Wednesday, 19 February 2014

Rivera Buf V

Somewhat similar to a Microamp, but with clever switching which effectively turned the booster into a buffer for bypass mode.  I've included an ICL7660S to provide the -9V for the circuit.

The original also included A/B switching at the output and a simple loop, so I've included a simple A/B wiring configuration on the layout in case anybody fancies including that too.  Adapt this with your favourite switching method if you also want to include an A+B option and add a true bypass loop if you want one.

I think this dates back to the 70s or 80s and so I can't find any manufacturers info about the pedal but did find the following information:

The Rivera brand is most famous for its very high quality amplifiers. It is offering new effect pedals these days but this one dates back from the 80's. These days boosters, loopers and A/B boxes are quite popular and Paul Rivera was quite a precursor by offering all three functions into one pedal. This buffer came on the market in many disguises: PMP buffer E945, PMG buffer E945, Rivera Buf IV and V. It is battery or mains powered and has a heavy and durable diecast chassis. Rivera also offered simpler versions like A/B boxes or simple loopers, and even used the box for its M-series and S-series amplifiers' footswitches.

The circuit of the E945 is very simple with a single op-amp taking care of the buffing and boosting duties, while the loop is post-buffer/booster. The pedal works really well and the amount of ultra-clean boost is quite staggering with an internal symmetrical supply of +/-12 volts. This E945 is ideal with a twin channel Blackface/Silverface amp or with a two amp setup giving a pseudo 4 channel rig with one simple pedal. 




22 comments:

  1. Maybe I'm missing something, but the original had a boost pot, didn't it...?

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    1. Silly me... :) Misunderstood the connections, thought that the Gain1 and Gain2 connections only go to the switch. I assume any single opamp would be ok in this one, right?

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  2. So, when the boost is on the buffer is not and vice versa?

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    1. When in bypass the inverting input and output of the opamp are linked by the switch which makes it a unity gain buffer. When switched on the link is removed which puts the 250K pot back in circuit which makes it a booster with the pot setting the gain level. In the far counter clockwise position of the pot, the effect will also be a buffer when switched on.

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  3. Verified. Simple nice clean booster with plenty of volume on tap. I didn't build the fancy switching, will use it true bypass. Also I used a TL071 as I have tons of those. Colors the tone a little, but barely noticeable.

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  4. A question though... Powered with 12V would the 7660S still yield +/-9V? Or would that be +/-12V?

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    1. Excellent, thanks for verifying. The 7660S will invert whatever voltage you put into it up to its maximum 12V. So yes if you put 12V in you'll get -12V out. I don't really like the idea of using these right at their maximum voltage though so I'd probably stick to 10V max or use an ICL7662 instead up to 18V.

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    2. Thanks for the info Mark, and also for the layout ;)

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    3. I personally prefer to take 11V or 12V zener from ground to ICL7660 pins 1 & 8. This way there's virtually no chance of frying the chip by accident.
      +m

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  5. Guys, do you happen to have the schematic for this? The one on FSB is not available anymore :(

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  6. If it helps: I have had a very good result putting in a JRC741D, instead of the original LF351. The sound was simply fuller, also richer in harmonics. :)

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  7. "The pedal works really well and the amount of ultra-clean boost is quite staggering with an internal symmetrical supply of +/-12 volts."

    So the original ran at 12v? and this is a 9v version?

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    1. ICL7660S can handle 12V, so if you feed it 12V, you'll get +12/-12V swing. Although the chip may burn up with 12.5V, so i'd recommend taking 12V zener in series with ~220 ohm resistor from ground to supply rail. I have no idea how the power supply is configured in the original, but my guess is that audible differences between +9/-9V and +12/-12V swings are small.
      +m

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  8. I need to learn more about power supplies for real. in the meantime, doesnt a -9v/9v supply have more 'headroom' than just a regular 9v supply? I saw you mention above that the icl7662 handles up to 18v? I could just sub that and use a higher voltage supply?

    thanks for the help IvIark

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    1. +9/-9V supply is the same as running non-swing design at 18V. +12/-12V results in 24V. So the headroom is as it would be with 18V (or 24V).

      Yes, ICL7662 is rated for 20V maximum input. You could then feed the chip with 20V and you'd get +20/-20V swing. But in this case, the LF351, rated for +/-18V would burn up in an instant.

      ICL7660S and ICL7662 are pin to pin equivalents, so you could use without any alterations to the circuit. In my personal opinion, the zener and a resistor is still a good thing to add as a protection.

      BTW. The "swing" means that the opamp gets negative voltage to its VCC-, positive voltage to its VCC+ and ground is the reference. Whereas more usual way (for pedals at least) to do things is to have positive voltage at VCC+, ground at VCC- and reference is created by other means - usually by its own voltage divider network of two resistors and a filter cap...
      +m

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    2. my man miro! thanks guys! demo will be up soon

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  9. so here's the million dollar question. What do i need to consider if i would like to make this an a/b/y switch? too much to consider? thanks!

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    1. You'll need three stomps (one for A/B, one for Y and one for boost). The AMZ style two channel splitter i've posted some time ago would probably be a good idea to use for the Y-mode...
      +m

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