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Old 14th June 2012, 04:30 AM   #1
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Default unpleasant "brightness"

I have an unpleasant brightness in my system. It is not on every recording but its definitely on some of them!! I have started using another pre amp so thats my first guess, but i will have to wait a week or so to get the RIAA checked as I dont have the gear myself. I am also changing the loading on the cartdrige. Its an Ortofon 2m red. What does any one else use?
How much of a difference does it make?
I find it strange that half my records sound fine and half have a very piercing high frequency to them.
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Old 14th June 2012, 08:01 AM   #2
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Ok forget cartridge loading for now. Good lesson for me about to much info and not enough knowledge, Hey i know what I am doing in my day job but I am not an EE.
Basically I misread the schematic (written very poorly In my humble) and one to many caps in the RIAA. All good now. sorry (very humble smile)
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Old 14th June 2012, 11:00 AM   #3
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Congratulations. I make assembly errors sometimes too, although writing a "wirelist" from the schematic, a practice I was taught in my first technician job, helps accurate construction.
I'm using a Shure M97HE cartridge purchased 1980? followed either by a Dynakit PAS2 preamp, or a Herald RA88a disco mixer. I had to replace the 1961 GI brand paper caps in 2011 due to a channel imbalance in the PAS2, which resulted in excessive brightness. I replaced the 0.20 uf 20% paper caps on the PC boards with 0.22 uf 5% polyester caps. By contrast, the disco mixer has the tone I am used to, albeit a little too much hum. I had to extensively modify the disco mixer to reduce hiss from JRC4558 op amps and hum from the too close power transformer and AC switch.
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Old 14th June 2012, 11:57 PM   #4
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Well i mostly blame the intructions . They are a bit inconsistent. This was the CCDA preamp on a Tetra Board. I had one to many caps in the RIAA network. But NOW!!! Magic!!
I have an Ortofon Red in a Technics 1200 thru a (very very quiet) tube pre amp into a Leak 20 and Kef Concord speakers and I am wrapped in it!! Replaced everything in the Leak with MKP caps and modern resistors. The B139 drivers were reconditioned. They were, i guess 40 plus years old?
I think the 1200 is the most modern bit in the system.
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Old 15th June 2012, 05:52 PM   #5
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I found modern metal film resistors helped my PAS2 preamp hiss some, but no effect in the ST120 amp. I think the theory says the more resistance the more the hiss, and tube preamps have some high values. The polyester caps made the PAS2 too bright, however, I like the sound of the modified RA88a disco mixer better at this time.
I think the 1966 design dynakit ST120 power amp is a copy of a Leak design, possibly a Leak Delta 70? Albeit with ****ier heat sinks, as the ST120 was prone to thermal runaway. Don't know what year the Delta 70 came out but the St120 output stage looks very similar on the schematic.
I don't have any old speakers worth refurbishing. A set of Altec Lansing Voice of the Theaters would be worth refurbishing, but I could never afford those and can't now, even ones with ripped cones. Heard some VOT's in 1966 in an actual cinema, as the behest of my High School band director. By contrast, my 1998 Peavey SP2 speakers are third generation copies of the VOT design, and I love the sound.
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Old 15th June 2012, 10:10 PM   #6
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Yes. I have neither money nor I expect the space. I do have some seas divers and have seen a suitable design for some modern IMF tl's. I have been pondering that for six months. There is no way I would spend the money that modern high end speakers cost.
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Old 16th June 2012, 12:57 AM   #7
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Quote:
Originally Posted by mikemac View Post
Yes. I have neither money nor I expect the space. ... There is no way I would spend the money that modern high end speakers cost.
I stumbled on these Peavey SP2's used for about $600 the pair. Most of the purists here sneer at Peavey, but at 1 W these sound great to me. Great VOT tributes. They are bar band rejects, sold in great haste after they left the road and were wondering what to do next. They look like a lot of setups and pack aways on the cases, but sound great. They live on stands, overtop the 1941 Steinway. Another "it has got to be out of this house by Saturday!!!" bargain. No employment after 42 years working is fun, you can watch flea markets and internet lists & stuff and jump on it in the middle of the day.
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Old 16th June 2012, 01:09 AM   #8
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You see, it is all fine the things that you are using, but you can not expect this stuff to give you the sonic results that you would like.

I think if you worked very hard on the Peavey and ran it with the ST70 properly modified that you would have a shot at making something that sounded halfway decent.

I didn't look up the Peavey units, but I will assume they have a compression driver and horn? The horn and compression driver you have there might be a source of your sonic annoyance.

Of course the Shure cartridge is also a "boom and sizzle" unit, imo.

And yes the cartridge loading makes a monster difference in terms of what the cartridge's response above 5khz or so will be...

I'll give you a quick "fix" to try.
Take some cotton balls, fluff them slightly, stuff them down into the throat of the horn - all the way down. Try to not compress them... start with 2-3, maybe 4... it may suddenly make everything sound WAY better.

Most of these inexpensive pro sound boxes are WAY hot on the top; the HF being too high in level compared to the mids, and tipped up on the top, as well as having some nasty harmonics on the top end as well. The cotton balls will tame that... if it is way too dull, experiment with the number of balls, and the fluffiness...

Also the reflection off the top of the Steinway can be a problem too...

throw a blanket over it and see...

etc...

_-_-bear
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Old 16th June 2012, 03:42 AM   #9
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Quote:
Originally Posted by bear View Post
You see, it is all fine the things that you are using, but you can not expect this stuff to give you the sonic results that you would like.

I think if you worked very hard on the Peavey and ran it with the ST70 properly modified that you would have a shot at making something that sounded halfway decent.

I didn't look up the Peavey units, but I will assume they have a compression driver and horn? The horn and compression driver you have there might be a source of your sonic annoyance.
Of course the Shure cartridge is also a "boom and sizzle" unit, imo.
And yes the cartridge loading makes a monster difference in terms of what the cartridge's response above 5khz or so will be...
I'll give you a quick "fix" to try.
Take some cotton balls, fluff them slightly, stuff them down into the throat of the horn - all the way down. Try to not compress them... start with 2-3, maybe 4... it may suddenly make everything sound WAY better.

Most of these inexpensive pro sound boxes are WAY hot on the top; the HF being too high in level compared to the mids, and tipped up on the top, as well as having some nasty harmonics on the top end as well. The cotton balls will tame that... if it is way too dull, experiment with the number of balls, and the fluffiness...

Also the reflection off the top of the Steinway can be a problem too...

_-_-bear
Actually the easiest fix is to leave the shrill plastic re-capped PAS2 preamp in the attic and use the disco mixer. Quite pleasant result. If I really want to burn 100 Watts, I can turn down the PAS2 trebel tone control about 1/8 turn.
The Peavey SP2 spec is +- 3 db 52 hz to 14 khz and my ears tell me (compared to the Steinway) that Peavey doesn't have the +-20 db production tolerance that the R**** S**** headphone brochure disclosed by mistake one time. The SP2 is a 15" woofer and 2" compression driver design, which is why I went and listened to them on piano source material. I was aware that the VOT was a similar design, although 4" or 5" compression driver in 1966. No hifi boutique has ever tried to sell me a speaker of that design.
The SP2's are the only speakers I have owned that makes the Dynakit ST70 sound inaccurate, compared to the Djoffe modification Dynakit ST120 transistor amp (transistor fixed crossover bias current mod). This is after a recent re-e-cap and output tube replacement of the ST70, but using the original design 7199 driver circuit. (1% HD quoted).
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Last edited by indianajo; 16th June 2012 at 03:58 AM.
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