Seriously, What the Hell? Shouldn't They All Sound the Same?

[1audiohack]

Hi All;

I am generally of the belief that one properly working solid state linear amp should sound much like any other, at least within reasonable comparisons.

I have Texas headphones in my office, 4435's in pretty close proximity to my desk and they run all day, every day and I know them better than any of my other speakers.

Since these are pretty much populated with "Chevy truck equivalent drivers" robust and easy to repair, the 4435's are the test bed for new and or repaired amplifiers once they have passed the basic VOM tests.

I have powered these with just about everything Crown ever made since the D series as well as many others and yeah they like power but they don't sound bad even on the lowly D45's.

A fully and I mean fully restored SAE2400 has been the power for the last couple of months. These are reported to be a very solid and revealing amplifier. Well, sounds pretty much like most others to me and if I had to give them a single word character description, it would be "bright".

I stacked a rack of UREI amps and EQ's for a period correct rack for my 4350's. They are rolling through the repair shop and the first came back recently, a 6290 that got really worked over. All the crappy punch down wire connectors were removed and all direct soldered. I guess that you can bias them a bit higher than stock since they are fan cooled to sweeten them up a bit and drive the THD lower so this amp got this treatment and much more.

I racked the 6290 yesterday after work and I'll be damned, I was really genuinely surprised. The 4435's have never sounded this big. They literally sound like different speakers and in a really good way. Seriously how in the hell can this be?

There have been M600 mono blocks, PS200's, PS400's, D45's,75's, D150 Series II's, Adcom 585's and mono block 565's, K1's and K2's, CE4000's, ITECH 5000HD's, some of Crowns first Chinese amps I forget the model numbers, and others and how? how is this old thing "The One"? Like no comparison, the one?

This is day two and I can't get over it.

I am actually excited for the 4350's now when before I just thought it would be cool to have a rack of UREI's and hopes they would sound "good enough".

Thoughts?

Barry.

[Ian Mackenzie]

Placebo?

The 4350's do have LIVE presentation. So a very transparent audio signal path will show up any problem with a recording or the source equipment.

The 6290 may have some performance criteria that make it less revealing of your source and signal path and therefore the perception of less bright or bigger presentation.

If the 6290 makes you happy thats all that matters.

[BMWCCA]

FWIW, I've been running my modest library system of L5s with a 6260 since finding one locally on-line for about $100 and it has been at least as satisfying as the PS-200 previously in this system. I do notice a difference when replacing a Soundcraftsmen Pro-Power Four with the PS-200 some time ago. The SC seemed to be bass-heavy in every system where I tried it against any of several Crown US-Made amps. I never expected to hear any difference.

[Mr. Widget]

Over the last 45 years or so I have occasionally heard definite differences in amps. The last time I performed a controlled comparison was with full range DD66000s comparing a pair of Parasound Halo JC-1s with a pair of Halcro DM-68s. They definitely sounded different. The Halcros were leaner and slightly harder sounding, the JC-1s had a slightly fuller sound that I preferred. Another listener may have preferred the Halcros.

Regarding a larger sound? I am not sure I have ever noticed an amp creating a larger sound with a given pair of speakers than another amp. I wonder what sonic qualities an amp can impart on a system that would impact the perceived image size.


Widget

[speakerdave]

In my less exacting messing around with UREI amps--used amps heard as-is, small sample size, not tested at the power limits--the 6290 was clearly a quite enjoyable amp. The 6260's not so much. I had 4333a's at the time.

I don't enjoy moving them around as much as I once did, though.

[rusty jefferson]

Barry,

Like you, I currently feel that amplifiers (solid state) of like design and specifications sound the same, especially after some extensive A-B-X tests I did with some engineering friends and a well known custom equipment designer/builder. Previous to those tests I felt I could hear
significant differences between a variety of amplifiers. During those tests I found none of us was able to successfully complete an A-B-X test between quite a variety of amplifiers unless there was a significant difference in input and/or output impedance between them, and even though we could correctly pass the test the differences weren't what you're describing.

It is however absolutely critical that the amplifiers being compared be perfectly voltage matched when you are comparing them. We matched them to +/- .002 volts (on one channel) with a 1khz test tone as one of the systems we were using was about 100db efficient. I suspect the UREI amplifier has more gain than the previous amp you were using and seems more dynamic. I imagine you have a high quality multi-meter you could use to match them? I'd be very curious to hear your thoughts after comparing them voltage matched.

[1audiohack]

First of all, thank you guys. This is what I had hoped for, a bit of peer review. I am not rebuffing anything that has been said so bear with me.

Ian, a clarification and more information. The speakers used in the office are 4435's. The signal path isn't terrible, it is a decent PC sound card, Claro Halo or something like that to a Bryston DAC followed by a Nakamichi CA-5 straight wire pre. Could be better no doubt but we're not driving it with an iPod.

Placebo is always possible / probable. I am not sure how strong the expectation bias works in reverse though. I had high hopes for the SAE and low expectations for the UREI.

The SAE is now at the house driving the Everest's where it continues to reveal its self as unremarkable. I love the warm glow of its meters though.

BMWCCA; I never expected to hear a difference either.

Hey Rusty; I get your critique 100%. The difference I hear is at nearly all level between quite low and very high. The 4435's small format compression drivers start to sound hard to me with any amp ≈ 100 Watts or ≈ 30 volts input. Small format driver blues.

So while voltage matching amps for some types of comparison is an absolute must, this is a difference experienced over a wide range of volume setting. I will attempt a better explanation of what I think I hear in a sec.

Mr. Widget; It is the dynamics that sound different and I have a hypothesis though terrible it may be.

speakerdave; This is of interest since I have a few 6260's in the 4350 to be rack. When they get back from repairs I will be interested to see it my experience is similar.

What I think I hear is dynamic expansion. I have compression / expansion effects in some of my live audio equipment and am familiar with their effects.

I am a data driven guy. With a little signal conditioning I can set up an electrical measurement with my TEF noise level analysis software that can track one each channel of two amps set to matching levels and then see if the voltage tracks with music rather than just noise or sine.

Man I need more audio time, my to do to explore list is so long.

Something is up and it might be all in my head but I don't think so. At least I hope not.

After day three, I still think this amp may be in this rack to stay.

Thanks again and all the best.
Barry.

[Ian Mackenzie]

Hi Barry,

Looking at the schematic and description it does have a Darlington output stage which back in the day was not that common.

Advantages
It offers very high current gain in comparison to single transistor.
It offers very high input impedance.
It uses few components and hence can be used for easy circuit designs.
It can amplify signal to larger extent.

This gives the designer more options to optimise the performance.

The GAS used Darlington topology in the Ampzilla power amplifier range which was highly regarded.
Back then there no audio power transistors. I have compared the Son of Ampzilla to a Marantz 140. The Son of Ampzilla sounded like a much larger power amplifier than the Marantz.

Most of the bad audible stuff occurs in a power amp output stage.

Edit

Having thought about it a bit more the 4435H exhibits a low impedance load on of 3 ohms or less to the power amplifier. While an amplifier may be rated for a 8 ohm load they are not going to deliver 2 x the power necessarily into a 4 ohm load. 1.5 x is more typical.

What happens is the amplifier flatlines under conditions approaching it maximum output into a 4 ohm load. If the load impedance of the loudspeaker varies as it does with the 4435 above 1000 hertz in passive mode a non linear situation can exist.

ie. 4 ohms 20-1000 hertz Amplifier A 450 watts
8 ohms 1000-20000 hertz Amplifier A 300 watts

4 ohms 20-1000 hertz JBL 6290 600 watts
8 ohms 1000-20000 hertz JBL 6290 300 watts

What is the significance to the Darlington power output staged used in the 6290? The 6290 delivers 2x the power (600 + 600 watts / 4 ohms continuously). Looking at the above comparison Amplifier A is going to be output voltage limited at frequencies below 1000 hertz before it reaches its output voltage limit into 8 ohms.

The JBL 6290 is a more Linear audio amplifier under these conditions.

When amplifiers get hot the transistors behave differently and effects linear or the Beta current gain. The Darlington output stage of designed correctly would be more linear. The human ear is actually quite sensitive to changes in low frequency amplitude.

This is a hypothesis and may explain why Barry describes the 6290 as a bigger sound using the 4435 monitors.

[1audiohack]

Hello All;

I don't have any issue at all drifting into other amps here. That is built into the premise of the thread.

My SRII has the end caps. I can scan one and print them if that's what you want. I could machine them but there is a very small "nearly not" radius in the two inside front corners that would be difficult to cut.

Derek when I power my SRII off with the front switch all lights immediately go out and stay out. My SN is 00076 if that means anything.

Wayner how close to going zero dB on the SRI do you ever get? I am pretty sure that the SRII will satisfy the top end of your M2's. If the input sensitivity is set the same as your SRI there should be no level difference until you approach the last three dB of headroom in the SRI. You are only dropping from 78V to 53V right? 175 Watts into the D2's ≈16Ω impedance ought to work I think. Using the SRII you are really only 3dB down from the suggested amp, the ITECH 5000HD that will deliver 100V per channel.

Barry.

[DerekTheGreat]

I have caps and can work on making a model for 3D printing... ...I've been powering my M2s with a pair of Studio Reference I amps... ...One of those SR I amps recently faulted. It requires service or maybe even replacement. Do you think using a SR II on the top end and SR I on the bottom would be okay? ...But I get pretty excited when anybody wants to talk about Studio Reference amps.

I'm pretty excited about these amps as well. Today I should have my SRII switched out from bottom to top. I noticed the noise floor is much better than before, but that could be because the transformer in one of my PS400's has a hum. The 2245H's the PS400 was powering are quiet. But now, with no transformer hum, the entire system is dead quiet. If you'd like to sell your dead SR-I, I'd be interested in it. 755 watts into each of my 2245H's should satisfy my power requirements and SPL goals

Hello All;

I don't have any issue at all drifting into other amps here. That is built into the premise of the thread.

My SRII has the end caps. I can scan one and print them if that's what you want. I could machine them but there is a very small "nearly not" radius in the two inside front corners that would be difficult to cut.

Derek when I power my SRII off with the front switch all lights immediately go out and stay out. My SN is 00076 if that means anything...

Barry.

I'd love a set of caps whenever you can get around to them, as well as some suitable fasteners if you could source them or point me in a direction where I could find some! Let me know how you'd like to be compensated when the time comes. Not even sure why mine are missing, like, why take them off?

Also good to know how your amp operates. The OCD sickness in my brain is kicking me for not having that defect in my SR-II repaired while it was on the bench. The potential total cost is what deterred me from pulling the trigger though, especially since it works fine otherwise and is still operating like the day it was made.

[BMWCCA]

My ODEP lights have always stayed lit when the power switch is turned off. I'd have to unplug and re-cycle the amp to see if they come on as soon as it is plugged in, or only after being powered up by the switch. Here's a section from the owner's manual. Interpret this as you will:

ODEP: Each channel has an ODEP indicator that shows the channel’s reserve energy status. Normally, the LEDs are brightly lit to show that reserve energy is available. In the rare event that a channel has no reserve, its indicator will dim in proportion to ODEP limiting. An ODEP indicator may also turn off under other more unusual circumstances (see Section 4.3).

[Mr. Widget]

The SAE is now at the house driving the Everest's where it continues to reveal its self as unremarkable. I love the warm glow of its meters though.

A number of years ago I too felt nostalgic for those big glowing meters, first I bought a Phase Linear 400... kept it a few weeks and let it go to the next happy owner, it didn't sound special at all. Then I found an SAE 2600 that was restored and being sold by a local used stereo shop. I kept it for a week and returned it. (The shop allowed a one week return policy.) Beautiful industrial design, but sonically? Not so much.

Now, those GAS amps? I still have a Son and Grandson... they are really wonderful small amps that like Ian mentioned, sound like much more powerful amps than they are. I wouldn't say they sound big, but they sound very refined and transparent. The Grandson is perfect as a HF amp in a big multi-amp system or a good amp for a smaller system.


Widget

[speakerdave]

. . . . Now, those GAS amps? I still have a Son and Grandson...The Grandson is perfect as a HF amp in a big multi-amp system or a good amp for a smaller system.

Widget

+1

[rusty jefferson]

Barry,

I'm not familiar with either of these amplifiers, but I'm intrigued by your observations. Casual interwebs reading appears to suggest the SAE amplifier has quite a complex variable gain operation that is prone to problems. Pitted relays in particular and failing resistors in the variable feedback circuit. Since you mentioned it was completely rebuilt, I assume these probably worn parts have been replaced? If those relay contacts are worn....

Also, it appears the maximum gain of the SAE is 24db? The UREI 6290 appears to have 33db of gain, in reference to my earlier comment about the gain difference. The connections on the UREI are unusual also. I assume you're using the barrier strip to make your connections as your preamp is single ended? The 1/4" and xlr jacks are differential 3 wire connections, not single ended. Also, there appears to be a connection for stereo or dual mono operation on the back? A dual mono signal could sound bigger than a stereo signal. Might want to try a test cd to verify.

[Ian Mackenzie]

It could be the difference in gain.

Mr Widget. On my comparison with a Marantz 140 power amp and Son of Ampzilla into a Klipschorn. The Son of Ampzilla was so obviously more powerful in this comparison in terms of loudness. The Marantz sounded compressed

Barry,

It your enjoying it leave it in there!

Generally if there is a real difference there is a reason behind it.

Technical it’s likely the 6290 uses local feedback around the higher current gain Darlington output stage. There may be voltage gain in the output stage. This can mean less global feedback and the negative side effects of that approach. Large Pro power amps typically used 5 or more pairs of parallel output devices for obtaining a safe operating area as a key consideration. But these devices had limited application for idealised beta current gain curves beneficial for audio amplifier crossover distortion back in the day. In recent times power transistors or audio are linear over a wider range of conditions. This makes biasing and the use of feedback more flexible. The Darlington has the advantage here while not necessarily being as reliable in Pro environments. Today there are far better bi polar power transistors for linear audio power amplifiers. Some with fast action thermal monitoring.

Bryston and Macintosh are probably a brand to make a real comparison with large power amplifiers.