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Old 10th Mar 2011, 11:33 pm   #21
Alistair D
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Default Re: Valve tremolo circuit

Re the EF80 not being Vari-Mu, oh how time fogs the brain. You are absolutely correct. IF amp valve = Vari-Mu. Wrong.

Tremolo = volume variation.
Vibrato = pitch variation.

Unless those terms apply to an electric guitar.

One thing I have learnt from this thread is that analogue Vibrato circuits are really variable phase shifters and not 'frequency changers' as I had always thought.

Al
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Old 11th Mar 2011, 8:38 pm   #22
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Default Re: Valve tremolo circuit

Hi Electronicman,

No problem at all, I’ll do a better scan and put it on the forum. I’m glad it was the project you were looking for.

You’re more than welcome to PM me and I can send a copy using my normal email account as well.

I’ve recently restored a Selmer Truvoice Stadium amplifier, which has Tremolo. This amplifier uses EF86 valves for both the oscillator and the modulation amplifier stage. Below is a link to the diagram :-
http://www.vintagehofner.co.uk/selme...matic/sta.html

Regards
Terry.
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Old 11th Mar 2011, 8:54 pm   #23
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Default Re: Valve tremolo circuit

I'm sure I recall reading (a long time ago...) that if the tremolo circuit was used to amplitude modulate only the mid and high frequencies, leaving the bass end alone, the ear interpreted this as a small frequency change.
Mind you, the ear sees amplitude changes as small frequency changes anyway as far as I know. As a tone gets louder it appears to move down in pitch slightly.
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Old 11th Mar 2011, 11:05 pm   #24
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Default Re: Valve tremolo circuit

Hi Electronicman,

I’ve attached a scan of the Practical Wireless Tremolo unit. If you want a better one I can email a JPEG – just PM me.

I’ve also attached a scan of a tremolo circuit from a 1961 copy of Radio Constructor.

Regards
Terry.
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File Type: pdf PW_Trem.pdf (404.0 KB, 567 views)
File Type: pdf RC_TREM.pdf (196.2 KB, 382 views)
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Old 12th Mar 2011, 4:43 pm   #25
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Default Re: Valve tremolo circuit

Hi Valvepower,

Thanks very much for the PDF's, they are just fine, and I really appreciate it.
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Old 13th Mar 2011, 12:05 am   #26
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Default Re: Valve tremolo circuit

The PW circuit does not have a high pass filter on the tremolo output, whereas the RC and Selmer designs posted do. The filter is designed to remove the thumping caused by the low frequency oscillator and it is well worth incorporating one if you go for the PW/FJ Camm design.

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Old 14th Mar 2011, 11:07 pm   #27
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Default Re: Valve tremolo circuit

Hi Ron,

Thanks for tip, I reread the RC article and will definitely incorporate a filter in all of my units.

I am now in the process of making up three units, which I hope to be able to run side-by-side to run some tests, not at the same time of course.
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Old 15th Mar 2011, 9:52 pm   #28
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Default Re: Valve tremolo circuit

Doesn't the Vox AC30 have a tremolo? I seem to remember fixing one of these a few years back and the tremolo wouldn't work due to the bottle swapper having paid a visit before me and mixed up the ECC83 and ECC82 valves. There may be a circuit for an AC30 out there somewhere you can refer to.
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Old 16th Mar 2011, 3:08 pm   #29
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Default Re: Valve tremolo circuit

Hi,

I found the circuit for the VOX AC30 whilst looking for the circuit for a VOX AC50 I'm going to restore.

Yes Alan, the AC30 has a high pass filter. This filter appears not to have too much of detrimental effect on the sound as guitar amplifiers have some LF roll off anyway.

Below link to the circuit for the AC30:

http://www.voxamps.com/downloads/circuits/ac301960.jpg

Regards
Terry.
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Old 21st Apr 2011, 6:30 pm   #30
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Default Re: Valve tremolo circuit

Hi,

Here is a follow up on this project. I have breadboarded (is that a word?) three types of circuits.

CCT-1 uses an ECC83 as the oscillator with an ECC82 as the amp.

CCT-2 uses an EF80 as the oscillator and an EF86 as the amp

CCT-3 uses an ECC83 as the oscillator and an EF86 as the amp.

I had trouble with CCT-1, which was the first one I tried, worked reasonably well the first time, then I re-did the whole thing so that I could have all three circuits side by side.

To my surprise CCT-1 did not work at all at first. Turns out that after a quick test where I found +40 V DC on the grid of the ECC83, that some of the capacitors I was using were leaky.

I ordered a few new capacitors and after putting them in, the thing worked quite well.

I then tried CCT-2, which is my favorite as I originally built this many many years ago. This worked very well, except that I had forgotten to add the feedback loop in the amp to give it unity gain. Once that was corrected it was OK.

I am now going to wire up CCT-3 next and see how that works.

Then I will go back to CCT-1, in which the oscillator waveform is distorted and I suspect, is the result of some resistors being out of tolerance.
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Old 24th Jan 2013, 5:10 pm   #31
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Default Re: Valve tremolo circuit

Hi Mr Electronicman,

I've been building this PW EF80 Tremolo and although the preamp is working great I can't get the trem to work. I've been through the circuit countless times and everything seems to be correct.

The two possibilities I haven't yet tried are the EF80 itself (just ordering one off ebay) although the things lit up like a Christmas tree. Or would there be any problem with the fact I've used a full wave bridge recitifier?

I was wondering also if you have a circuit with your voltages on?

I've got 300+ on the HT at the first cap.


Thanks in advance,

Tommy.
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Old 24th Jan 2013, 8:11 pm   #32
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Default Re: Valve tremolo circuit

Hi tommy,

The EF80 may be low on emission, or the electrolytic capacitor C9, is not present, or connected incorrectly. Also check that it is a 250uF, as the phase shift oscillator does run at a very low frequency.

VR2 controls the operation of V1, make sure that it is at the full end of it's travel, either CW or CCW depending on how you connected it.

The full wave bridge is not a problem, they only used a metal rectifier because it was cheap at the time.

I will have to reconnect my circuit as I have used the layout for something else before I can check some voltages, but I would guess that the voltage on the cathode of V2 Pin 3 should be around 1-2 volts, varying depending on the speed of the oscillator.
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Old 25th Jan 2013, 3:23 am   #33
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Default Re: Valve tremolo circuit

Thanks David for your rapid reply,

I had a 150uf in the C9 position as I had a few lying around and thought it would suffice, as soon as I put another one in parallel it started to modulate.

It's still not working as it should, so the EF80 may be at fault.

I also noted that the depth increases with the volume?? I'm sure that should be happening.

How critical do you think the values of the rest of the caps are?

Thanks again

Tommy
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Old 25th Jan 2013, 10:03 am   #34
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Default Re: Valve tremolo circuit

Hi,
The
re are several ways of getting tremolo, and indeed some for vibrato. I will have a look around my books to see what I might have available. Meanwhile, Jack Darr's "Electric Guitar Amplifier Handbook" has a section on tremolo/vibrato and is available to download (somewhere). I have the eight pdfs, if anyone is interested.

For those that are interested in the Practical Wireless Guitar Amplifier, here are some good pdfs.

Colin.
Attached Files
File Type: pdf PW_64_BP.pdf (1.60 MB, 259 views)
File Type: pdf PW_64_P32_36.pdf (663.4 KB, 236 views)
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Old 25th Jan 2013, 11:02 am   #35
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Default Re: Valve tremolo circuit

Back in post number 2, Mike pointed out the difference between tremolo and vibrato. There are lots of things written where a tremolo effect gets called vibrato. The whole business is messed up by the lever on a guitar that changes string tension being called the tremolo arm, when what it produces is actually vibrato.

A true vibrato effect has to modify the frequency of the note or chord. To do that menas either varying the frequency determining thing of the instrument itself, or by varying a delay element... This can be done with a charge-coupled device, digital memory, or by single-sideband frequency conversion (up by one amount, back down by a different amount)

So watch out for circuits claiming vibrato, look for a CCD or memory. SSB ones are very rare.

David
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Old 25th Jan 2013, 5:57 pm   #36
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Default Re: Valve tremolo circuit

Hi Tommy,

Glad you got it working. The other caps in the oscillator grid circuit control the frequency and the wave shape, and if you use new modern caps you should not have any problem. Same goes for the resistors, I used 470K as 500K are more difficult to find these days.

If you want to be a perfectionist, the three 470K resistors should all be variable and ganged so that as the frequency changes the wave shape remains a sine wave. Of course in practice you would be not be able to tell the difference at such a low frequency anyway.

The point about Tremolo and Vibrato is a good one, the Tremolo circuit you have built is an amplitude modulator, it varies the volume level of the output. As RW stated, a true Vibrato would vary the frequency which is a whole new ball game (Sorry for the Americanism).

The so called "depth" is in effect a volume change and so it will also change with the volume control.
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Old 25th Jan 2013, 6:20 pm   #37
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Default Re: Valve tremolo circuit

Hi Electronicman,

Thanks so much for your help, It will not beat me in the end.

I found this trem and vib circuit : already thinking about build this too.

http://s81.beta.photobucket.com/user...otron.jpg.html

I think it's based on the vox? and claims to do both frequency and amplitude mod.

another ball game? another kettle of fish!

Tommy
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Old 25th Jan 2013, 7:39 pm   #38
MrElectronicman
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Default Re: Valve tremolo circuit

Interesting circuit, but the vibrato is fake. Looks like the output of the preamp is split into two and goes through a high and low pass filter, then the output of the filters is amplitude modulated alternately then combined again, giving the impression of vibrato.

May sound quite nice if that's what you need though.
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Old 27th Jan 2013, 9:54 pm   #39
ColinTheAmpMan1
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Default Re: Valve tremolo circuit

Hi,

I have looked and looked and failed to find what circuits and explanations I thought I had. I am attaching two pdfs with a couple of circuits which show the Linear TP1 tremolo pre-amp. This was purchased constructed, as there seemed not to be a kit. I have since rebuilt it and modified it somewhat. I can guarantee that it works, because it is in a homebrew guitar amplifier of mine which is based on the RSC A11. Both the original circuit and my mod are attached, plus the instruction leaflet that came with the unit.

I will continue to look for other circuits, but am beginning to think that I may have imagined it.

As I said before, there are several ways of getting vibrato and/or tremolo. One of the earliest was in Fender amps, where the bias voltage on the control grids of a pair of push-pull output valves was modulated by a low-frequency phase-shift oscillator. Many people favour this, but it has the distinct disadvantage that if the amp has two channels, the vibrato is on both. If the second channel is being used for a vocal microphone, the effect of vibrato is less than great. Another detriment is that with the bias altering rhythmically, it will not always be at the optimum point for the output valves.

The next Fender invention was the "harmonic vibrato" which was more complex and used more valves to achieve its effect. It was probably too expensive and didn't survive for long, although it, too, has its adherents.

Marshall got onto the vibrato idea and used a low-frequency oscillator to turn a transistor (eugh!) on and off. This component was between the signal and earth of the channel to be effected, thereby periodically shorting the signal to ground (in the extreme setting of the depth control).

Fender's answer to that was to use the oscillator to power a neon bulb so that its light output pulsated. This was incorporated into a package with a light-dependent resistor (LDR) which was, like Marshall's transistor, across the signal and earth. The net result was similar to Marshall's.

Magnatone went totally crazy and came up with a circuit which used varistors and caused periodic phase-shifting. This was tremolo of a sort. Many people think that Magnatone amplifiers with this feature sound really good, but I couldn't comment from personal experience.

The Wurlitzer method using a mechanical scanner device has been mentioned and I am attaching a pdf document which goes some way to explaining this device. The document also gives some insight into the electronic update of this device which was to be borrowed by a famous British guitar amplifier manufacturer.

The circuit in Vox amplifiers (AC15 and AC30) was based on a circuit by Hammond and the first circuits had "secret" components hidden in cans similar to electrolytic capacitor cans. Dick Denney eventually came up with a circuit which he felt wasn't contravening any copyrights and these circuits became public. The circuit in the Vox is complex, to say the least. It originally only achieved one effect. There is an apochryphal tale of how Dick Denney was tinkering one day and managed to short something with a screwdriver. The result was the ability to get tremolo as well as some semblance of vibrato. It has to be said that the intensity of the vibrato effect is not that huge in practice. There is a pdf of a 1960 Vox AC15 using this circuit attached. Again, some feel that the Vox tremolo is wonderful, and so it is, but the speed is limited to three discrete settings and the depth, or intensity, is set with a preset and is therefore even more limited in practice.

Not many manufacturers used the idea of modulating the screen-grid of a pentode being used as an amplification stage. One exception was Dick Denney's AC15 of 1959, which I am attaching a pdf of. There were a few after-market add-on units (like the Linear TP1) and circuits from the electonics magazines that used this method.

There are also constructions that come up from time to time which claim to achieve a vibrato effect by pase-shifting. I am attaching one of these oddities to the next post.

I hope this is of some use.

Regards, Colin.
Attached Files
File Type: pdf Linear_TP1_txt.pdf (446.6 KB, 238 views)
File Type: pdf Dorf_TheWurlitzerVibrato.pdf (1.14 MB, 260 views)
File Type: pdf voxac151959.pdf (198.6 KB, 224 views)
File Type: pdf voxac151960.pdf (195.7 KB, 191 views)
File Type: pdf Linear_TP1_cct.pdf (375.8 KB, 203 views)
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Old 27th Jan 2013, 9:57 pm   #40
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Default Re: Valve tremolo circuit

I will have to zip Richard H. Dorf's take on a phase-shift "vibrato" add-on circuit, as the size of the pdf is 2686 KB.
Regards, Colin.
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