Studio Projects T3 circuit

[LevinGuitar]

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.






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 updated

Mod: Studio Projects T3 capacitors and tube mod - Gearspace.com

 

[Gus]

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?

 

[LevinGuitar]

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.

 

[LevinGuitar]

My draw of the schematic of the MXL V77 (should be similar to the SP TB1)

 

[Gus]

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. EDIT this is for the first post schematic

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]

what's C1 for?

 

[Khron]

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?

 

[xeawr]

alright, makes sense. C2 slipped my vision but yes, I meant those two caps around the tranny

 

[xeawr]

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]

Remove them for more RF interference.

 

[xeawr]

Got it! Do those need to be matched?

 

[Khron]

In an ideal case, yes (in order to maintain as high CMRR as feasible).

Got it! Do those need to be matched?

 

[LevinGuitar]

In the second gen of the T3 I found the R6 to have a second resistor in parallel (I had other T3 mic with same second resistor there).
Edit: I have realized that they lowered plate resistor to match 12AT7 tubes they are using now. So after all, the first gen used a 12AY7 equivalent tube?

 

[Lelandletham]

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?

Ya the stock capsule and transformer work very well. I put in a nos Jan 6072 and am RCA and it made a noticeable difference. Also I put a 800v 1uf 1% nos cap in for C3 and Gus is right it beefed up the low and low mids well in a pleasing way. I also changed out to other caps I forget which ones. Oh c10 for polystyrene 1% nos cap as well. These are honestly very good mics boars shell grill all heavy duty the old school one I have at least first model

 

[LevinGuitar]

The stock transformer is a good one, but Ami T14 is better. Also you should try a lower resistor for the cathode bias, take a look what was used in AKG C12. Higher quality C7 (and even lower capacitance) also will make a difference.

 

[kingkorg]

If anyone wants to sell the stock SP transformer i'll take it.

 

[soliloqueen]

honestly the biggest issue with these mics for me is the headbasket and body. I find that they ring kind of bad and it messes up the treble

 

[shabtek]

what is the grill made of? brass or ferrous metal? I have noticed all the pingy-ringy baskets attract a magnet.

you hear that knock-off manufacturers?

 

[Newton50]

My T3 mic is not working and I really miss using it. I've taken some voltage measurements on the mic.
There's 194vdc and 192vdc on each end of R6, ref. to the mic case.
There's 194vdc and 192vdc on each end of R6
Measured 56 / 62vdc on R7.
R8 measures about 23vdc.
Also, with the tube installed, I'm measuring about 0v AC between any of the transformer leads.
Swapped out tubes and it didn't help.
I'm thinking it may have a bad transformer. Does anyone have ideas concerning what's wrong with it?
Thank you for any input.

 

[Khron]

Also, with the tube installed, I'm measuring about 0v AC between any of the transformer leads.

Measured with what, and under what circumstances?