#26 pre amp

[Vinylsavor]

Hi!

still lacks mids ands lows.

Did you measure the frequency response?
As suggested above: Measure frequency response fully open and at lower volume steps.

Best regards

Thomas

 

[merlin el mago]

Rigth channel position 13th, it seems attenuator is gone because I only get 1Khz sinus when I push the attenuator.

 

[merlin el mago]

Can be the cause of bad sound?

 

[mthoi]

I have changed the 10R filament resistor from a Dale 50W WW to a pair of Ohmite Brown Devils 100W resistors. They are about 8-inches long a challenge to fit. However, the sonic improvements is well worth the effort.

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[Rod Coleman]

I have changed the 10R filament resistor from a Dale 50W WW to a pair of Ohmite Brown Devils 100W resistors. They are about 8-inches long a challenge to fit. However, the sonic improvements is well worth the effort.

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Good work, HMT!

You are using Filament Bias with your Coleman Regulators?

And these are the Brown Devils:

http://www.ohmite.com/cat/res_200.pdf

Are they the B20J10R?

The B20NJ10R would be an interesting comparison, with its Ayrton-Perry non-inductive construction.
Thanks for the report on the Resistors!

 

[iko]

Images hosted externally tend to disappear...

 

[mthoi]

Tx Rod - Yes, I am using filament bias with Coleman Regulators. Great product. Absolutely quite in a single chassis, and no hum on my Altec 288-8H/1505b horns.

The resistors are actually Ohmite L100J10R - 5%. I got a few and matched a pair to 9.9R.

 

[rclourenco]

I have changed the 10R filament resistor from a Dale 50W WW to a pair of Ohmite Brown Devils 100W resistors. They are about 8-inches long a challenge to fit. However, the sonic improvements is well worth the effort.

img-2010 - Servimg.com - Free image hosting service

Hi, can you share where you bought them?
Btw nice project.
Thanks

 

[mthoi]

I bought them from RS Electronics. They are also available from Element14.

 

[rclourenco]

I bought them from RS Electronics. They are also available from Element14.

Appreciated, thanks.

 

[merlin el mago]

Thomas any idea how to solve the issue?

 

[Vinylsavor]

Hi Felipe,

I already stated two times how to proceed. I cannot help any further if you don't follow the suggestions.

1. Get the TVC to work first in the 4dB step set up. Test each setting. You apparently have bad connections. You need to fix these

2. Do frequency sweeps as suggested to get a clearer understanding of 'lack of mids and bass'

Best regards

Thomas

 

[merlin el mago]

Hi Thomas,

You are right was a cold joint contact at the attenuator now is fixed, I tested with the scope the frecuency response and seems good. How can I do to the TVC works in the 2dBs steps?

Kind regards

Felipe

 

[Vinylsavor]

Hi!

So TVC works and sound is also good now?

Thomas

 

[merlin el mago]

Hi,

I can't appreciate the sound because with 4dBs steps sounds louder in my system (94dBs loudspeakers) also is a different kind of sound than a carbon pot.

Felipe

 

[Vinylsavor]

Hi!

So is the lack of mid/bass you mentioned gone or not? It is really hard to help with the little information you provide. I would not start to rewire the TVC until you are sure it sounds right and performs right. I did sent a detailed description how to wire for 2dB/steps. If you don't understand it please ask what exactly you don't understand.

Best regards

Thomas

 

[merlin el mago]

I don't understand the attached image.

 

[Noodle88]

I guess the first position is the lowest volume so would be -39db as u increase your volume it will become more +ve, until 0db is the loudest

 

[merlin el mago]

Yes I connected the 1st position to gnd

 

[merlin el mago]

Are correctly wired the input/output connections of my attenuator pot?