Impedance Matching Question

[Ron Resnick]

I have two pairs of the Electronic Visionary Systems ("EVS") attuators -- one pair of 1Kohm attenuators and one pair of 10Kohm attenuators.

I put the attenuators in-line between my pre-amplifier and my woofer amplifier to attenuate the line-level signal going into the woofer amplifier.

My preamp has an output impedance of less than 50 ohms. My tube amplifier has an input impedance of 45Kohms.

Would one of our engineers please calculate if I should use the 1K or the 10K attenuators?

(I am thinking the 10K attenuator, because it loads down the preamplifier less.)

Thank you!

 

[Holmz]

Where do you intend to be putting the attenuator? (at the preamp end or the amplifier end?)
(I would suggest putting it at the far end.)

I suspect that the 1k option would make the IC less of an “effects” cable.

 

[Ron Resnick]

Where do you intend to be putting the attenuator? (at the preamp end or the amplifier end?)
(I would suggest putting it at the far end.)

I suspect that the 1k option would make the IC less of an “effects” cable.

Amplifier end. But wouldn't the 1K load down the pre-amplifier more?

 

[Holmz]

Amplifier end. But wouldn't the 1K load down the pre-amplifier more?

Yeah true, however that that is not much of a load for a preamp.
The cable coming out of the device would have more of an effect as the impedance driving it goes higher and higher.

So the 1k variant should have about a 1k driving impedance.
The 10k variant would have a 10k driving impedance.
As the impedance goes up the cable’s inductance and capacitance become more and more of a thing.
But if it is at the amp end, then that is minimised, so it may not matter a whole lot.
If you were running the device at the source side, then you would almost certainly want the 1k flavour, unless you liked how the cable EQs the signal.

The optimal solution is likely to have someone open up the preamp and change the gain of the output stage. Then it is still driving with 50 ohm output impedance, and is “padded” down.

@DonH50 is probably the right fellow to weigh in.

 

[Ron Resnick]

Yeah true, however that that is not much of a load for a preamp.
The cable coming out of the device would have more of an effect as the impedance driving it goes higher and higher.

So the 1k variant should have about a 1k driving impedance.
The 10k variant would have a 10k driving impedance.
As the impedance goes up the cable’s inductance and capacitance become more and more of a thing.
But if it is at the amp end, then that is minimised, so it may not matter a whole lot.
If you were running the device at the source side, then you would almost certainly want the 1k flavour, unless you liked how the cable EQs the signal.

Thank you.

The optimal solution is likely to have someone open up the preamp and change the gain of the output stage. Then it is still driving with 50 ohm output impedance, and is “padded” down.

I am attenuating the input to only one amplifier, so there is no issue with pre-amp output gain.

@DonH50 is probably the right fellow to weigh in.

I agree. CQ Don, CQ Don, come in Don. . . Over

 

[DonH50]

@Ron Resnick got your message, busy weekend (coming off Christmas stuff plus our 40th wedding anniversary).

TL;DR quick answer: Use 10k-ohms in the absence of a whole lot more information and place attenuators near the power amp if you are not tweaking the level frequently.

My default answer is to use 10k-ohms because that is the minimum unbalanced (single-ended) load that many preamps are designed to drive. A low output impedance is not a guarantee of the ability to drive a low load as there are other limitations like maximum current/power output from the preamp (typically low, natch). Low loads increase preamplifier distortion.

A quick look at the P30A's web page did not show much in the way of specs for output impedance or recommended load, and the matching H30A has 10k-ohm unbalanced input impedance. Further searching didn't help much, though I found a reviewing stating the P30A's measured output impedance was 23 ohms single-ended (and about 1.8k-ohms balanced). You might ping Hegel to see what they say their recommended minimum load is. But 10k-ohms seems reasonable.

I assume you are driving using single-ended (RCA) connections from your P30A? How long is the cable from preamp to power amp? Are the attenuator and power amp all that are on that particular P30A output?

The attenuator is in parallel with the power amp's input, so the impedance the preamp sees varies with level. With no attenuation, the preamp will see 10k // 45k = 8k, which is probably the worst-case. Using a 1k-ohm attenuator the minimum load is about 978 ohms, a very low load for a typical preamp.

The situation gets complicated to explain though not too hard to analyze ( I have referenced previous work looking at cables and attenuators, see the link to the ASR forum articles). The biggest impact in this case is usually what load the preamp can handle, as the preamp's output impedance is usually low enough to drive a pretty long interconnect without significant loss or high-frequency roll-off. The trade is then preamp distortion vs. noise (lower attenuator impedance usually means higher distortion but less noise).

If you need to control the volume frequently then placing the attenuator near the preamp usually makes things easier, but the least impact on frequency response would be to place the attenuator near the power amp so the longer cable is from the low-impedance preamp output to the attenuator, leaving the higher-impedance attenuator's output driving the shorter cable to the power amp input.

HTH - Don

 

[Ron Resnick]

Congratulations on your wedding anniversary!

This helps a lot Don! Thank you for the answer!

 

[exupgh12]

I have two pairs of the Electronic Visionary Systems ("EVS") attuators -- one pair of 1Kohm attenuators and one pair of 10Kohm attenuators.

I put the attenuators in-line between my pre-amplifier and my woofer amplifier to attenuate the line-level signal going into the woofer amplifier.

My preamp has an output impedance of less than 50 ohms. My tube amplifier has an input impedance of 45Kohms.

Would one of our engineers please calculate if I should use the 1K or the 10K attenuators?

(I am thinking the 10K attenuator, because it loads down the preamplifier less.)

Thank you!

Ron,

Next time why not ask ChatGPT on those sorts of things?

I took your question to GPT, and here is the answer with an explanation:
To determine the appropriate attenuator to use between your preamplifier and your woofer amplifier, we need to consider impedance matching to ensure optimal signal transfer and minimal distortion.

Key Information:​

1. Preamp Output Impedance: Less than 50 ohms.
2. Amplifier Input Impedance: 45K ohms.
3. Attenuators: 1K ohms and 10K ohms.

Impedance Matching:​

• The general rule is that the load impedance (in this case, the attenuator) seen by the preamplifier should be significantly higher (typically 10x or more) than the preamp's output impedance. This minimizes signal loading.
• Similarly, the attenuator's output impedance should be low relative to the amplifier's input impedance to avoid signal loss or distortion.

Analysis:​

1. 1K Attenuator:
   • Input impedance: 1K ohms.
   • Load on preamp: The 1K ohm impedance is 20x higher than the preamp's 50-ohm output impedance, which is acceptable.
   • However, the 1K attenuator might present a lower impedance to the amplifier compared to the 10K option.
2. 10K Attenuator:
   • Input impedance: 10K ohms.
   • Load on preamp: The 10K ohms is 200x higher than the preamp's output impedance, resulting in virtually no loading effect.
   • Better suited for maintaining signal integrity due to its higher impedance and minimal interaction with the preamp.

Recommendation:​

The 10K attenuator is the better choice. It ensures:

• Minimal loading on the preamplifier.
• Proper impedance bridging between the preamp and the amplifier for optimal performance.

If you would like, I can explain further or provide additional technical details!

Detailed Technical Explanation:​

When choosing between the 1K and 10K attenuators, the goal is to maintain an impedance ratio that ensures:

1. Minimal signal loss: Avoid excessive loading on the preamplifier.
2. Proper driving of the amplifier: Ensure that the attenuator doesn’t significantly degrade the signal going into the amplifier.

Impedance Matching Considerations:​

1. Preamp Output Impedance (Z_out):
   • Your preamp’s output impedance is less than 50 ohms. The load it drives (in this case, the attenuator) should ideally have an impedance at least 10x higher to minimize signal degradation. A higher impedance prevents the preamp from working too hard and ensures the signal is not attenuated prematurely.
   • 1K Attenuator:
     • The preamp sees a load of 1K ohms, which is 20x the output impedance (1K / 50 = 20).
     • This is technically sufficient but might result in a slightly higher load on the preamp compared to a 10K attenuator.
   • 10K Attenuator:
     • The preamp sees a load of 10K ohms, which is 200x the output impedance (10K / 50 = 200).
     • This is an excellent impedance ratio, ensuring the preamp operates with minimal strain and negligible signal loss.
2. Amplifier Input Impedance (Z_in):
   • Your amplifier’s input impedance is 45K ohms. The attenuator’s output impedance should be as low as possible to avoid forming a voltage divider that unnecessarily attenuates the signal further.
   • 1K Attenuator:
     • The attenuator’s output impedance will be low (since its resistance is lower), making it easier for the amplifier to receive the signal.
   • 10K Attenuator:
     • The attenuator’s output impedance will be slightly higher than the 1K option but is still sufficiently low relative to the amplifier's input impedance (45K ohms). The amplifier will still receive an adequate signal with no significant loss.
3. Signal Integrity:
   • The 10K attenuator imposes less load on the preamp while still delivering a clean signal to the amplifier, making it a better choice for maintaining signal integrity across the chain.

Summary:​

• 10K Attenuator: Provides an optimal impedance bridge, preserving signal integrity and ensuring that both the preamp and amplifier operate efficiently.
• 1K Attenuator: Acceptable but introduces a slightly higher load on the preamp, which could be a concern in sensitive systems or when driving long cables.

Would you like help calculating how the attenuators affect the voltage signal or additional tips for optimizing your setup?

 

[sbnx]

Forums being replaced by AI. Now people can just ask AI: Should I buy product X or product Y.

 

[Ron Resnick]

Ron,

Next time why not ask ChatGPT on those sorts of things?

Happy new year!

Even as an amateur on the subject, I believed I knew the answer myself. This is why I wrote in the opening post that I believe that the 10K is the correct answer. I knew that you want to maximize the impedance difference between the output impedance of the preamp and the next stage.

I am a huge fan of ChatGPT. I use it 10 to 20 times a day. On engineering or technical or medical questions I have not found a single gaffe. But I've spent enough time on it to know that every once in a while it can get itself turned around.

There is no substitute for asking a genuine expert like Don if I want to be completely comfortable that I have received an accurate and authoritative answer.

Thank you for taking the time to ask ChatGPT.

 

[exupgh12]

Happy new year!

Even as an amateur on the subject, I believed I knew the answer myself. This is why I wrote in the opening post that I believe that the 10K is the correct answer. I knew that you want to maximize the impedance difference between the output impedance of the preamp and the next stage.

I am a huge fan of ChatGPT. I use it 10 to 20 times a day. On engineering or technical or medical questions I have not found a single gaffe. But I've spent enough time on it to know that every once in a while it can get itself turned around.

There is no substitute for asking a genuine expert like Don if I want to be completely comfortable that I have received an accurate and authoritative answer.

Thank you for taking the time to ask ChatGPT.

Happy New Year, Ron!

Like you, I’m also a fan of AI chatbots. Whenever I have doubts about an answer, I cross-check it with other chatbots like Perplexity, Gemini, or Claude AI to verify the information. It’s fascinating to see how these tools complement each other and enhance our understanding.

Wishing you and rest of the people in this wonderful forum a fantastic year.

 

[microstrip]

Fortunately in this particular subject chatbots will give us an acceptable, but reductionist and misleading answer, in my opinion acceptable in an objectivist driven audio forum but unacceptable in an high-end forum where perfectionists want to extract the best individual subjective performance of their systems.

Just to point that in my opinion the accepted use of current AI chatbots in a subjective hobby such as high-end stereo will drive the hobby in mediocrity.

I suggest people ask AI chatbots what they think about "audiophile bias"

Happy New Year!

 

[Ron Resnick]

Happy New Year, Francisco! Nice to see you back here!

 

[Kingrex]

I use chatGPT myself quite a bit. I find it lies quite often. You have to become an expert at circling around the answer It gave you then prod it repeatedly to get it to provide
Accurate information. The problem for most people is they don't know when it's giving inaccurate information and what additional questions to ask to get it to fully realize a more accurate result.

 

[Kingrex]

I am in the same boat as Ron. I have a tube pre with 100 ohm output impedance. I want to biamp. One amp is 35K input. The other is 10K input. I think the maker of my preamp said I should try and stay above 20K from the amp. I would be well below that if I were to parallel a 10K amp. I could ask a AI. But I think it would say I am walking a line.

 

[microstrip]

Ron,

Next time why not ask ChatGPT on those sorts of things?

I took your question to GPT, and here is the answer with an explanation:
To determine the appropriate attenuator to use between your preamplifier and your woofer amplifier, we need to consider impedance matching to ensure optimal signal transfer and minimal distortion.

Key Information:​

1. Preamp Output Impedance: Less than 50 ohms.
2. Amplifier Input Impedance: 45K ohms.
3. Attenuators: 1K ohms and 10K ohms.

Impedance Matching:​

• The general rule is that the load impedance (in this case, the attenuator) seen by the preamplifier should be significantly higher (typically 10x or more) than the preamp's output impedance. This minimizes signal loading.
• Similarly, the attenuator's output impedance should be low relative to the amplifier's input impedance to avoid signal loss or distortion.

Analysis:​

1. 1K Attenuator:
   • Input impedance: 1K ohms.
   • Load on preamp: The 1K ohm impedance is 20x higher than the preamp's 50-ohm output impedance, which is acceptable.
   • However, the 1K attenuator might present a lower impedance to the amplifier compared to the 10K option.
2. 10K Attenuator:
   • Input impedance: 10K ohms.
   • Load on preamp: The 10K ohms is 200x higher than the preamp's output impedance, resulting in virtually no loading effect.
   • Better suited for maintaining signal integrity due to its higher impedance and minimal interaction with the preamp.

Recommendation:​

The 10K attenuator is the better choice. It ensures:

• Minimal loading on the preamplifier.
• Proper impedance bridging between the preamp and the amplifier for optimal performance.

If you would like, I can explain further or provide additional technical details!

Detailed Technical Explanation:​

When choosing between the 1K and 10K attenuators, the goal is to maintain an impedance ratio that ensures:

1. Minimal signal loss: Avoid excessive loading on the preamplifier.
2. Proper driving of the amplifier: Ensure that the attenuator doesn’t significantly degrade the signal going into the amplifier.

Impedance Matching Considerations:​

1. Preamp Output Impedance (Z_out):
   • Your preamp’s output impedance is less than 50 ohms. The load it drives (in this case, the attenuator) should ideally have an impedance at least 10x higher to minimize signal degradation. A higher impedance prevents the preamp from working too hard and ensures the signal is not attenuated prematurely.
   • 1K Attenuator:
     • The preamp sees a load of 1K ohms, which is 20x the output impedance (1K / 50 = 20).
     • This is technically sufficient but might result in a slightly higher load on the preamp compared to a 10K attenuator.
   • 10K Attenuator:
     • The preamp sees a load of 10K ohms, which is 200x the output impedance (10K / 50 = 200).
     • This is an excellent impedance ratio, ensuring the preamp operates with minimal strain and negligible signal loss.
2. Amplifier Input Impedance (Z_in):
   • Your amplifier’s input impedance is 45K ohms. The attenuator’s output impedance should be as low as possible to avoid forming a voltage divider that unnecessarily attenuates the signal further.
   • 1K Attenuator:
     • The attenuator’s output impedance will be low (since its resistance is lower), making it easier for the amplifier to receive the signal.
   • 10K Attenuator:
     • The attenuator’s output impedance will be slightly higher than the 1K option but is still sufficiently low relative to the amplifier's input impedance (45K ohms). The amplifier will still receive an adequate signal with no significant loss.
3. Signal Integrity:
   • The 10K attenuator imposes less load on the preamp while still delivering a clean signal to the amplifier, making it a better choice for maintaining signal integrity across the chain.

Summary:​

• 10K Attenuator: Provides an optimal impedance bridge, preserving signal integrity and ensuring that both the preamp and amplifier operate efficiently.
• 1K Attenuator: Acceptable but introduces a slightly higher load on the preamp, which could be a concern in sensitive systems or when driving long cables.

Would you like help calculating how the attenuators affect the voltage signal or additional tips for optimizing your setup?

There are so many things being wrong in this post that it is not possible to write an helpful corrections to it in a reasonable time. Mainly Ron's problem was wrongly formulated to ChatGPT from start .

It is known that we can't discuss with AI bots in such matters - they will omit the critical audiophile aspects and dominate with long extensive verbiage.

Properly used AI tools are great to make us more efficient and reliable - we should not expect them to turn ignorant people in experts.

 

[DasguteOhr]

I am in the same boat as Ron. I have a tube pre with 100 ohm output impedance. I want to biamp. One amp is 35K input. The other is 10K input. I think the maker of my preamp said I should try and stay above 20K from the amp. I would be well below that if I were to parallel a 10K amp. I could ask a AI. But I think it would say I am walking a line.

100ohm really with tubes what tubes in there?
What amps blade and 845 ?
why not install volume pot in one these amps in backside near rca input. My tip exsample

 

[Lagonda]

There are so many things being wrong in this post that it is not possible to write an helpful corrections to it in a reasonable time. Mainly Ron's problem was wrongly formulated to ChatGPT from start .

It is known that we can't discuss with AI bots in such matters - they will omit the critical audiophile aspects and dominate with long extensive verbiage.

Properly used AI tools are great to make us more efficient and reliable - we should not expect them to turn ignorant people in experts.

Are you calling Ron ignorant Francisco ?

 

[microstrip]

Are you calling Ron ignorant Francisco ?

Sorry, concerning Ron question formulated in post #1 any one not knowing about Thevenin theorem is an ignorant. This apparently simple question is complex in reality.

BTW, you can ask ChatGPT about this theorem.

 

[Kingrex]

Its my First Sound preamp. Its a 6922 tube. The internet says its 1200 ohms.

The amp is my Found Music Blade. KT88 PP. About 35k input. Was considering a Schiit Ragnarok 2 paralleled on the woofers. The Ragnarok 2 is 10k input.

In parallel I think the pre would see about 6.7k. Kind of low? I don't know the math so much.