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Tri amp questions


TexDrone

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For the tech savvy audiophiles, I have some tri-amp questions. 

 

My hardware for this project consists of Heresy 1 cabinets, filled with all new Crites speakers, each speaker driver is directly connected to a separate pair of binding posts on the back of the cabinet... for a total of six posts per cabinet. Do I need to put a cap, polyswitch, etc between the high amp and the tweeters? Or just go direct from amp to speaker driver on low, mid, and highs?

 

My amps are identical brand and model, Parasound 275 v2. See attached photo for amplifier connections. Should I leave the amps set at 8ohm? There are a several other settings on the back of the amps that might come into play, but I have not changed anything from 'stock' configuration. ie:  L and R levels are turned to max, High Pass Filter is off, Stereo is enabled (picture shows mono), and Speaker Load is set to 4-8 Ohm.

 

In front of the amps is a MiniDSP 4x10 HD and a pre-amp. I am studying the 4x10 software and setting up initial configurations at the moment. With the amps on, volume level on the pre-amp turned to zero, I can hear a small amount of 'noise' on the tweeters (not sure the technical term for this type of noise) ... it's similiar to what you might hear on a vinyl record during the lead-in to the first track. My options seem to be to turn down the 'levels' (gains?) on the back of the high amp OR I could change the default gain structure inside the 4x10. See attached from MiniDSP manual. All of the MiniDSP internal jumpers and switches are still in default positions. 

 

Just curious if anyone here has done this before and already knows the correct combination(s) or can point me in the right direction. Thanks!

275v2_back.jpg

MiniDSP_page_16.png

MiniDSP_page_17.png

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15 hours ago, TexDrone said:

Do I need to put a cap, polyswitch, etc between the high amp and the tweeters?

Only if your amplifiers are unreliable, i.e., if they have failed in the past in short circuit fashion or power supply A/C is no longer rectified to DC.  It's the direct coupling of the amplifiers to drivers which increases the fidelity of the setup, eliminating the added reactance of passive crossover circuitry that your amplifiers have to deal with.

 

15 hours ago, TexDrone said:

Should I leave the amps set at 8ohm?

In order to lower the output impedance of the amplifier, I'd use the 4 ohm settings--all the time.  Only if using very high output impedance amplifiers (i.e., transconductance amplifiers) would a recommend using the higher output impedance settings.

 

15 hours ago, TexDrone said:

...not sure the technical term for this type of noise...

"Noise" is a good term.  Sometimes called the "noise floor" of the amplifier.

 

15 hours ago, TexDrone said:

My options seem to be to turn down the 'levels' (gains?) on the back of the high amp OR I could change the default gain structure inside the 4x10.

Usually, turning down the amplifier gain is the first thing to try.  I'd recommend reading up on "gain staging" or "gain structure" to help you understand the concepts used:

https://www.minidsp.com/applications/dsp-basics/gain-structure-101

 

EDIT: By the way the following text in that miniDSP link, above, isn't something that I recommend actually.  It's better to set the gain of the DSP to the maximum that the drivers can take (voltage input or integrated power over time) or the maximum that you ever want to hear in order to protect your drivers from overload (the most common reason why driver diaphragms are destroyed):

 

Quote

DSP output level

As a general rule, the maximum DSP output level should be equal to or greater than the signal level required to drive your amps to full output power.

 

Chris

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1 hour ago, Chris A said:

In order to lower the output impedance of the amplifier, I'd use the 4 ohm settings--all the time.  Only if using very high output impedance amplifiers (i.e., transconductance amplifiers) would a recommend using the higher output impedance settings.

 

I was mistaken, the amplifiers have two settings, 4-8 Ohm and 2-3 Ohm. The manual has this to say about the two settings:

Quote

The Speaker Load switch gives the Model 275 the flexibility to drive very low impedance loads.

 

Such situations can occur when the Model 275 is asked to drive multiple pairs of speakers.

 

For a single pair of 4 ohm or 8 ohm speakers the Speaker Load switch may be set to its 4-8Ω position.

 

The Speaker Load switch must be set to 2-3Ω whenever the load will be lower than 4 ohms. Speaker loads below a 4 ohm impedance can cause the Model 275 v.2 to rapidly overheat and cause audible distortion.

 

These are examples that require the 2-3 Ω setting:

 

1. Driving two pairs of speakers whose impedances are unknown.

 

2. Driving two pairs of speakers whose impedances are each lower than 8 ohms. For example, two pairs of 4 ohm speakers driven simultaneously = 2 ohm load.

 

3. Driving three pairs of 8 ohms speakers simultaneously = 2 .66 ohm load.

 

4. Driving a single 4 ohm speaker in Bridged Mono operation = 2 ohm load

 

5. Driving two 8 ohm speakers in Bridged Mono operation = 2 ohm load Note: For the coolest possible operating temperature we recommend setting the Speaker Load switch to 2-3 ohms even if you are using a single pair of 8 ohm speakers.

 

 

After reading the amplifier manual I am slightly more confused. What do you think?

 

 

1 hour ago, Chris A said:

Usually, turning down the amplifier gain is the first thing to try.  I'd recommend reading up on "gain staging" or "gain structure" to help you understand the concepts used:

https://www.minidsp.com/applications/dsp-basics/gain-structure-101

 

EDIT: By the way the following text in that miniDSP link, above, isn't something that I recommend actually.  It's better to set the gain of the DSP to the maximum that the drivers can take (voltage input or integrated power over time) or the maximum that you ever want to hear in order to protect your drivers from overload (the most common reason why driver diaphragms are destroyed):

 


I am glad you brought this up. These two paragraphs are from the 'Gain Structure 101' section. On my 4x10 HD model I can alter the input and output gain structure, I am unclear if this is the case with all MiniDSP models or not. Out of the box the 4x10 HD is set at 2V input gain and 0.9V output gain. My 4x10 HD is connected to the output of my preamp, which has 12 dB of gain according to the manufacturer. The way I read this, I should lower the input gain inside the 4x10 to 0.9v... and probably leave the output gain alone at 2V. Am I getting closer??

 

Quote

 

The gain of a component is the ratio of its output signal level to its input signal level. A preamp with 12 dB of gain, for example, would generate an output signal four times higher than the input signal (with the volume control turned all the way up). A buffer is a special type of component that has 0 dB or unity gain - the output signal is the same as the input signal. A DSP component typically has 0 dB of gain, although some units may vary from this or have switchable input or output levels.

 

If the DSP is connected to a preamp output, then the 0.9 V input setting is usually preferred, as the signal is already attenuated in the preamp. In most domestic systems, 0.9 V RMS (the maximum DSP output level) will drive the system to high levels, but if higher analog signal levels are needed into the power amps, a unit such as the miniDSP Balanced 2x4 or miniDSP 2x8 kit can be used.

 

 

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23 minutes ago, TexDrone said:

After reading the amplifier manual I am slightly more confused. What do you think?

I'd use the 4-8 ohm setting.  The 2-3 ohm setting is nice to have (i.e., someone worked harder to provide that capability, which says that your amplifier is pretty stable, or conversely, it has a larger output transformer that can take output loads down to 2 ohms).

 

23 minutes ago, TexDrone said:

On my 4x10 HD model I can alter the input and output gain structure, I am unclear if this is the case with all MiniDSP models or not.

All the DSP crossovers that I've personally used have separately input and output channel gains.  This is in the digital domain, so all that means is the input and output channel data words are separately able to multiply by a channel gain.

 

23 minutes ago, TexDrone said:

The way I read this, I should lower the input gain inside the 4x10 to 0.9v... and probably leave the output gain alone at 2V. Am I getting closer??

Try it.  If the channels are noisy or sensitive to adjustments, then you probably need to change the gain structure.  I'm a big fan of trying different configurations and listening to the results.  I've found a lot of advice that's "set in stone", really isn't when I try different approaches.  Of course, it does help to think in engineering terms--what's really occurring internally--to keep analog noise, digital quantization errors, and overall adjustability within bounds and find a good set of operating points.  You can experiment, but remember to keep things closer to nominal values (it's like living a good life: "moderation in all things").  It usually takes some experimenting to achieve this, no matter how many calculations are made.

 

Chris

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6 hours ago, Chris A said:

  I've found a lot of advice that's "set in stone", really isn't when I try different approaches.  Of course, it does help to think in engineering terms--what's really occurring internally--to keep analog noise, digital quantization errors, and overall adjustability within bounds and find a good set of operating points.  You can experiment, but remember to keep things closer to nominal values (it's like living a good life: "moderation in all things").  It usually takes some experimenting to achieve this, no matter how many calculations are made.

 

Chris

 

Thanks Chris, I will try changing the input gain jumpers and see what happens. I'm sure I will be back with even more questions. 😁

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TexDrone, I tri-amped my K-Horns with a miniDSP 2X4HD for each channel. I had noise in the mid and hi speakers and made L-Pads to drop the sensitivity of the speakers. The noise is generated by the DSP.

 

Chris, I have often wondered if on the DSP I could up the gain at the input by say 3db or even 6db and then drop the gain on the DSP outputs by a corresponding 3 or 6 db on the theory that if the low level signal from the pre-amp is down near the noise floor of the DSP then by boosting the signal level as it enters the DSP the noise added by the DSP will also be attenuated when the gain is cut as the signal leaves the DSP.

 

I have also noticed that noise is far more evident when a USB cable is attached to the miniDSP.

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On 4/10/2021 at 5:52 PM, TexDrone said:

I have some tri-amp questions. 

 

My hardware for this project consists of Heresy 1 cabinets, filled with all new Crites speakers, each speaker driver is directly connected to a separate pair of binding posts on the back of the cabinet... for a total of six posts per cabinet.

 

My amps are identical brand and model, Parasound 275 v2.

 

On 4/11/2021 at 10:44 AM, TexDrone said:

 the amplifiers have two settings, 4-8 Ohm and 2-3 Ohm.

 

Nice amps. I think the 2 - 3 Ohm setting may be safer for the bass amp when powering the individual woofers, so the amp will run cooler. The mid-range and tweeter amps can probably be set at 4 - 8 Ohms, because those drivers have higher resistance voice coils. 

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7 hours ago, Khornukopia said:

 

 

Nice amps. I think the 2 - 3 Ohm setting may be safer for the bass amp when powering the individual woofers, so the amp will run cooler. The mid-range and tweeter amps can probably be set at 4 - 8 Ohms, because those drivers have higher resistance voice coils. 

 

Thanks, I will give that a try!

 

17 hours ago, Wirrunna said:

TexDrone, I tri-amped my K-Horns with a miniDSP 2X4HD for each channel. I had noise in the mid and hi speakers and made L-Pads to drop the sensitivity of the speakers. The noise is generated by the DSP.

 

That is interesting you should mention L-Pads. I have seen them on partsexpress but have no idea exactly what they are for. How exactly did you make/install your L-Pads?  

 

On 4/11/2021 at 12:07 PM, Chris A said:

Try it.  If the channels are noisy or sensitive to adjustments, then you probably need to change the gain structure.  I'm a big fan of trying different configurations and listening to the results.  I've found a lot of advice that's "set in stone", really isn't when I try different approaches.  Of course, it does help to think in engineering terms--what's really occurring internally--to keep analog noise, digital quantization errors, and overall adjustability within bounds and find a good set of operating points.  You can experiment, but remember to keep things closer to nominal values (it's like living a good life: "moderation in all things").  It usually takes some experimenting to achieve this, no matter how many calculations are made.

 

I adjusted the input gain jumpers and it seemed to help, but it did not 'solve' the problem. I ended up having to set the gain on the high amp at ~25% and the mid amp to ~40% in order to quiet them down. 

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10 hours ago, TexDrone said:

That is interesting you should mention L-Pads. I have seen them on partsexpress but have no idea exactly what they are for. How exactly did you make/install your L-Pads?  

 

TexDrone, I found that the miniDSP added noise that did not increase when the volume control on the preamp was turned up. After a bit of googling I found a suggestion to use an L-Pad to reduce the speaker output which included the noise and that in turn required an increase in gain to bring the level back up to where it would be without the L-Pad, but the noise stayed reduced.

 

http://www.sengpielaudio.com/calculator-Lpad.htm  shows how.             

 

My project is https://community.klipsch.com/index.php?/topic/195572-bc-dcx464-as-the-mid-hi-drivers-for-a-k-horn/

 

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12 hours ago, Wirrunna said:

 

TexDrone, I found that the miniDSP added noise that did not increase when the volume control on the preamp was turned up. After a bit of googling I found a suggestion to use an L-Pad to reduce the speaker output which included the noise and that in turn required an increase in gain to bring the level back up to where it would be without the L-Pad, but the noise stayed reduced.

 

http://www.sengpielaudio.com/calculator-Lpad.htm  shows how.             

 

My project is https://community.klipsch.com/index.php?/topic/195572-bc-dcx464-as-the-mid-hi-drivers-for-a-k-horn/

 

 

Thanks!

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