Anyone know what the "tiny terror" circuit is?

[Blue Rock]

Correction!

gain 12AU7 (Sino), PI 12AT7 (Sino).

Sorry, I mixed up the two valves... 1:st valve (gain) 12AT7 and 2:nd PI 12AU7.

[Blue Rock]

Correction

With 12AX7 at PI it's even better, less compression and more attack, still with smooth overdrive. Gain at 2-3 o'clock, tone at max, volume 10 o'clock (15 W setting).
This is a Terror I like!

Mixed up the valve positions so the above mentioned is the 12AX7 as 1:st valve and 12AU7 as PI.

[Thomeeque]

Hi! Where do you mean "the bright cap" is located?

IMO there's only one, which could be called "the bright cap" and it's 100pF cap on first gain pot.. for low gain setting it will have probably significant influence.. T.

[strangebru]

IMO there's only one, which could be called "the bright cap" and it's 100pF cap on first gain pot.. for low gain setting it will have probably significant influence.. T.

So could this 100pF "bright cap" be changed (raised I guess) to go in the opposite direction to make sound even brighter?

Or is the previously discussed 470pF cap the better one to change to make sound brighter? Did we ever fully establish that this was the cap that John G was talking about when he said "Try removing the cap off the second gain stage or reducing its value."?

[Thomeeque]

So could this 100pF "bright cap" be changed (raised I guess) to go in the opposite direction to make sound even brighter?

I'd say no - by increasing it's capacity you would just lower the frequency, where boost starts.

Or is the previously discussed 470pF cap the better one to change to make sound brighter?

Yes, I'd start here..

Or you can try to add "bright cap" to second gain pot!

Or do both.

And you can try to add "bright cap" to master volume pots as well btw. (but keep it symmetrical)

Or in parallel with one or both of 68kohm resistors (and maybe increase those resistors value to - lets say - 220kohm..?)

There lot of room to play, but be prepared, that you can get into oscillations if you gain it to much..

Enjoy!

Did we ever fully establish that this was the cap that John G was talking about when he said "Try removing the cap off the second gain stage or reducing its value."?

Probably not, but I can establish that now - John has sent me his schematics via e-mail meanwhile, and it's obvious.

T.

[John G]

Hi,
Just thought I would clarify that the Schem of the TT I found on the net has the second gain stage anode resistor with a 4n7F cap across it. It has been pointed out that that schem in incorrect and it is in fact a 470pF. Removing this cap will improve upper brightness.
The cap across the volume control bleeds high frequencies but is dependant on the setting of the control ie with control down (ccw)more frquencies will be passed compared to when the volume is fully maxed (cw) then the cap is shorted out so will have no effect. This arrangment is usefull when you lower the volume you get a lift in treble, like the brite switch on a Fender amp.
I hope this clears things up.
John G

[strangebru]

Hi,
Just thought I would clarify that the Schem of the TT I found on the net has the second gain stage anode resistor with a 4n7F cap across it. It has been pointed out that that schem in incorrect and it is in fact a 470pF. Removing this cap will improve upper brightness.
The cap across the volume control bleeds high frequencies but is dependant on the setting of the control ie with control down (ccw)more frquencies will be passed compared to when the volume is fully maxed (cw) then the cap is shorted out so will have no effect. This arrangment is usefull when you lower the volume you get a lift in treble, like the brite switch on a Fender amp.
I hope this clears things up.
John G

Is that 470pF cap just for tone shaping or is it also for controlling oscillations, maybe unaudible oscillations that can only be seen on a scope? Have you tried removing it in your amp? If it does help control oscillations, what value do you think would be good if I just wanted a little more bright but didn't want to risk oscilations?

[John G]

Hi,
To answer your questions, yes and yes ! Try reducing the value to say 100pF, on my clone I dispenced with it all together. Yours may behave differently, try it and see.
John G

[MFTech]

Ask and ye shall...

FYI: I drew out the schematic on an earlier Korea Tiny Terror some time ago. It seems there are a couple differences from Admiral's schem... although, I might have made an error... any other drawers out there to confirm?

1) Coupling cap C15 into PI is .0022uF on mine (.047uf on Admirals)
2) Tone control circuit is located right after master volume rather than after PI. (C13 cap is .047uF rather than .0022uf)
3) R19 is 100K (connected to V2 plate) rather than 68K

All else is the same... as I said, it's probably my mistake. Not the easiest layout to trace being a dual sided PCB.

P.S. The guys at Mercury Magnetics are working on a Tiny Terror tranny upgrade kit like the Epi Jr kit. They made it sound like it was going to be absolutely killer... I plan to use the kit to build a PTP version of the TT from scratch. Although, nothing wrong with the stock TT!

[Thomeeque]

FYI: I drew out the schematic on an earlier Korea Tiny Terror some time ago. It seems there are a couple differences from Admiral's schem... although, I might have made an error... any other drawers out there to confirm?

1) Coupling cap C15 into PI is .0022uF on mine (.047uf on Admirals)
2) Tone control circuit is located right after master volume rather than after PI. (C13 cap is .047uF rather than .0022uf)
3) R19 is 100K (connected to V2 plate) rather than 68K

All else is the same... as I said, it's probably my mistake. Not the easiest layout to trace being a dual sided PCB.

P.S. The guys at Mercury Magnetics are working on a Tiny Terror tranny upgrade kit like the Epi Jr kit. They made it sound like it was going to be absolutely killer... I plan to use the kit to build a PTP version of the TT from scratch. Although, nothing wrong with the stock TT!

Hi!

Would you mind to share your schem (even you think there are errors)? Btw. I know that mathia has drawn schem (or at least fragments) out of his OTT unit circuitry, maybe he would not mind to share it either (he has found some differences too btw.).

T.

[MFTech]

Hi!

Would you mind to share your schem (even you think there are errors)? Btw. I know that mathia has drawn schem (or at least fragments) out of his OTT unit circuitry, maybe he would not mind to share it either (he has found some differences too btw.).

T.

UPDATE: I doubled checked the TT & I did have a couple errors on my schematic. Everything on Admiral's schematic appears to be correct with the exception of R19. (resistor following V2 stage) It is 100K in my chassis rather than 68K as on his schematic.

[John G]

Hi,
A amp tech mate of mine had a TT on the bench briefly, only had a very short time to look as customer was waiting.
He did confirm thet the 68k was in fact 100k and all rest seems to be accurate as per the Admirals schem, except the the Master Volume was marked on the pcb as 100k log ???, unfortunately he had no time to measure.
With the 0.1uF caps feeding the M/V then maybe the 100k is correct. ie a better low frequency roll off point.
Any coments.
John G

[MFTech]

Hi,
all rest seems to be accurate as per the Admirals schem, except the the Master Volume was marked on the pcb as 100k log ???, John G

For pots, I have:

GAIN: 500KA dual
TONE: 500KB
MASTER: 100KA dual

[MFTech]

Here is an updated TT schem that has voltages, some part locations, & couple component value corrections.

here ya go...

[John G]

Hi ,
Thanks for the update, much appreciated.
PS there is an 4A PC mount fuse in the heater line.
John G