Studio Projects T3 circuit
« on: February 18, 2020, 05:40:38 PM »
Here is my draw of the schematic of my T3 (first gen).

Any thought on it?
The valve is the stock one, unbranded (see pic) and very similar to the the China 12AT7/12AX7. Do China ever made a 12AY7?  Anyway it seems to be low noise.

https://imgur.com/a/QGublnQ
https://imgur.com/a/jyl6TYE
https://imgur.com/a/blBONkt
https://imgur.com/a/1k3NqWc

The body is big enough to fit other transformers and better caps. I wonder if there is a way to make it something close to U67 like D.Thomas made on his CM67, using k67, 6072 and BV8.

Edit: Schematic update with correct resistor values
« Last Edit: February 20, 2020, 03:15:03 PM by LevinGuitar »


Gus

Re: Studio Projects T3 circuit
« Reply #1 on: February 18, 2020, 07:26:27 PM »
You might want to keep the stock capsule and transformer.

What don't you like about it?

Try different tubes. Try a  NOS 6072 (not green paint) 12AY7 or NOS 12AT7

trace the circuit again use a known China tube microphone schematic to compare against.

What is values are written on the red resistors?




« Last Edit: February 18, 2020, 07:33:54 PM by Gus »

Re: Studio Projects T3 circuit
« Reply #2 on: February 19, 2020, 06:40:44 PM »
I have some nos 12ay7 to try, sure. But I want to make it sound a bit deeper and more transparent. I already saw the difference between that transformer and the AMI T14 in my MXL V77:
https://www.gearslutz.com/board/so-much-gear-so-little-time/1268817-mxl-v77-vs-wrabler-mkvi.html

But I don't want to spend 130€ again in a imported transformer, so maybe I will try a Lundahl.

D.Thomas uses a BV8 but he also uses a cathode follower circuit, using a plate follower I guess I'll have to use something with higher ratio?

I'll try the AMI in the T3 also, just to see.

Edit: I updated the schematic because I missed the ground connection to the trasnformer and the remaining resistor values.
Updated again with correct values.

« Last Edit: February 20, 2020, 03:42:37 PM by LevinGuitar »

Re: Studio Projects T3 circuit
« Reply #3 on: February 26, 2020, 11:04:19 AM »
My draw of the schematic of the MXL V77 (should be similar to the SP TB1)

Gus

Re: Studio Projects T3 circuit
« Reply #4 on: March 01, 2020, 09:45:28 AM »
With the stock circuit the only thing I would maybe change is C3 type and maybe value, IMO C4 is not needed, you might like the stock cap.

Try different tubes sometimes you need to try a number of the same type and brand as well as other brands. Don't be surprised if you end up trying 10 or more.

I would not change a 797 capsule(I am assuming it is a 797 capsule) just to change it and I would  work with the stock transformer before changing it.

There has been a good deal of information shared at this site over the years.

Just changing part to change them is not a great idea you can sometimes make things worst.

Question every thing you read about microphones adjustments on the web.

Record before and after, sometimes a adjustment can make it worst but you can learn from that.

Can you EQ it after the microphone preamp and get the sound you want? If so that is good information.

xeawr

Re: Studio Projects T3 circuit
« Reply #5 on: March 01, 2020, 10:52:53 AM »
what's C1 for?

Khron

Re: Studio Projects T3 circuit
« Reply #6 on: March 01, 2020, 12:03:33 PM »
Assuming you mean the schematic attached to the first post, C1 and C2 basically shunt the very high frequencies (well above audio range) to ground (the thicker black line, which also goes to the "bottom" of C5.


what's C1 for?
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

xeawr

Re: Studio Projects T3 circuit
« Reply #7 on: March 01, 2020, 05:57:25 PM »
alright, makes sense. C2 slipped my vision but yes, I meant those two caps around the tranny

xeawr

Re: Studio Projects T3 circuit
« Reply #8 on: March 01, 2020, 05:59:58 PM »
waiiiit, now I get it. Aren't these the ones that we routinely remove in the apex 460 mods? Would you recommend lowering their value (from 100nF to say 22nF) or removing them altogether?

Gus

Re: Studio Projects T3 circuit
« Reply #9 on: March 01, 2020, 06:19:08 PM »
Remove them for more RF interference.


xeawr

Re: Studio Projects T3 circuit
« Reply #10 on: March 02, 2020, 11:18:31 AM »
Got it! Do those need to be matched?

Khron

Re: Studio Projects T3 circuit
« Reply #11 on: March 02, 2020, 11:27:58 AM »
In an ideal case, yes (in order to maintain as high CMRR as feasible).

Got it! Do those need to be matched?
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans


 

Related Topics

  Subject / Started by Replies Last post
33 Replies
17126 Views
Last post October 24, 2013, 07:52:44 AM
by ln76d
0 Replies
1112 Views
Last post November 09, 2005, 10:44:47 AM
by Snatchman
10 Replies
2360 Views
Last post March 19, 2013, 04:52:29 AM
by RuudNL
33 Replies
10101 Views
Last post June 01, 2013, 06:58:47 AM
by Paul678