Teac A-H500i Repair?

[OAV]

Hey everyone first post on here so hi from the UK! Long term lurker first time poster... Please feel free to move this if their is a better place for it - I have a Teac A-H500i intergrated amplifier to repair from a client, Over 20 years old.. Reported issue was a 50hz mains hum plus the harmonics coming through the loudspeakers.. barely affected by the volume position. I have measured the output and I am getting arond 500uV of background noise from the amplifier with a peak at 50hz of 100uV plus the harmonics. just audible very very close to the speaker.. now to me for the use case of the amplifier and its spec sheet this is typical performance for this amplifier.. The client has already recapped the main filter caps and pre amp board. The only thing I have been able to achieve is reducing the gain of the amplifier.. it has a over 42dB of gain for a single ended linear amplifier that seems massive to me? 100mv of input gives 12.6volts out, the pre amp provides x10 gain and the power amp x12.6 gain for a total of x126 voltage gain! It seems massive for any amplifier! because the pre amp and power amp boards are seperate a simple voltage divider to the input of the power amp boards reduces overall gain to 26dB which seems more sensible and improves things massively background noise overall down to under 100uV, the pre amp seems to have no problem with high level inputs. Does anyone have one of these to compare? Am i missing something is this supposed to be some unicorn of an amplifier? Client would rather I fix the problem - But I'm not sure their is one

Many Thanks
OAV

 

[staticV3]

Hi @OAV! Welcome to ASR.

According to the A-H500i's Service Manual, the Amp has 0.5mVrms of Z-wt residual noise, or 0.2mVrms with A-wt applied to attenuate the mains leakage (CD Direct input, input shorted):


If you can confirm these values on your bench, then it seems like your client is asking for a rework/modification, rather than a repair.

The specifications also confirm your measured gain at 180mVrms to reach 50W into 8Ω -> 20*log10(sqrt(50*8)/0.18)=40.91dB of gain.
Pretty high indeed.

 

[OAV]

Hi @OAV! Welcome to ASR.

According to the A-H500i's Service Manual, the Amp has 0.5mVrms of Z-wt residual noise, or 0.2mVrms with A-wt applied to attenuate the mains leakage (CD Direct input, input shorted):
View attachment 370668

If you can confirm these values on your bench, then it seems like your client is asking for a rework/modification, rather than a repair.

The specifications also confirm your measured gain at 180mVrms to reach 50W into 8Ω -> 20*log10(sqrt(50*8)/0.18)=40.91dB of gain.
Pretty high indeed.

Thanks @staticV3 - as I though, and that is a lot of gain!

 

[Schlippwhip68]

Hey everyone first post on here so hi from the UK! Long term lurker first time poster... Please feel free to move this if their is a better place for it - I have a Teac A-H500i intergrated amplifier to repair from a client, Over 20 years old.. Reported issue was a 50hz mains hum plus the harmonics coming through the loudspeakers.. barely affected by the volume position. I have measured the output and I am getting arond 500uV of background noise from the amplifier with a peak at 50hz of 100uV plus the harmonics. just audible very very close to the speaker.. now to me for the use case of the amplifier and its spec sheet this is typical performance for this amplifier.. The client has already recapped the main filter caps and pre amp board. The only thing I have been able to achieve is reducing the gain of the amplifier.. it has a over 42dB of gain for a single ended linear amplifier that seems massive to me? 100mv of input gives 12.6volts out, the pre amp provides x10 gain and the power amp x12.6 gain for a total of x126 voltage gain! It seems massive for any amplifier! because the pre amp and power amp boards are seperate a simple voltage divider to the input of the power amp boards reduces overall gain to 26dB which seems more sensible and improves things massively background noise overall down to under 100uV, the pre amp seems to have no problem with high level inputs. Does anyone have one of these to compare? Am i missing something is this supposed to be some unicorn of an amplifier? Client would rather I fix the problem - But I'm not sure their is one

Many Thanks

Just bought one of these exact amps going on 0 bad reviews. Its an old one but going to give it a go and even if warranted get it recapped. Its a monoblock system is a small box!