Hello,

at the moment, i play around with tweaking my shortly build TS Circuit.
For a versatile Sound i added an 2x ON/OFF/ON toggleSwitch, to change
between normal Clipping - CompCut (like the Fulldrive2 can) and Distortion, that removes the Clipping diodes from the FeedBackloop of the OP Amp including the 51p cap and adds a 100p Cap to the FeedBackLoop and 3 1n4004 Diodes from Signal to Ground (just before the Level Control)

The Sound is good so far, but specially in the classic Overdrive Setting
i feel the Sound is too compressed.
In the CompCut Mode the Sound is Boosted clean till 9 o Clock Drive with Humbucker and 11 o Clock with SingleCoil - from there the OPAmp starts to clip for itself (not bad, very crispy) - i have to add, that i changed the DrivePod from 500K to 1Meg.

Im Thinking of removing the Input or Output Buffer, or both to get a more
dynamic sound and more punch.
Did anybody build a TS Circuit without the Buffers yet?
I'd Like to know your experiences with that... does it kill the good Sound?

Thanx for suggestions !!

Oliver

I don't think the input/output buffers make a very big difference.  The various circuits I have breadboarded based on the TS sound basically the same, so removing the buffers doesn't "kill" the sound.  The input buffer will probably have the most distinct effect on the sound, as the effective input impedance of most BJT opamps changes with the gain.  

I recommend trying a CMOS op amp.  This gives two advantages:

Gain independent, and very High input impedance.
More colorful clipping...That is, if you're using it in a mode where the opamp clipping is more drastic than the external diode clipping.  From what I understand, the BOSS MetalZone uses CMOS opamps for this reason.

The "compressed" sound may be fixed by using LEDs or multiple series diodes(higher turn-on voltage) in place of the 1N914 clipping diodes.

Another thought I had is that this may not actually be a "compression" effect, but high frequency cut-off and slew rate effects.  Changing the 500k pot to 1Meg  begins to allow gains that exceed the gain capacity of some op-amps at mid to high frequencies.  I recommend using an IC with a broader unity gain bandwidth than the RC4558 (though this one is not bad).  The 1Meg pot accomplishes a possible gain of 2000 in the TS passband for an ideal opamp.  This brings the high frequency 3 dB point down to 1 or 2 kHz assuming a GBP of 3-4 MHz.   Generally, it is good not to roll off guitar untill about 5kHz.

A better way to get more drive is to add a gain stage before the clipping stage, then add more diodes in series with the clipping diodes to maintain a similar "clipping threshold" on the signal.  Then the further hard clipping drive from cranking the gain will come from the opamp rails...and if the opamp is CMOS, it will have a more pleasant (In my opinion) overdriven sound.  You may also want to change the "V/2" reference to 3V to assymetrically clip the opamp...and regulate the opamp's Vcc to 7V to bring the clipping rails closer so that you can get more immediate "distortion" with less gain so that slew rate effects are decreased.

Sorry if I'm filling you full of too many ideas.  I hope something in there was helpful

I don't think the input/output buffers make a very big difference.  The various circuits I have breadboarded based on the TS sound basically the same, so removing the buffers doesn't "kill" the sound.  The input buffer will probably have the most distinct effect on the sound, as the effective input impedance of most BJT opamps changes with the gain.  

I recommend trying a CMOS op amp.  This gives two advantages:

Gain independent, and very High input impedance.
More colorful clipping...That is, if you're using it in a mode where the opamp clipping is more drastic than the external diode clipping.  From what I understand, the BOSS MetalZone uses CMOS opamps for this reason.

The "compressed" sound may be fixed by using LEDs or multiple series diodes(higher turn-on voltage) in place of the 1N914 clipping diodes.

Another thought I had is that this may not actually be a "compression" effect, but high frequency cut-off and slew rate effects.  Changing the 500k pot to 1Meg  begins to allow gains that exceed the gain capacity of some op-amps at mid to high frequencies.  I recommend using an IC with a broader unity gain bandwidth than the RC4558 (though this one is not bad).  The 1Meg pot accomplishes a possible gain of 2000 in the TS passband for an ideal opamp.  This brings the high frequency 3 dB point down to 1 or 2 kHz assuming a GBP of 3-4 MHz.   Generally, it is good not to roll off guitar untill about 5kHz.

A better way to get more drive is to add a gain stage before the clipping stage, then add more diodes in series with the clipping diodes to maintain a similar "clipping threshold" on the signal.  Then the further hard clipping drive from cranking the gain will come from the opamp rails...and if the opamp is CMOS, it will have a more pleasant (In my opinion) overdriven sound.  You may also want to change the "V/2" reference to 3V to assymetrically clip the opamp...and regulate the opamp's Vcc to 7V to bring the clipping rails closer so that you can get more immediate "distortion" with less gain so that slew rate effects are decreased.

Sorry if I'm filling you full of too many ideas.  I hope something in there was helpful

Which CMOS opamp would you recommend?  I know there's a plethora of them around.

Phillip

sorry about the double post.  I found a good CMOS opamp that substitutes pin for pin with the RC4558:

Quotedescription
The TLC272 and TLC277 precision dual
operational amplifiers combine a wide range of
input offset voltage grades with low offset voltage
drift, high input impedance, low noise, and speeds
approaching those of general-purpose BiFET
devices.
These devices use Texas Instruments silicongate
LinCMOS technology, which provides
offset voltage stability far exceeding the stability
available with conventional metal-gate processes.
The extremely high input impedance, low bias
currents, and high slew rates make these costeffective
devices ideal for applications previously
reserved for BiFET and NFET products. Four
offset voltage grades are available (C-suffix and
I-suffix types), ranging from the low-cost TLC272
(10 mV) to the high-precision TLC277 (500 µV).
These advantages, in combination with good
common-mode rejection and supply voltage
rejection, make these devices a good choice for
new state-of-the-art designs as well as for
upgrading existing designs.

Datasheet:
http://focus.ti.com/lit/ds/symlink/tlc272.pdf

$0.96 from mouser electronics

some more suggestions (more expensive):

OPA743  ( high gain BW product 7MHz) not available from mouser
OP27, or equivalent TS922  (available from mouser)

And here's a list that I found of CMOS OP AMPS but I haven't looked at the datasheets to determine how suitable they would be for audio applications:

LMC 6001 AIN      CMOS ultra ultra-low input current op amp (25fA)
LMC 6442 AIN      CMOS dual micropower RRIO single supply op amp
LMC 6464 AIN      CMOS quad micropower rail-to-rail op amp
LMC 6494 AEN      CMOS quad rail-to-rail op amp
LMC 660 CN      CMOS quad op amp (for low-Z loads)
LP 324 N      Quad micropower op amp
LPC 660 IN      CMOS quad op amp (for hi-Z loads)
OP 07 EP      Low offset/drift op amp

I just did a quick search on some of the IC's in that list.  None of those would be a good replacement in a TS circuit.  The OP27 is not CMOS, but it WOULD be a good choice to experiment with.  It has a higher bandwidth and slew rate.

of the CMOS opamps from the list, the LMC6494 may be acceptable, but not optimal, since we are more concerned with bandwidth than offset voltages...that's what most of these CMOS high precision opamps are used for...I was using them for a temperature sensor circuit where gain is not an issue.

I just looked at the datasheets for the OPA743 series:
OPA743   single 741 type pinout
OPA2743  dual opamp (Good TS replacement)
OPA4743  quad

.0008% THD !  Very quality

Datasheet:
http://www.scanti.ru/docs/datasheets/sbos201.pdf

Available from DigiKey @ $3.11 per OPA2743....quite a bit more expensive than your average TL072 or RC4558

:shock:  :shock:  :shock:

OK, head is smouldering.....

Many THANKS for those abound Informations!!!
I Try step by step changing and listen if it hits my taste.

[KLICK!] *heating the SolderingIron*

bye
Oliver      

Hi,

a short reply to your hints...:

i desoldered one Side of one of the 1N914 in the feedbackloop and added
a 1N4004 in Series with it.
I sounds much better now in OverdriveMode - more open and naturally closer to a real Tubeclipping.

i desoldered the 1K resistor at the second OPAmp (that goes to the Tonecontrol) and tried a 10K
It is great, because it increases the Level, but with more Gain and Tone turned to the hights it begins to fiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiip..
I changed it to a 3K3 and it sounds more crispy and has a louder Level, if needed.

I played around with some Settings and im really satisfied now!

The Sound comes really very close to my old Hohner Orgaphon, when that Amp is cranked up..

bye
Oliver    

I put a TS932 (ST Microelectronics) cmos opamp in my reissue TS9 and TS9-DX, and replaced the clipping diodes with red/green leds. When I bought the TS9 it was lifeless, so much so that I was wondering why there was so much fuss about the TS. After the mods it sounds amazing, and I regularly get asked about my sound at jam nights.

I suspect that most similar cmos opamps with rail-to-rail output drive will behave similarly. I believe the key factor is how the output circuit copes with the sudden changes in output current as the diodes go in and out of clipping.