VC508_Line_Out_Without_Speaker_Kill

[kleuck]

It's yours ? Geee, one of the few that led me to the use of inductances, for the best, it was and still is an awesome idea !

[hewo]

Thankyou Steve C and kleuck for your responses

Glad to see someone got some benefit from my old circuit!

Just in case it isn't obvious: If you're connecting the circuit across your existing speaker, you don't need the big 8.2 ohm resistor and inductor.

1. agree: simplistic implement right on the back of the spkr magnet
2. I have previously epoxied those black plastic rectanguloid female receptacles directly onto the magnet. And it takes a hammer to shear it off!
3. It was necessary to do this to feed a slave spkr and idle the internal spkr in the combo.
4. Now here we have a different story: magnetism WILL IMPART disturbance to this tiny isolation xfmr since it too will be epoxied onto the plane of the magnet.
5. But there is a solution: MU METAL, and I believe it is the same metal used in either the laminations or wrap around shield on transformers. Magnetism tensors can not penetrate through MU METAL. The MU METAL can be epoxied 1st onto the plane of the spkr magnet, as an undercoat
6. Any precautionaries?
Thanks in advance

[hewo]

Thankyou Steve Conner for your responses

Glad to see someone got some benefit from my old circuit!

Just in case it isn't obvious: If you're connecting the circuit across your existing speaker, you don't need the big 8.2 ohm resistor and inductor.

1. when the 10K pot wiper is earthed, will secondary xfmr windings over draw current w/ the 1K8 resistor omitted?

[Steve Conner]

My original circuit shows a resistor "R" in series with the pot track to limit current in this situation.

Kleuck left it out, instead he installed one in parallel with half of the pot. You could call it a law bending resistor, but it is installed on the wrong half for that.

Even with the resistor R fitted, a high-powered amp could conceivably burn out a tiny transformer, as the full speaker voltage is applied across the primary. I did this because I wanted to overdrive the transformer, to generate lots of low-frequency distortion, simulating over-excursion of a guitar speaker cone.

Why on earth would you want to epoxy things to the back of the speaker magnet? Get some "No More Nails" and goop it to the bottom of the cabinet.

[Chuck H]

Get some "No More Nails" and goop it to the bottom of the cabinet.

When I put my resistive attenuator in combo amps I bend a piece of aluminum sheet to recess between the rear baffles. That way there's no need to reach into the rear of the cab to use the new circuit. The aluminum doesn't need to be very thick because the bends improve rigidity. They also inset the controls so there's nothing sticking out the back of the amp. If you don't mind the cosmetics it could be more easily mounted by screwing to the ouside of the rear baffles too.

[hewo]

Thankyou Steve C and Chuck H for your responses

When I put my resistive attenuator in combo amps I bend a piece of aluminum sheet to recess between the rear baffles. That way there's no need to reach into the rear of the cab to use the new circuit. The aluminum doesn't need to be very thick because the bends improve rigidity. They also inset the controls so there's nothing sticking out the back of the amp. If you don't mind the cosmetics it could be more easily mounted by screwing to the ouside of the rear baffles too.

1. (Steve C) insert the nulled pot protective resistor between the secondary winding hotside and the high leg of the pot. this way, this protective resistor precludes overdrawing current with the pot dialed to zero. kleuck's protective resistor affords same protection too but parallels current paths thru the pot track and the protective resistor. and this will desensitize the sound engineer's dialing resolution somewhat. either topology has its shortcomings. why have any tie of the wiper back to the winding's hotside at all? it doesn't appear needed to be tied back does it?
2. the reason i decided on the magnet rear plane to affix the lineout assemblage is because it is rock solid and minimizes wiring lengths, esp in the magnetism envelope there. i found the MU METAL flat piece inside the old fashioned CRT that computers no longer use for video screens. how man discovered, or concocted, this weird type of metal is strange. thing is, the epoxy is only as strong as the decal affixed onto the factory magnet of the speaker. i don't want to deface that decal. i can always shear off the epoxied MU METAL and lineout assemblage need be in the future. and yes, the magnet plane is readily accessible for the sound engineer's male guitar plug.

[kleuck]

Kleuck left it out, instead he installed one in parallel with half of the pot. You could call it a law bending resistor, but it is installed on the wrong half for that.

Hehe, took a little time to remember why i put this resistor : actually i put a "treble bleed" on the pot to have an other way to tune the brightness of the sim, but ended not using it, why i did remove the cap but not the resistor and draw it is a mystery

[hewo]

Thankyou kleuck and Steve C for your responses

Hehe, took a little time to remember why i put this resistor : actually i put a "treble bleed" on the pot to have an other way to tune the brightness of the sim, but ended not using it, why i did remove the cap but not the resistor and draw it is a mystery

1. okay i found on hong kong ebay tiny impedance matching trannies, seven dollars free delivery.
2. question now is why can't i select super high input impedance into 600 ohms?
3. the hong kong seller has several trannies into 600 ohms that are super high impedance, 40K, 120K, 360K and etc.
4. assuming inductance resistance trivial energy transfer loss, say <6%, what's the disadvantage of selecting super high input impedance?
5. does it mean the secondary voltage wil be less than the required amount, say 1vac rms, when selecting super high impedances?
6. remember kleuck advised 1.5K impedance on the primary windings?
7. i built a super flyweight wrigley's chewing gum half stick sized preamp, battery included, to buffer a rosewood bridge mounted flyweight barium piezo disc w/ the preamp mounted on my acoustic guitar's stika spruce soundboard to prevent weight mass loading of the soundboard vibration. it was that super-sensitive toshiba negative channel jfet that allowed 30microampere battery draw from the lithium coiin battery. using this same principle, can't i do the same from the speaker's terminals to feed the same kind of 600 ohm output signal to the sound engineer? the tube amps (vc508 and 5F1) both have power tranny available low ac voltage to rectify and power the super sensitive toshiba n-jfet. someboady in the commercial world probably did this already and marketed it as a DI box with option to input speaker or instrument high impedance right?
8. thank you in advance.

[Steve A.]

Why on earth would you want to epoxy things to the back of the speaker magnet? Get some "No More Nails" and goop it to the bottom of the cabinet.

I'm "hooked" on industrial strength velcro so that is how I would do it. (Some of my amps have patches of velcro on the top to hold a pedal- most of my pedals have velcro on the bottom.)

When I put my resistive attenuator in combo amps I bend a piece of aluminum sheet to recess between the rear baffles. That way there's no need to reach into the rear of the cab to use the new circuit. The aluminum doesn't need to be very thick because the bends improve rigidity.

Are you using the aluminum sheets available at hardware stores? Do you know the approximate gauge or thickness? (When I was working at the sheet metal shop as HVAC service manager back when I was on the sunny side of 50 I got to use the equipment in the shop and would bend up really nice footswitch enclosures out of 1/4" aluminum with their brake- I wonder if the cheap brakes at Harbor Freight could handle that? They had a sloped top and a flat bottom but no sides so I wouldn't use them for FX pedals.)

Steve Ahola

[hewo]

Chinese_5F1_Schematic

+1
hewo, does the guitar still sound "right" through other amps? Do you want or expect all amps to sound the same? Do you need a balanced line out for some particular reason? can you post a schematic of the amp for evaluation of the master volume circuit?

Incidentally, you don't seem to like this amp. Why don't you get a different amp?

1. The Peavey Rage 108 paper speaker 4 ohm problem already was resolved (put the amp at ear level not on the floor)
2. The 5F1 MV problem was resolved (parallel the 1M Audio carbon track with a 182K half watt fixed resistor)
3. Steve A also recommended inserting a 1K to 2K half watt fixed resistor to feed signal into the 6V6GT input control grid, calling it a "grid-stopper", because of the MV variance from legacy schematic. I did not do this. The MV's wiper goes directly into the 6V6GT input grid. What's the danger without Steve's "grid-stopper". When MV wiper is earthed, excessive current will flow from the plate into the grid and fry the delicate 6V6GT input control grid which is comprised physically of very fine mesh delicate screen?
4. The other variances from legacy 5F1 are the utility line switch gating BOTH line and neutral (DPST), the DPTT HTAC selection/standby [300vac_none_330vac], the NFB cutout switch, the 470uF 50wvdc 6V6GT cathode bias augment cutout switch, the single guitar input receptacle feeding paralleled pair of 68K half watt resistors (still legacy, input 1), the ac cooling fan sponge mounted topside on the PT's bell cover with impinging air onto bell cover, the ac snubber cap across utility's line and earth, and the NC speaker 1/4" receptacle (same as the NC guitar input 1/4" receptacle).
5. I am not posting the schematic since it is available already. BTW, I did not copy legacy layout wiring which chooses to route wiring underneathe the motherboard. Instead I routed low-level energies away from the utility's and HTAC, keeping length's minmal (anti-aerial-reception). And there is only one tiepoint earth, one stud of the PT's closest to the hot side 1st condenser.
6. I'll post cellphone camera pics.
7. I've discovered the 330HTAC has remarkable fidelity (telecaster) and headroom! Somebody said don't do it (330HTAC) here but I did flip that DPTT and 372DC is okay onto that shuguang 6V6GT, louder, clearer. Telecaster is stock fender pickups, music store owner gave me both because the windings open circuited but it was pretty easy to repair them. The Peavey pickups in the tele were too too loud (ceramic magnets)

[Steve A.]

3. Steve A also recommended inserting a 1K to 2K half watt fixed resistor to feed signal into the 6V6GT input control grid, calling it a "grid-stopper", because of the MV variance from legacy schematic. I did not do this. The MV's wiper goes directly into the 6V6GT input grid. What's the danger without Steve's "grid-stopper". When MV wiper is earthed, excessive current will flow from the plate into the grid and fry the delicate 6V6GT input control grid which is comprised physically of very fine mesh delicate screen?

Since "grid-stoppers" are apparently an invention of my own I guess I better patent the idea.

The stock 5F1 design doesn't need the grid stopper since the 6V6 is driven by the .02 coupling cap with a fixed 220k grid load. Replacing the 220k resistor with a 1M pot (bypassed with a fixed 182k resistor) changes things. For one thing with the MV set to 10 you now have a 153k grid load which will produce a weaker signal than the stock 220k resistor. (If you wanted to raise the grid load back up to 220k you would bypass the pot with a ~282k resistor- ok to go up a bit to the next higher standard value.)

The grid stopper should smooth out the signal a bit. One trick of the trade is to follow a MV with a grid stopper roughly 10% the value of the pot. Like adding a 100k resistor after a 1M pot. However the MV is usually feeding a preamp tube and not a power tube. One way to get around using a grid stopper would be to add something like a 10k resistor to the "tail" of your pot. By doing that you would not be connecting the grid of the 6V6 directly to ground at the minimum position of the pot. And with the 1M/280k MV set to 10 you would essentially have the stock 5F1 circuit driving the 6V6.

[hewo]

Thank you Steve A for your responses

Since "grid-stoppers" are apparently an invention of my own I guess I better patent the idea.

The stock 5F1 design doesn't need the grid stopper since the 6V6 is driven by the .02 coupling cap with a fixed 220k grid load. Replacing the 220k resistor with a 1M pot (bypassed with a fixed 182k resistor) changes things. For one thing with the MV set to 10 you now have a 153k grid load which will produce a weaker signal than the stock 220k resistor. (If you wanted to raise the grid load back up to 220k you would bypass the pot with a ~282k resistor- ok to go up a bit to the next higher standard value.)

The grid stopper should smooth out the signal a bit. One trick of the trade is to follow a MV with a grid stopper roughly 10% the value of the pot. Like adding a 100k resistor after a 1M pot. However the MV is usually feeding a preamp tube and not a power tube. One way to get around using a grid stopper would be to add something like a 10k resistor to the "tail" of your pot. By doing that you would not be connecting the grid of the 6V6 directly to ground at the minimum position of the pot. And with the 1M/280k MV set to 10 you would essentially have the stock 5F1 circuit driving the 6V6.

1. I errored writing 182K fixed resistor. It actually is the 282K half watter (I did the math to achieve equivalence 220K tie down 6V6GT input grid with the 1M audio pot; could have just as easily swapped that 1M audio pot with a 250K audio pot).
2. But was I correct about "frying" the 6v6GT's delicate input control grid screen meshing with wiper earthed? I don't want to fry that shuguang 6V6GT which sounds so wonderfully "alive" especially after playing half an hour onwards (what's going on here? circuitry and tube thermal equilibrium?)
3. Anyway, I'll insert the grid stopper 1K or 2K half watter just to protect the mesh from frying. It won't hurt the sound since it's nothing compared to the 220K tie down value.
4. Nobody wants to answer my question of swapping out that DPTT [300htac_none_330htac] with another switch that features an independent DPST [5Y3GT_DIODE] to change rectification mode. Does such a switch even exist? Otherwise I will be forced to abandon the MV altogether to use it's chassis mounting penetration for DPST rectification selection.
5. And nobody has answered my question whether 372DC (330htac applied) onto the 6V6GT and OT is unhealthy in the long run (over-voltage?)
6. cedist advised checking out sound with a 12 inch super power speaker to see if compliance would be compromised. I have a home built slave sporting an original 1980's EVM12L eight ohm. This particular speaker has superior sensitivity but I don't know if the 5F1 puny chinese OT will freak out trying to drive such a sensitive 300rms watts speaker? I have a decibel meter and found out that sensitive speakers make VERY BIG noise when the lithium penlight battery (1.5dc) is momentarily touched onto the speaker's terminals. But I don't know whether this is the same analogy when the puny chinese OT is applied onto a super sensitive speaker rated for 300rms watts.

[kleuck]

1. okay i found on hong kong ebay tiny impedance matching trannies, seven dollars free delivery.
2. question now is why can't i select super high input impedance into 600 ohms?
3. the hong kong seller has several trannies into 600 ohms that are super high impedance, 40K, 120K, 360K and etc.
4. assuming inductance resistance trivial energy transfer loss, say <6%, what's the disadvantage of selecting super high input impedance?
5. does it mean the secondary voltage wil be less than the required amount, say 1vac rms, when selecting super high impedances?
6. remember kleuck advised 1.5K impedance on the primary windings?
7. i built a super flyweight wrigley's chewing gum half stick sized preamp, battery included, to buffer a rosewood bridge mounted flyweight barium piezo disc w/ the preamp mounted on my acoustic guitar's stika spruce soundboard to prevent weight mass loading of the soundboard vibration. it was that super-sensitive toshiba negative channel jfet that allowed 30microampere battery draw from the lithium coiin battery. using this same principle, can't i do the same from the speaker's terminals to feed the same kind of 600 ohm output signal to the sound engineer? the tube amps (vc508 and 5F1) both have power tranny available low ac voltage to rectify and power the super sensitive toshiba n-jfet. someboady in the commercial world probably did this already and marketed it as a DI box with option to input speaker or instrument high impedance right?
8. thank you in advance.

I do not recommend 1K5 on the primary actually : i find useful to tame the voltage directly in the Xformer, so i searched one with a 600 Ohms output and a slightly higher primary, the TM022 fits these criteria (1K5/600)
If you choose a Xformer with a high resistance on the primary, you will end with a too low voltage first, second the inductance will be very different and you will have to do extensive tests to find the right cap, third i'm not sure the resulting sound would be good, as you need an inductance with a low series-resistance when you are building a filter for lows -for example, there's a huge difference in Wah when using different inductors with the same inductance but different series-resistance.

[hewo]

Thank you kleuck for your responses

I do not recommend 1K5 on the primary actually : i find useful to tame the voltage directly in the Xformer, so i searched one with a 600 Ohms output and a slightly higher primary, the TM022 fits these criteria (1K5/600)
If you choose a Xformer with a high resistance on the primary, you will end with a too low voltage first, second the inductance will be very different and you will have to do extensive tests to find the right cap, third i'm not sure the resulting sound would be good, as you need an inductance with a low series-resistance when you are building a filter for lows -for example, there's a huge difference in Wah when using different inductors with the same inductance but different series-resistance.

1. high impedance primary results in too little energy transfer to the sound engineer.
2. my original taste for the toshiba n-channel jfet to provide sound engineer's energy was disapproved simply because of the legacy resistor divider topology utilized in the commercial industry.
3. it is apparent active circuitry is superior because of its impart of energy from the power supply which is readily available. a superior sound engineer signal can be derived from the speaker terminals via such active circuitry that is powered by the readily available heater supply
[3.15vac_CT_3.15vac]. The TL072 opamp has incredibly high input impedance and supporting circuitry can be tailored to suit input output impedances, and, cut or boost. The costing wins with active circuitry, and, the reliability and stability will be superior in comparison to the passive topologies of an isolation impedance matching transformer we have under discussion. I will concoct a single channel n-jfet, 2sk170, using a lithium battery utilized in the automobile's ultra-miniaturized keychain (12dc, plenty headroom, class A). these devices do not guzzle gas (1000hrs!) so the battery concept is prudent over entanglement into the heater's power supply. and it is magnetically transparent to the speaker's tensors where it will be affixed (ref Steve A velcro).
4. a socket will be utilized for the TO-92 since square waves will be authenticated, and this does corrupt the junction channel over a significantly long period of operating time. there's four resistors (1/8 watt), two tantalums, the lithium bat, sensing wire, and the 1/4" receptacle. no pot is necessary. I'll get pics after its concocted. these jfets are incredibly sensitive (super high Gm).

[kleuck]

I'm not sure active circuitry can be considered superior, depends on you goals.
Theoretically, you can achieve a more precise simulation of a given speaker, but i do not agree.
What are actually achieving most active simulators ? They try to emulate the speaker's frequency response, fine.But it's a poor way to simulate a speaker imo, because
1) Curves are drawn with a 1 watt signal, are you under the impression that your speaker sounds the same under 1 watt or under 25 ? That's not the case with our tube amps with very low -if any- damping factor.
2) I own two very different sounding speakers, though the curves are (almost) exactly the same, minus the efficiency, so what the fuck ?
3) You will need a Xformer anyway to achieve ground-lift.
So, for me, active sims are way to complicated for a not-so-perfect result.
Added to that, for a good result, you will need more than a TL072 i think, most simulators are using a quad aop or two dual (see Marshalls, or the condor sim) the only simpler ones are the Mesa, but they use inductances anyway
The good thing with active sims is that you can -Mesa did- use a power Aop to do both the sim and a headphone out, which is clever.