Setting up a diy spring reverb

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Setting up a diy spring reverb

Post by grahamgrant »

Hi all, I’m trying to set up a diy dual mono spring reverb using a headphone amp, but can’t quite work out the best way to do it.

I have two tanks which have an input impedance of 150 ohms and and output of 12,000 ohms.

I will be taking the unbalanced mono jack out from my Tascam m216 effects send and somehow splitting the signal, driving the two tanks and then returning TWO unbalanced jacks to the M216 effect in.

I am going to get a vintage hifi amp of some description and taking a trs to twin rca from the headphone out to drive the two tanks.

The returns from the two tanks can go into an Allen and Heath zed10 which has two hi-z inputs and then out to the effects in.

What I’m trying to work out though is how to take the unbalanced jack out from the m216, duplicate it and then convert into a left and right rca to go into the hifi amp.

Also, I’m not sure what kind of hifi amp to get - will a small 20watt amp have a strong enough signal from the headphone amp to drive two 150 ohm tanks?

I would also like to reduce any hum and interference as much as possible, so am wondering whether I should be balancing the signal periodically even though it will then become unbalanced.

And to make things harder I have zero knowledge of electronics, so can’t do anything involving soldering, so can only use off the shelf components.

Any advice gratefully received! There’s a few bits online about doing this, but is either very technical or overly simplistic, and nothing that covers taking a mono signal and then splitting it.

Thank you in advance,

Graham
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Re: Setting up a diy spring reverb

Post by resistorman »

I don't think it will be a good idea to plug an actual amplifier in, you could burn up the transducers? I would try a simple headphone amp like this:

https://www.amazon.com/Behringer-HA400- ... 000KIPT30/
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Re: Setting up a diy spring reverb

Post by resistorman »

In fact, maybe you could drive them with your headphone out from the Tascam.
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Re: Setting up a diy spring reverb

Post by ef37a »

resistorman wrote: Sat Jun 10, 2023 2:40 pm I don't think it will be a good idea to plug an actual amplifier in, you could burn up the transducers? I would try a simple headphone amp like this:

https://www.amazon.com/Behringer-HA400- ... 000KIPT30/

Well maybe so but the old Fender stand alone reverb units did hit the coils pretty hard with a 6V6 amp. (actually it wasn't a 6V6 but a similar 12W pentode the name of which escapes me!)

Graham, I really think this project is doomed to failure since you say you cannot solder and have zero electronics knowledge. I don't want to be unkind but if you cannot work out how to get a stereo TRS source to two RCA plugs you are going to really struggle with the rest of the job.

Dave.
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Re: Setting up a diy spring reverb

Post by resistorman »

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Re: Setting up a diy spring reverb

Post by ef37a »

resistorman wrote: Sat Jun 10, 2023 2:59 pm Using something like this:
https://www.amazon.com/Devinal-Splitter ... NKFMH?th=1

Aw shucks R man! Now you gone an TOLD him!

To be a bit more helpful? i would use a small mixer such as the Xenxy 502/802 and drive the coils from the FX out buffered by the HA400 amp and return to a stereo line input.
In guitar amps, spring verbs also feed back a portion of the output to the drive amp to get decaying repeats. A bit of creative plugging about might produce a similar effect.

Fork! I am interested now! I might look for a cheap tank and have a play.
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Re: Setting up a diy spring reverb

Post by Wonks »

There’s normally some signal filtering on the way in to reduce the low and high frequency content.
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Re: Setting up a diy spring reverb

Post by sonics »

If you can teach yourself some basic electronics and learn to solder (which I highly recommend!) then you might consider Scott Hampton's kit.
You can buy a pre-made power supply for that.
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

resistorman wrote: Sat Jun 10, 2023 2:40 pm I don't think it will be a good idea to plug an actual amplifier in, you could burn up the transducers? I would try a simple headphone amp like this:

https://www.amazon.com/Behringer-HA400- ... 000KIPT30/

Yes, as I explained I will be using the headphone out of the amp. I want to use a hifi amp rather than a headphone amp is that the former will have tone controls to reduce the low frequency send to the spring as to not overload it, whereas the vast majority of dedicated headphone amps don't have tone controls.
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

resistorman wrote: Sat Jun 10, 2023 2:44 pm In fact, maybe you could drive them with your headphone out from the Tascam.

Good idea, although I want the tone shaping as above, however I forgot about the headphone out from the Tascam so thank you for reminding me!
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

ef37a wrote: Sat Jun 10, 2023 2:54 pm
resistorman wrote: Sat Jun 10, 2023 2:40 pm I don't think it will be a good idea to plug an actual amplifier in, you could burn up the transducers? I would try a simple headphone amp like this:

https://www.amazon.com/Behringer-HA400- ... 000KIPT30/

Well maybe so but the old Fender stand alone reverb units did hit the coils pretty hard with a 6V6 amp. (actually it wasn't a 6V6 but a similar 12W pentode the name of which escapes me!)

Graham, I really think this project is doomed to failure since you say you cannot solder and have zero electronics knowledge. I don't want to be unkind but if you cannot work out how to get a stereo TRS source to two RCA plugs you are going to really struggle with the rest of the job.

Dave.

Dave, apologies if it wasn't clear, although I think it was - the FX send from the M216 is unbalanced mono. I need to duplicate this signal to create a dual mono send to the hifi amp, as the M216 has two unbalanced FX returns which can be panned L and R. I'm well aware how to get a stereo TRS to twin RCA.
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

resistorman wrote: Sat Jun 10, 2023 2:59 pm Using something like this:
https://www.amazon.com/Devinal-Splitter ... NKFMH?th=1

See comment above - I'm trying to convert unbalanced mono to twin rca.
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

ef37a wrote: Sat Jun 10, 2023 3:54 pm
resistorman wrote: Sat Jun 10, 2023 2:59 pm Using something like this:
https://www.amazon.com/Devinal-Splitter ... NKFMH?th=1

Aw shucks R man! Now you gone an TOLD him!

To be a bit more helpful? i would use a small mixer such as the Xenxy 502/802 and drive the coils from the FX out buffered by the HA400 amp and return to a stereo line input.
In guitar amps, spring verbs also feed back a portion of the output to the drive amp to get decaying repeats. A bit of creative plugging about might produce a similar effect.

Fork! I am interested now! I might look for a cheap tank and have a play.

Thanks, that's useful though. I don't want to buy yet another Mixer, but it might be possible to do something with the Allen and Heath Zed10 I mentioned in my post which will be handling the hi-z output from the spring tank. What would be the benefit of using a mixer over a hifi amp though?
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

sonics wrote: Sat Jun 10, 2023 5:09 pm If you can teach yourself some basic electronics and learn to solder (which I highly recommend!) then you might consider Scott Hampton's kit.
You can buy a pre-made power supply for that.

Thank you so much, This looks really useful, although a bit expensive to ship to the UK. My past attempts at soldering have been ropey to say the least, but I think it's time to learn!
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Re: Setting up a diy spring reverb

Post by resistorman »

GrahamGrant2 wrote: Sat Jun 10, 2023 5:18 pm
resistorman wrote: Sat Jun 10, 2023 2:59 pm Using something like this:
https://www.amazon.com/Devinal-Splitter ... NKFMH?th=1

See comment above - I'm trying to convert unbalanced mono to twin rca.

From your headphones out, which are stereo unbalanced, which will give you separate feeds or a mono signal, whatever you're feeding it.
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Re: Setting up a diy spring reverb

Post by James Perrett »

ef37a wrote: Sat Jun 10, 2023 3:54 pm i would use a small mixer such as the Xenxy 502/802 and drive the coils from the FX out buffered by the HA400 amp and return to a stereo line input.

I've been checking out the service manuals...

It may be worth saying that the output stage of the HA400 is very similar to the aux output on the A&H Zed 10 (which the OP already owns). They both use the same chip to drive the output but the HA400 has a 47 ohm resistor in series with the output while the Zed 10 has 75 ohms. So the mixer could, in theory, drive the reverb tank directly from the FX output (or the main outputs as they share the same design).

Interestingly, while Behringer are happy to drive headphones directly from an op amp chip, Allen and Heath use a more substantial circuit to drive headphones by adding a couple of transistors to the output of the op amp on the headphone output.

The advantage of using the mixer is going to be more versatile eq with an extra midrange stage when compared to the amplifier and you would be keeping all the electronics in one place with no balanced/unbalanced issues. Using a hifi amp also opens you up to potential issues with grounding.
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

James Perrett wrote: Sat Jun 10, 2023 8:04 pm
ef37a wrote: Sat Jun 10, 2023 3:54 pm i would use a small mixer such as the Xenxy 502/802 and drive the coils from the FX out buffered by the HA400 amp and return to a stereo line input.

I've been checking out the service manuals...

It may be worth saying that the output stage of the HA400 is very similar to the aux output on the A&H Zed 10 (which the OP already owns). They both use the same chip to drive the output but the HA400 has a 47 ohm resistor in series with the output while the Zed 10 has 75 ohms. So the mixer could, in theory, drive the reverb tank directly from the FX output (or the main outputs as they share the same design).

Interestingly, while Behringer are happy to drive headphones directly from an op amp chip, Allen and Heath use a more substantial circuit to drive headphones by adding a couple of transistors to the output of the op amp on the headphone output.

The advantage of using the mixer is going to be more versatile eq with an extra midrange stage when compared to the amplifier and you would be keeping all the electronics in one place with no balanced/unbalanced issues. Using a hifi amp also opens you up to potential issues with grounding.

Thanks James, that’s really useful and thank you for finding the specs. I think I’ll need to do some fiddling with the various routing on the zed 10 as fx and aux outs are mono, but I still need to split the signal somewhere to turn the mono fx out from the M216 to a dual mono before they go into the two separate tanks and then come back to the hi z inputs of the zed 10 before then returning to the two fx ins on the M216. I think it might be possible, thank you for making me think differently about it and makes it simpler.
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

resistorman wrote: Sat Jun 10, 2023 7:20 pm
GrahamGrant2 wrote: Sat Jun 10, 2023 5:18 pm
resistorman wrote: Sat Jun 10, 2023 2:59 pm Using something like this:
https://www.amazon.com/Devinal-Splitter ... NKFMH?th=1

See comment above - I'm trying to convert unbalanced mono to twin rca.

From your headphones out, which are stereo unbalanced, which will give you separate feeds or a mono signal, whatever you're feeding it.

Clever! Hadn’t thought of that, would then still need to go into separate mixer or hifi amp for tone shaping, but it gives me a dual mono signal. Need to clean the pot as it’s a bit scratchy, but excellent idea, thank you.
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Re: Setting up a diy spring reverb

Post by resistorman »

GrahamGrant2 wrote: Sat Jun 10, 2023 9:08 pm
resistorman wrote: Sat Jun 10, 2023 7:20 pm
GrahamGrant2 wrote: Sat Jun 10, 2023 5:18 pm
resistorman wrote: Sat Jun 10, 2023 2:59 pm Using something like this:
https://www.amazon.com/Devinal-Splitter ... NKFMH?th=1

See comment above - I'm trying to convert unbalanced mono to twin rca.

From your headphones out, which are stereo unbalanced, which will give you separate feeds or a mono signal, whatever you're feeding it.

Clever! Hadn’t thought of that, would then still need to go into separate mixer or hifi amp for tone shaping, but it gives me a dual mono signal. Need to clean the pot as it’s a bit scratchy, but excellent idea, thank you.

They make them as TRS 1/4" breakout/ splitter to 2-1/4" TS also.
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Re: Setting up a diy spring reverb

Post by ef37a »

Sorry Graham! Brain totally blanked that you have a ZED 10. So do I and so you have both FX and AUX sends. You might still need more power/volts than these can supply in which case the HA400 would I am sure serve (James? Bear with)

Yes, I am sure the headphone output of the ZED would drive the tank but then the drive level will be all mixed up with the H/P POT and I think the Main Mix pot. Coming from AUX or/and FX (two tanks) means the level is set by the channel pots (and EQ*) and of course FX/AUX sends but monitoring is not involved. You will do no damage to mixer or tank coils by trying those feeds. AS ALWAYS! setup 'cold' and keep controls at minimum and advance slowly.

You might also find that the HZ 'line' inputs are a bit short on gain? The OP of tanks can be quite feeble so might need to go into an XLR mic input. Bit tricky until you can solder!

James, you have me at an advantage. I have only a block diagram of my ZED 10. Any chance of a .PDF?

*And EQ might well be necessary. When I fitted a tank in a 100 W valve head some years ago the sound had a horrible 'honk'. I cobbled up a parallel T notch filter to fix it.

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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

ef37a wrote: Sun Jun 11, 2023 7:57 am Sorry Graham! Brain totally blanked that you have a ZED 10. So do I and so you have both FX and AUX sends. You might still need more power/volts than these can supply in which case the HA400 would I am sure serve (James? Bear with)

Yes, I am sure the headphone output of the ZED would drive the tank but then the drive level will be all mixed up with the H/P POT and I think the Main Mix pot. Coming from AUX or/and FX (two tanks) means the level is set by the channel pots (and EQ*) and of course FX/AUX sends but monitoring is not involved. You will do no damage to mixer or tank coils by trying those feeds. AS ALWAYS! setup 'cold' and keep controls at minimum and advance slowly.

You might also find that the HZ 'line' inputs are a bit short on gain? The OP of tanks can be quite feeble so might need to go into an XLR mic input. Bit tricky until you can solder!

James, you have me at an advantage. I have only a block diagram of my ZED 10. Any chance of a .PDF?

*And EQ might well be necessary. When I fitted a tank in a 100 W valve head some years ago the sound had a horrible 'honk'. I cobbled up a parallel T notch filter to fix it.

Dave.

Thanks Dave, that’s really useful. I’m away from home at the moment, but back tonight so will have a play. I think hi z line ins will be ok as they have a hidden extra gain button which you access with a pin at the back of the mixer specifically for low gain vintage equipment, so I think it should work, fingers crossed!
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Re: Setting up a diy spring reverb

Post by James Perrett »

ef37a wrote: Sun Jun 11, 2023 7:57 am James, you have me at an advantage. I have only a block diagram of my ZED 10. Any chance of a .PDF?

*And EQ might well be necessary.

I found it on Electrotanya

https://elektrotanya.com/allen-heath_ze ... nload.html

It is just a collection of circuit diagrams and service bulletins (useful if you fancy modifying yours to the latest spec though much of it appears to be surface mount).

Eq will almost certainly be needed. I used to take the output of my Laney spring reverb from the footswitch socket which came direct from the reverb tank. I just fed it into the mic input on an MM mixer with its 4 band eq and took out some of the high midrange.
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

Well it works, and pretty well at that. A little bit of noise, but not insurmountable.

I now want to try out some different tanks, but I can’t find many with the same input and output impedance levels. I read that you should use a tank with a hi impedance output, ie 10,000 ohms. If I used one with a lower output impedance, e.g. 2500 ohms, would that work as well? Or one with a higher input impedance than the 150ohms I’m currently using?
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Re: Setting up a diy spring reverb

Post by James Perrett »

The voltage level from a low impedance output would be lower so it might better match the mic input on your mixing desk. A high impedance input would be easier to drive.
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Re: Setting up a diy spring reverb

Post by ef37a »

Graham, I will bet your noise problem is because you are not driving that tank hard enough?
I have dug out my Big Book of Fender Amplifiers and I find they drive the tank via a transformer from a 12AT7 valve with both sections in parallel. That means the valve can deliver a couple of watts (the transformer is rated at 3.5W). The Fender tank has an 8 Ohm input coil, yours is 150 Ohms so if you translate 2W into 150R you get 17 volts rms, that's around +26dBu!
I am not suggesting you need to be hitting it that hard but I guess you need a good 10V or +22dBu. (that is about the limit for most small mixers)

The recovery amplifier is 1/2 a 7025 double triode (essentially a 12AX7) and gives I estimate around 35dB of gain and the 7025 is a pretty low noise valve.

If you have a digital multimeter hang it on the input to the tank and try to find some more drive signal. If you don't have a meter I strongly suggest you get one.

Dave.
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Re: Setting up a diy spring reverb

Post by Wonks »

Tanks for valve amp circuits have input impedances in the 8-16 ohm region (and 500-600 ohm output impedance) but you don’t want to go that low.

Solid state circuit tanks are often around 150ohms input impedance, and the output can vary considerably, but normally 2.4k ohms or higher.

Also take into consideration (if you haven’t already) the tank orientation. Some are designed for flat mounting, some vertical with the long side down and some vertical with the small end facing down. Mount them in the wrong position and they’ll sound bad.
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Re: Setting up a diy spring reverb

Post by GrahamGrant2 »

Thanks all, some very useful suggestions! Turns out for some reason I can't fathom, when I plug a cable into the FX out then channels 1 and 2 decide to start being noisy. There's also some noise on the reverb tank outs, but I think that's just the nature of them. In the context of a mix, the noise isn't noticeable. The Tascam M216 is a noisy bugger in general though!
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