How might I play two basses through the same cabinet?

#102
Wasnex said:
The final choice is a small mixer. I used an Ashley MM508 for several years. Instead of plugging my upright bass's piezo pickup directly into a line level input I used a Shure A95U to convert the signal to mic level. This seemed to sufficiently buffer the piezo for a good sound. FYI piezos tend to sound awful if they aren't loaded properly. Ideally you want an amp or DI with a 10 meg ohm input. Examples of DIs include Countryman Type 85 or Type 10 and Radial PZDI. Some companies make preamps (Fishman) and dedicated inline buffers (Barcus Berry) for this purpose. Some companies make amps with piezo optimized inputs. Take a look at the Euphonic Audio Doubler.
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Let me dispel some myths regarding input impedance, since this is mostly marketing driven (with a FEW cases where engineering backs this up). The point of diminishing returns regarding input impedance is between 500k and 1M, this applies to about 95% of all pickups. The only real exception is some that utilize very small crystals, but these are not very common. For active pickups, like those found on many guitars, input impedance is more or less a non-issue as the pickup signal comes out of the guitar already buffered. For MOST passive pickups, once you go higher than 1M, other tradeoffs come into play (specifically increased noise floor as well as RFI susceptibility) MOST really small crystals being used that I am familiar with are incorporated within an active preamp system so that the highest impedance portion of the wiring is also the shortest, and all the EMC control can be factory provided.

In the case of the Ashley MM508 (I have a few of these, along with a dozen of Yamaha's similar offering, the M-406), the impedance of the mic input is roughly 6k, and the impedance transform ratio of the A95U is about 100:1 so it practice you are probably seeing about 300-500k input impedance (based on reflected impedance of the mixer's input stage) going into the transformer. This is why it works "ok", you are not actually buffering the signal but performing an impedance transform (which gives up voltage in exchange for current, and can be done entirely passively)
 
#103
agedhorse said:
Let me dispel some myths regarding input impedance, since this is mostly marketing driven (with a FEW cases where engineering backs this up). The point of diminishing returns regarding input impedance is between 500k and 1M, this applies to about 95% of all pickups. The only real exception is some that utilize very small crystals, but these are not very common. For active pickups, like those found on many guitars, input impedance is more or less a non-issue as the pickup signal comes out of the guitar already buffered. For MOST passive pickups, once you go higher than 1M, other tradeoffs come into play (specifically increased noise floor as well as RFI susceptibility) MOST really small crystals being used that I am familiar with are incorporated within an active preamp system so that the highest impedance portion of the wiring is also the shortest, and all the EMC control can be factory provided.

In the case of the Ashley MM508 (I have a few of these, along with a dozen of Yamaha's similar offering, the M-406), the impedance of the mic input is roughly 6k, and the impedance transform ratio of the A95U is about 100:1 so it practice you are probably seeing about 300-500k input impedance (based on reflected impedance of the mixer's input stage) going into the transformer. This is why it works "ok", you are not actually buffering the signal but performing an impedance transform (which gives up voltage in exchange for current, and can be done entirely passively)
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For the record I am referring to true piezo pickups like the Underwood, Fishman BP-100, and some of the Barcus Berry pickups that do greatly benefit from being loaded with higher impedance. FYI The Underwood and BP-100 are still available and are quiet common with upright bass. These pickups tend to sound awful when plugged directly into a typical instrument amp, but can sound nice if an inline buffer is used. Understood that additional buffering is not needed when the instrument has a built in preamp or buffer.

My apology for misusing the term buffer with the A95U. Clearly the device provides impedance transform and level matching. Understood that the A95U doesn't provide the optimal level of impedance for a piezo pickup or even get close. However, using an A95U with piezo pickups like the Underwood or Fishman BP-100 and plugging into a mic level typically gives a significant improvement in tone over plugging directly into a line or instrument level input. This might be helpful info for the OP who is using an upright bass and did not get good results using a mixer
 
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#104
You are kind of mixing up levels and impedances. Typical instrument inputs are instrument level AND 1M impedance (they can vary from 500k to about 2M depending on design with 1M being the most common). The Shure transformer isn't going to get you any higher than 500k and in practice will be a bit lower.

Line level is both higher level and lower impedance, with anywhere between 10k and 50k being used, and 10k-22k being the most common.

Where the myths of the need for higher impedances came from was that back 20-50 years ago, there were quite a few amps that were much lower than the 1M that we take for granted today. One of the very first commercial products that I designed about 35 years ago, back when Don Underwood, Larry Fishman, Lee Barcus/John Berry and Carl Countryman, were also starting out, was acoustic instrument pickups. Back then, it wasn't uncommon to find an instrument input on a solid state amp of less than 100k, this was in fact a real issue. Nowadays, 1M is pretty common and for most pickups is the best balance between freq. response, noise and damping. I remember with players using Countryman DI's, modifying pickups by adding a 1.5 - 2M, 1/8W resistor inside the plug to bring down the impedance which reduced the low end flabbiness and increased definition. Even the Underwood, which is a smaller crystal, does best for most players round 2M. There were some pickups used in violas and violins that did better around 5M, but it was found that a small bridge mount mic typically sounded way more natural than any pickup on these instruments.

This has been my experience based on manufacturing both pickups AND the associated electronics. While I no longer manufacture pickups, I did (up until about 4 years ago) continue to design on-board electronics for acoustic instruments (including for some of the biggest companies in the world).
 
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#105
agedhorse said:
You are kind of mixing up levels and impedances. Typical instrument inputs are instrument level AND 1M impedance (they can vary from 500k to about 2M depending on design with 1M being the most common). The Shure transformer isn't going to get you any higher than 500k and in practice will be a bit lower.

Line level is both higher level and lower impedance, with anywhere between 10k and 50k being used, and 10k-22k being the most common.

Where the myths of the need for higher impedances came from was that back 20-50 years ago, there were quite a few amps that were much lower than the 1M that we take for granted today. One of the very first commercial products that I designed about 35 years ago, back when Don Underwood, Larry Fishman, Lee Barcus/John Berry and Carl Countryman, were also starting out, was acoustic instrument pickups. Back then, it wasn't uncommon to find an instrument input on a solid state amp of less than 100k, this was in fact a real issue. Nowadays, 1M is pretty common and for most pickups is the best balance between freq. response, noise and damping. I remember with players using Countryman DI's, modifying pickups by adding a 1.5 - 2M, 1/8W resistor inside the plug to bring down the impedance which reduced the low end flabbiness and increased definition. Even the Underwood, which is a smaller crystal, does best for most players round 2M. There were some pickups used in violas and violins that did better around 5M, but it was found that a small bridge mount mic typically sounded way more natural than any pickup on these instruments.

This has been my experience based on manufacturing both pickups AND the associated electronics. While I no longer manufacture pickups, I did (up until about 4 years ago) continue to design on-board electronics for acoustic instruments (including for some of the biggest companies in the world).
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Thanks...I believe I am on the same page with you. I still believe some care is warranted if you want optimum sound from an unbuffered piezo pickup as some current devices do not have 1Meg input impedance.

I really like the Radial JDI on keyboards and the J48 on electric bass. I doubt either of these would be an ideal choice for an Underwood or similiar piezo pickup because of their input impedance. The JDI input Z is listed as 140K and J48 is listed as 220K, both of which are well below the 2Meg you say is approximately optimum for the Underwood. Because I love the sound of the J48, but wanted to be prepared to deal with a piezo equipped upright I bought a Radial PZDI. From what I understand, the PZDI is a variation on the J48 and the input is switchable between 220K, 1Meg, and 10Meg. I don't own an upright anymore or I would go play with the buttons.

I totally get the benefit of using mics rather than piezo pickups on a string section. In my experience an open mic doesn't work very well on fiddle or upright bass in a loud rhythm section so we try and make our contact pickups sound as good as we can.
 
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#106
Wasnex said:
Thanks...I believe I am on the same page with you. I still believe some care is warranted if you want optimum sound from an unbuffered piezo pickup as some current devices do not have 1Meg input impedance.

I really like the Radial JDI on keyboards and the J48 on electric bass. I doubt either of these would be an ideal choice for an Underwood or similiar piezo pickup because of their input impedance. The JDI input Z is listed as 140K and J48 is listed as 220K, both of which are well below the 2Meg you say is approximately optimum for the Underwood. Because I love the sound of the J48, but wanted to be prepared to deal with a piezo equipped upright I bought a Radial PZDI. From what I understand, the PZDI is a variation on the J48 and the input is switchable between 220K, 1Meg, and 10Meg. I don't own an upright anymore or I would go play with the buttons.

I totally get the benefit of using mics rather than piezo pickups on a string section. In my experience an open mic doesn't work very well on fiddle or upright bass in a loud rhythm section so we try and make our contact pickups sound as good as we can.
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The J48 sounds fantastic on electric bass, but absolutely horrible on an unbuffered piezo, because of the 220k input. The PZDI is very similar to the J48, with the addition of a variable HPF and a few other things, but also has the 220k/1M/10M impedance switch. From personal experience, I find that the 10M setting gets extremely uncontrolled with a Realist, which is known to work best with lower impedance. By "uncontrolled", I mean the lows get flabby and it becomes VERY feed-back prone. The whole feel of each note is off, almost like you're playing a rubber-band. With the impedance switched to 1M, it becomes much tighter and more feedback resistant.

I never tried the Full Circle with the PZDI, but I know it always benefited from a higher Z than the Realist when I had it. That is to say, it's all pretty dependent on each pickup as to what works best.
 
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#107
The flubby bass response is in part due to the lack of damping that the 10M input impedance provides. This is a common problem with such a high impedance.
 
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#109
lowfreqgeek said:
The J48 sounds fantastic on electric bass, but absolutely horrible on an unbuffered piezo, because of the 220k input. The PZDI is very similar to the J48, with the addition of a variable HPF and a few other things, but also has the 220k/1M/10M impedance switch. From personal experience, I find that the 10M setting gets extremely uncontrolled with a Realist, which is known to work best with lower impedance. By "uncontrolled", I mean the lows get flabby and it becomes VERY feed-back prone. The whole feel of each note is off, almost like you're playing a rubber-band. With the impedance switched to 1M, it becomes much tighter and more feedback resistant.

I never tried the Full Circle with the PZDI, but I know it always benefited from a higher Z than the Realist when I had it. That is to say, it's all pretty dependent on each pickup as to what works best.
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Cool. My experience with the original Realist was it sounded very natural into 1 Meg.

The Full Circle sounded awful on the two basses I have heard it on. Uneven response across the strings and boxy. Acoustically the basses sounded great so I don't think it was an issue with bridge setup. The player who owned it bought an Erhlund EAP and preamp...I have never heard a more accurate contact pickup. Awesome choice if you have a good sounding bass.

I was just looking at Radial website and noticed the SB-4. I has 5Meg input impedance, but what really got me excited is the 1/4 inch output is buffered ($79). As you probably know, the thru on the PZDI* and the Countryman DI's is not buffered, so I can see a potential use for the SB-4.

*Correction It has been pointed out that the PZDI has a concealed button that can be used to set the thru to buffered.
 
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#110
Wasnex said:
Cool. My experience with the original Realist was it sounded very natural into 1 Meg.

The Full Circle sounded awful on the two basses I have heard it on. Uneven response across the strings and boxy. Acoustically the basses sounded great so I don't think it was an issue with bridge setup. The player who owned it bought an Erhlund EAP and preamp...I have never heard a more accurate contact pickup. Awesome choice if you have a good sounding bass.

I was just looking at Radial website and noticed the SB-4. I has 5Meg input impedance, but what really got me excited is the 1/4 inch output is buffered ($79). As you probably know, the thru on the PZDI and the Countryman DI's is not buffered, so I can see a potential use for the SB-4.
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My Full Circle sounded really nice into a 4.7Meg input on my Phil Jones Super Flightcase. It didn't sound good into anything around 1Meg. I got a new bass and didn't want to put adjusters in the bridge, so I opted for the Realist, which works great at 1Meg.

The PZDI has a little button on the side that sets the 1/4" thru to buffered. It's a little push button. I've used the SB-4 and it was OK, but the HPF is too high (80-100Hz), and the 5Meg input was high enough to start getting flabby in the low end. The PZDI is where it's at.
 
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#111
lowfreqgeek said:
My Full Circle sounded really nice into a 4.7Meg input on my Phil Jones Super Flightcase. It didn't sound good into anything around 1Meg. I got a new bass and didn't want to put adjusters in the bridge, so I opted for the Realist, which works great at 1Meg.

The PZDI has a little button on the side that sets the 1/4" thru to buffered. It's a little push button. I've used the SB-4 and it was OK, but the HPF is too high (80-100Hz), and the 5Meg input was high enough to start getting flabby in the low end. The PZDI is where it's at.
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We tried the Full Circle into 1Meg and 10Meg and it equally sounded awful at both.

Thanks for pointing this out! Some of Radials literature indicates that the thru is direct instead of buffered. I bought the PZDI with the assumption the thru was hardwired like on most DIs. Honestly I wondered why Radial would do this as it seems like such a serious oversight. I am so happy to learn that there is a cleverly concealed button that can be used to toggle the thru between direct and buffered. I am truly thrilled!
 
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#112
agedhorse said:
The flubby bass response is in part due to the lack of damping that the 10M input impedance provides. This is a common problem with such a high impedance.
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I used Countryman Type 85 for several years. I am surprised I never really noticed any serious problems as they have 10Meg inputs. Perhaps this could be part of why my techs at that time liked the BSS AR116 better on electric bass.
 
#113
Wasnex said:
I used Countryman Type 85 for several years. I am surprised I never really noticed any serious problems as they have 10Meg inputs. Perhaps this could be part of why my techs at that time liked the BSS AR116 better on electric bass.
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Possibly.

The reason (imo) the Countryman was so successful is because it was one of the first readily available active di's, its input impedance was higher than all the passive di's available at the time, they were well built, rugged, combined an active input with a transformer output, could be ground lifted, etc. I think the product would have been even better if the input impedance was between 1M & 2M but when you are a leader you have to make some design choices without the benefit of hindsight.
 
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#114
agedhorse said:
Possibly.

The reason (imo) the Countryman was so successful is because it was one of the first readily available active di's, its input impedance was higher than all the passive di's available at the time, they were well built, rugged, combined an active input with a transformer output, could be ground lifted, etc. I think the product would have been even better if the input impedance was between 1M & 2M but when you are a leader you have to make some design choices without the benefit of hindsight.
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I prefer my Radials but find the Type 85 to be quite acceptable.

Thanks for the education. Previously I thought 1Meg was about the minimum for piezos and 10Meg was ideal. I now understand the 1Meg is close to ideal and 10Meg is too much.

I did want to backtrack a little and discuss the Shure A95U further, as I think the device or similar line matching transformer could be part of a solution for the OP.

The OP tried using a mixer and did not get good results. He did not explain why. One common problem is mixers typically have 1/4" line level inputs that do not provide sufficient gain for basses and guitars. Usually mic levels input will have enough range of adjustment to accommodate instrument level, however an adapter of some sort must be used to access the XLR plug typically used on mic level input. Suitable adapters include DIs or line matching transformers like the Shure A95U. In my experience a DI or line matching transformer offers far superior results to a hardwired 1/4" to XLR adapter.

For several years, I used the Ashley MX 508 to switch between electric and upright bass. The rig was extremely versatile and provided great fidelity. When I first got the mixer, I built and tried an unbalanced 1/4" to balanced XLR adapter. I don't remember exactly what the results were, only they were not good with either electric bass or upright bass. Both instruments sounded great with the A95U. I connected each instrument to an A95U using a 1' or 2' cord. One A95U was semi-permanently attached to the upright bass's tailpiece using tie wraps and foam. For the electric bass I secured the 1/4 to 1/4 connection using gaffer tape and looped the assembly around the instruments strap.
 
#115
An adapter from 1/4" to xlr going into a mic input will have WAY too low of an input impedance (around 3k) and way too much gain whereas using that transformer will bring the level down while bringing the impedance to the source up.

Be sure the transformer taps are wired correctly.

Typical DI transformers don't offer as large of a transform ratio, so the input impedance will be closer to 25-50k.
 
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#116
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