trinityamps.com

I have an "sIII clone" made from a salvaged PT and an unknown brand OT.
The sounds I get are good, but when fully above 8 on the TMB channel I get a swirly, phasing sound.

The PT I'm using is not to the specs of stephen's design.
When loaded I get only 305V at the plates of V4 and V5.

Reading here and on 18watt I'm assuming that the phasing sound is the PI that is overloading.
The voltages around V3 are:
1/2/3/6/7/8
190/50/71/190/50/71

So I believe I have two options to try out,

* change R13, R14 to 250k to dump some signal.
* Or maybe I could lower R22 to lower the voltage drop to V1,2,3.
(and as a result get more headroom in the PI, and preamp stages ???)

The voltage drop over R22 now is 50V.
so current is 6,1mA.
If I wanted to raise everything about 20V,
6,1mA x 30V = =- 5kohm.

If someone can correct me where I went wrong or give opinions, ...
please do.
Thanks

Before you change anything try this.

Measure your B+ before the 1.5K resistor, R28. Then, remove the rectifier tubes and temporarily install two diodes effectively creating a Solid State rectifier and see what the voltages do. If they go up (you need about 20 - 30 volts) then see if the sound goes away. If you can live with that, then add a sag resistor and close it up. If you cant, then start changing parts & experimenting.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks for your help, stephen !

Before R28 I measure 340Vdc, R28 is 1,8k (I couldn't find 1k5).
After R28 measures 310V.

I should better explain what I changed :

The tube rectifier was replaced with a silicon bridge rectifier.
C13 and 14 are 200uF
R28 is 1k8ohm

R18 and R19 are 250k
C7 is 0,022uF (was noisy when I tapped it with a chopstick, I changed it but had only 0,022uF around)
There is no Master volume

On the normal channel I did the clean mod as you described,
anode has 1k5ohm to ground. C16 and R27 removed.

Unloaded (heaters on, HT interrupted) I measure 290Vac at the secondary, it drops to 270Vac when loaded.


I must stress : this is !NOT! a kit from trinityamps !

I have parallelled R28 with a 6k8 resistor,
giving a resistance of about 1k4 together.

The phasing is still there
voltages
B+ is 340V
After R28 I have now 322Vdc.

V3:
1/2/3/6/7/8
200/53/78/200/53/78

next thing I tried was parallelling R22 with 22k,
to become +-6k.

powered up, and huray the swirl is definitly a lot less.
powered down,
powered up
measured voltages

hit a bass note ... the swirl is back ??

Did you try to replace any tubes?? I once had a problem with an 18 watt TMB amp that sounded similar and it required me to replace the EL84s.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I've tried 3pairs of el84s,
and I replaced V3 too.

Next thing I tried,

47k for R12
not better, back to 56k.

Parallelled R13 and 14 for 250k.
not better, back to 500k.


I don't know what I can try next.

Since both channels do not behave the same way, the problem could be around v2. It shares v1 & v3 with the normal channel so less likely.

Could be oscillations, so try moving the wires around v2 and in the TMB controls. Assume you have shielded wire to v2?

Can you post any pics?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Yep, shielded wire from the tmb controls to V2.


I'm not too keen on showing pictures because I really should rebuild the whole board.
The orange board material is not too heat resistant, I used it because I had it on hand, and wanted to get started fast.
So, resoldering things is a disaster ...

These photos are old and before all the mods I did.
I'll take some new ones.

thanks for helping

Try running the coax to v2 over top of the board, not underneath.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Steven with the help,

No luck with moving the coax above the board,

I did move some other wires too, but it's too late to turn it up loud now.

I noticed that with all tmbchannel-controls on 10, R2 and R3 are sensible to tapping. It makes a popping sound through the speakers.
The other channel doesn't do that, but ofcourse the gain is much less over there.

Yes, this can happen. I've seen that as well. Got to think some more about this.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I uploaded some new pictures.


you see what I mean by melting the board

I noticed in the 2nd of the new pix that there is a resistor not soldered on the far right,and in the 6th pic I see the twisted black wires on V1 look to be melted together...

Thank you for looking,

Those heater wires are not really melted together,
that would certainly blow the main fuse.

The loose resistor and electro-cap is a temporary modification of the normal channel.

I've rebuilt the whole amp,
every value as in the original design.

Same swirl !!
I'm stumped.

Different power trannie since a few months back.
Same output trannie, I'm starting to suspect the trannie.

V1: 1/131 3/0,9 6/134 8/0,9
V2: 1/161 3/1,5 6/243 8/159
V3: 1/193 2/49 3/71 6/191 7/49 8/71

V4: 3/10,2 7/326 9/306
V5: 3/10,2 7/326 9/306




look here for pictures:
http://smg.photobucket.com/albums/v54/perki/18watt/sIII/sIII%20version2/?albumview=slideshow



How can I track this problem down ?

Read this over, does it seem like the same problem to you?

viewtopic.php?t=942

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Re: Your sIII Clone Swirling sound:

I listened to your clip:

http://www.trinityamps.com/clips/ward_sIII_Output1-2.mp3

I cant detect any phasing sort of sound. I hear a tiny buzz - Maybe but overall the sound is fine. To me I think it sounds pretty good.

It's hard to tell on the recording. I have seen a lose ground solder cause buzz on louder passages.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps