Low voltage tube overdrive

Vitallka · Post by **Vitallka** » 02 Mar 2022, 10:35

Hi there. I am from Ukraine and I want to present you my project of low-voltage tube overdrive on a 6И1П (soviet analogue og ECH81).
Scheme:
https://app.box.com/s/flczcj62gqmv1n8jllnzcg4u3m00oj33

Sound is recocrding on a blackberry q10 (tube overdrive - tube SE - 1x12 Seventy80):
https://app.box.com/s/sr1b4yq1qk6x7evbz8wdh6cbdmudfqf3

bajaman · Post by **bajaman** » 03 Mar 2022, 09:29

Hope you are safe - thanks for an interesting design

Vitallka · Post by **Vitallka** » 03 Mar 2022, 13:14

There is no fighting in our area, but we thank you all for your support and sympathy.
I have made a similar scheme of fuses on lamps, but we still need to redraw the scheme. After a while I will share the scheme - you can use any pentodes of low power

ppluis0 · Post by **ppluis0** » 03 Mar 2022, 14:16

Hi Vitallka,

It's good to read that you're out limits of the most conflicting areas in your country. I hope that this nightmare ceases soon and the normal life can be reached again.

Regarding your design: perhaps many others dual tubes can be adapted to this same topology. EG.: ECF80, ECF801; 9A8; 6U8; 6CG8, etc.

Several types of triode/pentode manufactured for TV application are waiting an opportunity to bring out distorted sounds for us

Cheers,
Jose

bmxguitarsbmx · Post by **bmxguitarsbmx** » 03 Mar 2022, 21:25

Vitallka,
Those are impressive tones. Has a really nice "gurgle" to the tone (if that makes sense). Are there tone controls on the "tube SE" amplifier that you are using to achieve the balance?
Best wishes to you and your people!
BMX

Vitallka · Post by **Vitallka** » 20 Dec 2023, 18:21

I decided to go back to low anode power pedals again. After going through several different combinations of different tubes, I decided to use 6ф1п (analogue ecf80). This scheme has also undergone changes, but here is the final version.

Tink · Post by **Tink** » 20 Dec 2023, 20:15

Sounds great

luix · Post by **luix** » 21 Dec 2023, 17:50

Really nice sound!

I don't know how did you recorded the samples but I can hear some noise, using high voltage tubes in space charge mode (low anode voltage) makes them more noisy.

A solution I've tested with tube driver is to filter the anodic supply at least with a capacitance multiplier circuit, a BC550C will be more than enough.
Filtering the heater using constant current supply is a good solution too but it cost more due to power dissipation, Pd = (28V-6.3V)*0.5A = ca 11W so the transistor should be heatsinked.

Another thing you can do is to use the triode as first stage since triode usually have lower noise.

Vitallka · Post by **Vitallka** » 21 Dec 2023, 20:17

During recording, the guitar pickups could be affected by electromagnetic fields from the computer's pulsed power supply units or the pedal itself. By the way, the noises disappear when the volume on the guitar is reduced to zero.
And in the first stage there are zener diodes, which are very noisy, and without the R21 resistor, the pedal made a lot of noise. After installing the resistor, the audible noises were greatly reduced.
I use a 12V switching power supply for power, two converters are installed in the pedal itself: LM2596 (from 12V to 6.3V) and XL6009 (from 12V to 28V). Previously, I used a 7815 + 10V zener diode chip to filter the anode supply, to increase the filtering voltage, but several of these chips burned out, so I switched to RC filtering.
If a triode is used as the second stage, the sound will be completely different and there will be much less overload.

luix · Post by **luix** » 21 Dec 2023, 20:36

Vitallka wrote: ↑21 Dec 2023, 20:17
If a triode is used as the second stage, the sound will be completely different and there will be much less overload.

OK so the topology should be that depicted.

Vitallka wrote: ↑21 Dec 2023, 20:17 I used a 7815 + 10V zener diode chip to filter the anode supply, to increase the filtering voltage, but several of these chips burned out, so I switched to RC filtering.

this smells like high frequency oscillation supplied to the 78xx, main suspects are the SMPS, let's control the switching frequency, it should be well beyond the classic 20kHz to avoid cross-modulation with audio signal and strange noise or drone notes.
78xx regulator have really poor power disspiation, I've used them on early stage of my electronic adventures, a BJT and an Opamp will work much better in terms of noise rejection and dissipation.

tubes are very prickly about grounding, you should also study a good pcb or grounding scheme.

but if the noise is not annoying you the pedal is perfect! just have fun

Vitallka · Post by **Vitallka** » 21 Dec 2023, 21:09

Somewhere I read an article about expanding the frequency capabilities of the 78xx, where they suggested installing a ferrite bead as a choke in front of the microcircuit. But then the ferrite ring should probably have a cut so that there is no saturation with direct current.
To power the anodes in this power pedal, the 7815 chip is quite enough. It was just my experiments that brought her to destruction

ppluis0 · Post by **ppluis0** » 22 Dec 2023, 10:49

Vitallka wrote: ↑21 Dec 2023, 20:17 And in the first stage there are zener diodes, which are very noisy, and without the R21 resistor, the pedal made a lot of noise. After installing the resistor, the audible noises were greatly reduced.

Hi Vitalika,

Nice design, but what happen if you bias the first transistor with a conventional resistor divider instead zeners ?

Cheers,
Jose

Vitallka · Post by **Vitallka** » 22 Dec 2023, 19:40

Zener diodes in the first stage (if I understood the essence of the question correctly, because I use a translator) do not serve for bias (the bias is organized from the red LED), but perform a completely different role - they soften the sound.
If you have any fuzz on silicon transistors, you can experiment with a similar connection of zener diodes and the sound will be completely different.

henris42 · Post by **henris42** » 14 Mar 2025, 01:26

Hi, cool design. Mind if I try that on the Eurorack format? It needs some adjustment, we can have max 24V (its +-12), and heater needs to be done via DC/DC, otherwise we'll just run out of juice. (Or adapt to 12V tube - there is usually bit more power on + side. That would still need a capacitor bank for startup probably)

Capacitance multiplier is probably a good idea, although the voltage headroom is rather low..

Vitallka · Post by **Vitallka** » 15 Mar 2025, 04:50

Hello. Of course, I am not against your experiments with Eurorack. You can even use a DC/DC converter while waiting for the anode voltage to be obtained.