each other are so different than the expected voltages doggears both got in his module and were predicted by ltspice sim? They seem much lower in both amps. Bottom line will it affect the performance of the amplifier?

Right now one of my amps is spot on with the simulation. I’m expecting it to drop after installing the 7908 and the amplifiers to balance out. Wondering why the other amp just doesn’t come up to match the first. When oongbac first posted his voltages he also had one amp spot on and the other measuring low like mine.

 

[Spacecowboy]

The voltages in the sim are at +8 to -15 vs +15 to -8

 

[Janalex]

Oh gotcha. Thanks. So no change in performance

 

[fritzmyname]

Wow I'm really excited by these news! I can't wait to update the wiring and report back! Thank you all!