to ensure FP3 is not straining with multi amps.

Nutube · 1815

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Offline Nutube

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on: April 11, 2013, 06:47:31 PM
My FP3 has 2 output I am planning to use 2  RCA splitter to create 4 output
Output 1will feed a midbass amp (50k input impedence)
Output 2 will feed a tvc volume control and feed the Welbourne starchief 45 ( I dont know the input impedence) which drives the midrange horn and tweeter.
Output 3 feeds a Dahlquist lp 1 best estimate 25k input impedance which feeds a transistor amp bridged 560 watt to the sub
Out 4 reseved for my 2a3 if want to drive just the tweeter in the future.
I am concern with imput inpedance and resultant strain on the preamp.
Audio friends suggest using a pair of 5: 1 wide bandwidth transformer and position its use before the existing RCA out. The explanation is that  this way my FP3 preamp  will handle the multiple amps better.

If this is a correct approach can you suggest the specification of such a transformer an a good brand candidate.
Appreciate any thoughts.

Present configuration
I am currently running one fp3 rca to midbass amp the other rca to my tvc volume control.  It has 2 output female RCAs.
One pair female RCA feeds my 45 amps;  the other  to the dahlquist then feeding the sub.
I have thus far been unattentive to the impedance mismatch....It sounds ok to me but thought that I would be able to extract more out of the FP3 by improving the impedance matching. In my challeged way of putting it.... .I want to not strain the FP3 and hope to gain more air spatial imaging etc etc...you know the nirvana syndrome
Thanks look forward to your various input on this. ..

FP 1,2,3, Seduction, 45, Paramount 300B, Paraglow2A3; Dehavilland 845, Eico pp 805,Adcom 555 mono, Sota star saphire ugraded Nova motor & bearings,  Et 2.5 carbon wand on Shelter 901, Koetsu rosewood Sig., on magnesium wand, grado sumiko etc. Custom Edgarhorn with Seismic sub


Offline Paul Joppa

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Reply #1 on: April 11, 2013, 08:54:04 PM
It is unclear whether you have a problem or not, because the biggest risk is the TVC which has no specs.

That said, a suitable transformer would probably have a 15K primary. Here are three candidates:

1) Edcor makes a variety that are quite inexpensive and pretty good; I've measured two different examples.

2) The classic is the Altec 15095, available in a mumetal can with octal plug for connection

3) Magnequest makes a B7-15K

If it were me, I'd get a pair of cheap Edcors and see what you hear - be sure to give them 50 hours or more of breakin before making judgements! That way, you're not out much if is not the problem. If it does what you want then it's worthwhile to spend the big bucks on one of the others.

Be aware that a 15K:600 ohm transformer will reduce the signal voltage by 15dB. If you are using the FP-III switched attenuators, that's five clicks quieter.

Paul Joppa


Offline Nutube

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Reply #2 on: April 13, 2013, 06:56:05 AM
thanks for the input Paul very helpful.
Odered edcors.
I am not hearing a problem currently..... ..since this theory was dropped on me ...if true then it may give me positive benefits have a less strained Fp3 was my assumption.. also it is a reversible operation and somehing I can manage.
Very glad you pointed out lower volume 4 or 5 clicks....if I went higher say 8:1 will i gain back  some volume?
Meaning losing 2 or 3 clicks instead of five.?

FP 1,2,3, Seduction, 45, Paramount 300B, Paraglow2A3; Dehavilland 845, Eico pp 805,Adcom 555 mono, Sota star saphire ugraded Nova motor & bearings,  Et 2.5 carbon wand on Shelter 901, Koetsu rosewood Sig., on magnesium wand, grado sumiko etc. Custom Edgarhorn with Seismic sub